EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: JBeale on May 10, 2018, 09:31:52 pm
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I'm interested in this thing: wikipedia, https://en.wikipedia.org/wiki/Tiltmeter (https://en.wikipedia.org/wiki/Tiltmeter) You can use a simple pendulum, or a water-filled U-tube, but it seems the better ones work like a bubble level (spirit level) in a carpenter's tool. They use some electrolytic fluid instead of alcohol, and internal electrodes to read out the bubble position accurately. I'm interested in resolving for example one arc second (1/3600 degree).
The concept is simple enough, but I guess it's a small market. So far it looks like any connectorized tiltmeter module with better than 0.001 degree resolution costs over $1k just for the module. Anyone know if you could buy a bare electrolytic bubble capsule itself somewhere, if I wanted to roll my own?
"Spectron SH50058-A-003" http://www.spectronsensors.com/datasheets/SDS-116-3106.pdf (http://www.spectronsensors.com/datasheets/SDS-116-3106.pdf) is an example of the kind of thing I have in mind, but I believe that particular one is not intended or priced for the individual experimenter.
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Are you trying to detect the movement of the Moon. :)
If you made a pendulum 1m long, you'd have to detect a movement of the bob of 0.0048 mm.
http://www.seika.de/english/html_e/FAQ_e.htm (http://www.seika.de/english/html_e/FAQ_e.htm)
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This sounds similar to the recent thread looking for a cheap arcsecond rotary encoder. An arcsecond is difficult in a small space. The Starrett 199 Master Level is on this order, but no electrical connections. I wouldn't trust those types of connections anyway and would probably try something like photo sensors to detect the bubble. Precision levels usually have the curvature ground into the ID of the tube. No idea how they do it. You can buy the tubes, but not cheap for the good ones. Looking at vial makers, none seem to list better than arcminutes. Glass is pretty flexible, and you don't need much curve, so I'd try supporting the ends of a moderately long tube and just warp it slightly by pressing up on the middle.
If you want to try something different and have some space, there's a trick using two mirrors. You drill a hole in one and put a contrasting ring around it. View another mirror through the hole from a distance away, and you get the infinite reflection typical of such things. It's extremely sensitive, though I'm not sure how to instrument it and not sure if it gets you to arcseconds. You can also build a primitive interferometer with two mirrors having less than 100% reflectivity. Shine a laser through them. A lens can get you rings rather than a spot, reducing the sensitivity to whatever you might need.
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In the earlier thread, the cheapest solution was 2 load cells vertically tied together, one 90 degree rotated, with a weight suspended on the bottom cell and the top one tied to your vertical frame of reference. The 2 load cells were tied to precision ADCs and with a little math, you got the tile along the x and y axis as the load cells reported bend off axis. Note that due to the positioning of once axis load cell detector being above the other, you need to mathematically correct for it's position.
Obviously, if you only need to measure bend/tilt along 1 axis, life becomes easier.
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Thanks for the responses guys, these are interesting ideas which I had not thought of before. I have some experience with load cells and 24-bit ADCs, under load I know they are sensitive to any vibration (acting as a seismometer). The cheap ones will also creep.
The optical mirror idea is interesting. Could use a split-photocell as a spot-position detector. I had a setup like that before; I think my resolution was limited by light scattering from random dust passing through the air (it was a good dust / air quality monitor!) but the idea does work.
The neat thing about the electrolytic bubble sensor with electronic readout by AC bridge is it is so compact, mechanically simple, and less-sensitive to air drafts, etc. than a big pendulum, but still has quite good resolution. Just the sensor itself is a bit specialized and pricey. Maybe I should get ambitious and try to make one. There is a low-resolution tiltmeter for 2 axes that is a simple vial half-full of electrolyte and five wires sticking up inside, one central wire and four corners, those get you maybe 0.01 degree. The high-res ones are drawn as slightly-curved glass tubes with inside electrodes that may be plated on; I don't know how they do that.
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I bought a special bubble level years ago and it did not work for me. I threw it away so I cannot get the name. I think it was 1 degree max. I called the company and the reason it did not work was the "friction" needed to get the fluid to move (or ball inside the fluid). It was not cheap. A bubble level is not the way to get high resolution.
I got it to measure the tilt of a building. Electronic levels are much better.
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Thanks for the responses guys, these are interesting ideas which I had not thought of before. I have some experience with load cells and 24-bit ADCs, under load I know they are sensitive to any vibration (acting as a seismometer).
Vibration due to to the mass of your pendulum is a fixed frequency like a clock pendulum and you can completely eliminate it by software (ie tuned notch filter). As for other seismic noise, to make it operate with the same response as any other direction of gravity sensor, it is nothing more than a low pass filter. Basically averaging many samples. Though the device isn't tiny as optically looking at a bubble, it will still be really small as you would use load cells similar to that in scales which measure fractions of a milligram and your pendulum mass would be about the weight 10-50mg.
Use only 5v or less on the excitation voltage to minimize temp build up and drift in the resistive elements.
https://www.aliexpress.com/item/0-100g-200g-300g-750g-Electronic-Scale-Aluminum-Alloy-Weighing-Sensor-Load-Cell-Weight-Discount-50/32670225988.html?spm=2114.search0104.3.229.d9834197VZ03X8&ws_ab_test=searchweb0_0,searchweb201602_3_10152_10151_10065_10344_10068_10130_5722815_10342_10547_10343_10340_5722915_10548_10341_5722615_10696_10084_10083_10618_10139_10307_5722715_5711215_10059_308_100031_10103_10624_10623_10622_5711315_5722515_10621_10620,searchweb201603_25,ppcSwitch_5&algo_expid=bc25c045-4366-4798-b9fa-00bca22a66a4-37&algo_pvid=bc25c045-4366-4798-b9fa-00bca22a66a4&transAbTest=ae803_1&priceBeautifyAB=0 (https://www.aliexpress.com/item/0-100g-200g-300g-750g-Electronic-Scale-Aluminum-Alloy-Weighing-Sensor-Load-Cell-Weight-Discount-50/32670225988.html?spm=2114.search0104.3.229.d9834197VZ03X8&ws_ab_test=searchweb0_0,searchweb201602_3_10152_10151_10065_10344_10068_10130_5722815_10342_10547_10343_10340_5722915_10548_10341_5722615_10696_10084_10083_10618_10139_10307_5722715_5711215_10059_308_100031_10103_10624_10623_10622_5711315_5722515_10621_10620,searchweb201603_25,ppcSwitch_5&algo_expid=bc25c045-4366-4798-b9fa-00bca22a66a4-37&algo_pvid=bc25c045-4366-4798-b9fa-00bca22a66a4&transAbTest=ae803_1&priceBeautifyAB=0)
https://www.aliexpress.com/item/100g-small-range-high-precision-weighing-sensor-load-cell-weight-sensor/32776835270.html?spm=2114.search0104.3.250.d9834197VZ03X8&ws_ab_test=searchweb0_0,searchweb201602_3_10152_10151_10065_10344_10068_10130_5722815_10342_10547_10343_10340_5722915_10548_10341_5722615_10696_10084_10083_10618_10139_10307_5722715_5711215_10059_308_100031_10103_10624_10623_10622_5711315_5722515_10621_10620,searchweb201603_25,ppcSwitch_5&algo_expid=bc25c045-4366-4798-b9fa-00bca22a66a4-40&algo_pvid=bc25c045-4366-4798-b9fa-00bca22a66a4&transAbTest=ae803_1&priceBeautifyAB=0 (https://www.aliexpress.com/item/100g-small-range-high-precision-weighing-sensor-load-cell-weight-sensor/32776835270.html?spm=2114.search0104.3.250.d9834197VZ03X8&ws_ab_test=searchweb0_0,searchweb201602_3_10152_10151_10065_10344_10068_10130_5722815_10342_10547_10343_10340_5722915_10548_10341_5722615_10696_10084_10083_10618_10139_10307_5722715_5711215_10059_308_100031_10103_10624_10623_10622_5711315_5722515_10621_10620,searchweb201603_25,ppcSwitch_5&algo_expid=bc25c045-4366-4798-b9fa-00bca22a66a4-40&algo_pvid=bc25c045-4366-4798-b9fa-00bca22a66a4&transAbTest=ae803_1&priceBeautifyAB=0)
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This one is pretty clever and claims to measure three hundred and sixty degrees of tilt to an accuracy of one ten-thousandth (0.0001) of a degree.
https://hackaday.com/2016/05/05/clever-and-elegant-tilt-sensors-from-ferrofluid/
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Nice. But if you can get that resolution with inductance, why couldn't you do it with the capacitive sensors? Which are simpler to construct.
So how would you calibrate something like that? Try to turn it smoothly with some intense gear reduction at 1 turn per day?
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I designed some angle sensors a few years ago. I can tell you that you will have problems. Electrolytic sensors do not have the accuracy you need, and suffer from temperature effects as well. They also share a problem with pendulum type sensors as well, which is damping. Bandwidth vs damping is a big issue that can plague you. I ended up with a mems accelerometer which was good to about 1.5 minutes. For one second you will need something exotic, likely optical. A sensor based on an interferrometer would be a good bet, but will be relatively big and expensive.aul
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Bandwidth is less of an issue because I'm measuring geophysical creep, for example a 10 minute time constant is OK.
So the claim of <0.0001 arc degree resolution and <0.0008 arc degree null repeatability for SH50055-A-009 on http://www.spectronsensors.com/datasheets/SDS-116-3106.pdf (http://www.spectronsensors.com/datasheets/SDS-116-3106.pdf) is just a lie? Wouldn't be the first one on a datasheet, and it's a small company but it seems they've been around for ~80 years. There are other companies that claim arcsecond resolution also.
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Just a few hints on something in the league of 0.00006° or 1µm/m:
capacitive pendulum
https://www.wylerag.com/en/products/inclination-measuring-sensors/digital-inclination-sensors/zerotronic-inclination-sensor/#specifications (https://www.wylerag.com/en/products/inclination-measuring-sensors/digital-inclination-sensors/zerotronic-inclination-sensor/#specifications)
optical fluid detection
http://metrology.leica-geosystems.com/en/NIVEL230_1680.htm (http://metrology.leica-geosystems.com/en/NIVEL230_1680.htm)
capacitive level
https://www.hahn-schickard.de/en/services/sensors/inclination/electronic-spirit-level/ (https://www.hahn-schickard.de/en/services/sensors/inclination/electronic-spirit-level/)
-branadic-
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The capacitive sensor looks interesting. A bubble in dielectric fluid changing relative capacitance on a normal PCB with some pads forming an electrode pattern, seems like a pretty simple thing to try out.
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To me the Seika one seems easier to build than the bubble approach, to get precise movement of the bubble you need an extremely precise curve for the bubble to move along.
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Precise curves may be needed if you need accuracy over a large angular range. I am looking for very high resolution tiltmeter, but I do not need it linear or accurate over a large range. Ultimately I only care about very small deviations, much less than 1 degree from a nominal setpoint that would be an initial differential null point. I think it may be good enough to simply have some concavity of large but unknown radius, and then calibrate the sensor externally. As the saying goes, everything is linear to first order :-)
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The capacitive sensor looks interesting. A bubble in dielectric fluid changing relative capacitance on a normal PCB with some pads forming an electrode pattern, seems like a pretty simple thing to try out.
Well, it's not as easy as it seems, the dome needs precise machining and some surface finishing. The pcb design was a challenge too and the sensor mounting wasn't trivial. A well understood model to calibrate the sensor is necessary as well as the equipment to calibrate it ;)
To me the Seika one seems easier to build than the bubble approach, to get precise movement of the bubble you need an extremely precise curve for the bubble to move along.
The Seika sensor is at least a bubble approach too and only a copy of the 1-axis sensor Hahn-Schickard developed and transfered to:
https://www.2e-mechatronic.de/en/category/sensor-technology/ (https://www.2e-mechatronic.de/en/category/sensor-technology/)
Unless you can't make this type of sensor very big you will never get the required resolution. By the way, the dielectric fluid is one of the main secrets inside those sensors ;) and the amount of fluid needs to be very precise.
-branadic-
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Bandwidth is less of an issue because I'm measuring geophysical creep, for example a 10 minute time constant is OK.
So the claim of <0.0001 arc degree resolution and <0.0008 arc degree null repeatability for SH50055-A-009 on http://www.spectronsensors.com/datasheets/SDS-116-3106.pdf (http://www.spectronsensors.com/datasheets/SDS-116-3106.pdf) is just a lie? Wouldn't be the first one on a datasheet, and it's a small company but it seems they've been around for ~80 years. There are other companies that claim arcsecond resolution also.
70 not 80 same as me ha ha
I also want to measure geophysical creep so I called them but they were closed (3pm on Friday) but Kevin answered and told me the SSY0271 costs $130 (just a random pick because they said this was "low cost"). He was not sure if this would be right and the engineer would be back Monday
My creep is I built a 10x12 building on a land fill on the side of a hill. The building is strong enough that it could roll down the hill without damage (I sure hope not). Over the years I jacked it up and put fill under it and leveled it. It seems to stop moving the last 5 years (which is good because I got old in the last 5 years). But I would like a tilt recording so I am interested in what you are doing. Can you tell more about your creep? Do you want to record the data? If so what format? My guess is CVS (spreadsheet) format is best so it could be plotted.
Also how would you power it? ie AC or batteries.
Monday I will talk to the company. I would trust their specs but you can talk to them about them. Seems a good find. :-+
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The Seika sensor is at least a bubble approach too
I was talking about the NG4i from the first link to Seika. (http://www.seika.de/english/html_e/FAQ_e.htm)
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I was talking about the NG4i from the first link to Seika.
I know, you detect the covering of a dielectric fluid with the electrodes so half of the content is air, thus a bubble.
-branadic-
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For an accurate low cost tiltmeter I suggest a Chinese machinists level bubble vial. The machinist's levels are good to 10 seconds when read visually. So optical sensing the bubble position with a photodiode array should get you to a fraction of an arc second.
http://www.shars.com/4-master-precisions-level-1 (http://www.shars.com/4-master-precisions-level-1)
The vials for machinist's levels are ground internally to a very large radius curve. The price is dependent upon how long the body is, so a short one saves money for your application.
However, as you are more concerned with change than accuracy, you could simply bend precision glass tube to make your own vials. The downside of that is that tilt in the cross direction leads to an error. So you would need to mount two on orthogonal axes. Use a slab of scrap stone kitchen counter top. Drill holes through the stone for clamps, lay the tubes flat on the stone and clamp the ends loosely. Slip a piece of of the thinnest shim stock you can find under the center of the tubes and tighten the clamps. The tube will deform to a uniform curve of large radius. You'll need precision shim stock of two different thicknesses which are as close to each other. Ideally you want 0.xxx0" and o.xxx5" material.
Connect the shim stock as one terminal in a capacitive bridge with two pieces of copper foil for the other terminal of the capacitors. Use something like a 5-10 MHz xtal clock chip as the signal for the capacitive bridge and attach a JFET input instrumentation amplifier to the copper foil pads. Adjust the position of the slab so that the amp outputs are close to zero. You'll need to hermetically seal the whole thing with a bag of silica gel and preferably a shot of dry nitrogen gas before closing it up. Or pull a hard vacuum on it.
You can, of course, also use optical sensing for homemade vials.
Have fun and let us know more about the project. I'm a geophysicist. I've never done any tiltmeter work, but am well aware of it. There are companies that can measure submillimeter deformations over miles using satellites or aircraft and laser or radar interferometry. It's pretty mind boggling stuff.
BTW another approach would be to use a differential pressure sensor with a liquid filled tube on each port. That's likely to be fragile though.
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A standard 200mm machine level delivers 20µm/m (4,13sec or 0,00115°). Optical detection is one possible solution. But forget about the word low cost, as long as you have no possibility to calibrate the sensor on an already existing Acutronic or similar gear.
There is information on Wyler website on how their Zerotronic works, maybe you can copy that capacitive readout pendulum system or simply spend 3k€ on it.
What you could try is a thermal inclination sensor. Use a flex pcb, place a heater (resistor) in the middle and two NTC next to the heater (one on its left and right side). Put this setup in an evacuated package, this way you create a simple 1-axis thermal inclination sensor. For sure not as effective like a similar MEMS device, but worth a try on a low cost scale.
Another approach could be the mentioned vial together with a CCD from a flatbed scanner plus some microcontroller... many ways to go.
-branadic-
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The specs on high end Starretts are 0.0005"/10" or 0.0001"/10" which correspond respectively to 10 arc seconds and 2 arc seconds. The Chinese ones such as I linked are good to 0.0005"/10" visually.
Verifying and calibrating a level with gauge blocks on a surface plate is not rocket science. I can do 50 millionths over 8" with my $50 level and set of blocks. That's about 1.3 arc seconds. For $300-400 you can do 1-2 millionths over the length of the level. It will take a long time to do though, as you'll have to wait for the blocks and level to cool off each time you change the stack. And you have to have very stable room temperature. You'd probably have to leave the room if you wanted to 0.02 arc second accuracy (1e-6"/10"). Otherwise radiated body heat would disturb things.
In the case of a tiltmeter, one is rarely, if ever, interested in the actual angle. That's really pretty meaningless as you do not know how long a distance it applies to unless you're using long baseline fluid level tiltmeters such as shown in the wikipedia article. Those have severe issues with thermal gradients. In most cases all one is interested in is the fact that the earth has deformed.
All in all, electronically sensing a bent piece of glass tubing is probably the most sensitive option for a low cost device. The geophysical application is not like other angular measurements.
However, an NXP MPXV5004DP 0 - 3.92 kPa differential sensor is cheap. I'll leave as an exercise what change in water level is full scale for that sensor. But with a 24 bit strain gauge ADC from eBay it will be staggeringly sensitive and quite precise. Albeit, accuracy will be very tedious to obtain.
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I have a Taylor-Hobson Talyvel, a very sensitive electronic level, used for machine alignment. When in factory calibration, it is supposed to be accurate to 0.2 arc seconds. I certainly believe mine to 1 arc second.
It has a small aluminum pendulum suspended by 5 TINY wires. It has 2 steel discs on the ends of the pendulum that are very close to a pair of inductive proximity sensors. I THINK these sensors are just solenoid coils, but don't know for sure. There is also a pair of magnets that span an aluminum part on the pendulum, acting as an eddy current brake. You can pick the sensing head up and place it on a surface, and it will settle to full accuracy in less than 3 seconds. (A master precision level usually takes at least 30 seconds for the bubble to stop moving.)
Just for anyone who is not aware how small an arc second is, this level will be completely off-scale with a human hair under one end.
Jon
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If the Talyvel can resolve 0.2 arc-seconds (1 micro-radian) that is impressive. I haven't seen a dimensioned drawing, but from the photos of this online http://www.spectrum-metrology.co.uk/electro-optical-metrology/clinometers.php (http://www.spectrum-metrology.co.uk/electro-optical-metrology/clinometers.php) the pendulum is not larger than 10 cm, meaning the end of the pendulum is resolved to better than 100 nm. Capacitive sensors can do that; apparently magnetic ones can as well.
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Hmm. Might be a good project for a class 9 bearing from an old hard drive.
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Please read the specifications carefully:
Angular range: 1600 seconds (±600 seconds calibrated) *
Best Accuracy: 0.2 seconds
System Accuracy: ±1 seconds over central 100 seconds, ±6 seconds over ±600 seconds
Where is best accuracy achived, at zero point?
System accuracy is ±1" (±4.85µm/m or ±0.00028°) over ±50" (±242,41µm/m or ±0,01389°) that means a five times worse accuracy near zero point and ±6" (±29.09µm/m or ±0,00167°) over ±600" (2908,87µm/m or 0.16667°). That is not as amazing as it seems at first glance. If you compare that with a Wyler Zerotronic ±0.5° the Wyler is the winner.
-branadic-
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If the Talyvel can resolve 0.2 arc-seconds (1 micro-radian) that is impressive. I haven't seen a dimensioned drawing, but from the photos of this online http://www.spectrum-metrology.co.uk/electro-optical-metrology/clinometers.php (http://www.spectrum-metrology.co.uk/electro-optical-metrology/clinometers.php) the pendulum is not larger than 10 cm, meaning the end of the pendulum is resolved to better than 100 nm. Capacitive sensors can do that; apparently magnetic ones can as well.
Mine is a Talyvel 3 or 4, I forget the model. My sensing unit is slightly bigger overall. The pendulum might be about 3 cm long, and hangs about 2-3 cm from the support.
Jon
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Hmm. Might be a good project for a class 9 bearing from an old hard drive.
Nope, the bearings all have some sticktion. All of these sensitive inclinometers have no bearing or other friction.
Jon
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Please read the specifications carefully:
Angular range: 1600 seconds (±600 seconds calibrated) *
Best Accuracy: 0.2 seconds
System Accuracy: ±1 seconds over central 100 seconds, ±6 seconds over ±600 seconds
Where is best accuracy achived, at zero point?
System accuracy is ±1" (±4.85µm/m or ±0.00028°) over ±50" (±242,41µm/m or ±0,01389°) that means a five times worse accuracy near zero point and ±6" (±29.09µm/m or ±0,00167°) over ±600" (2908,87µm/m or 0.16667°). That is not as amazing as it seems at first glance. If you compare that with a Wyler Zerotronic ±0.5° the Wyler is the winner.
-branadic-
You have to know the conditions these specs were made at. Is this to retain this level of calibration over the full temperature range? What about time? Is it supposed to keep the zero calibration for a year, until sent back to the factory for re-certification? I think these conditions may apply.
I can only speak for how well my unit works, which is phenomenal. If I want to do a real zero to the earth, I set up my surface plate and zero the plate in by flipping the sensor back and forth, until the reading does not change in 4 90 degree positions.
Then, it will stay in cal for the whole day. I know that by placing the sensor on my 3500 Lb lathe and walking to the opposite end of the bed, the level shifts by one arc second. That is my body weight shifting the concrete floor slab.
Jon
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Hmm. Might be a good project for a class 9 bearing from an old hard drive.
Nope, the bearings all have some sticktion. All of these sensitive inclinometers have no bearing or other friction.
Jon
I'd certainly agree that friction is a significant issue with the HD bearings, probably a major problem. But if there is a pendulum, there is a bearing. So long as one is careful, a razor blade on a flat surface will work. It's just fragile. Of course, these are not things expected to survive being dropped on the floor.
I'm clearly going to need to play with a pair of RF oscillators tuned by capacitor plates on a pendulum feeding a mixer and frequency counter.
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Making a geometrically stable and low-friction pivot may be non-trivial, if you want very good performance. The knife-edge idea is simple, but I gather not the best available solution. Here is a brief survey from the related field of horizontal seismographs:
http://www.myeclectic.info/SeismoPivots/seismopivots.htm (http://www.myeclectic.info/SeismoPivots/seismopivots.htm)
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Interesting link, thanks.
A seismograph is different in that the mass being supported is much larger. As noted in the link, chemical balances use polished agate equilateral triangles.
I'm quite fascinated by the resolution of the Talyvels.
The crossed rods suspension seems particularly easy to implement using ground drill blanks. If I were interested in geophysical tiltmeters, I'd probably still go with the bent tubing, But I have a lathe and mill and have application for something like the Talyvel. My machinist's level is actually good enough, but I'm a bit of a general metrology nut. A sub-second of arc electronic level would be a cool project.
Please post followups of what you do. I was hopelessly corrupted by Claire Stong's collection of "Amateur Scientist" columns which came out in 1962. "For less than the average price of a set of golf clubs, you can smash atoms in your backyard"
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But if there is a pendulum, there is a bearing. So long as one is careful, a razor blade on a flat surface will work. It's just fragile.
That's why the Talyvel uses 5 hair-thin wires to suspend the pendulum, no friction there. And, i have dropped it about 18" from a lathe bed into the chip pan, and it seemed to suffer no harm - to my great relief! This is a $4000 instrument, although I was lucky enough to get it for less than 20% of that on eBay, due to a really bad description. But, I knew what I was looking at, so went with the photos, not the words.
Jon
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But I have a lathe and mill and have application for something like the Talyvel.
Yes, I have a machine shop at home, too. And, I got a fairly BIG lathe about 16 years ago:
http://pico-systems.com/sheldon.html (http://pico-systems.com/sheldon.html)
And the bed needed to be resurfaced. I started out with a straight edge, but but realized a 25" straight edge cannot properly test a 72" lathe bed.
I built a mini-carriage that I could mount dial indicators or the Talyvel on and check slope at 3" positions along the bed, and then correct the hills
and valleys. Then, I could use the straightedge to test for smaller scale variations. It all worked out REALLY well, the lathe is amazing to use.
I occasionally drag out the Talyvel to check things, but don't use it often.
Jon
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Nice machine. I've just got a Clausing 10 x 20 with only 54 feeds. But I like how you reground yours. Mine could stand some attention.
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Did a very quick test today, some 34R 0603 resistor as a heater on a flexible circuit board, 1k NTC 0402 on both sides of the resistors. No optimization and no special package to prevent air currents. The NTCs were measured with some digitizing prototype board. It worked pretty well. Tilting the board between +/-90° showed big changes in differential resistance. So chances are that by optimizing and special packaging such a discret thermal sensor will deliver quite good results.
-branadic-
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Slide the thinnest feeler gauge you have under one end and tell us what the change is.
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Slide the thinnest feeler gauge you have under one end and tell us what the change is.
Slide a single HAIR under one end and see if you can see the reading change. If not, it is in the carpenter's level class.
A master precision level will go off scale with one hair under the end, over a 10" length.
Jon
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The specs on high end Starretts are 0.0005"/10" or 0.0001"/10" which correspond respectively to 10 arc seconds and 2 arc seconds. The Chinese ones such as I linked are good to 0.0005"/10" visually.
Verifying and calibrating a level with gauge blocks on a surface plate is not rocket science. I can do 50 millionths over 8" with my $50 level and set of blocks. That's about 1.3 arc seconds.
How are you doing that if your $50 level is graduated in 500 millionths over 10"? I really do not like the looks of the Shars level, but I may buy the 8". The Starretts are too expensive for me...
Also, when I wanted to measure my surface plate, I tried a front surface mirror on the plate and used a laser about 10m away to reflect the beam back onto grid paper for ~1asec/1mm resolution.
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You set up the surface plate so it's level by reversing the level. You then setup a pair of stacks of gauge blocks say 1.00000" and 1.000050".
The statement was in reference to fitting the level vial for capacitive sensing and calibrating it. You'd need a large set of grade AA blocks rather than the B blocks I have to setup the example above. My blocks have an uncertainty of 50 millionths. I don't recall the smallest incremental difference I can create. But I can make measurements at least to 0.0005" increments and linearly interpolate.
I have a partially completed interferometer project for checking my gauge blocks I hope to be able to work on again soon. I've got the HeNe laser, splitters and mirrors (from old CD & DVD drives). All I need is time and precision rails.
I suggested the short Shar's level because the OP wanted to measure geophysical tilt. So all he needs is the vial. An 8" or 10" is much more satisfactory for setting up machine tools. The larger the body of the level, the more work making the body flat and hence the higher the cost.
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We are just about the same, I suspect. I think my blocks are 50 millionths too, and I have another nicer Polish set with a somewhat recent cal sticker (I don't run a commercial shop). I picked up a AA Rohn 24x48x6 surface plate that I would like to check/verify the characterization and cal, it looks too good...
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If you figure out a way to verify surface plates to a tenth without a Talyvel or an autocollimater please post to the metrology group. I've wrestled with how to do this for a long time. The frustrating part is Edmund sold WW II surplus autocollimaters for almost nothing in the 60's.
It seems to me that some copper foil strips in the appropriate locations on a vial combined with a trimmer capacitor would produce a very sensitive indicator. After all IIRC the 0.0005/10" is 1/8" from the center point, at least on my level.
I don't have any qualms about the Chinese levels. You might need to scrape them, but I learned to do that 20 years ago. As long as I don't have to do it too much it's rather pleasant.
I very much want a 24" x 36 AA plate. I haven't bought one because I want a zero ledge which is a little hard to find cheap and shipping is as much as the plate. And at 450 lbs, a real headache to move. Rather than ledges, I'd prefer to drill holes in the sides and epoxy threaded inserts to hold things in place.
John Meshna sold core frames from the MIT test machine for $6. Unfortunately, a lot of money if you're 12 and it was over 40 years before I understood the historical significance of the core frames and where they came from. But I do have a Singer card with core memory and an uncut IC wafer as well as an early IBM logic card bought from Meshna for the transistors. I'd pulled them, but miraculously found them. So I plan to replace them and try to cleanup the mess I made 50 years ago.
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I was just looking in a metrology text which showed an older (analog meter) version of the Talyvel. The pendulum unit appeared to be no more than 3-4" high. It was stated in the text that it uses an LVDT sensor and was sensitive to 1 arc second and that it takes about 1 second to settle.
A piece of 0.010" music wire and watch jewels would seem to be a pretty robust and sensitive pivot. Buying suitable jewels is not cheap ($24 each in the instance I found). However, it might be possible to salvage them from a thrift shop mechanical watch. Music wire is available as fine a 0.003". Guitar strings are more readily available, but only go down to 0.008" that I have seen.
LVDTs are pricey, but their construction is quite simple. It's 3 coils with a movable core. The center coil has a sine wave applied and the measurement is made by comparing the amplitude of the signals in the other coils. So making one should not be very difficult.
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The Talyvel really piqued my interest so this morning I considered every possibility for sensing a pendulum to one arc second.
I've come up with an interesting possibility. A pair of photodiode reflective object detectors with a pair of first surface mirror on a pendulum.
Take a look at the current vs distance plot on page 5 of this:
https://www.fairchildsemi.com/datasheets/QR/QRE1113.pdf (https://www.fairchildsemi.com/datasheets/QR/QRE1113.pdf)
The response is nearly linear from 0 to 0.5 mm and they are $1.01 quantity 1. With an MCU with a 12 bit ADC, that gives a 0.125 micron resolution. The tangent of one arc second is 5e-6. So with a 2.5 cm pendulum you'd have one second of arc resolution. A 10 cm pendulum would give 1/4 arc second resolution which should suffice for an arc second level.
For the pendulum support 0.0005 or 0.001 feeler gauge stock should work fine. Because the level will be reversed for calibration, any residual bend will be cancelled out. Starrett 0.005" stock is $15/ft on Amazon, but 0.001" stock is $2.80/ft from Victor Machinery Exchange. With suitable stops on pendulum movement it should also be quite robust.
One can scavenge suitable mirrors from old CD & DVD drives.
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That might be the simplest way, although if you're going to do optical displacement sensing, I think you can do better by using a collimated beam (eg laser pointer) reflecting from a mirror on your pendulum onto a split photodiode (position sensor). That's how they measured the deflection of AFM tips (atomic force microscope) down to the nanometer level.
Although it is angle-sensing rather than distance-sensing, so for a rigid pendulum you could make it as short as you want, what matters is the optical lever arm between the mirror and the detector.
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I was looking for a photodiode array for doing angular sensing when I found the device I referenced. Did you look at the datasheet? With two of those 0.25 mm from a target the performance should be there. The mirrors are somewhat gilding the lily as just painting the pendulum flat white would give almost the same result.
There's a whole lot more to an AFM than just the sensor.
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This appears relatively simple- a traditional glass spirit bubble level, with three foil electrodes stuck on the outside, and a simple circuit to detect differential capacitance change as the bubble moves. The alcohol fluid has a dielectric constant around 80 and the air bubble near 1, so the capacitance change signal is good enough to resolve 0.05 arc seconds, so they claim. Published as ARC-11344 by Michael G. Dix et.al., Ames Research Center in Mtn.View back in 1981.
"A Simple Tiltmeter" in NASA Tech Briefs Fall/Winter 1981, p. 319
Single page description: https://www.docdroid.net/enKb2ed/nasaames-simpletiltmeter.pdf (https://www.docdroid.net/enKb2ed/nasaames-simpletiltmeter.pdf)
Original PDF incl. 150+ other pages: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100027513.pdf (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100027513.pdf)
It seems almost too good to be true. If this was reliable, I don't know why anyone would use the more expensive electrolytic sensors, which do not claim much better resolution. The high-sensitivity bubble levels are themselves not super cheap, although it is apparently possible to make them yourself: http://fer3.com/arc/m2.aspx/Making-your-own-spirit-level-vialswithout-attached-pictures-Morrow-jan-2012-g17728 (http://fer3.com/arc/m2.aspx/Making-your-own-spirit-level-vialswithout-attached-pictures-Morrow-jan-2012-g17728)
photos illustrating above: http://fer3.com/arc/m2.aspx/Making-your-own-spirit-level-vialsanother-attempt-send-Morrow-jan-2012-g17731 (http://fer3.com/arc/m2.aspx/Making-your-own-spirit-level-vialsanother-attempt-send-Morrow-jan-2012-g17731)
Or for $50 + shipping you can buy such a high-sensitivity bubble capsule:
https://www.leveldevelopments.com/products/vials/ground-vials/5955101-ground-vial-15-x-96mm-sensitivity-0-01mmm/ (https://www.leveldevelopments.com/products/vials/ground-vials/5955101-ground-vial-15-x-96mm-sensitivity-0-01mmm/)
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This is all really interesting stuff- thanks everybody for the links!
Some time ago I had to build a micro torque meter. It was basically a pendulum off a shaft. As the shaft was rotated and the pendulum raised to the 90 degree position, the torque was easily calculated. I used a Gurley optical encoder good to about 0.001 degree. The trick was the bearing- I used a Newway 1/4" air bushing. Zero friction and perfect location. https://www.newwayairbearings.com/catalog/air-bushings/ (https://www.newwayairbearings.com/catalog/air-bushings/)
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Those bubble levels can be sensitive to defects or contamination on the inner surface. So the bubble can see some "friction" / sticking. How much depends on the quality.
Besides getting the level sensitive, one also needs a way to calibrate / find the zero position. Depending on the stability this might need a way to repeat the zero adjust just before use - one might want to do that anyway if the surface to measure is not that smooth / flat. So measuring both ways around would be just a version of averaging over a few positions.
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Those bubble levels can be sensitive to defects or contamination on the inner surface. So the bubble can see some "friction" / sticking. How much depends on the quality.
Besides getting the level sensitive, one also needs a way to calibrate / find the zero position. Depending on the stability this might need a way to repeat the zero adjust just before use - one might want to do that anyway if the surface to measure is not that smooth / flat. So measuring both ways around would be just a version of averaging over a few positions.
Clearly you've never used a 10 second level. If the level is not true from use to use, there is a serious problem with warping of the frame. Time to rescrape it true.
A level is the easiest instrument to calibrate, bar none. The center is the midpoint between 180 degree reversals. Proper vials are ground internally rather than bent so that cross slope doesn't effect them.
The biggest issue in use is thermal expansion. That's why there are insulated pads spaced away from the body of the level so that it will not warp from handling.
For an unattended instrument such as the OP wants, capacitance sensing is excellent. I'm not sure about how well that works in a shop environment as I've not tried it.
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I also see various sellers of "Glass Inclinometer Tubular Bubble Level Cylindrical Spirit Vial High Accuracy" around $25 on ebay. Looks to be a glass tube 100mm long and 14 mm diameter. Who knows but for the price, it might be worth a shot.
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Be careful, sometimes they state "organic glass" which is nothing but a plastic ;)
-branadic-
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For those vials, what does this spec mean?
Accuracy: 4"/2mm
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I also see various sellers of "Glass Inclinometer Tubular Bubble Level Cylindrical Spirit Vial High Accuracy" around $25 on ebay. Looks to be a glass tube 100mm long and 14 mm diameter. Who knows but for the price, it might be worth a shot.
:-+ Thanks I think this will solve my "problem" (a tilting building). Over 25 years I have jacked up the building over 3 feet (it was built on a compost pile |O) , Once I dropped it 12 inches (a really loud noise). Once it leaned 15 degrees (it is 15 feet high). I have not jacked it during the last 3 years because it "looks" OK. It is very heavy, a 12 ton jack will not even budge it. It takes 2-20 ton jacks on one end to jack it up. It is framed with 4x6s and sheathed with 1 1/2 in of 13 ply plywood and 1 inch of stucco. It can be easily moved around on steel rollers.
FYI If you ever move a house do not put rollers under the whole thing. The building may roll by itself, mine did. After that I saw a 3,000 sq ft house move. To move it the last 2 feet, they put rollers under one end, lifted the other with jacks and pushed it off the jacks.
This looks to be the same thing:
https://www.aliexpress.com/item/Size-14-96mm-Accuracy-4-2mm-Glass-High-Accuracy-inclinometer-Tubular-Bubble-Level-Cylindrical-spirit-level/32558917931.html (https://www.aliexpress.com/item/Size-14-96mm-Accuracy-4-2mm-Glass-High-Accuracy-inclinometer-Tubular-Bubble-Level-Cylindrical-spirit-level/32558917931.html)
They include a spec chart. I ordered 3 and now I have to figure out how to mount them. I cannot find anything about "organic". Since they sell plastic vials, I think it is safe to assume these are glass. In my case I want to prove the building has stopped moving. So after it is mounted, I will take one picture each month.
The dimension that would lean the most is 12 feet. Can someone help me read this. The accuracy is 4"/2mm What does this mean?
First if the accuracy is correct - how would I see it? One division? (there are 9 divisions on each end)
How many inches of drop over 12 feet would one division be? At 12 feet and one division, what would the degree be? In the mean time I will look on YT to see how to read a vial. :-DD
Thanks
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The accuracy is 4"/2mm What does this mean?
I just asked that question and was thinking about it. I copied a picture of the vial and pasted it into my drawing program, scaled it to 100mm, and I measured 2mm between graduations.
I suspect the accuracy spec is that the bubble moves 2mm with 4 seconds of tilt. I will put that into other units... But each line is 4 seconds.
and... it's looking like 76 millionths over 4 inches...
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How many inches of drop over 12 feet would one division be? At 12 feet and one division, what would the degree be? In the mean time I will look on YT to see how to read a vial. :-DD
Thanks
If one division is 4 seconds, that is just tan(0.0011) x 12 feet = 0.003 inches drop.
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For something like leveling a house a water level is the way to go. My Dad did that to a two story town house in Brooklyn Heights that was built in 1807. Among Dad's papers we found the elevations Dad had taken with Mother's help on her birthday a month before I was born.
Dad would jack in the basement with 25 ton screw jacks on 3 corners and Mother ran from sight glass to sight glass checking and calling out the reading to Dad.
BTW Using a hydraulic jack to raise something like a house is a bad idea. Screw jacks are much safer as they cannot suddenly drop the load the way a hydraulic jack can.
The bare vials for $25 sounds about right with levels going for $55 - $85 depending on length. I have an ominous feeling that I'm about to start Yet Another Project. Please post when you get the vials. Capacitance sensing should allow reading them to ridiculous resolution and accuracy.
Edit: $11.28 with free shipping? I'm doomed!
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I'm interested in ...
JBeale since you are looking into glass vials and I assume you are doing something electronic. Maybe I could fund your work if you make me one. In my case I am not interested in wireless. I would like to install a 100 foot wire and set up an alarm that would be a light. If this might be possible PM me. A CVS record of movement would be nice. I am flexible.
thanks
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Edit: $11.28 with free shipping? I'm doomed!
Misery loves company, or I will be entertained :-DD
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$11.28 is impressively cheap, if the vial does resolve 4 seconds of arc per 2 mm division. Indeed my application is long-term monitoring of a structure due to questions about the ground stability, and I wanted to find something with enough resolution to pick up very slow creep in a reasonable time, and cheap enough so I could use several sensors, because I would not trust just one device at one measurement location. Adding some electrodes for capacitive readout should give plenty of resolution. It will be at least a month before I even start on that project though, so I won't have any results to report for a while.
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If one division is 4 seconds, that is just tan(0.0011) x 12 feet = 0.003 inches drop.
That is crazy. Where did 0.0011 come from? Yikes maybe it is too sensitive! Darn I already ordered them.
Here is something - at least now I know what the 2mm means (distance between lines)
https://www.leveldevelopments.com/sensitivity-explained/ (https://www.leveldevelopments.com/sensitivity-explained/)
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If you look at the table in your link https://www.leveldevelopments.com/sensitivity-explained/ (https://www.leveldevelopments.com/sensitivity-explained/) at the bottom you see that 0 deg 0 min 4 sec = 0.0011 degrees. That is where tan(0.0011) came from, which is 1.92E-5 which means a rise/run slope of 19.2 um/m, which is also 0.0027 inches over 12 feet.
With a sensor like that on a typical structure, I think you'll see a day/night change as soil humidity and temperature changes around the foundation; maybe also seasonal changes, very likely shifts due to soil moisture when it rains, etc. Resting on the concrete slab of a garage, I'm sure it would record the change in tilt depending on whether a car is parked there or not.
EDIT: 4"/2mm is a standard format for reporting the sensitivity of level vials, and matches the most sensitive commonly available type, and those are generally about the size, shape and appearance of the ebay/alibaba photos for this unit. A few years ago I got one that looks similar to this from ebay but housed in a square aluminum shell, and I think it does have roughly that sensitivity (just leaning on my shimmed and solid workbench moves it offscale). Of course online as everywhere else, buyer beware.
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Are you sure the 4" isn't just the length in inches = 100mm.
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If one division is 4 seconds, that is just tan(0.0011) x 12 feet = 0.003 inches drop.
That is crazy. Where did 0.0011 come from? Yikes maybe it is too sensitive! Darn I already ordered them.
Here is something - at least now I know what the 2mm means (distance between lines)
https://www.leveldevelopments.com/sensitivity-explained/ (https://www.leveldevelopments.com/sensitivity-explained/)
Not to worry. I'm sure someone here will be happy to buy them. I tried to order one, but AliExpress did some things which made me uncomfortable when I tried to pay using PayPal. So I decided to punt for now. As interested as I am, I have far too many projects already.
But I did laugh when I read your post, as i t was clear you didn't realize what 2 seconds of arc meant. Actually, in most houses you could use them as a burglar alarm. The bad guy would have to be able to fly to get by one.
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Are you sure the 4" isn't just the length in inches = 100mm.
I am pretty sure 4" is 4 seconds and 100mm is the length
Refresher course:
https://www.youtube.com/watch?v=bpzM0PUH5wM (https://www.youtube.com/watch?v=bpzM0PUH5wM)
Now I have to find a arc-tan refresher course. Good mental exercise. The least "accurate" is 90" and I have to work the math to figure the change in 12 feet. Just doing a ratio calc I come up with 0.06 inches per division ? (I have to find a scientific calculator)
very likely shifts due to soil moisture when it rains,
This is a really big deal. Every winter I surround the area with at least 8 - 12x16' tarps. If I can get these levels working, next winter I will not use tarps and check what soil moisture does. I expect mounting on a wall will be hard. I must be able to re-level the level so when it goes off scale I can get it back reading. I need to look at change not the absolute angle. I have a good digital level for that. Going to start looking for thin shims. whew
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During a drought in Dallas I noticed a 3/8" gap in the brick work of my garage. I moved the soaker hose from the outer perimeter of the patio to the gap in the concrete slab next to the garage. After a couple of days the gap closed.
4"/2mm levels will move when you walk up to read them. For your application less sensitive vials would be better.
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But I did laugh when I read your post, as i t was clear you didn't realize what 2 seconds of arc meant.
True :-DD
Actually, in most houses you could use them as a burglar alarm. The bad guy would have to be able to fly to get by one.
This is still shocking to me that a liquid level could measure these small angles :-DD
I ordered a couple of these:
https://www.aliexpress.com/store/product/High-Precision-spirit-level-90-2mm-10-41mm-water-level-tool-bevel-protractor-Accessories-for-measuring/1960842_32560066552.html (https://www.aliexpress.com/store/product/High-Precision-spirit-level-90-2mm-10-41mm-water-level-tool-bevel-protractor-Accessories-for-measuring/1960842_32560066552.html)
In case I cannot work with the other ones.
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I am sure this action-packed video will be the hit of Youtube: https://youtu.be/9ocW3byVysI (https://youtu.be/9ocW3byVysI)
It shows the level linked below, resting on the concrete slab floor of my garage, as I walk past it. It is sped up 4x to make the shift easier to see.
The red marks are 2 mm apart. Looks to me like my weight tilts the slab about 1 arc-second, at a rough estimate.
If instead I put the level in the house on the wood floor, my weight affects it much more.
https://www.aliexpress.com/item/Free-shipping-Mechanical-equipment-dedicated-bar-level-tooling-with-mounting-holes-level-level-142X21X20MM/32827782884.html (https://www.aliexpress.com/item/Free-shipping-Mechanical-equipment-dedicated-bar-level-tooling-with-mounting-holes-level-level-142X21X20MM/32827782884.html)
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A 151 page doc on this:
https://www.wylerag.com/fileadmin/pdf/compendium/Compendium_eng_2013.pdf (https://www.wylerag.com/fileadmin/pdf/compendium/Compendium_eng_2013.pdf)
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I am sure this action-packed video will be the hit of Youtube
That's nuts, had no idea
For very large spans, just a tube and liquid
https://en.wikipedia.org/wiki/Water_level_(device) (https://en.wikipedia.org/wiki/Water_level_(device))
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Here is another video to compare to the first. This time, the level is resting on the kitchen counter, which tilts as the floor underneath flexes (house is typical wood-frame construction; wood floor supported by wood joists). First my 7-yo walks past (53 lbs). Then I walk past (170 lbs) so that is about a 3:1 weight ratio, and the total deflection of the level is also roughly in that ratio. We walked very slowly, and the video is sped up 4x to make it less tedious, because the level takes several seconds to respond. In fact I probably didn't walk slowly enough for it to quite show the full deflection.
So as long as your burglars move slowly, it seems you actually could use an arcsecond tiltmeter as an home intruder alarm, at least in this kind of timber-frame house. I read about a case recently where some guys low-crawled along a hallway to avoid tripping the active PIR motion-sensor alarm. Even with a ~3 second time constant, a high-resolution tilt sensor might have detected that situation.
https://youtu.be/_0OUdvOpVwQ
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Watching your videos (thanks by the way), I realize I probably will not be able to use the vials I ordered. So I am looking at round levels on their store. They can sense 1 degree and if I did my trig right, that works out to be 0.2 inches in 12 feet. (can someone check my math)
This is more reasonable.
Here is their store:
https://haccury.aliexpress.com/store/1960842/search?spm=2114.12010615.0.0.62c072ddjIZxAA&SearchText=bubble&origin=n&SortType=price_desc (https://haccury.aliexpress.com/store/1960842/search?spm=2114.12010615.0.0.62c072ddjIZxAA&SearchText=bubble&origin=n&SortType=price_desc)
Here is their most expensive one:
https://www.aliexpress.com/store/product/HACCURY-Metal-Level-Bubble-Universal-Flange-Bubble-Level-for-Loader-Crane-Four-Colors-Size-100-75/1960842_32865653759.html (https://www.aliexpress.com/store/product/HACCURY-Metal-Level-Bubble-Universal-Flange-Bubble-Level-for-Loader-Crane-Four-Colors-Size-100-75/1960842_32865653759.html)
It has "5/1000" on it, whatever that means
Here is a better place to learn about them:
https://www.leveldevelopments.com/products/circular-levels/surface-mounted-circular-levels/ (https://www.leveldevelopments.com/products/circular-levels/surface-mounted-circular-levels/)
So today I will learn about circular levels :-+
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I recalled that I had a 1.5" long bare vial ("new old stock" from ebay) with good sensitivity. Seemed almost a shame to break open the box noticing the date mark from 1944, anyway this does work. I used some copper foil tape and the 4-diode bridge circuit shown in the NASA Tech Brief (ARC-11344) linked earlier. Input was 5 Vpp 300 kHz sine wave. The recommended matched set of low-capacitance diodes I'm sure would be better, my random 1N34 discrete diodes have much more capacitance, and it varies with DC bias, so as my cheap function generator output amplitude changes, so does the output offset. But I can still see the result is quite sensitive. As I roll my chair around even slightly on the wood floor of my office/workshop, the output shifts 0.1 mV or more. With the whole thing sitting open on the workbench it is of course also very sensitive to my hand waving over it, I can get 10 mV or more of shift just moving my hand near one electrode, so you certainly want this in a shielded box.
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Update: I put the tilt vial + diode bridge in a metal box, and set three ball-bearings on the bottom so it could sit on just three well-defined points, and not wobble uncertainly.
Having done that, I'm prepared to believe all the visible variations in the output voltage are real tilt measurements, and not some kind of noise. There is a slowly rising background curve, in this case just under 1 mV per hour, likely from humidity changes affecting the wood frame of the house. On top of that, a sharp step change whenever I walk into the room and sit at the desk with my weight flexing the floor, which returns to the previous curve when I leave the room. There are also some much smaller wobbles, which might well correspond to activity elsewhere in the house.
It's interesting to make such a sensitive measurement with a simple all-passive circuit, no transistors or opamps (apart from the Keithley 196 DVM measuring the output, of course).
EDIT: Seems I could certainly clean up the layout, for example that long red wire going to the smaller copper electrode on the right will shift the output many 10s of mV, just with a small bend towards or away from the ground plane. Looks like we are measuring femto-farads of capacitance change here, so the wires to sense electrodes should be an absolute minimum length.
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That's pretty awesome
Having done that, I'm prepared to believe all the visible variations in the output voltage are real tilt measurements, and not some kind of noise. There is a slowly rising background curve, likely from humidity changes affecting the wood frame of the house, and a sharp step change whenever I walk into the room and sit at the desk with my weight flexing the floor.
You can largely confirm by rotating box 180 to point other direction, should decrease in similar way
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What's the sensitivity of the WW II vial?
A similar setup using a 4"/2mm vial mounted to a concrete pier might even detect the moon deforming the earths crust.
Alfred Loomis, the financier who retired to Tuxedo Park to develop radar in the late 20's, bought a couple of the best pendulum clocks made. They were several thousand dollars each. Later he was involved with developing ovenized crystal oscillators. Comparisons soon showed the effect of the moon on the pendulum clocks.
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Still uncalibrated, but progress. I made a smaller diode bridge with two SOT23 packages each being a diode series pair, and they are low-capacitance parts with <1.0 pF at Vf = 0: On Semi MMBD352LT1G. Used short wires to the electrodes. Seemed safer to solder the wire first, and only then apply the copper tape to the glass vial, which worked but was tricky to handle.
Placed the sensor on my concrete garage slab since the floor of the house was not stable enough. I'm convinced I see a clear tilt signal when standing to one side or the other of the sensor as my weight locally tilts the big concrete slab, probably by a few arcseconds. On top of that, a continuing background drift, and a low level of random noise.
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Very impressive results, I would've never believe such sensitivity is possible! :-+
What is the cause for the steady increase in voltage reading (in the last chart), and why the tilt variations are all almost rectangular? If you move slowly from left to right, will you see a triangle shaped variation instead of the square shaped one?
Is there any hysteresis in the sensitivity of the tilt detector?
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It is neat to see the supposedly solid concrete floor bend (slightly) under my weight. I only just got this new version of the tiltmeter working today. I may be able to say more about its properties after running it a few days. The steady background trend could be a real physical tilt (anything from differential heating, hydration of soil, etc.) or could be some electronic artifact. I have it sitting on a smooth "surface plate" which is in turn resting on the concrete slab, so I can reverse it 180 degrees and see if the trend also reverses. To do that cleanly I should have the vial precisely level with the housing, which it is currently not. I will try reversing it after acquiring some more data.
I'm only sampling once every 2 seconds, so the rectangular shape of the offset when I stood still nearby, is because I moved into and out of position on either side of the sensor quickly enough that it appears nearly instantaneous on the plot. If I had instead moved very slowly past it, I would have expected to see a smooth curve, instead of the rectangular pulse.
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When you say you stood to the left and right of the sensor, is that the sides or the ends of the sensor, I think it should show very little change at the sides and max at the ends.
When you've run it for a few days, I think there's a good chance you'll see the 12hr 25min and 24hr 50min Moon/tides cycle.
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That thing will be a hell of a chore to calibrate. Level is easy, that can be done electronically by reversal. So long as you stand in the same place.
The only way I can think of would be to use a 10 ft piece of heavy 2" square tubing w/ 3/8" walls. put the sensor in the center and use a surface plate and gauge blocks in 0.0001" increments at one end. And that would only get you 0.17 arc seconds. Using B grade blocks the uncertainty would be about 0.085 arc seconds. And that completely ignores air currents and temperature differentials in the tube or heating of the gauge blocks.
It's truly amazing.
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Yes, calibration would be- interesting. I meant I stood near the left end and right end of the capsule. I was trying to make a detectable signal, so I stood where any deflection due to my weight would have the largest response. As you suggest, in the orthogonal direction there is very little sensitivity.
The data covering 11 hours last night looks very strange. Starts out with a nearly linear drift but then gets more complicated. The plot shows two "sudden" step-changes during the night (taking place over a few minutes, and most of the shift within 30 seconds). Looks very odd and nothing obvious happened inside or outside at those times. I also have a seismometer in the garage and that didn't see anything either. Now I'm starting to want another sensor, to see if this is some kind of sensor artifact, or something real.
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The step-changes might be some discharges. Somewhere in the whole apparatus, I suspect there is a capacitor acting like an integrator. That constant increase in voltage shows there is an integrator somewhere.
Capacitors with small charges can be suddenly discharged by energetic particle, like e.g. cosmic rays. Not sure if this is the cause of discharges. It might be as well caused by the measuring instrument doing an auto-zero calibration.
Anyway, you got yourself a hell of an intriguingly sensitive instrument! :clap:
I want one, too, just for the fun of playing with it. :-DMM
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"The plot shows two "sudden" step-changes during the night (taking place over a few minutes, and most of the shift within 30 seconds)."
Different expansions with temperature changes correcting themselves ? You've got glass glued to metal.
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The data covering 11 hours last night looks very strange. Starts out with a nearly linear drift but then gets more complicated. The plot shows two "sudden" step-changes during the night (taking place over a few minutes, and most of the shift within 30 seconds). Looks very odd and nothing obvious happened inside or outside at those times. I also have a seismometer in the garage and that didn't see anything either. Now I'm starting to want another sensor, to see if this is some kind of sensor artifact, or something real.
You're embarrassing me. I'm a geologist (igneous petrology) who then spent his career in geophysics and I don't have a tiltmeter or a seismograph :-(
But I *did* get four polarizing microscopes which I am refurbishing. Unfortunately, almost 40 years later I have only a very rudimentary notion of how to use one despite having spent 9 months using one all day, every day.
I studied the calibration problem a bit. The only viable method looks to me to be a Michelson interferometer, a 100:1 lever and a micrometer head with a 10:1 belt drive. And even then you might need to multiply the movement by repeated bounces in an optical flat to get adequate resolution from the interferometer.
I live a little over a mile from a lake, so I should be able to detect the rise and fall of the water in the lake with one of these.
I knew that these could be very sensitive, but I'm still stunned at how simple it is. Naturally I shall need at least two mounted orthogonally on bedrock.
I'd like to see details about your seismograph. I read all the articles in C. L. Stong's "The Amateur Scientist" when I was a kid. And even though I am not an earthquake guy, I'm quite familiar with the design problems.
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I did build one of the swinging-door type Lehman horizontal seismographs a while back, but the current one I simply purchased. It is vertical-only, uses a 5 Hz geophone which was extended with some kind of active electronics to have useful sensitivity down to below 0.5 Hz. It's the basic model from https://raspberryshake.org/products/raspberry-shake-1d/ It plugs into your home network and the "Raspberry Shake" company archives your seismic data 24/7 for access from anywhere, which is quite convenient.
At the moment (12:40 pm PDT) the tiltmeter drift rate has been picking up the past few hours, with maybe with two more step-changes in the opposite direction as the ones last night. I definitely need a second sensor to tell if these are just an instrument artifact, but I'll have to wait until the new capsules come in from aliexpress to build another one. I'd give it about an even chance to be caused by something wierd about my (quickly constructed) sensor circuit.
If you zoom in to samples 25441 - 26122 (0.8 to 0.9 mV), you can detect a tiny step up and then down, which exactly matches the timing of me leaving and then returning in a car that was parked on the driveway outside.
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You should consider a MEMS sensor for the seismograph. The orthogonality of those is not very good, but you've got a sensor that will easily allow calibrating out any errors.
I spent quite a lot of time working on this subject 5-10 years ago. for multicomponent seismic recording. Never did anything with it, but I did work out how to correct for the sensor errors with a very simple setup that could be built from a scrap hard drive (for the sake of the class 9 bearing) and an optical prism.
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This is capacitive sensing right? Have you thought about using a CDC (capacitance-to-digital converter)?
Have you measured capacitance? What size is it?
What if you paint the electrodes directly on the vial using some silver ink? Your copper tape include some adhesive, that can cause your drift issue due to relaxing effects or humidity, beside any mechanical relaxing by mounting the vial.
-branadic-
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All I can say with the gear I have handy is that the total capacitance change is less than 1 pf. A CTD converter might be good to try. I don't know if those also measure a difference of two external capacitors eg. Cx - Cy, or ratio Cx / Cy, or an absolute reading? The real signal is the differential capacitance, which the simple diode bridge measures directly.
Yes, I am also wondering about that sticky adhesive-backed copper tape and possible drift. If I could make solid electrical contact to silver paint that might be good. Or even very thin plain metal foil which is superglued on and/or lacquered over, might be more mechanically stable.
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Might be useful to download a copy of the General Radio 1615-A capacitance bridge and the 1605-A Impedance Comparator. Both use a "simple" tapped transformer to make differential measurements and achieve great sensitivity and stability. You don't need 80% of the circuitry, just a transformer wound on a toroid and a few other things. Probably both on the IET site or BAMA.
My surface grinder is on a cement floor. I use an accelerometer to balance the wheels. There's an obvious change in amplitudes as I walk around near the machine. That baffled me at first, because how could that possibly change balance, then I realized the the coupling to the 4 leveling feet was changing, so the vibrational amplitudes through the frame changed. Cement floors, unless unusually thick, are quite flexible on the scales we're talking about.
Somewhere I've got a book about building DIY weather instruments and I think they covered seismographs too. No matter what you're building, a copy of Building Scientific Apparatus by Moore, Davis & Coplan should be an essential item on the shelf. It covers little of what we're talking about specifically, yet is applicable beyond measure.
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For reference, here is the Type 1615-A Capacitance Bridge, from p.60 of https://www.ietlabs.com/pdf/Manuals/1620_im.pdf (https://www.ietlabs.com/pdf/Manuals/1620_im.pdf)
I guess that's one way to do it, but my existing circuit is also simple (it doesn't use a transformer, anyway). I will need to investigate what the factors affecting the stability are. Without measuring anything, I suspect I'm resolving differences of femto-farads just with the simple diode bridge.
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No matter what you're building, a copy of Building Scientific Apparatus by Moore, Davis & Coplan should be an essential item on the shelf. It covers little of what we're talking about specifically, yet is applicable beyond measure.
I've got three editions and a duplicate of one. But I'm shocked to learn there is a 4th and I don't have it. Worse yet, it's been available for 9 years. So time to buy another book.
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All I can say with the gear I have handy is that the total capacitance change is less than 1 pf. A CTD converter might be good to try. I don't know if those also measure a difference of two external capacitors eg. Cx - Cy, or ratio Cx / Cy, or an absolute reading? The real signal is the differential capacitance, which the simple diode bridge measures directly.
Without measuring anything, I suspect I'm resolving differences of femto-farads just with the simple diode bridge.
Take a look at AD7746 (+/-8pF) and with additional guard AD7747 (+/-4pF) both with 24bit resolution, you get down to aF. You can try PCap01AD made by ACAM even though somewhat more complicated to get it run but with aF resolution as well. There are other CDC's available but I wouldn't recommend them.
All three can measure differential capacitance. PCap01 measures with the third electrode either grounded or floating while AD products do have an excitation signal on the third electrode. You can choose what you prefer.
-branadic-
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TI has a few capacitance to digital converters, too. They are cheaper than their AD counterparts.
http://www.ti.com/sensing-products/capacitive-sensing/capacitance-to-digital-converters/products.html (http://www.ti.com/sensing-products/capacitive-sensing/capacitance-to-digital-converters/products.html)
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Cheaper yes, but not easy to handle and you need a lot of external components. The only interesting part from them is maybe FDC1004. Easy to go is AD774x, but more performance gives PCap01. PCap02 and PCap04 are not of interest here, because you want low noise and high resolution.
If I had a vial I could paint electrodes with silver ink on it, add either PCap01 or AD7746 board to it and reproduce the results. Any recommendation where to get an equal glas vial?
-branadic-
Edit: Found your vial used is still available at ebay, (https://www.ebay.de/itm/W-A-Moyer-Sons-Vintage-Level-Vial-Type-L-1-A31314-Bubble-Level-NIB/192433183719?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649) I ordered a few and hope to reproduce your results soon.
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Thanks for finding the vial on ebay. Sure enough, that looks like the exact part. It is 1.5" long and it comes in that box. I wonder what the actual sensitivity of the "Type L 1 A31314" vial is.
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I spent 5 mins on google and could not find the spec.
Also, I wonder if there is a fancy way you could wind magnet wire around it. Perhaps have half coils on top that loop around the bottom half coils so you can reverse direction?
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I think it is some custom specific precision vial. Further more it is not clear to me if it's a Top Ground Vial, an Ordnance Vial or a Reversion Vial (https://wamoyer.com/glass/precision/). However, doesn't make any difference at the moment. Hopefully it doesn't take to long for them to arrive, to get a first impression of what resolution can be reached. I have a Leica Nivel 230 and a Wyler Zerotronic to compare with on our test bench.
-branadic-
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Based on the photos I believe it is an "Ordinance Vial". I'm very interested to hear what your findings are, given you have some good measurement tools to compare with.
Knowing I would be reassembling it later, I just used hot glue to temporarily hold it against the bottom of the diecast box housing. I wanted the glue to hold the glass flat against the metal, but I have read that cheap hot glues are 50% wax by volume, with a horrendous (!) thermal expansion coefficient. Now that I know the circuit works, I should try for a more kinematic mount, maybe spring wire holding the vial against a v-groove pillow block at each end.
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I'm trying to invent some kind of interesting mounting for my vials too... plan to sink this into the roughed-out base here, but need an adjusting mechanism.
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Here are photos of the mount in my Chinese machinist's level
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one more
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Cool, I wondered what was in there. If I understand its operation, the right side is a pivot (with pinch screws to position in center and probably take up some pivot slop) that is jacked by the screw on the left.
I figure I can make an old piece of "lead" pipe work for a carrier if I do not find a chunk of cast iron. Some name brand appears to use aluminum tubing, or perhaps it is stainless?
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The vial is sitting in the metal tube with a thin clear plastic ring around it. There's access to the adjustment screw through the top cover. The pointed screws are behind the insulating side handles. The points are probably the actual pivots and the pin is just so they can be set. If you think about the tolerances (this is a 10"/2mm vial) the slop of a pin in a hole would make it unworkable. 10" over the ~5" vial is 0.00025"
I'd suggest using a pair of good grade O rings to hold the vial in a metal tube. Set the adjustment screw in minimum position, tighten the pivot screws so they *just* dimple the metal and then adjust for level. Use a pin which is 3-5 thou smaller than the hole to allow free movement over the adjustment range without straining the tube. It's really just there as an aid for setting up the vial so it can be adjusted.
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Thanks for those photos! I was just thinking about how to do the leveling adjustment. I assumed I would need some compound lever to reduce the motion, since even a 80 TPI micrometer leadscrew would be awfully fiddly lifting a 10 cm long lever arm, if you are resolving at the arc-second level.
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I think many levels and old transits used plaster of Paris to bed in the vials.
Too fussy for most, but if you have the machining capability, you can make a differential screw for adjustment.
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I was expecting to see plaster of paris when I opened it up. Long term that's probably more stable. Thanks for bringing that up. I got somewhat distracted by the pointed screws which I did not expect to see and which took some thinking to figure out.
Edit: For a capacitance sensed vial plaster of paris around the electrodes would cause problems, but O rings would let one pour plaster into the ends without it running down to the electrodes.
BTW I haven't used it in quite a while, so I don't recall how fiddly it is to adjust. I habitually test levels by reversal every time I use them. I remember I did it, but that is all. It's certain to be "breathe on the screwdriver" and it moved too far.
I'm quite eager to get some 4"/2mm vials and duplicate your work.
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Too fussy for most, but if you have the machining capability, you can make a differential screw for adjustment.
I've never heard of a differential screw. Please explain.
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Thanks for those photos! I was just thinking about how to do the leveling adjustment. I assumed I would need some compound lever to reduce the motion, since even a 80 TPI micrometer leadscrew would be awfully fiddly lifting a 10 cm long lever arm, if you are resolving at the arc-second level.
Indeed...photos are awesome and appreciated! These are usually over 100+ cm. I think my pivot will be 5"
I think on the order of 20 degree turn of the leveling screw would be one full division (for 4" graduated vials, 80 tpi).
I think many levels and old transits used plaster of Paris to bed in the vials.
Too fussy for most, but if you have the machining capability, you can make a differential screw for adjustment.
Yes! now you temp me with complexity and elegance.
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FYI - Received my two vials which are too sensitive for me (I forgot my trig). Also got two less sensitive vials. Pretty fast shipping.
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Use your Google-foo and do an image search on differential screw. Lots of images that are better than any description I can give. Basically it subtracts the motion of two very closely chosen thread pitches. The difference can be stupidly small, in fact errors in machining can be larger than the motion of the screw, so don't make it too fine.
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.. differential screw ..
Interesting :-+
https://www.youtube.com/watch?v=rxjKOlP-XQU (https://www.youtube.com/watch?v=rxjKOlP-XQU)
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Piece of cake, Trip to hardware store, a hacksaw cut and some epoxy or silver solder. The only hard part is aligning it and finding left hand threads.
I'm surprised I hadn't encountered the idea before.
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Depending on how you do it, you don't even need a left handed screw. In the image above, the whole screw moves forward through both nuts. It's only the slight difference in pitch that causes the movable nut to move. The more compact way to do it is with concentric parts, and you turn the central "nut" that's both internal and external threaded, to move one of the screws. I think Lansing sold a diff mic that was actually made for them by Starrett. Burleigh sold one for a while that was made by Slocomb. Newport sells one, and Thor Labs too! None are cheap.
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I spent 5 mins on google and could not find the spec.
I've contacted W. A. Moyer & Sons and hopefully they are communicative enough to give some specification on Level Vial Type L1 A31314. My experience with companies beyond the great lake is not that positive when asking for informations about their products.
-branadic-
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After being stuck with 75 year old stock for years, the ebay seller must be wondering why his L1A31314's are now selling like hot cakes. :)
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Lol, has the price gone up yet?
Now I'm wondering how I will thread a fancy differential screw into that chuck of scrap iron I have? I was considering an 88/92 TPI combo.
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Seems like any kind of threaded mechanism will be expensive and take up some space. Assuming it can be set once and for all, there's something to be said for the time-honored simplicity of plaster of paris. Dirt cheap and compact. One-time only, but has unlimited adjustment range and you can make progressively finer adjustments to the vial as the paste gradually stiffens during the set.
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Yikes! That would be the equivalent of a 2024 tpi screw! 1/88 - 1/92 = 0.00049 per turn. Geometry errors will probably cause it to move back and forth more for each turn, than it moves forward or reverse, unless you're really good at making the parts.
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After searching a while in the web I'm now sure that sensitivity of the vial is in the order of 20"/2mm. There are similar vials available on ebay (https://www.ebay.de/itm/Ersatz-Wasserwaage-Glaslibelle-Wasserwaage-mit-Blase-Rohrenlibellen/142296755255) that can be used for this purpose. There are also vial with 3"/2mm (https://www.ebay.de/itm/Ersatz-Wasserwaage-Glaslibelle-Blase-Empfindlichkeit-Feder-100x-9-5mm/132588613741) available.
-branadic-
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Yikes! That would be the equivalent of a 2024 tpi screw! 1/88 - 1/92 = 0.00049 per turn. Geometry errors will probably cause it to move back and forth more for each turn, than it moves forward or reverse, unless you're really good at making the parts.
Yes, and at 5" pivot, would give me 6 divisions per turn. It sounds easy as I would single-point them on 1/4" drill rod.
Any suggestions on where to start looking? I think easy would be an 8-36 / 8-32 screw. I think I have both of those taps. That gives me 1 division for every 10° screw rotation.
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Seems like any kind of threaded mechanism will be expensive and take up some space. Assuming it can be set once and for all, there's something to be said for the time-honored simplicity of plaster of paris. Dirt cheap and compact. One-time only, but has unlimited adjustment range and you can make progressively finer adjustments to the vial as the paste gradually stiffens during the set.
Yeah? I cannot see that working. I'd watch it for hours and hope it cured enough, and overnight it will take a set and sag. I expect it would happen, not tried it.
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Seems like any kind of threaded mechanism will be expensive and take up some space. Assuming it can be set once and for all, there's something to be said for the time-honored simplicity of plaster of paris. Dirt cheap and compact. One-time only, but has unlimited adjustment range and you can make progressively finer adjustments to the vial as the paste gradually stiffens during the set.
:-+
I was about to buy this:
https://www.aliexpress.com/item/-/32857223430.html?spm=a2g0s.13010208.99999999.261.7ed13c00BqqI0W (https://www.aliexpress.com/item/-/32857223430.html?spm=a2g0s.13010208.99999999.261.7ed13c00BqqI0W)
then I doubled checked my math and at 12 feet 1 degree is 2.5 inches not .2 inches (unit error) that I first thought. This time I think I will go back to vials but 4" is much too sensitive but I like the 100mm length.
Can someone check my math - at 12 feet 4" is .003 inches ( tan(4/3600) x 144 = .003 inches )
.003 is too little for me and 2.5 is too much. So I will continue to look but the plaster idea sure solves the mounting problem. I think 1 inch max is the most I could tolerate then I would have to re-level the building which is a full days job.
How to calibrate a glass vial and document the results? In my case (not 4") I was thinking of measuring the heights at the end of a 12 foot board for each division and make good notes in a notebook that will be attached to the wall inside the building.
Found this one 5'/2 mm x 100mm ->
https://www.aliexpress.com/item/High-Quality-Level-Vial-Bubble-Glass-Tube-Spirit-Level-Measurement-Instrument-5-2-mm-14-100MM/32879077293.html (https://www.aliexpress.com/item/High-Quality-Level-Vial-Bubble-Glass-Tube-Spirit-Level-Measurement-Instrument-5-2-mm-14-100MM/32879077293.html)
Can someone check my math again (sorry but I am learning) :
At 12 feet 5' means the difference between marks is 0.2 inches ?
If so I will mount 2 of these at right angles in plaster of paris. My next question is how deep should I ? I am thinking about 1/3 diameter? I would like to be able to remove them just in case I screw something up.
Also found this on how to calibrate a glass vial:
https://www.leveldevelopments.com/wp/wp-content/uploads/documents/Engineers-Level-Calibration-Instructions.pdf (https://www.leveldevelopments.com/wp/wp-content/uploads/documents/Engineers-Level-Calibration-Instructions.pdf)
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then I doubled checked my math and at 12 feet 1 degree is 2.5 inches not .2 inches
I thought you'd have found that 0.2inch -> 2.5inch error long ago!
Making a giant 24ft circle, and then dividing down the circumference, both these are correct.
"at 12 feet 4" is .003 inches ( tan(4/3600) x 144 = .003 inches )"
12ft x 12inch * 2pi / 360 / 3600 * 4" = 0.00279 inch.
"At 12 feet 5' means the difference between marks is 0.2 inches"
12 * 12 * 2pi / 360 / 60 * 5 = 0.209 inch.
I wouldn't have much clue on how to calibrate, I'd guess you'd move an amount of 10 or 20 divisions and then interpolate for the smaller divisions.
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1/4" in 12' is 6 minutes of arc. (atan( 0.25/144))
Fluid (water or mineral oil) levels are far more appropriate for building movements. The problem with a level vial is the length over which the angle applies is hard to determine. It's not the length of the vial, it's the length and straightness of what it's attached to.
A fluid level at each foundation pier is unambiguous.
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What do you guys think of this:
https://www.aliexpress.com/item/HACCURY-100-75-20mm-Stainless-Steel-Spirit-Level-Metal-Universal-level-for-Pump-ruck-Piling/32774959769.html (https://www.aliexpress.com/item/HACCURY-100-75-20mm-Stainless-Steel-Spirit-Level-Metal-Universal-level-for-Pump-ruck-Piling/32774959769.html)
I think the 5 and 10 are minutes. I like the looks, it matches the three windows that are from a Disney submarine (Florida). One sub was dismantled and the others (13 or 14) went to other Disney resorts. I got 4 windows and one seat.
It is hard as hell communicating through Aliexpress, so I need to confirm the 5/10 before I order.
If I get this, I will screw it to a piece of birch and set the birch with plaster of paris
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I could be wrong but unless it clearly says minutes, I assume degrees. If so your link shows a rather low-resolution device, looks like up to 10 degrees, and only one division per degree.
If you want a 2D level, at least this one clearly indicates it has 4 divisions per degree (eg. 15 minute). https://www.aliexpress.com/item/HACCURY-High-Quality-Metal-Universal-Bullseyes-Level-Spirit-Level-bubble-Black-Color-accuracy-15-2mm/32832307350.html (https://www.aliexpress.com/item/HACCURY-High-Quality-Metal-Universal-Bullseyes-Level-Spirit-Level-bubble-Black-Color-accuracy-15-2mm/32832307350.html)
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I think the first one is intended for leveling RVs and such and is degrees. The packaging certainly suggests an external mounting such as one would want in such an application.
The second one looks as if it would be great for setting up machinery to get it approximately leveled before switching to an arc second level. Amazingly, just the vial alone is $1.98.
https://www.aliexpress.com/item/HACCURY-66-10mm-Spirit-Bubble-level-Degree-Mark-Surface-Circular-Level-Bubble-for-Measuring-Tool-Green/32789406307.html (https://www.aliexpress.com/item/HACCURY-66-10mm-Spirit-Bubble-level-Degree-Mark-Surface-Circular-Level-Bubble-for-Measuring-Tool-Green/32789406307.html)
This style would be easy to mount and not much more money than the bare vial. Washer shims would level it quite easily as 15 minutes is about 0.007" over the ~40 mm radius of the mounting holes. Lapping washers to thickness on a wet piece of 100 grit wet or dry sandpaper on a flat surface (plate glass or stone countertop) would be very quick and easy. Just wet the paper down on both sides and do figure 8's with the washer until it's the required thickness. The water on the back of the paper holds it flat to the surface very nicely.
https://www.aliexpress.com/item/HACCURY-90-17mm-High-precision-level-Construction-Machinery-Level-bubble-universal-protractor-Shell-Black-Bubble-Green/32668111401.html (https://www.aliexpress.com/item/HACCURY-90-17mm-High-precision-level-Construction-Machinery-Level-bubble-universal-protractor-Shell-Black-Bubble-Green/32668111401.html)
For @ez24's application I think it's ideal.
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Here's a possible differential screw arrangement- it turns out you can easily buy a straight 3/8 x 27 tpi tap. Never heard of it, but there it is. Make a bronze plug threaded 3/8 x 27 on the OD. Drill and tap it 1/4 x 28 (common tap). Knurl a section on the top to grip, or slot it for a coin or screwdriver. Put the plug in the plate you want to move (tapped), and attach a 1/4 x 28 screw to the fixed surface below. That will give you an equivalent 756 tpi adjustment screw. 27 tpi is a common pipe thread, so almost all imperial lathes will have a setting or gear for it.
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ez24, I don't know how temperature dradients affect this, but I like the old idea of a hydrostatic hose balance.
A hose surrounding your building with 3 or 4 stubs at the corners to monitor the level.
(Water need some anti live/ant freezing components , and maybe a glycerin/oil topping to reduce vaporation)
Capacitive (or optic) level monitoring...
One could regulate the water level ( hose volume) on one corner (if your house has corners ;) .. submarine windows sound geek ), so the others show the difference ...
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Here's a possible differential screw arrangement- it turns out you can easily buy a straight 3/8 x 27 tpi tap. Never heard of it, but there it is. Make a bronze plug threaded 3/8 x 27 on the OD. Drill and tap it 1/4 x 28 (common tap). Knurl a section on the top to grip, or slot it for a coin or screwdriver. Put the plug in the plate you want to move (tapped), and attach a 1/4 x 28 screw to the fixed surface below. That will give you an equivalent 756 tpi adjustment screw. 27 tpi is a common pipe thread, so almost all imperial lathes will have a setting or gear for it.
Thanks, Conrad! Now you know my Logan has a quick-change gearbox with a threading range of 4 to 224 TPI, and it skips 27. I think my Jet is the same way, but it does metric as well. The tap would allow me to make a steel die, and that would likely serve well on a piece of bronze.
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I could be wrong but unless it clearly says minutes, I assume degrees. If so your link shows a rather low-resolution device, looks like up to 10 degrees, and only one division per degree.
If you want a 2D level, at least this one clearly indicates it has 4 divisions per degree (eg. 15 minute). https://www.aliexpress.com/item/HACCURY-High-Quality-Metal-Universal-Bullseyes-Level-Spirit-Level-bubble-Black-Color-accuracy-15-2mm/32832307350.html (https://www.aliexpress.com/item/HACCURY-High-Quality-Metal-Universal-Bullseyes-Level-Spirit-Level-bubble-Black-Color-accuracy-15-2mm/32832307350.html)
You are right ! :-+ At first they said 5' but I wrote back and spelled out the words and they wrote back 5-10 degress. So this is out.
The latest "in" :
https://www.aliexpress.com/item/High-Quality-Level-Vial-Bubble-Glass-Tube-Spirit-Level-Measurement-Instrument-5-2-mm-14-100MM/32879077293.html?spm=a2g0s.9042311.0.0.75ec4c4d4szs3u (https://www.aliexpress.com/item/High-Quality-Level-Vial-Bubble-Glass-Tube-Spirit-Level-Measurement-Instrument-5-2-mm-14-100MM/32879077293.html?spm=a2g0s.9042311.0.0.75ec4c4d4szs3u)
What is really "good" is this seller is the same (different company names) as the 4" 2mm x 100mm and Eric was concerned that I was getting my orders mixed up. I am getting old (70) and senile so I really appreciate his checking on me. So I ordered some 5' 2 mm x100 mm vials
I also ordered this
https://www.aliexpress.com/item/Full-Metal-Professional-Gradienter-Surveying-Camera-Tripod-Head-Measurement-Leveler-Level-Regulator-3-8-Screw-Mount/32334881870.html?spm=a2g0s.13010208.99999999.264.4c293c00RDugYc (https://www.aliexpress.com/item/Full-Metal-Professional-Gradienter-Surveying-Camera-Tripod-Head-Measurement-Leveler-Level-Regulator-3-8-Screw-Mount/32334881870.html?spm=a2g0s.13010208.99999999.264.4c293c00RDugYc)
I will take out the center screw and cork and fill in with plaster of paris that I will color with food dye. I want to recess the vials and if I glue them, I do not want the glue to show. Since the vials are bigger than this mount, I will have to figure the mounting after I get everything.
I want to make this look as good as I can.
Thank you JBeale for starting this topic :-+
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Thank you JBeale for starting this topic :-+
Yes, and how is the electronic level coming along? Are you still measuring plate tectonics and the gravitational pull of the moon on your driveway?
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Why are you fixed on aliexpress? Ebay seller offers a UK located 3"/2mm vial, much more trustworthy.
https://www.ebay.com/itm/Ersatz-Wasserwaage-Glaslibelle-Blase-Empfindlichkeit-Feder-100x-9-5mm/132588613741 (https://www.ebay.com/itm/Ersatz-Wasserwaage-Glaslibelle-Blase-Empfindlichkeit-Feder-100x-9-5mm/132588613741)
-branadic-
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https://www.aliexpress.com/item/HACCURY-90-17mm-High-precision-level-Construction-Machinery-Level-bubble-universal-protractor-Shell-Black-Bubble-Green/32668111401.html (https://www.aliexpress.com/item/HACCURY-90-17mm-High-precision-level-Construction-Machinery-Level-bubble-universal-protractor-Shell-Black-Bubble-Green/32668111401.html)
For @ez24's application I think it's ideal.
Thanks rhb but 1 degree is too much. I calculate this is 2.5 inch drop at 12 feet. I once had this drop and was lucky it was to the side so I used some 6x6s as shoring as I jacked it up. It is 10x12 but 15 feet high (has a loft). I was scared shitless and I do not want to go through that again. I do not know what I would have done it was leaning over the edge of the canyon (cannot use shoring). So with the 5' and at a max of 10' works out about 1/2 inch. This is when I can start making plans to lift it. It is a 1/2 day job for two people (for safety). It takes 2 - 20 ton jacks to lift one side. Two 12 ton jacks will not budge it. I have a large collection of jacks :-DD One thing I have learned and that is how to move buildings.
Be sure to let us know what you do with your 4" vials.
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> how is the electronic level coming along?
Several days of operation shows a big temperature-dependent offset. Likely related to my casual use of cheap hot-melt glue (I think it is 50% wax) to temporarily hold the capsule in place. That material has a huge(!) thermal expansion coefficient. No time for experiments recently, but next chance I get, I will try some plaster for mounting instead.
Update: I did a comparison with an ebay 4"/2mm level and I believe the sensitivity of the prototype capacitive readout level is about 1" = 25 uV, while short-term noise = 2 uV rms so I have a noise level of about 0.1 second of arc (RMS), and maybe about 0.35 seconds peak-to-peak (rough visual estimate); not too bad. Longer-term drift is awful, but I hope to improve that.
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English version of brandadic's listing.
www.ebay.com/itm/Replacement-Glass-Vial-Spirit-Bubble-Level-nib-Accurate-100mm-x-9-5mm-Clear/142762523186 (http://www.ebay.com/itm/Replacement-Glass-Vial-Spirit-Bubble-Level-nib-Accurate-100mm-x-9-5mm-Clear/142762523186)
They do 45"/2mm which is still too sensitive for ez24 ?
"Thanks rhb but 1 degree is too much. I calculate this is 2.5 inch drop at 12 feet."
On this round one, you'd quite easily see around 1/10 degree = 0.25 inch drop at 12ft ?
https://www.ebay.com/itm/Acrylic-Large-Spirit-Bubble-Level-GR-Liquid-66mm-Bulls-Eye-Bullseye-Vial-Round/132378829060 (https://www.ebay.com/itm/Acrylic-Large-Spirit-Bubble-Level-GR-Liquid-66mm-Bulls-Eye-Bullseye-Vial-Round/132378829060)
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... I like the old idea of a hydrostatic hose balance. ...
Thanks
At first I did not like the idea of using a water hose because years ago I used a 1/2" x 100 ft clear hose that only lasted a couple of uses because of the minerals in the water coated the inside (I should have used distilled water). But now I am starting to like the idea.
I would use "funny pipe" (the best flexible pipe there is) and some sort of glass tubes (the sun is hot is So Calif). So as I wait and work on my 5' vials I will think how to do this. I will mount them on the ground around the building. I like the idea of having two systems, one inside and one outside.
I did not understand the pipette idea - now I do :-+ I am thinking of using funny pipe (again the best pipe in the universe) and somehow connect to pipettes (the pipe comes with 1/2 pipe threads) - install the pipettes in 2" ABS (protection from sun) - cut slots in the ABS so I can see the pipettes. Take 3 - 90 lb bags of concrete and put on the ground and drive a steel stake into the bags. Wet the bags- when hard - fasten the ABS pipe to stake - install pipettes :-+
The ends need to be open for air so I need to figure out how to keep out the bugs -- any suggestions ?
Boy I wished I had thought of this 20 years ago |O
This is extremely important to me. If this building (I call it the "villa" - because it cost me as much as a villa) gets out of control, I will have to sell my house. The next buyer will tear down my house and put up a million dollar house (my house is crap but the land is valuable). The villa will be worth keeping and with the house gone they could get machinery to the bottom of the canyon and brace the villa the correct way. I once tried to rent my house out - three parties came over and all they all wanted to see was the villa because it has an ocean view - the only ocean view I have
The reason I built a villa on a compost pile was because of the ocean view (a big mistake) At the time I did not realize how insane I am.
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Why are you fixed on aliexpress? Ebay seller offers a UK located 5"/2mm vial, much more trustworthy.
https://www.ebay.com/itm/Ersatz-Wasserwaage-Glaslibelle-Blase-Empfindlichkeit-Feder-100x-9-5mm/132588613741 (https://www.ebay.com/itm/Ersatz-Wasserwaage-Glaslibelle-Blase-Empfindlichkeit-Feder-100x-9-5mm/132588613741)
-branadic-
I am located in Calif. I cannot read the ad but I see a " 3" /2mm ". I think this is a typo. I once saw this PIE vial on Aliexpress but I cannot remember the details.
I have had good luck with Aliexpress. I believe blueskill said it was because they are closely regulated by their government.
Because of my experience my ordering goes like this 1. Aliexpress 2. Amazon 3. Walmart 4. Desperation 5. Finally ebay
Of course Chinese made stuff is Chinese made stuff. I only use Amazon for expensive items.
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> how is the electronic level coming along?
Several days of operation shows a big temperature-dependent offset. Likely related to my casual use of cheap hot-melt glue (I think it is 50% wax) to temporarily hold the capsule in place. That material has a huge(!) thermal expansion coefficient. No time for experiments recently, but next chance I get, I will try some plaster for mounting instead.
Do you need any more 4" vials ?
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Turn the pipettes tip up. You'll need to check when reading them to make sure that the tips aren't plugged. Mineral oil from the drugstore should be immune to most problems. The graduation numbers will be upside down, but that should not be a problem as you will be interested in relative movement. You're really concerned about the movement of the piers on which the house rests, not the house itself. As long as the piers don't move, movement of the house doesn't matter. The piers moving does. The ground the piers rest upon moving matters. That's one of the issues with using level vials in the house. Houses are pretty flexible. And piers can move even when the surface of the earth is not. However, if you have a water level on the house supports, a water level on the ground and a bubble vial in the house you'll know for certain what is moving. It sounds as if you are adjacent to a cliff or very steep slope. A water level on the ground near the house and one as far away from the cliff as you can get is important. If the ground is moving underneath you, you need to know about it before there is a landslide, not when it happens.
I'd also suggest using PEX tubing, which is likely what you're describing as it has become very popular for plumbing. Epoxy the pipette to a PEX fitting and then attach to the PEX. I don't know how PEX does in sunlight, so a piece of black polyethylene to protect if from sunlight might be a good idea. I have no idea what "funny pipe" is. PEX uses brass fittings which are clamped to the tubing by a copper ring.
That round level I linked is graduated to 0.6" in 12 ft. It's the same vial as StillTrying linked. So as a daily spot check you'll quickly notice if you've had 1/4" movement in 12 ft. In fact, given the sensitivity of the eye to circular centering, I suspect you'd immediately notice a movement of 1/8" or less in 12 ft if you have it accurately centered.
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English version of brandadic's listing.
www.ebay.com/itm/Replacement-Glass-Vial-Spirit-Bubble-Level-nib-Accurate-100mm-x-9-5mm-Clear/142762523186 (http://www.ebay.com/itm/Replacement-Glass-Vial-Spirit-Bubble-Level-nib-Accurate-100mm-x-9-5mm-Clear/142762523186)
They do 45"/2mm which is still too sensitive for ez24 ?
"Thanks rhb but 1 degree is too much. I calculate this is 2.5 inch drop at 12 feet."
On this round one, you'd quite easily see around 1/10 degree = 0.25 inch drop at 12ft ?
https://www.ebay.com/itm/Acrylic-Large-Spirit-Bubble-Level-GR-Liquid-66mm-Bulls-Eye-Bullseye-Vial-Round/132378829060 (https://www.ebay.com/itm/Acrylic-Large-Spirit-Bubble-Level-GR-Liquid-66mm-Bulls-Eye-Bullseye-Vial-Round/132378829060)
Thanks even 90" is too sensitive (I have a couple of these). I have been looking at these bullseyes for awhile now. Took another look at them to see how you can read 1/10 degree. Since each degree has 4 divisions, the difference is 1/4 degree. I think I could see 1/8 (I have an old set of eyes), so that would be good enough.
I like this seller:
https://www.aliexpress.com/item/Circular-Bubble-Level-Spirit-Level-Measuring-Device-Krenometer-For-Crane-Size-90-17mm-1PCS/32837969646.html?spm=a2g0s.9042311.0.0.5a4a4c4dmmtNp5 (https://www.aliexpress.com/item/Circular-Bubble-Level-Spirit-Level-Measuring-Device-Krenometer-For-Crane-Size-90-17mm-1PCS/32837969646.html?spm=a2g0s.9042311.0.0.5a4a4c4dmmtNp5)
So I ordered this - I think it a better fit for the tripod head than the 100mm 5' vials.
I will use the 5' vials for a x-y measurement. This will help determine how much to raise end side. The circular will help me to place concrete bags at the bottom. The pipettes will show what the earth is doing (not always the same as the villa).
:-+ :-+
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I *really* want to emphasize that the major issues you face are soil compaction under the foundation and incipient slope failure (aka landslides). You really need to measure both using a fluid level system. Measurements in the house with a level are just a convenient means of alerting you to the need to check the fluid level measurements. You cannot accurately measure soil compaction and ground movement with a level vial. Fluid level systems are the *only* thing that will handle those issues appropriately. A high resolution tiltmeter will tell you something is happening, but not what.
There are solutions to soil compaction, but incipient slope failure is really expensive to mitigate. If you detect that it's time to sell.
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Yeah, all the round ones are 60mm dia, and 4 divisions per degree, = 0.625 inch at 12ft.
This one is very cheap for me, the 2nd pic is 70mm across on the screen, I measured it, and the 1/4 deg. divisions are very clear, although not the bubble.
https://www.ebay.com/itm/Bullseye-Spirit-Level-Large-Round-Circular-Bubble-Vial-60mm-Caravan-Furniture/222588993994 (https://www.ebay.com/itm/Bullseye-Spirit-Level-Large-Round-Circular-Bubble-Vial-60mm-Caravan-Furniture/222588993994)
I've never had any problem with fleabay from here, even when it's a gift from HK(2 weeks), never used CH.
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You're really concerned about the movement of the piers on which the house rests, not the house itself. As long as the piers don't move, movement of the house doesn't matter.
There are no piers, the villa sits on bags of concrete or whatever I can get under it. A bag is 3 1/2 ", a 2x6 is 1 1/2 inches. I also use 3/4 and 1/2 plywood. I designed the villa to be movable. I built it 12 feet from its current location and moved it with rollers made from 2 " pipe filled with concrete. This was a major error. It moved 6 feet by itself toward the edge of the cliff. It stopped 2 feet from the edge. Years later I watched a house move and they said that was very very very dangerous, I know. What they do is put rollers under one side and jack up the other side with hydraulic jacks at an angle. If done correctly the jack will slip off at the correct time. If not they push it off the jacks. Very safe and clever. They got a 2,000 sq ft house within 1/4 inch where it was suppose to go. Once the building falls off the jacks it will not move.
It sounds as if you are adjacent to a cliff or very steep slope. A water level on the ground near the house and one as far away from the cliff as you can get is important. If the ground is moving underneath you, you need to know about it before there is a landslide, not when it happens.
Yes to very steep slope, but there is bedrock 12 feet away where I can place the reference level.
I'd also suggest using PEX tubing, which is likely what you're describing as it has become very popular for plumbing. Epoxy the pipette to a PEX fitting and then attach to the PEX. I don't know how PEX does in sunlight, so a piece of black polyethylene to protect if from sunlight might be a good idea. I have no idea what "funny pipe" is. PEX uses brass fittings which are clamped to the tubing by a copper ring.
I have a 100' roll of 1/2 PEX but funny pipe is better (immune to the sun) and can be buried.
https://www.toro.com/en/professional-contractor/irrigation-sprays/super-funny-pipe (https://www.toro.com/en/professional-contractor/irrigation-sprays/super-funny-pipe)
I use this for everything outside and in 25 years not one failure. I have a 150 foot line hooked up to a hose bib faucet at 100 psi for over 20 years now and in some areas it is exposed to the sun.
That round level I linked is graduated to 0.6" in 12 ft. It's the same vial as StillTrying linked. So as a daily spot check you'll quickly notice if you've had 1/4" movement in 12 ft. In fact, given the sensitivity of the eye to circular centering, I suspect you'd immediately notice a movement of 1/8" or less in 12 ft if you have it accurately centered.
I bought it. It will be the go to level. The 5' vials will be a double check. The pipettes will monitor the hill.
Now I have a question about taking pictures and will post a question about this
thanks
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There are no piers, the villa sits on bags of concrete or whatever I can get under it.
Have you thought about putting some piers under it and stabilizing it? People add basements under existing houses, so adding some piers for a 10' x 12' building should be pretty straight forward.
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There are no piers, the villa sits on bags of concrete or whatever I can get under it.
Have you thought about putting some piers under it and stabilizing it? People add basements under existing houses, so adding some piers for a 10' x 12' building should be pretty straight forward.
Impossible There is at least 6 feet of concrete rubble under it. I cannot access it with machines. Wished I could but I would have to go down at least 20 to hit the bedrock then drill into the rock because it is on a slope.
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From the description it sounds as if you have several issues:
The soil is compacting under load. This can be particularly severe if it has high organic content.
The soil is being pushed down slope by the load.
The soil is moving down slope under its own weight.
The first two can be mitigated by increasing the surface area upon which the structure rests. The last can only be resolved by piers drilled into bedrock of sufficient strength to resist the shearing force of the soil. It also resolves the first two.
In many respects, pouring a larger, heavily reinforced concrete slab adjacent to the villa and moving the villa onto that might be the best option. One could bore piers with a portable auger 6-10 feet and fill those with concrete and rebar tied into the rebar in the slab. That will mitigate near surface soil compaction and also the effects of expansive clays. It won't stop the movement, but would slow it down a great deal. The slab will still move, but with piers under the house which rest on the slab, compensating for the movement just requires jacking and inserting a shim from time to time. Once the house is resting on the new slab, cast concrete piers in place with a steel plate on top. Every time you get 1/8" of settling, slide a sheet of 1/8" plate on top of the stack.
Of course, all this is speculation without pictures of the situation.
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In case of interest, here's the output of my garage floor tiltmeter this morning starting at 7:10 am. One vertical division (20 uV) is just under 1 arc-second, per my very rough calibration. The time axis units are hours. After sunrise as things warm up, the output drift becomes large, which you see towards the right. There are some other interesting features:
Time Event
----------------------------------------------------------------------------
0.77 a large spike from my weight as I walk right next to the sensor
0.86 small ~0.4 asec tilt up from car in the driveway leaving
1.14 ~3 asec tilt down from car in the garage leaving, with slow recovery
1.4 - 1.8 about half-hour of increased noise, as slab adjusts to departure of car (?)
----------------------------------------------------------------------------
The thing I'm now curious about is that time interval for about a half-hour starting at t= 1.4 with increased noise, maybe 0.3 asec or so. This is not a one-time event; I have seen a similar period of such noise starting after the car leaves the garage, having been parked for some time. I wonder if it's related to the concrete, the soil underneath, or something else.
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Very interesting. ez24 sent me a couple of the 4"/2mm vials which arrived today. No copper foil tape though, so it will be a while before I can replicate this.
The rebound after the car leaves is the opposite of what happens when a load is a suddenly applied to saturated soil. The noise may be related to ground water movement. The behavior is similar to backpacking mattresses with light foam and a air tight envelope. If you just open the valve it will gradually inflate itself, but with a very small pressure differential the flow is very slow. The pore spaces in the soil need water flow to expand.
If it is caused by movement of water it will correlate with changes in the weather. The effect will be stronger after rains and weaker during dry spells as the zone of saturation moves up and down.
It will be interesting to see what the arrival of the car in the garage looks like.
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The thing I'm now curious about is that time interval for about a half-hour starting at t= 1.4 with increased noise, maybe 0.3 asec or so. This is not a one-time event; I have seen a similar period of such noise starting after the car leaves the garage, having been parked for some time. I wonder if it's related to the concrete, the soil underneath, or something else.
This is probably real. The whole house creaks and groans when readjusting to the changes forced upon it. I've been in the basement of our house, and been convinced somebody is walking upstairs, but it is just the whole house readjusting to temperature changes of the roof, or maybe air pressure changes.
Jon
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How did you correlate inclination to voltage? Do you have a long-term data-set?
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My "calibration" was simply observing the voltage change as I stood close, then far away on the garage slab relative to the sensor in realtime, as compared with the simple 4"/2mm manual-readout bubble level in the same place on the surface plate. I found an indicated 2" of deflection from the bubble level, and about 50 uV change on the voltage readout. So, about 25 uV per arcsecond. Roughly, it's by no means accurate, but I'm confident it's the right order of magnitude at least.
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@JBeale
How did you solder to the foil tape? On the vial or before? I can think of 3 options for the capacitor plates:
copper foil
silver paint
segments of 0.567 ID brass tubing mounted separately from the vial with springs to press into place.
I'm not sure how to ensure a reliable connection to silver paint and I have no experience with the copper foil tape. How good is the adhesive long term? The brass tubing seems to me the most stable option over 20 years.
I'm just getting started with two 4"/2mm vials courtesy of @ez24 which are 0.560 diameter. The Chinese pivot using pointed screws requires a thick wall tube, so I'm thinking gas pipe with the top and bottom cut away and annealed before setting the vial in plaster of paris. Then mount with a differential adjustment screw in a piece annealed steel channel.
I have in mind bolting these oriented NS-EW under my deck to bedrock, so long term stability is desirable. I'm about a mile from a large Corp of Engineers lake, so I should see lots of interesting effects from the water level changing in the lake.
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It was too scary to solder the foil afterwards, I was worried about the vial. So I soldered first, then peeled off the backing and stuck them on. It was quite fiddly to do this with the sticky tape and short fragile wires, but I managed it, with help of long-nose pliers and tweezers. There is some question about whether the adhesive may allow some relative movement; I don't know. I was thinking plain Cu foil which is held in place with a layer of shellac or similar, might be more stable, but I don't know that either.
If you use a thicker electrode eg. brass tubing, it may not be tight against the glass vial, might cost some sensitivity. Might also cause temperature effects, if the geometry changes from expansion with temperature. If you use a spring against it, that would have to be some non-conductive type. But most likely all of these possibilities work, and the difference between them may be small. All part of the fun of this game, I guess!
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I *like* plain Cu foil held in place with nail polish. Shellac is hygroscopic and water soluble. Nail polish is polystyrene dissolved in toluene. That should be stable for a very long time. Actually, the self stick should be OK with an overcoat of nail polish and the adhesive simplifies placement.
Any thoughts yet about a long term data logger? I assume you're using a 34401A or similar at present. I'd like to build a dedicated data collector using one of the 24 bit, 90 samples per second chips used for digital scales and something like an ESP32 to collect data and then upload it once a day via WiFi.
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Funny thing, it's easy to find adhesive-backed copper tape, but seems plain Cu foil is less common. This might work, https://www.amazon.com/Genuine-Copper-Leaf-Sheets-Blattgold/dp/B00RJNB992/ (https://www.amazon.com/Genuine-Copper-Leaf-Sheets-Blattgold/dp/B00RJNB992/) ...though it may be hard to solder to superthin Cu leaf without tearing it. They also offer a specialized "Metal Leaf Adhesive" whatever that is, but I'm sure nail polish works.
My meter is another antique, a Keithley 196 DMM from ebay. Only uh, 9 years out of cal... I have played around with many different 24-bit ADCs. For my needs the tilt meter doesn't need a fast readout, 1 Hz is more than enough and for that you can go with a simple one like LTC2400 talking with any sort of microcontroller- I usually use a Teensy or Arduino type for longer term datalogging. I have some of those that have been working for some years.
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From the description it sounds as if you have several issues:
The soil is compacting under load. This can be particularly severe if it has high organic content.
Yes - a 6 foot compost pile that last time I checked was 1/2 " (10' of concrete rubble on top of it) with water flowing through it
From the description it sounds as if you have several issues:
The soil is being pushed down slope by the load.
The soil is moving down slope under its own weight.
Yes to both - attached poor Google pic - some trees have been removed
From the description it sounds as if you have several issues:
The first two can be mitigated by increasing the surface area upon which the structure rests. The last can only be resolved by piers drilled into bedrock of sufficient strength to resist the shearing force of the soil. It also resolves the first two.
Surface area - I put 100's of yards of concrete rubble around it. For years I checked Craigs List for free rubble
Piers drilled into bedrock is the really for sure answer - way beyond my ability to pay for them. What I am going to do is print out your response and give a copy to the next owner
Of course, all this is speculation without pictures of the situation.
I went down there today and took pictures. Good news and bad news.
Bad - the area looks like crap - it looks like a junk yard - very depressing - 2 years ago a storm snapped a 6x12 " beam in a structure next to the villa. For 3 years I have tried to figure out how to fix it. I get very depressed every time I see it :palm:
Good - it has not moved in 3 years :-+ Three years ago (Mar 2, 2015) I bought this :
https://smile.amazon.com/gp/product/B006JR8XBG/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
And measured 0.00 on a door frame (two readings at right angles). Today I measured again and it reads the same.
Another door frame reads 0.45 lean towards downhill, but I cannot remember if I checked it 3 years ago.
When I built it, I used cheap HF levels.
Actually I do not understand why it has not moved
I will post pictures in a few days, I need to recover from the shock of the mess and damage
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It was too scary to solder the foil afterwards, I was worried about the vial.
I just finished machining a nice slip-fit into an aluminum tube with press-fit endcaps. I was getting worried about thermal expansion and cracking.
The 4" vials are a little touchy, but really you see movement on your concrete slab? I had mine set up on a kitchen counter, substantial wood frame house (2x6 joists and 2x10 subfloor, 16" tile, granite counter tops) and I only see about 8" movement when I stand to either side.
rhb - a big drop of lipstick red nail polish on each end of the vial to hold it in place in my aluminum tube? I might be able to get my assembly put together tonight.
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A suggestion:
Dig a post hole 2-3 ft deep in an area which is the least disturbed by human activity (fill, gardening, etc). Make two piles, the upper part of the ole and the lower part of the hole. Spread it out and let it dry.
Then sift out all the material that will not pass through an 1/8" hardware cloth screen. Set that aside. Take the material form the top and bottom sections that passed through the screen, mix it thoroughly and measure off by division enough to fill a wide mouth gallon jar (available from any restaurant by asking) 4 deep with dirt.
Divide the material that didn't pass through the screen in the same fraction as you put in the jars. Rinse it and pour the water in the appropriate jar.
Fill with water, set somewhere where it can sit undisturbed for several days and stir like mad to get all the sand, clay and organic matter entrained in the water. Then let it settle until the water is clear enough to see the sediment on the bottom looking through the mouth of the jar.
Do this for the upper and lower part of the hole and label the jars when you do it.
Once it settles, you'll have a good estimate of the soil composition by looking at the layering in the jars. That will provide very important information for choosing a mitigation strategy.
In central Texas swelling clays are a huge problem. But rather than drill some footings to bedrock, the recommended solution is to water your house with a soaker hose on a timer. Woe unto you if you ignore it as I did. My house moved enough to break a window and open a 3/8" gap in the garage wall. What happens if every time it rains, the clay expands and a little bit is forced out the side from under the house. Then it dries out and the house settles a little bit. Over the course of a few years it becomes a major problem. The only solution is to dig holes 3-4 ft deep all around the perimeter of the house that extend under the slab. A thick slab of concrete is poured in the bottom of each hole and after that has cured for a week, the house is leveled with jacks and more concrete is poured in the hole to hold it.
What this does is move the support of the house down below the layer of soil which is subject to drying and thus stable. Typical cost for this is $15-18k. There are other methods using short driven piers, but there is no control over where they go, One of my foundation engineering textbooks has a picture of one of these where they excavated after driving and the end of the series of piers threaded on the cable makes an arc and is headed for the surface.
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@JBeale I have a rolling mill and plenty of copper wire. Time to put the rolling mill to serious work making plain copper foil. Should I make a foot or so extra for you.
@metrologist Nail polish should do the trick. Lots of electronics has that on the screws to keep them from moving. i assume you made the walls of the Al tube thick enough that tightening the pivot screws won't deform the tube. If there's any question, drill some shallow holes with a #60 drill for the pivots.
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I'm still waiting for the vials to arrive. In the meantime I prepared a board from another project with PCap01-AD capacitance to digital converter and the firmware/config. First step will be to reproduce the results with the copper foil. Next step is to improve the way how the electrodes are attached to the glas without force or glue such as silver ink or similar ways. Step three will be, how to attach the vial to a base. One solution cold be an optical flat, but they are rather expensive.
-branadic-
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@metrologist Nail polish should do the trick. Lots of electronics has that on the screws to keep them from moving. i assume you made the walls of the Al tube thick enough that tightening the pivot screws won't deform the tube. If there's any question, drill some shallow holes with a #60 drill for the pivots.
What makes you think I'd have such foresight? The tube started as thin-walled tube and had maybe 2mm skimmed out of it. I didn't even want to use aluminum and hoped to find an old piece of thick-walled iron pipe - but used what I had. I'm still kind of working out the mounts, they may just end up being vertical studs and nuts.
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The 4" vials are a little touchy, but really you see movement on your concrete slab? I had mine set up on a kitchen counter, substantial wood frame house (2x6 joists and 2x10 subfloor, 16" tile, granite counter tops) and I only see about 8" movement when I stand to either side.
You don't have to take my word for it, this link contains the video.
https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/msg1566820/#msg1566820 (https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/msg1566820/#msg1566820)
In the video background at top, you see the concrete surface of the slab it is resting on. The bubble shows a small, but noticeable movement, I estimate 1/4 division which is 1 arc-second. That was when I moved to within a few feet. If I stand immediately next to it, I get at least 2 arc-sec of movement. Other people have reported a similar amount of motion on a slab floor.
Also, as you see in the other video here, my kitchen countertop responds in a similar way to yours.
https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/msg1567927/#msg1567927 (https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/msg1567927/#msg1567927)
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You need a 3 point mount with a cross vial in the direction of two balls. If you want a flat base buy a machinist's level for $50-80. If you're setting up a reference surface for long term monitoring get a small piece of stone counter top.
My offer of plain copper foil is open to any who are interested. Just send me a PM with a mailing address and I'll send 4 inches per vial you want to prepare.
An R-10 O ring is a good fit for the 4"/2mm vials I got from @ez24. That's what I plan to use to force the foil against the vial while I wait for the adhesive to set.
I'm glad to hear I'm not the only one who paints himself into a corner.
But I hear my lawn mower calling....
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The countertop fragment is a great idea. I see Amazon also offers "Grizzly G9647 6-Inch by 8-Inch by 2-Inch Granite Surface Plate, No Ledge" for $34.
https://www.amazon.com/Grizzly-G9647-6-Inch-Granite-Surface/dp/B0000DD0KC/ (https://www.amazon.com/Grizzly-G9647-6-Inch-Granite-Surface/dp/B0000DD0KC/)
They claim a +/-0.0001" surface (tenth mil), which is probably not a specified value for a countertop.
I have access to a mill so I could make my sensor bottom surface reasonably flat.
For purposes of fixed long-term monitoring, I'm not sure if that's preferred over a 3-point mounting.
I want to be able to reverse it 180 degrees at any time to check zero drift, but so long as the supporting surface is flat, that should work either way.
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If you want to check for drift by reversal use a surface plate and 3 point mounting. Or hand lap a scrap of counter top at the mount contact points using the surface plate to set the level and then the level to monitor the lapping.
Drill two holes in the counter top and epoxy threaded inserts in place to hold the vial assembly in place. Then set the counter top in concrete in your observatory. If you really want to refine it, set press fit jig bushings in the mounting plate, use those to set hardened dowels with epoxy or molten sulfur.
But if you're doing that you need to set the levels perpendicular to a few arc seconds to justify the labor. So still more work.
Then you'll need a Lacoste-Romberg gravimeter station to monitor lunar changes in the gravity vector.
If there is significant ground water withdrawal where you live, you'll be able to observe that extremely well even without the gravimeter.
Time to start making copper foil.
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I'd never tried this before. Not surprisingly it's not as easy as I'd hoped. I can make foil 0.0035 thick but I'm having a lot of problems with the edges crinkling. Copper work hardens very quickly, so I can only make a couple of passes before annealing.
I *think* that I need to anneal, clamp the ends and stretch the center so the crinkles go away or are at least diminished.
It may be that I'm trying to get too much a reduction in a single pass and the rolls are deflecting. It's 80 F in my shop, so I think I'll sit in the A/C and read up on rolling.
Rolling wire is not that hard. I got good results rolling 12 AWG, but it's only 0.15" wide. But I made over 2 ft of that before I decided to try rolling a slit and flattened inch long section of copper pipe.
I'll probably dig around for some 8 AWG ground wire and try that in the morning when it's cooler. For the vials I have foil 0.3-0.6" wide seems to me about optimal.
Edit: I got 2 ft of 4 AWG, (0.20 diameter) and rolled a 2" piece to 0.0045" thickness and 0.25" wide. The 2" piece turned into 3' of foil tape. I'm going to try a piece of copper pipe again, but this time annealing, stretching straight and annealing again between passes through the rolling mill. It gets rather tricky once you get below about 0.020"
Edit 2: The bubble in my vials is approximately 0.25" x 1.4" . That suggests that the optimal capacitor plates are 0.25" x 1.5" on the top and 0.25" x 4.5" on the bottom. That should maximize the effect of the bubble on the capacitance. I made 33" of tape, so I have enough for 2 more vials besides what I need for myself. I broke the piece while working it, so 2" will actually make enough for 5 vials. So I'll be happy to practice using my rolling mill fi anyone wants sensor tape..
BTW I got the mill via an Harbor Freight Insiders club circular for $165 which is about 1/3 to 1/2 what Rio Grande charges for the same or similar.
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I'm the opinion that plaster of paris is a very bad idea. Even though CTE is in the order of 12 - 20ppm/K it absorbs water and swells. This is what you don't want.
-branadic-
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Is there any material you could recommend for the purpose? Would grout or portland cement be better?
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If you want an idea on how to mount the level vial take a look at how they managed it in precision levels like shown here:
(https://www.roeckle.com/WebRoot/Store13/Shops/62116134/5B12/4357/F8CF/4551/3D49/0A0C/6D02/B542/Justiereinrichtung.jpg)
Source (https://www.roeckle.com/epages/62116134.sf/en_GB/?ViewObjectPath=%2FShops%2F62116134%2FProducts%2F%22408x%2F200%2FJust%22)
It's a V groove with the mentioned differential screw on the right and a pivot on the left. What is missing here is the base the cross beam is mounted to.
What you can do is to mount the vial in a fixed V groove e.g. made out of Macor and zero the level by software instead mechanical.
-branadic-
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Thin set tile mortar should work just fine if you're concerned about plaster of paris.
I had a piece of 1/2" American standard gas pipe. It's 0.622 ID vs 0.560 OD for the vial, so I'll just use epoxy at the ends of the vial.
As my mill is not set up to run at the moment I chain drilled the pipe and filed it. I then cleaned the paint off the pipe using plumbers cloth backed sanding strip. I'll probably roll some shim stock to center the vial in the pipe.
The total range of this vial is 2 minutes, so I don't see a viable way to avoid the differential screw for a 5" long mount. Full range is 0.0015"
I'm copying the Chinese mount as it's simple to do with minimal tools. I'll mount the PCB on the side of the pipe. It's welded pipe, so I plan to anneal it before assembly.
To make the differential screw I plan to chuck a piece of 5/16" rod in the drill press and drill it out to take a #12-28 screw. After the hole is drilled I'll thread the rod 27 tpi with a die, cut off a short piece, tap the inside #12-28, insert the #12-28 screw and secure it in place with a lock nut.
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I'm not sure I understand what you are planing to do, but I fear this kind of mounting will result in a lot of parasitic capacitance, if copper electrodes have been attached to the vial. This is just an experience of 12 years dealing with capacitve sensors.
Thus my suggestion was to use a base made out of Macor (machinable ceramic) with a V groove and to contact the electrodes by some spring alike flat pieces of nickel sheet.
-branadic-
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If it doesn't work for a capacitance sensor, I can always use it as a normal vial mount.
However, in this case, I don't think the stray capacitance matters. I gave a lot of thought to the stray capacitance problem. So long as the only thing moving is the bubble the strays should null out during the electronic calibration. Mechanical leveling is still required because of the very small dynamic range of the vial.
My chief concern right now is the 10 degree tilt of the assembly pin holes. They don't really matter as the pointed screws are the functional pivots in the Chinese design. But it annoys me that I made the mistake and I'm trying to figure out how to correct it without starting over. Except for a bandsaw and drill press, this is all bench work.
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I got the mounting frame mostly done today, but I need to get some stainless steel foil wrap to anneal the frame before going further. Otherwise it will warp over time.
The background noise is probably surface waves. You could make an interesting seismograph using orthogonal pairs of vials. With 3 stations you could measure direction and velocity. By making up the vials and covering them with heatshrink, they could be set in thin set mortar with something like an ESP32 or a LoRa node to perform the data transfer. That would be fairly easy and cheap to do. The electronics would need to be able to detect that the bubble was centered since you would not be able to see the bubble when placing them. I found that I could hold the bubble on a 4"/2mm vial by pushing up or down on the table it was resting on.
Wherever you live you should be able to observe periods of increased road traffic. You'd need to sample faster, but I don't recall what the typical spectral range for surface waves So I'll look that up tomorrow.
I suspect that multiple stations would make a dandy intrusion detector which could plot every footstep.
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I tried building the circuit using the 4"/2mm vials from aliexpress. I used the regular adhesive-backed copper tape again; I think it's probably good enough. I made the two top electrodes a little narrower than the bubble. This time I used 1.8432 MHz 14-pin DIP can squarewave +5V oscillator from the junkbox plus a 74HC buffer to drive the circuit, and made the two 0.01 uF caps 0.002 uF instead, all the rest was the same. My crude screw-on-end-of-lever arm calibration indicates the full output range of -220 mV to +240 mV covers just 31 arc-seconds. In quiet moments I see about 80 uV of noise which would correspond to about 5 milli-arc-seconds. Not sure if my calibration correct but if so, that's plenty sensitive for my needs. This vial seems to take over 10 seconds to respond after a step change, much slower than the smaller and less sensitive, 1.5 inch long antique vial I used to start with.
EDIT 11-June: A quick test indicates the vial is roughly twice as sensitive- on average- as claimed. Added output graph. My above noise estimate almost certainly optimistic. After a 7-hour run overnight, I see the output has sudden jumps as large as 6 mV, or 0.4 arc-second per my rough calibration. The bubble will track infinitesimal level changes only if the interior is absolutely smooth. My guess is that the supplier did not waste time making the interior surface of this $12 vial any smoother than needed for a simple visual readout, so my circuit is showing the surface roughness as steps in the response. Also possible these were cheap because they were rejects. It's a little disappointing, but not entirely unexpected.
EDIT 2: The vial was not cleanly or securely mounted, so I cannot rule out the step changes overnight as related to thermal expansion + roughness of my own mounting surface. I will try to make a better mount later.
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Nice build. However, more confidence would give a V-block (https://www.norelem.com/us/en/Products/Product-overview/Flexible-standard-component-system/01000-Basic-elements-Subplates-Discs-Profiles-Angle-plates-Tombstones/Profiles/01640-V-block-machined-all-sides-grey-cast-iron-or-aluminium.html?search_keywords=01640-01X100) as available at Norelem.
(https://www.norelem.com/xs_db/BILD_DB/0/www/750/01640.jpg)
-branadic-
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I see the output has sudden jumps as large as 6 mV, or 0.4 arc-second per my rough calibration.
How much movement would it be (in red external gradations) during the logging night?
Could the jumps be because of the red reading marks painted on the outside of the vial?
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V-block from Norelem: V-block (https://www.norelem.com/us/en/Products/Product-overview/Flexible-standard-component-system/01000-Basic-elements-Subplates-Discs-Profiles-Angle-plates-Tombstones/Profiles/01640-V-block-machined-all-sides-grey-cast-iron-or-aluminium.html?search_keywords=01640-01X100)
The V-block looks like a nice idea (EDIT: although with the cheap vials with non-constant OD, better to support only at the ends). Note my photo shows only a temporary support while I was soldering. My electrical measurements were made in a heavy-gauge steel rectangle tube, 0.12" wall thickness. It is rigid and provides electrostatic shielding all around. Last night the vial was however simply resting flat on the unfinished interior metal surface of the tube. Differential thermal expansion could be causing it to be supported by different small bumps, tilting it slightly (?)
The steps in the output are of all different sizes and appear randomly distributed, so I don't think they are related to the exterior red marks.
It is possible to grind an interior profile into your own vial, starting with straight glass tubing, as described below. It is a similar idea as grinding your own telescope mirror. This way, you would have some control over the final surface finish.
---
text: http://fer3.com/arc/m2.aspx/Making-your-own-spirit-level-vialswithout-attached-pictures-Morrow-jan-2012-g17728 (http://fer3.com/arc/m2.aspx/Making-your-own-spirit-level-vialswithout-attached-pictures-Morrow-jan-2012-g17728)
photos: http://fer3.com/arc/m2.aspx/Making-your-own-spirit-level-vialsanother-attempt-send-Morrow-jan-2012-g17731 (http://fer3.com/arc/m2.aspx/Making-your-own-spirit-level-vialsanother-attempt-send-Morrow-jan-2012-g17731)
---
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I just finished my differential screw. For convenience, I used a 1/4"-28 bolt which I drilled through and tapped #6-32 as that was what seemed the best local hardware store and simple tooling option That's only 224 tpi, so not as good as using a 27-28 tpi combination, but I'll use a long handle wrench made for the purpose. The long lever arm will make up for the coarser turn ratio.
I through drilled the bolt by using a drill press as a lathe and then tapped. So a continuation of the doing it the hardway. I shall *not* make the second one this way. I'll use my mill and lathe, but I wanted to demonstrate you don't need a machine shop. Tapping the bolt was pretty nerve wracking as I broke a #6-32 tap a few days ago and did not want to break another.
First photo is the drilling setup. The second is the screw and the other parts. These will now await the arrival of SS foil for the annealing process.
I don't think that a continuous V block is a good idea as the outsides of the vials are not all that precise. I think two point support preferable.
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The V-block looks like a nice idea. Note my photo shows only a temporary support while I was soldering. My electrical measurements were made in a heavy-gauge steel rectangle tube, 0.12" wall thickness. It is rigid and provides electrostatic shielding all around.
While I'm still waiting for the vials I already ordered the V-blocks in different lengths and began to construct the electrical and reliable connections between the electrodes and the PCap readout circuit.
For comparison, would you like to give us some dimensions of your electrodes on the first and second vial? Hopefully post office hurries up soon, can't wait to reproduce the results.
I don't think that a continuous V block is a good idea as the outsides of the vials are not all that precise. I think two point support preferable.
But that is exactly the way how it's done on machine levels. ;)
-branadic-
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I don't think that a continuous V block is a good idea as the outsides of the vials are not all that precise. I think two point support preferable.
But that is exactly the way how it's done on machine levels. ;)
*Not* on mine. Take a look at the photos I posted previously of my Chinese level.
The V block is certainly fine if the vials are made of accurately round constant OD tubing. But my vials are out of round by 0.002-0.004". I've not attempted to check diameter along the length.
I think how you do it is as much dependent upon what you charge as anything. At $800+ one would not be happy with the Chinese construction. But at $50 it's pretty clever. I rather doubt that levels with V block supports use $12 Chinese vials.
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But at $50 it's pretty clever. I rather doubt that levels with V block supports use $12 Chinese vials.
Maybe that is the big difference between your and my construction. I won't use Chineese vials. Thus, a V-block with grinded faces is the more precise way that I can go with. In the groove I will integrate a spring made of a piece of nickel sheet, that connects to the common electrode. I will then use two seperate bridges made of plastic or Macor with another nickel spring inside, that connects to the hot electrodes. This is what I currently design in CAD.
-branadic-
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Maybe that is the big difference between your and my construction.
In part difference in application. I'm interested in a cheap 2 axis tiltmeter with a $50 BoM that would provide remote data collection via LoRa to an Internet connected relay node. I think that's probably doable using the Chinese vials set in thin set on location. The cost of alternatives is a significant impediment in a lot of geophysical applications.
Such a system would make real time monitoring of subsidence due to ground water pumping practical. At present the best option for such problems is airborne synthetic aperture radar or Lidar, both of which limit how often you can afford to collect data. There are a lot of locales where this is a huge issue.
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I was looking at a diff screw using 1/4-20 and M8x1.25 or I think 6-32 and M5x0.8 would be too much.
All roughing done except the ends of the vial carrier. I will machine standard clevis rod ends and use vertical diff screw and the pivot might just be a vertical screw with nut underneath for coarse adjust if not pointed pivots coming in from each side (the the Chinese level).
I really wish I had a surface grinder. I "leveled" this with shims and then measured my lathe bed had 1 thou of twist. I'm surprised I got it that close using a high quality carpenter level.
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After a 7-hour run overnight, I see the output has sudden jumps as large as 6 mV, or 0.4 arc-second per my rough calibration. The bubble will track infinitesimal level changes only if the interior is absolutely smooth. My guess is that the supplier did not waste time making the interior surface of this $12 vial any smoother than needed for a simple visual readout, so my circuit is showing the surface roughness as steps in the response.
Your very first plots seemed to show a stop in the drift just before the jumps, perhaps they all need a very small amount of vibration now and and again to keep the bubble moving.
A small buzzer or speaker in the box that does a quick buzz every minute or so!
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The pointed pivots in the Chinese level are, I think, quite clever. Even if they are not exactly coaxial, if they are tightened with the level approximately true using the pivot and the differential screw, then the angular adjustment range is so small that it doesn't matter. There is a 15x price difference between a cheap Chinese level and a Starrett or other top tier make.
When you look at the V bed construction example that was posted you can see why they are so pricey. Vials ground inside and out and a *very* close fit pivot. The pivot holes are jig borer work on that design. If the vial arm is 5" long on a 0.0001" in 10" level the pivot has to fit to less than half that.
The 1/4-28 & 6-32 differential screw I made this morning was pretty simple to do. Getting the drill bit centered under the bolt is the hardest part. With a lathe it's quite trivial. It's a little less than 1/3 the sensitivity of the 27-28 combination Conrad suggested. BTW The 27 tpi thread is the US recommended standard for thin wall tubing. The 5/8" -27 thread is the standard for microphone stands.
Yesterday I saw a steel version of this:
https://www.ebay.com/itm/Mic-Stand-Adapter-5-8-27-Male-Threaded-to-Hot-Shoe-for-Microphone-Mount-/272625442310 (https://www.ebay.com/itm/Mic-Stand-Adapter-5-8-27-Male-Threaded-to-Hot-Shoe-for-Microphone-Mount-/272625442310)
But now I can't find it. There are also brass versions. So one of the knurled nuts could be brazed in place and the center drilled and tapped 28 tpi. On the other hand 27 tpi taps and dies are under $10 each in smaller sizes.
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Yes, but the imperial/metric combos result in 1270 and 4064 TPI. At a 5" pivot, that would yield 8 or about 2.5 divisions per turn. I may start with an M8x1.25 screw and single-point thread the end for 1/4-20, or I cheap out and just drill the M8 screw and braze in a 1/4-20 that is turned down and pressed in.
Your screw does not look concentric. How do you plan to attach it to your carrier tube?
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I'm hoping it's "concentric enough". If not I'll use my lathe and do it properly. However, I could also use a captive nut if it's close. I think it's more a problem of not being coaxial, rather than not being concentric. So bending the 6-32 screw a little may solve it.
I was a little disappointed in the result. I've done better.
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For comparison, would you like to give us some dimensions of your electrodes on the first and second vial? Hopefully post office hurries up soon, can't wait to reproduce the results.
I adjusted them relative to the size of the bubble, with the goal to make the top electrode just a little bit less wide than the bubble. You can see in the photo the bubble is still visible around the edges of the top electrodes.
For the second, longer vial (the 4"/2mm one), I think the top 2 electrodes were 5 or 6 mm wide, and 37 mm long, and there is a gap of maybe 3 mm between the two top electrodes. The bottom electrode runs nearly the length of the capsule, except leaving the very ends free so the end mounts can contact the glass directly, and it wraps around a little bit more than 1/2 the circumference of the cylinder. At first I tried just 1/2 circumference and then decided it didn't look right, but I don't think the exact dimensions of the bottom electrode affects the result much. If you wanted to make the bottom electrode more narrow, so a continuous V-groove mount could contact the glass directly all the way across, I think that would still work nearly the same.
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I concluded that what mattered was the amount of bubble between the electrodes, which led me to bubble width top and bottom electrodes . But that is merely an analysis leading to a conjecture. Either of which may well be wrong.
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Looks to me like my 4"/2mm vial has a "sticky" bubble, where both the leading and trailing edge of the bubble gets separately stuck in spots, and then suddenly moves to catch up. I suspect the true surface tilt of my garage slab is a smoothly varying function of time, mostly driven by ambient temperature. When measuring the overall bubble position overnight into the morning for 12 hours, I am seeing a jerky and sometimes perhaps even non-monotonic output at the sub-arc-second level. The sudden steps are as large as 10 mV or 2/3 arcsec. Each step occurs over a period of 10 to 15 seconds, which seems to be roughly the response time of this vial. (EDIT: by 2/3 arcsec I mean the fraction, in other words 0.667 arcsec)
I think $12 may simply be too cheap to expect better performance. You could add a buzzer or vibrator motor to "tap the vial" but I'm not convinced you then necessarily get to the desired minimum-energy point, perhaps just another random metastable sticky spot. I notice this
https://www.leveldevelopments.com/products/vials/ground-vials/5726101-ground-vial-15x95mm-sensitivity-0-02mmm/ (https://www.leveldevelopments.com/products/vials/ground-vials/5726101-ground-vial-15x95mm-sensitivity-0-02mmm/) and they claim to do their own manufacturing in the UK (not the Far East). Apparently 15 mm diam x 96 mm long is a standard size. They are offering vials with sensitivity of 4"/div at $30 and 10"/div at $25, so I'm going to give them a try.
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The sudden steps are as large as 10 mV or 2/3 arcsec.
That would be visual. I imagine there could be some units better than others. Mine seems to oscillate as it settles. For example on the desk, if I move to the other side, the bubble will move a couple+ divisions and then retract slowly to rest. Maybe I'm not seeing it in RT, so I should record it.
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I do not observe the stickyness visually on my vial either. I think it happens only with extremely slow level changes (for example, exactly the ground motion I am trying to measure). The largest step was 2/3 asec which for visual reference is still only 1/6 of one division, and when I say "sudden" it is over a period of about 10 seconds. I easily get more motion than that just from shifting my weight on the concrete floor of my garage, so I don't think it would stand out visually. Maybe I should not say the level vial is bad, it's just that the capacitive readout is very good. Based only on electronic noise, it resolves bubble position to 10 microns, which is around 5 milli-arcsec using a vial of this sensitivity. That is 100x smaller angle change than this 2/3 asec step. Likely could do even better with a slower lowpass filter than the few-second time constant I have now.
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Have you verified it's not your readout circuit? You could install a differential capacitor instead of the electrodes to make sure it's stable and you are not hunting the white rabbit.
-branadic-
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Or I could just tilt the level up 90 degrees. I think that would move the bubble into the end and away from both top electrodes, so I would see a stable output. I'll try that later today.
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This is another way to go, you're right. I wonder how temperature influences your circuit and thus output voltage, beside temperature influence of the bubble itself.
My vials are still resting in Frankfurt, since four days now. :--
Hopefully the vials I ordered from UK will arrive earlier. I almost finished CAD design and the required parts today.
-branadic-
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I do not observe the stickyness visually on my vial either.
I mistook your comment as 2 to 3 arcsec... You did not see this with the other vial, and it seems within expectation from my pov. I'm just going to use mine visually, unless I come across some obscure reason to need more sensitivity, such as building a "repeat-o-meter" to verify my surface plate, but there may be better way do to that a-la the methods described earlier.
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I ran the circuit overnight with the vial turned 90 degrees (pointing straight up), so the electrodes see just the fluid with no bubble. There was no hint of the discrete steps that I saw with the vial resting level, the noise looks random. The typical peak-to-peak noise level over a period of minutes was about 30 uV, and the total DC drift overnight was 0.8 mV. I believe the mV and larger size steps must be from the bubble motion.
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Seems logical, you'd have surface tension and such. Maybe the other vial uses a different fluid - I think it's typically alcohol?
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I would expect that a glass vial "spirit level" always uses alcohol. If it used plain water, it would likely break if it is ever stored below freezing. I guess you could test this by storing it in a freezer! I expect the "stickyness" of the bubble edges is related to the interior glass surface cleanliness. For example I'd expect the sticky behavior if there are random small patches on the glass that have different surface energies, due to different molecules locally exposed on the surface. If the glass is perfectly smooth and also clean, the bubble should not have a preference for any position except balanced at the very top.
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The content is either alcohol or hydrocarbon, such as Diethylether (https://www.roeckle.com/epages/62116134.sf/de_DE/?ObjectPath=/Shops/62116134/Categories/Technische_Daten).
As expected the vials from UK arrived earlier. Yeah, time to start applying some copper electrodes and the PCap01 board. Results coming soon.
-branadic-
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The inside of my 4"/2mm vials is frosted. It is clearly visible with a 14x Hasting's triplet. So that is likely a source of sticking. The need to fully polish the inside may be a significant cost factor in the manufacture of the commercial microradian sensors.
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My setup works incredibly good and shows very high resolution. My setup currently lays on a table with some aluminium blocks on each side of the vial. What I can say for now is:
1. I need the V-block as fast as possible
2. I have to move the setup to our basement and to the grounding
3. The electrodes are slighly different, that can be seen by the response due to inclination of each single capacitor and the calculated difference, so glued electrodes are not the best choice for the resolution I get with the IC, but that is
4. I have to develope a temperature compensate for the setup
-branadic-
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The inside of my 4"/2mm vials is frosted. It is clearly visible with a 14x Hasting's triplet. So that is likely a source of sticking. The need to fully polish the inside may be a significant cost factor in the manufacture of the commercial microradian sensors.
Yes you are quite right. I see this also, now that I used a magnifier on it. The inside surface of the vial has a bumpy or pebbly texture so it is much rougher than the outside surface. I think you can get away with that amount of roughness, if you only use the vial visually.
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I managed a 30x photo with the red line clearly hovering over and reflecting off the inside surface, that matches the photos presented above. The texture (highs/lows) seems orders of magnitude more granular than the measured response, 2/3 arcsec.
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It will be interesting to hear what reports are on the UK made vial. I suspect that a minor amount of post acquisition processing would clean up the steps in a satisfactory manner. Especially so if they occur at the same spots.
0.0001"/10" is a very demanding spec for a hand level and you're pushing way beyond that.
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The W. A. Moyer & Sons Vintage level vials arrived today as well.
For comparison JBeale, what is you repitition rate? I currently configured PCap01 reading two capacitors plus compensation measurement. This results in a repitition rate of 6.1Hz including temperature measurement.
-branadic-
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I am only logging data once every 2.1 seconds. The Keithley 196 DMM itself converts and updates the local readout at maybe 5 Hz (?) but there is a digital low-pass filter option I have enabled, giving a final time constant of a few seconds.
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It occurred to my while getting lots of face time with my pillow (norovirus :-( that a small solenoid that got pulsed just before a reading might solve the sticking problem.
Can we get closeups of different vials?
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Next week I should have some UK-made vials to compare. The price difference is only about $20 per vial so for the small quantity I want, I can't justify a lot of extra design effort. A vibration source should do something to reduce the sticking, but if you're trying for sub-micron positioning of the vial for long-term monitoring (my application) but then whacking it for every reading, it feels like an unavoidable tradeoff against how rigid and stable the mount can be made. I should add the one Aliexpress-sourced, so-called 4"/2mm vial I measured was actually about 2x more sensitive than claimed. Maybe they ground the glass with coarse grit only and did it for 1/2 the proper time, but anyway just to underline I think that source's process and quality control is roughly zero.
EDIT: The photos on the link below are the type of vials I received. The close-ups I posted above are just a higher-mag look at these same parts, showing the pebbly texture of the interior surface.
https://www.aliexpress.com/item/Size-14-96mm-Accuracy-4-2mm-Glass-High-Accuracy-inclinometer-Tubular-Bubble-Level-Cylindrical-spirit-level/32558917931.html (https://www.aliexpress.com/item/Size-14-96mm-Accuracy-4-2mm-Glass-High-Accuracy-inclinometer-Tubular-Bubble-Level-Cylindrical-spirit-level/32558917931.html)
EDIT_2: FWIW I'm interested in measuring things generally, as in the old C.L.Stong AmSci columns that I enjoyed also, but in particular my motivation here is catching the earliest possible hint of a structure (my house, specifically) slip-sliding away downhill. I know at high resolution there will be diurnal effects, temperature, humidity, irrigation, precipitation effects, seasonal effects etc. also, which is all OK. The tiltmeters used on volcanoes may use other technology because they resolve better than 0.01 micro-radian, that is 0.002 arc-second. https://earthscience.stackexchange.com/questions/10220/how-are-data-from-tiltmeters-used-to-monitor-volcanic-activity (https://earthscience.stackexchange.com/questions/10220/how-are-data-from-tiltmeters-used-to-monitor-volcanic-activity)
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Did you ever post a photo of the Chinese vials as received? I don't recall seeing one.
I certainly agree about the extra cost of the UK vials if they are made to a better standard.
Do you live near a volcano or fault zone? Those are the principle application for high precision tiltmeters aside from monitoring susbsidence from underground pumping of oil or water.
You've rekindled a childhood interest in whole earth geophysics generated by C.L. Stong's book of Amateur Scientist columns. I am feeling the need to build a seismograph or two.
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Measured a first characteristic curve of my UK vial (3"/2mm) (https://www.ebay.de/itm/Ersatz-Wasserwaage-Glaslibelle-Blase-Empfindlichkeit-Feder-100x-9-5mm/132588613741) in the range of +/-0.06° and in steps of 0.001° today. Forgot to copy the values of the reference sensor to my USB stick for comparison, but will do that on monday. Measurement for temperature compensation algorithm and long term stability is actually running during weekend, so I will have this data on monday as well.
The x-axis equals a measurement time of 3:48h.
-branadic-
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That is amazingly linear. I'm more impressed with such a setup than the response of the vial. How is such accomplished?
±0.06° is ±216 arcseconds, or ±54 divisions on the vial, and in roughly 4 arcsecond steps. The bubble will be forced into the end long before the end of a cycle, so I am a bit surprised it's that linear. ???
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±0.06° is still within the grinded range of the 11mm x 96mm (100mm total length) vial, without the bubble moving to the ends of the vial. I measured against a Nivel230 on an inclination test bed we have for high resolution inclination sensors. To be honest, the vial wasn't adjusted, layed only on two grinded parallel spacers and showed an offset in zero position of the test bed.
The curve looks much noisier than it actually is, it's just a plot artefact. I have to verify the positions with the Nivel230 data to make a statement on accuracy, but it's quite promissing for such a cheap solution.
The test bench is a granite slab with three spheric mountings underneath, two of them are moved by pushers up and down and have glass scale sensors with 50nm resolution for control and the third mounting is fixed in height, thus the slab is inclined by the pushers around the third mounting.
-branadic-
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Measured a first characteristic curve of my UK vial (3"/2mm) (https://www.ebay.de/itm/Ersatz-Wasserwaage-Glaslibelle-Blase-Empfindlichkeit-Feder-100x-9-5mm/132588613741) in the range of +/-0.06° and in steps of 0.001° today.
That plot looks quite good; it is a promising result. There may be some hints of nonlinearity over the displayed range but not easy to see on this plot. I'm curious what it looks like with even smaller steps.
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Not to forget all the imperfections by the copper tape electrodes cutted by hand, but yes that looks really good. I prepared the second 3"/2mm vial with a little more attentation to detail while applying the copper tape electrodes. I also prepared one of the W. A. Moyer & Sons Vintage level vials and will measure them both soon.
-branadic-
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±0.06° is still within the grinded range of the 11mm x 96mm (100mm total length) vial, without the bubble moving to the ends of the vial.
Maybe you have a different vial. Mine has 9 lines each side and estimated 9 divisions between the graduations, a total of 27 divisions of 4 arcseconds. 108 total arcseconds the bubble moves between ends, or 0.03 degrees end-to-end, ±0.015.
At any rate, I hear my extra vial calling for such experimentation.
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Yes my vial is different, I linked it in the post above.
(https://i.ebayimg.com/images/g/AQUAAOSw7WZa15ki/s-l1600.jpg)
The bubble can move more than just between the outer divisions without touching the ends of the vial.
-branadic-
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That is a much finer grind on the inside surface than the Chinese vial I have. It's not polished, but your tests suggest it is good enough.
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Exact, you can see the dim area of the vial.
-branadic-
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Added plot of the reference sensor. I come to the conclusion, that 30s for measuring a single step is to short. The bubble or the test bench hasn't stabilized during that time.
-branadic-
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In case of interest, a visual reference for some of the vials recently discussed here. All of them have some visible texture to the interior surface (eg. ground, but not really polished)
https://www.ebay.com/itm/W-A-Moyer-Sons-Vintage-Level-Vial-Type-L-1-A31314-Bubble-Level-NIB/192433183719 (https://www.ebay.com/itm/W-A-Moyer-Sons-Vintage-Level-Vial-Type-L-1-A31314-Bubble-Level-NIB/192433183719)
https://www.aliexpress.com/item/HACCURY-Size-14-100mm-Accuracy-4-2mm-Glass-High-Accuracy-inclinometer-Tubular-Bubble-Level-Cylindrical-spirit/32558917931.html (https://www.aliexpress.com/item/HACCURY-Size-14-100mm-Accuracy-4-2mm-Glass-High-Accuracy-inclinometer-Tubular-Bubble-Level-Cylindrical-spirit/32558917931.html)
5726/101 – Ground vial, Ø15x95mm, sensitivity 0.02mm/m
5725/101 – Ground vial, Ø15x96mm, sensitivity 0.05mm/m
from https://www.leveldevelopments.com/products/vials/ground-vials/ (https://www.leveldevelopments.com/products/vials/ground-vials/)
EDIT: A preliminary overnight readout test of the 0.02mm/m vial from UK shows it also has "sticky" behavior. When the tilt is changing very slowly (eg 1 or 2 arcsec per hour) as in geophysical applications, the output displays sudden jumps on the order of 1 arc-second, similar to what I saw before with the 4"/2mm aliexpress vial. I suspect you do not encounter this if you do a test with large enough or rapid enough steps that the bubble never quite stops moving. I am now thinking if I could make a mounting that has a continuing wobble of say 5 arcsec, to keep the bubble moving just slightly, and then average it out. In the below graph, the tilt overnight through mid-morning is roughly tracking with ambient temperature, but I believe it to be a true tilt signal and not just a readout tempco, because it passes through the null point (output = 0.000 volts).
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Got some feedback from W.A. Moyer Company today. They couldn't find anything, but the vial must have been a special Military Spec ordnance vial made for the U. S. army during WW2. The numbering is very close to the numbering system used by a company named Keuffel & Esser who made optical equipment.
Looks like I need some measurement to calculate sensitivity.
-branadic-
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From the size I'd guess that the Moyer's vials were made for laying in mortars in anticipation of the invasion of the Japanese mainland. Experience in the island hopping campaign had made the military planners *very* pessimistic about casualties and material losses. If we invaded, they did not want to run out of equipment. So they ordered mind boggling quantities of stuff. Thankfully it was never needed.
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Received one V-block from Norelem as well as a 3D printed vial holder (a first draft for some testing). The vial is fixed inside the V-block using some rubber gasket ring elements between vial holder and vial. It works wonderful as expected. The vial holder as well as the recycled board needs some redesign and the V-block some machining (grinding on top and bottom), but sure enough I will have a full level vial based inclination sensor soon.
-branadic-
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Why so much copper right to the very ends of the vial, doesn't the last 25-30% of it just reduce the sensitivity.
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I think because the effects can still be measured out to the very ends, it give the vial a much larger range.
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I think because the effects can still be measured out to the very ends, it give the vial a much larger range.
If the bubble is completely under 1 side of the copper, can you still see the difference on where the bubble is? I also would have expected that you need a change in surface area, so when a bubble is completely under one copper piece, it does not matter where it is...
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Each electrode is almost as long as the bubble, so yes you can measure a difference if the bubble is completely under one electrode and that is where the linear range of the capacitive difference measurement ends.
-branadic-
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Each electrode is almost as long as the bubble
Ooh, that was not clear to me in the picture. From the picture above it seemed the electrode is almost twice as long as the bubble, hence the question of "StillTrying" and me if it would not be better to make the electrodes approx the same length as the bubble...
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Ooh, that was not clear to me in the picture. From the picture above it seemed the electrode is almost twice as long as the bubble, hence the question of "StillTrying" and me if it would not be better to make the electrodes approx the same length as the bubble...
To be honest, the picture shown is not the latest one. The electrodes were shortend after some tests to a length a lil' bit longer than twice the bubble length.
Measured the behavior of the sensor today on a manuel test bed and I'm totally amazed by the performance. Without any noise generated by motors/pushers I crossed the limit of resolution of our reference, a Zerotronic ±1° (https://www.messwelk.de/Gesamtkatalog/#page_30). To be fair enough, the measurement range is in the order of ±0.35° / ±21' / ±1260" / ±6.10865mrad, but cost is far below 3.000 bucks. :)
But don't listen to me, say it with pictures. :-+
-branadic-
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Measured the behavior of the sensor today on a manual test bed and I'm totally amazed by the performance. Without any noise generated by motors/pushers I crossed the limit of resolution of our reference, a Zerotronic ±1° (https://www.messwelk.de/Gesamtkatalog/#page_30). To be fair enough, the measurement range is in the order of ±0.35° / ±21' / ±1260" / ±6.10865mrad, but cost is far below 3.000 bucks. :)
Very clean looking graph from your sensor, congratulations on that impressive performance!
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Very clean looking graph from your sensor, congratulations on that impressive performance!
Thanks JBeale and yes you are totally right, this is an impressive performance, even if you compare repetition rates (1Hz vs. 6.1Hz).
I'm sure if you change to a more modern way of reading the capacity, you will get excellent results. Make the distance between both electrodes as small as possible, so you don't loose anything.
And not to forget temperature compensation. Your circuit will have excess temperature coefficient by rectification.
-branadic-
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I am interested to try the C2D circuit approach when I have more time. I couldn't do any more work on it lately, but here is 6 days of data from my old simple circuit, on the garage slab. I added a slow 10-second-per-rev gearmotor with an offset weight on the shaft, all on a wood plank that is flexible enough to give the sensor a slow tilt wobble of several arcsec; that seems to have fixed the "sticking" steps I saw before. The one big step near the start is a manual readjustment to prevent going offscale, although it still did at the peaks over the next few days. With the wood plank, the whole thing may just be a humidity sensor, however all the smaller-scale features on the graph I checked do correspond exactly in time to real events, like a car driving into or out of the garage.
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Mesaured the temperature stability of my setup together with the CDC today. Therefore the sensor was tilted by 90°, so that the vial is looking to the sky and each electrode is fully covered by the inner fluid. With the aquired data I did a temperature compensation comparison. Attached are the results. The large spikes seem to be my presence disturbing the measurement. However, with the temperature compensation coefficient I can now calibrate the sensor against a reference to deliver the final angle.
-branadic-
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I'm amazed that you are unaware of TI's FDC1004 EVM demo kit and the excellent data logging software available for it.
Would like to know how the FDC compares to your NASA bridge.
I'm using the FDC1004EVM to monitor the position of 40 micron oil droplets inside an air filter at work.. So far we're happy with it.
Steve
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Hi Steve,
if you refer to me, I use a PCap01 for my sensor not a NASA bridge. It's cheap, low power as per principle, has a DSP integrated that is sleeping while measuring so the complete calibration can be integrated writing some lines of assembler, needs only a few external components and has 3 additional resistive ports beside 8 capacitve ports. And since I fully understood how to configure it, how to programm it and how data has to be processed to get the best results, there is no need for me to use FDC1004. Nevertheless, we have evaluated FDC1004, but with worse results compared to PCap01. So PCap01 became the best sucessor for expensive and "dumb" AD7746 chasing atto farads, at least for me.
-branadic-
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I recently purchased a few 20"/2mm levels from Aliexpress and when they arrived they were all off by minutes.
https://www.aliexpress.com/item/HACCURY-High-Precision-Metal-Long-Level-Bubble-Precision-Equipment-Installation-Bubble-level-Accuracy-0-1mm-m/32856559241.html (https://www.aliexpress.com/item/HACCURY-High-Precision-Metal-Long-Level-Bubble-Precision-Equipment-Installation-Bubble-level-Accuracy-0-1mm-m/32856559241.html)
The best one was about 1' off while the other two were more like 3-5 minutes off. So I did a little dremel/file job and now they are within about 1-5" which I about what I wanted. We'll see if they drift over time as I have no idea how they affixed the vial to the Al enclosure. I suspect that you'd want some compliant adhesive that kept it in place but offered some compliance with temp change or force application.
Brian
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Tried to calibrate my sensor, but without success since the Zerotronic is much noisier, slower and of less resolution. Need to wait unit our Nivel 230 is back in house to see if it is any better. Meanwhile I can further optimize my setup and design the final circuit board.
-branadic-
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Is anyone going to make an X,Y (N-S, E-W) one. :)
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Easily combine two single axis sensors and align them to perfectly match 90° to realize a two axis sensor.
If you are asking for a circular spirit level based two axis sensor instead, there is a patented solution (https://www.hahn-schickard.de/en/services/sensors/inclination/electronic-spirit-level/) available.
You won't get better results with a DIY solution based on commercially available circular spirit levels. Don't ask me why, I can't speak about it as this is part of the secret of the sensor design.
-branadic-
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Received one V-block from Norelem as well as a 3D printed vial holder (a first draft for some testing). The vial is fixed inside the V-block using some rubber gasket ring elements between vial holder and vial. It works wonderful as expected. The vial holder as well as the recycled board needs some redesign and the V-block some machining (grinding on top and bottom), but sure enough I will have a full level vial based inclination sensor soon.
-branadic-
Are you saying that you bought a v-block and then two point mounted the vial with O rings? If so, why bother with the v-block?
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Are you saying that you bought a v-block and then two point mounted the vial with O rings? If so, why bother with the v-block?
No, you misunderstood me. I used a segment of an o ring on the upper side as some sort of spring to elastically fix the vial into the V-block.
-branadic-
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slightly off-topic: clearly not "high precision" but I found an android app ("clinometer + bubble level" by plaincode) which uses the phone's 3D accelerometer to report the phone's angle with 0.1 degree resolution. After doing its builtin 180 degree calibration step, the actual precision is reasonably good. It does averaging, so there is a settling time. There is a 1-D mode with the phone on edge, and 2D with the phone flat facing up. Best with phones that do not have rounded backs, and have one edge flush without protruding buttons.
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Can say for now, that resolution of my sensor (sample rate: 3.05Hz) is even better compared to Leica Nivel230 (sample rate: 1Hz, range: ±1.1mrad, resolution: 1µrad, accuraccy 1σ: 5µrad, accuracy 2σ: 10µrad). So now the golden question: How to calibrate this sensor without having a better reference?
Both (Nivel and Zerotronic) are not accurate enough and even the Leica's measurement range is to small.
-branadic-
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Would you please explain what the plots show?
What is your estimate of the resolution? I seem to recall a small fraction of an arc second.
The only thing I can think of that *might* work is something I saw in a NASA tech brief. They needed a precise angle at very high resolution (though less than this). They used a turned disk with a steel tape pulled by a micrometer head to rotate the shaft. In your case you'd need at least a pair of 10:1 levers constructed in that fashion. But if the disks were turned between centers and then mounted in the same fashion it should be quite accurate and easy to construct.
Visualize a pair of stepped disks with a 1" diameter section and a 10" diameter section. Pulling on the 10" section pulls a tape on the 1" section which is attached to the 10" section of the other disk. So the distance is divided by 100. You might be able simply to interpolate between steps of 0.0005" using a single disk. That would give you 10 second calibration points. A good digital mike reading to the tenth would give you 2 second calibration points.
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First picture shows the response in x-axis of Leica Nivel. As can be seen two steps on a manuel test bench have been performed during searching for zero on Leica Nivel. The unit of Leica Nivel is mrad, thus one division equals 2µrad (2µm/m).
Second picture is the response of my inclination sensor in counts on the same change of angle, which was measured in parallel. It hasn't been calibrated yet, thus counts.
The small steps in my measurements close to zero signal of Leica Nivel (the test bench needs a while to settle down after a change in angle which can be seen clearly) are due to colleagues entering and leaving the lab :palm: With a lot of fantasy you can see them also in the signal of Leica Nivel.
-branadic-
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Would you mind to share the raw data for the 'calibration' graphs? I would like to have a go at some filtering/correlation of the data to see how close these graphs match.
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Would you mind to share the raw data for the 'calibration' graphs? I would like to have a go at some filtering/correlation of the data to see how close these graphs match.
Sorry, but no. I'm currently on that topic by myself.
-branadic-
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I'm getting ready to build some of these and have been studying the NASA Tech Brief schematic. It *looked* obvious until I looked at it closely.
Did anyone work out a theory of operation? I'm having trouble understanding the circuit concept.
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In general terms it is a differential capacitance meter. It does work, but my experience is that the ultimate sensitivity is significantly limited by mechanical (or possibly chemical) effects on the inside of the bubble capsule. I used four different capsules from 3 different sources and they all had "sticky" behavior which limited resolution to a much lower level than just the electronic noise would otherwise indicate. They are still pretty sensitive though.
In case of interest- a few months ago I encountered a significantly better design, although the electronics are much more complicated. It has been developed by several people over a period of 10+ years and is called FMES (fluid mass electrolytic seismometer) and is intended as the name suggests, to be seismometer with a horizontal velocity output obtained by integrating and bandpass-filtering the tilt signal. However, there is an internal node voltage that is proportional to DC tilt, so it can be used as a sensitive tiltmeter as well (although the signal does drift with temperature). I have built three units now and I think they work pretty well. Note it takes a LONG time to fully settle down after initial startup, like three days or more. Maybe internal bubbles resolving and/or electrolyte concentration gradients diffusing.
Description of FMES: https://docs.google.com/viewer?a=v&pid=forums&srcid=MTEwNTY3NjcxMDQ3NjEzMjgwMDYBMTMxMjUwODI3MDY3MzY1NTcyMDEBUFdScUMtNnRFZ0FKATAuMgEBdjI&authuser=0
Discussion of FMES: https://groups.google.com/forum/#!topic/psnlist/ih4p__5cGW0
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What did you use for the diode bridge in the NASA design? Those appear to be used as matched 1 pF capacitors. And unobtainable except as NOS parts.
I had originally thought it was a typical capacitance bridge, but on closer inspection, I'm quite baffled as to how it operates.
Thanks for the link to the other design.
BTW have you considered that the settling time might actually be very low frequency physical motion? It might be interesting to examine data over several days after dropping a 50 lb bag of sand on the floor 10-20 ft away. Big earthquakes make the earth ring for weeks.
Have Fun!
Reg
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Any diode will do it, as long as all 4 of them are as identical as possible. Those are Ge diodes (and thus the +/-0.7V range == 2 x Vf for Ge) but Si should work just fine. The circuit is supposed to be symmetrical in order for the DC output to be linear with the ratio between the two vial's capacitive arms.
Another thing, the device output voltage is linear only around zero, or as long as the output DC is very small in comparison with Vf. For bigger capacitance differences between the vial arms, it won't be linear at all.
There will always be an AC component over the DC one, but the AC is supposed to be attenuated by the low pass RC filter on the right end of the schematic (0.1uF and 100K).
Another thing to consider is the impedance of a 0.01uF at 300KHz, which would be about 53 ohms. It is 2 orders of magnitude lower than the 5K6 resistor series with the bridge. If we set the generator for 300KHz and 5Vpp, this will be about 50mV of AC across the diode bridge. Small enough to consider any diode as a linear device for a swing of only 50mV around whatever decent DC static point. This small enough swing (and the symmetry of both the voltage waveform and the bridge arms) will make the whole thing a nice charge averaging circuit (one vial arm will have a bigger C because of the vial's tilt, thus its corresponding capacitor will accumulate a bigger charge then the other arm, because everything else is supposed to be symmetric). The two charges Qleft arm and Q right arm of the vial will end up averaged by the 0.01uF put across the bridge.
The first 0.01uF, in series with the generator is there just to be sure no DC possible offset from the generator will go into the bridge, and vice-versa to be sure no DC generated by the bridge will go back into the generator (a DC voltage pushed back into the generator's output would be bad, because it might affect the waveform symmetry for example - depends of the generator, but most of all we don't want any DC offset from the generator to go to our Vout). Symmetry in both the waveform and the bridge arms (identical transfer functions for all 4 diodes) are essential for this circuit. The waveform itself is not important as long as it's symmetrical and has no DC.
The 0.01uF inside the bridge is to integrate the charge imbalance over many periods of the 600KHz bridge switching. Ideally, the output voltage would be to be read across this diagonally 0.01uF inside the bridge, yet the author choose to read the DC voltage over the whole RC (5.6K and 0.01uF), thus adding the full 5Vpp swing from the generator over the DC we need. This full AC will be diminished by the 100K and 0.1uF RC low pass filter at the output.
My guess is this AC pollution was done to keep a common ground between the AC generator, the ground electrode of the vial and the DC voltmeter (for better shielding and noise rejection of the whole thing). If it were to have a floating DC voltmeter, will be much better to read the voltage across the bridge directly, without including the series 5k6 resistor.
Forgot to mention, the vial arms' capacitances are suppose to be very small in comparison with all other capacitors in the schematic, probably pF if not fractions of pF (no idea how small, didn't plugged any numbers). The absolute value is not important, only the ratio C_left/C_right of the vial.
Later edit:
Trying to proof reading the text afterwards, and realized that, without proper schematic and numbering of the components, it is all just a big TL;DR.
;D
https://www.docdroid.net/enKb2ed/nasaames-simpletiltmeter.pdf (https://www.docdroid.net/enKb2ed/nasaames-simpletiltmeter.pdf)
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Very helpful. I bought 10 of the CA3039 diode arrays via eBay this morning. I'm going to start work on a Wien bridge oscillator for the signal. Probably the 2nd or 3rd iteration in Jim Williams' paper.
The thing that's messing with my mind is the topology of the diodes. I went through over a dozen texts on electronics measurements today and could not find anything that remotely resembled the NASA circuit.
Everything had the detector across the arms of the bridge and no connection inline with the source and ground.
I'd love to know more about the circuit's origins. As I understand what you wrote, the diodes are being used as small matched capacitors and should never turn on.
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For what it's worth, this photo shows the parts that I used for the diodes:
https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/msg1583374/#msg1583374 (https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/msg1583374/#msg1583374)
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I didn't lookup the datasheet for CA3039 before, and wrongly assumed they are discrete Ge diodes, but now I see it's an array of Si diodes (Vf is 0.7V in the datasheet). Now I don't understand why the expected DC range of Vout specified by the author is +/-0.7V and not +/-1.4V. Will give it a second look tomorrow, do a SPICE simulation, and try to come up with a cleaner explanation.
Anyway, I considered those diodes rather as a bridge of (controlled) resistors than as a bridge of capacitors.
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It occurs to me that there may be a NASA patent that explains it.
When I redraw the bridge part leaving out the input and output sections I'm dumbfounded. The nodes that I'd expect to be connected to the detector are instead connected to ground via the sense capacitors. It is unlike any bridge circuit in ~17 texts which included the NBS electrical measurements volume from1963 and Terman & Pettis. My library is rather disorganized, so I *might* have a book that describes the circuit, but at this point I think it's probably original.
I was impressed before. Now I am simply in awe. This is not your Dad's capacitance bridge. Whoever designed this was *really* good.
I'm left going, WTF? We know from experiment that it works, but it looks like nothing I've ever seen. At this point I have to rank this as being in Jim Williams or Bob Pease territory. Or for the ignorant, an act of God.
Reg,
much befuddled.
BTW I found a half bridge circuit built around a Signetics NE5512 that looks as if it would work quite well in this application in "The Modern Measuring Circuit Encyclopedia" by Rudolf Graf. I'm quite sure it came from a datasheet or app note.
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I was impressed before. Now I am simply in awe. This is not your Dad's capacitance bridge. Whoever designed this was *really* good.
This sort of offshoot results from investment in the space program. I used to receive NASA Tech Briefs, and every issue was packed with mind-expanding innovations. Many were patented, but patents expire (now) after 20 years, and then they're public domain. This sort of thing is exactly why I'd much prefer tax dollars being invested in the space program than in many of the other, ahem, things that occupy the federal budget. This kind of development benefits everyone on the planet.
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I redrew the circuit as the 0.01 uF & 5.6K resistor forming a low pass filter with a diode bridge across it. If we consider a 5 Vpp signal input at 300 KHz, there is 50 mV across the bridge which is not enough to turn on the diodes. They still conduct enough though to charge the fF caps formed by the vial electrodes.
I'm not convinced that analysis is correct, but it's the best I've been able to do so far. How that becomes a measurable DC voltage still eludes me.
I'm clearly going to be spending a lot of time studying the circuit and reviewing the behavior of the PN diode in minute detail especially at low forward potentials.
I'm also going to have to learn to use LTspice and similar.
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I'm also going to have to learn to use LTspice and similar.
When this circuit was being discussed last year, I decided to model it in 'Qucs', in order to learn how to use that software:
https://en.wikipedia.org/wiki/Qucs
I can't say that I understand the circuit much better (I'm not an EE), but I did experience a few 'ah-ha' moments, while plugging different component values in.
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A simulation won't reveal how it works, but it is helpful here to quick check hypotheses: assume it works in some way, then make some predictions according to the hypothesis, then check the predictions using the simulation in order to see if the prediction is fulfilled.
So far I get it how it works, can explain it in a short novel, but don't have yet that clean and intuitive explanation in just a few words. Still looking for that, if I'll ever found one.
As a slightly offtopic thought, I found out why the reverse voltage of CA3039 diodes is so low (about 5V). The diodes are most probably made from transistors with collector-base junction short circuited, like in this other array of diodes, CA3019 (see starting from page 94 of 379, ICAN-5299, Application of the RCA-3019 Diode Array http://the-eye.eu/public/Books/Electronic%20Archive/RcaLinearIntegratedCircuitsAndMosfetsApplications_text.pdf (http://the-eye.eu/public/Books/Electronic%20Archive/RcaLinearIntegratedCircuitsAndMosfetsApplications_text.pdf) )
I feel that that diode bridge with capacitors on it is something that I should have known by now, and back in the days of analog era it was probably a basic topology for all kinds of stuff, from power rectifier to RF modulation, yet I'm bamboozled by this particular schematic. It's easy if we think about each diode as a controlled switch series with an average resistor, but not clean enough for a nice intuitive explanation.
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I put a 0.25" strip of copper foil and a 1.25" strip on the vial. After cutting the 0.25" strip in the middle and doing a probe calibration I get 3.9 pF when the bubble is at the unconnected end and 3.4 pF when it is at the connected pad end. So the total capacitance change is around 500 fF. I doubt those are accurate values, but they do give an order of magnitude estimate. The values repeated when I rotated the sheet of cardboard that the vial and LCR45 were sitting on.
The attached photo shows the vial with the copper foil applied. The foil proved very difficult to handle, but maybe with practice I'll get better.
There was never a patent issued to the authors, so no explanation from that direction. The CA3039 diodes have a reverse bias capacitance of 1 pF or less. I've attached the datasheet for convenience.
I'll have 10 RCA CA3039s in a day or two and can complete construction of the basic circuit. My initial focus is understanding the circuit operation, so I'll just do it dead bug style on a piece of single sided PCB with everything stuck down with hot melt glue.
Once I've convinced myself I understand how it works I'll tackle how to mount the two vials I have and build a stable PCB with 2 bridges and an MCU to read the data and log it while I consider what to do next.
The aim of my project is to use two sets of orthogonal levels to measure the surface deviation of a surface plate. One set of vials will be attached to the surface plate so that as the floor moves under the plate the MCU can calculate the difference between the planes determined by the reference vials and a movable tester with 3 point contact with the surface using sapphire swivel feet. Initially I'll just display strike and dip of the plate surface along with relative elevations of the feet. Later I'll figure out a way to get location so I can generate a contoured surface.
I'm using 2"/2 mm vials instead of the 5"/2 mm vials in the NASA Tech Brief. Assuming 10 cm between supports on the test probe, I should get resolution on the order of 10 nm! So I might have to buy some lower resolution vials.
I bought a 7" x 14" Chinese mini-lathe which I plan to rescrape to be accurate to 0.0001" and then install a lapped plain journal bearing to replace the OEM deep groove ball bearings. That should provide me with a convenient and reasonably inexpensive high precision toolroom lathe.
I bought an ER-32 collet chuck to replace the 3 jaw and a full set of collets. I'm also going to make a drawbar MT 3 mount for fixture plates for holding larger work. That setup should allow me to make good differential screws, unlike my drill press based attempt.
Reg
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I found this patent: Diode-quad bridge circuit means (US3883812A) https://patents.google.com/patent/US3883812 (https://patents.google.com/patent/US3883812).
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I get 3.9 pF when the bubble is at the unconnected end and 3.4 pF when it is at the connected pad end. So the total capacitance change is around 500 fF. I doubt those are accurate values, but they do give an order of magnitude estimate.
Varying the size of the bubble would likely change the dynamic range - not that doing so is really an option after-the-fact! :)
Maybe dramatically shorten the leads, get the meter closer to the DUT? I'd expect 500 fF of change just by waving your hands near the test leads in the photo.
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@mycroft found the rosetta stone. I didn't craft my patent search very well.
The operation is gradually becoming more clear from just studying the circuit and considering an order of magnitude analysis. The patent should make it all clear.
As I remarked, this is not your Dad's capacitance bridge.
This was designed to be very cheap. There are a lot of ways to measure small changes in capacitance. It will be very interesting to compare different sensing circuits. For the purposes of measuring very small deviations from flatness of a surface plate, this circuit should work very well.
As the CA3039 is hard to obtain I plan to compare that to the implementation @JBeale linked using the 2 diode arrays. It should work just as well with those.
I'll work out some vial attachment that makes it easy to test different bridge circuits. After a year of buying test gear like a drunken sailor, it's time to build stuff.
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See
https://www.eevblog.com/forum/metrology/volt-nut-meeting-2019-in-stuttgartgermany/msg2253138/#msg2253138 (https://www.eevblog.com/forum/metrology/volt-nut-meeting-2019-in-stuttgartgermany/msg2253138/#msg2253138)
EEVBLOG Forum User Branadic will talk about it.
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I found this patent: Diode-quad bridge circuit means (US3883812A) https://patents.google.com/patent/US3883812 (https://patents.google.com/patent/US3883812).
Thanks, starting from that one, there are a few more similar patents, some much older (1955):
https://patentimages.storage.googleapis.com/79/b2/c4/dfca62cf25a852/US3883812.pdf (https://patentimages.storage.googleapis.com/79/b2/c4/dfca62cf25a852/US3883812.pdf)
http://www.freepatentsonline.com/3545275.pdf (http://www.freepatentsonline.com/3545275.pdf)
https://patentimages.storage.googleapis.com/b2/5f/4f/7d758d81925b9e/US3271669.pdf (https://patentimages.storage.googleapis.com/b2/5f/4f/7d758d81925b9e/US3271669.pdf)
http://www.freepatentsonline.com/3318153.pdf (http://www.freepatentsonline.com/3318153.pdf)
http://www.freepatentsonline.com/3260934.pdf (http://www.freepatentsonline.com/3260934.pdf)
https://patentimages.storage.googleapis.com/44/e5/7b/5182b82aa9a452/US3012192.pdf (https://patentimages.storage.googleapis.com/44/e5/7b/5182b82aa9a452/US3012192.pdf)
https://patentimages.storage.googleapis.com/c0/82/cd/7ece43283ed779/US2929020.pdf (https://patentimages.storage.googleapis.com/c0/82/cd/7ece43283ed779/US2929020.pdf)
Later edit
A new one, forgotten from the initial list:
https://patentimages.storage.googleapis.com/71/41/61/b940d5c5a526b3/US3869676.pdf (https://patentimages.storage.googleapis.com/71/41/61/b940d5c5a526b3/US3869676.pdf)
Some are almost the same, I don't know come they are considered distinct patents.
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This is a very interesting article by the authors of patent US3883812 (Harrison and Dimeff): A Diode‐Quad Bridge Circuit for Use with Capacitance Transducers. You can find it at https://aip.scitation.org/doi/10.1063/1.1685975
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This is a very interesting article by the authors of patent US3883812 (Harrison and Dimeff): A Diode‐Quad Bridge Circuit for Use with Capacitance Transducers. You can find it at https://aip.scitation.org/doi/10.1063/1.1685975
...and for $30 you can actually read it! |O
Any chance you have the actual PDF file available outside of a paywall?
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This is a very interesting article by the authors of patent US3883812 (Harrison and Dimeff): A Diode‐Quad Bridge Circuit for Use with Capacitance Transducers. You can find it at https://aip.scitation.org/doi/10.1063/1.1685975
Wow, thanks again!
Now, seriously, how do you find these?
What search terms/search engines do you use, please?
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...and for $30 you can actually read it! |O
Any chance you have the actual PDF file available outside of a paywall?
"Diamonds Are A Girl's Best Friend", and Sci-hub is a researcher's best friend. ;)
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Now, seriously, how do you find these?
With respect to patents, once you have one patent, additional references are easy to find and you can quickly become buried in data. To just scratch the surface, read the patent itself - most contain a list of references to prior and/or related art. Chase those down and you can quickly develop a 3D network of dozens/hundreds of related references. Some will be patents (domestic and foreign), others will be standard publications of all kinds.
Then go down a 4th orthogonal axis into the same or related Patent Class(es), which is how the PTO categorizes applications. These will be related but perhaps not with 1:1 mapping to the original. And of course all of these searches can then stem from any of THOSE references too.
If you want to go further, hit the PTO's website and look at the file wrapper for any of the patents (original or referenced). That will reveal not just more patents, but even non-patent references that the Patent Examiner reviewed while prosecuting the patent application. Each of those, in turn, can reveal more references that THEY relied upon, ad infinitum.
You can go REALLY deep down some of these rabbit holes. I've lost entire afternoons and evenings chasing one thread or another like this. It's intellectually stimulating but the hours pass quickly....
EDIT: All of the above searches are totally free. The applicant or the PTO may have paid to find the references, but the results of their research is in the public domain.
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I searched by authors and diode bridge. There are some jewels in this article, for example:
Second, it makes little difference in the
performance of the circuit when used with capacitance
transducers if the excitation waveform is sinusoidal, sawtooth, triangular, square, rectangular, or whether it has a
symmetrical or an unsymmetrical duty cycle.
This is a very interesting article by the authors of patent US3883812 (Harrison and Dimeff): A Diode‐Quad Bridge Circuit for Use with Capacitance Transducers. You can find it at https://aip.scitation.org/doi/10.1063/1.1685975
Wow, thanks again!
Now, seriously, how do you find these?
What search terms/search engines do you use, please?
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I make high resolution inclinometers mainly for marine use https://www.jmsensors.fi (https://www.jmsensors.fi)
Resolution is 0.001 degrees (RMS at 10 Hz, much lower after averaging). Accuracy 0.005 degrees + 0.5%. Long term stability (years) better than the accuracy. Measuring range +-17 degrees. The basic model is 1 k€ (USB connection, Windows software and IP68 aluminium enclosure). I don't think you can find cheaper ones with similar specs.
I also make an OEM model, which can be temperature calibrated for very good offset stability (typical +-0.01 and max +-0.02 degrees -20C - 80C).
I use a MEMS sensor and calibrate each sensors at 1 degree intervals.
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I make high resolution inclinometers mainly for marine use https://www.jmsensors.fi (https://www.jmsensors.fi)
Resolution is 0.001 degrees (RMS at 10 Hz, much lower after averaging). Accuracy 0.005 degrees + 0.5%. Long term stability (years) better than the accuracy. Measuring range +-17 degrees. The basic model is 1 k€ (USB connection, Windows software and IP68 aluminium enclosure). I don't think you can find cheaper ones with similar specs.
I also make an OEM model, which can be temperature calibrated for very good offset stability (typical +-0.01 and max +-0.02 degrees -20C - 80C).
I use a MEMS sensor and calibrate each sensors at 1 degree intervals.
I'd have to rate this as blatant advertising. It shows no knowledge of the thread. The discussion in this thread is at least two orders of magnitude (100x!) more sensitive than your product.
Please behave better. A tutorial series on applications for your product are, I'm confident, most welcome. But, you are in nerdland. You do not want to discover what nerds will do to sales puppies. It's really quite appalling.
So, either step up to the plate and blow us away with what you know about measuring small angles, or please, go away quietly and don't do this again.
Or to put it another way:
If you can quote chapter and verse, I'll listen. If not, I think you should move one.
Nobody in particular,
Reg
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Who was the UK supplier of vials? I need at least four 2"/2 mm vials. @ez24 gave me a couple (I broke one :-(
I may get some more Chinese, but I want to compare with UK for my application.
But I *do* have my CA3039s! So once I recover from my gratuitous folly, I'll get a bridge going.
Many thanks to those who have been tracking down the theory via the patents.
When I calculate the theoretical possibilities and look at the cost I am blown away by what a very low BoM cost design can do.
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I make high resolution inclinometers mainly for marine use https://www.jmsensors.fi (https://www.jmsensors.fi)
Resolution is 0.001 degrees (RMS at 10 Hz, much lower after averaging). Accuracy 0.005 degrees + 0.5%. Long term stability (years) better than the accuracy. Measuring range +-17 degrees. The basic model is 1 k€ (USB connection, Windows software and IP68 aluminium enclosure). I don't think you can find cheaper ones with similar specs.
I also make an OEM model, which can be temperature calibrated for very good offset stability (typical +-0.01 and max +-0.02 degrees -20C - 80C).
I use a MEMS sensor and calibrate each sensors at 1 degree intervals.
I'd have to rate this as blatant advertising. It shows no knowledge of the thread. The discussion in this thread is at least two orders of magnitude (100x!) more sensitive than your product.
Please behave better. A tutorial series on applications for your product are, I'm confident, most welcome. But, you are in nerdland. You do not want to discover what nerds will do to sales puppies. It's really quite appalling.
So, either step up to the plate and blow us away with what you know about measuring small angles, or please, go away quietly and don't do this again.
Or to put it another way:
If you can quote chapter and verse, I'll listen. If not, I think you should move one.
Nobody in particular,
Reg
I'm sorry you feel that way. I just noticed this thread a few days ago. I read all of it before replying. The original question was about long term measurement and 0.001 or better resolution for which just a module was said to cost more than 1 k. I felt my inclinometer might be a solution for the original problem. Then the conversation went to very high resolution reading of a bubble in a vial. But was decent long term stability or temperature stability achieved? Not much point doing long term measurements without good stability. Of course very high resolution may have some other applications even without stability.
I can see my post regarded as marketing or even spam. I don't really do that. It must have been more than a year since the last time I linked my homepage to any forum.
I don't really know what is the resolution limit of my inclinometer with averaging, since it has not been used for applications needing sub 0.001 degrees resolution. It's dynamic response is quite fast, about 10 Hz. So it's quite different from the vial bubble one. As I said I get 0.001 RMS at 10 Hz and averaging reduces it with SQRT(n) as long as the stability effects come into play or noise can no longer be averaged out. I do know it's clearly better than 0.001 degrees, but I haven't really had any need to measure very long term. With one minute averaging you would get 600 samples and 0.001/SQRT(600)= 4e-5 degrees RMS in theory, but then you don't need much of a temperature change to cause more even with temperature calibrated ones.
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MEMS based inclinometers suffer from drift due to a mixture of different materials with different t.c. forming the sensor element. Even burn-in can only reduce initial drift, but not fully eliminate it. Thus, MEMS-based inclinometers with capacitive principle are limited by physical constrains. Discussions with companies like murata confirmed that. In most cases their noise figure is defined by FFT, since their main use is vibration detection.
The only way to come across with this limitation, which is not given by the silicon itself, is to use a different methode of measuring the displacment of the seismic mass instead of capacitive measurement. The capacitive measurement also adds an additional portion of displacement due to electrostatic forces. Thus, longterm stability of current MEMS inclinometers is not that great, limiting the use of them for arcsec accuracy and resolution. But I can tell you, there is work in progress to overcome this limitation.
Vial based or fluid based inclinometers are a very simple approach with very good longterm stability. In most cases the readout circuitry or the mounting of the sensing element inside a package are the limiting factors on longterm stability, not the sensing element itself. The fluid defines the dynamic of the sensor. With such elements resolution in the arcsec and sub-arcsec range can be achieved, while having very big measurement range of several angular degree.
-branadic-
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I have used this MEMS chip since 2007 and had a lot of discussion with chip designers way before the company was bought by Murata. They still have the factory in Finland and all the designers I have been contact with are Finnish.
All the data I have given is based on my own measurements. I haven't really measured very long time stability, but my sensors have been used years in applications were 0.01 degrees long term drift would be noticed and I haven't heard any problems with that. Humidity and temperature will have an effect on long term stability rate. I still haven't found one needing recalibration to achive the specs I gave earlier. What kind of stability has been achieved with vial reading discussed in this thread?
Unfortunately they are discontinuing the chip I'm using due to subcontractor ASIC process change. They are developing a new one with about the same specs. I'm just ordering the current one hopefully lasting long enough for the new chip to be available. The discontinued chip seems to be totally unique. I haven't seen any other with comparable specs.
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Who was the UK supplier of vials? I need at least four 2"/2 mm vials. @ez24 gave me a couple (I broke one :-(
Level Developments:
https://www.leveldevelopments.com/products/vials/ (https://www.leveldevelopments.com/products/vials/)
For the UK manufactured vials.
The chap on ebay.co.uk trading as 'caterpiller_red' is (I believe) selling imported Indian manufactured vials. The photos show them marked 'PIE', which seems to stand for 'Paragon Instrumentation Engineers'.
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My question is, why do a bubble vial is even needed, in the first place?
A bubble vial makes sense for a passive device, read by reading the marks with naked eye, but when reading the tilt electronically, why?
A simple bowl (or some other type of container) with some electrodes around it will do it just fine, maybe even better then the vial, with it's hysteresis in bubble's move because of the not so well polished interior of the glass. The fluid itself can be the ground electrode, and two piece of Al adhesive tape on top would make the two measuring capacitor electrodes.
:D
Later edit:
To go a little further, maybe having some liquid is also not a good idea, because of its inertia. But capacitors are the simplest possible component to manufacture in a DIY regime. Literally everything is a capacitor. Easy to make 2 capacitors and connect them to that measuring bridge.
Maybe a simple ball bearing, suspended with a metallic wire inside a jar will be enough as a tiltmeter or even as a seismometer. The jar is fixed to the earth, the ballbearing ball's inertia will act as a reference. Two Al foil stick on the jar will make the capacitors. Eventually 4 foils to make X-Y axes measurements and find the direction were the shake/wave is coming from. A 3rd sensor for the Z axis would be harder to imagine, but not impossible. Maybe a ball bearing suspended with a metallic resort. I bet the exact waveform in 3D can be deduced by knowing the elasticity constants of the spring and the weight of the inertial ball.
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A bubble vial makes sense for a passive device, read by reading the marks with naked eye, but when reading the tilt electronically, why?
I guess it is because it is possible to manufacture a bubble vial, which amplifies the extremely small movement of the vial into much bigger movement of the bubble and the fluid. 0.001 degrees is less than 2 um on a 10 cm vial length. How would you detect that small movements? Any bearing will cause problems. One problem of a vial is very limited scale. But it's quite a task to get a wide scale together with very high resolution.
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I'd have to rate this as blatant advertising. It shows no knowledge of the thread. The discussion in this thread is at least two orders of magnitude (100x!) more sensitive than your product.
Please behave better. A tutorial series on applications for your product are, I'm confident, most welcome. But, you are in nerdland. You do not want to discover what nerds will do to sales puppies. It's really quite appalling.
So, either step up to the plate and blow us away with what you know about measuring small angles, or please, go away quietly and don't do this again.
Or to put it another way:
If you can quote chapter and verse, I'll listen. If not, I think you should move one.
Nobody in particular,
Reg
Maybe the moderator(s) will let you preview all posts in the future to ensure they are of sufficient interest to you and meet your standards.
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The bubble vial has the virtue that high sensitivity is easily attained. It's pretty hard to beat for simplicity and cost.
A pendulum and LVDT as used in a Talyvan is a lot more complex.
The NASA Tech Brief noted that the application did not require the sensitivity of a commercial inclinometer. Given that the NASA design was reading 0.05 seconds and a change of vial would result in 0.01 arc seconds should give some idea of how sensitive the commercial tiltmeters are.
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A bubble vial makes sense for a passive device, read by reading the marks with naked eye, but when reading the tilt electronically, why?
I guess it is because it is possible to manufacture a bubble vial, which amplifies the extremely small movement of the vial into much bigger movement of the bubble and the fluid. 0.001 degrees is less than 2 um on a 10 cm vial length. How would you detect that small movements? Any bearing will cause problems. One problem of a vial is very limited scale. But it's quite a task to get a wide scale together with very high resolution.
And capacitance is straightforward with fluids. Water has an incredibly high dielectric constant, way more than traditional "high DE" materials like tantalum. I haven't looked into the DE of oils such as are commonly used in vials like these but the point is that basing an inclinometer on the movement of a bubble in fluid has several advantages that are hard to replicate in other ways. It's hard to imagine a mechanism simpler than a bubble in a sealed glass vessel.
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The "spirit" in a spirit vial is *not* alcohol. It feels like acetone, but smells different.
I'd like to know what it is.
In the meantime I suggest that if you break one, or think you might have, you place it outdoors until the contents evaporate.
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My question is, why do a bubble vial is even needed, in the first place?
A bubble vial makes sense for a passive device, read by reading the marks with naked eye, but when reading the tilt electronically, why?
I can tell that 1µm/m stability over 24h is achivable with a capacitive, temperature compensated readout approach of a spirit vial. It's even harder to separate stability of the sensor from movements of the ground, even with high resolution inclinometers such as Leica Nivel or Wyler Zerotronic as reference.
I'd like to know what it is.
Well, some companies claim it's alcohol or hydrocarbonate.
-branadic-
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I found this a very interesting thread. I own a two-head Talyvel 4 which I repaired and calibrated, and used to map my surface plate. I am going to experiment with making my own capacitive-readout bubble level as described here and in the NASA Tech Brief document from 1981.
From what I could tell, three people in this thread (JBeale, branadic, and rhb) have built these devices.
branadic read his using an MPT PCap01 capacitance-to-digital chip, and also characterized and removed the effects of temperature dependence.
JBeale and rhb interfaced with the NASA "circulating diode bridge" circuit. JBeale started with 1N34 diodes, then shifted to using On Semi MMBD352LT1G diode arrays, then also increased the clock frequency to 1.8 MHz. Rhb used old-stock RCA CA3039 diodes and some other, and also rolled his own copper foil. With some help from another member here, he also located the patents that explained the operation of the "circulating diode bridge", which is clever and not trivial.
For myself and future readers, since the last posts in this thread were more than a year ago, I was hoping that the three of you might provide some brief summaries of the "end state" of your experimentation, and also say something about "lessons learned". If any others reading this have also build these devices, it would be nice to hear from you too!
Cheers,
Bruce
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We have a patent pending, so I can't say anything about the sensor.
Using the above mentioned circuit also involves a lot of IP build up over several years that I can't share, as this IP is what we earn money with when developing capacitive sensors for our customers.
-branadic-
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We have a patent pending, so I can't say anything about the sensor.
OK, I understand. Anyway, your posts, pictures and plots above are interesting and helpful.
Hopefully JBeale and rhb can provide a follow-up to their previous posts.
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Sadly, I broke the vial :-( That revealed that the Chinese vial was not fully ground making continuing seem a bit pointless. And I didn't feel like buying UK made vials. It also prompted a lot of reflection on methods for doing this. The context can completely change the best choice. In JBeale's case, the Chinese vials would be OK. For me, trying to measure the lake level from my house not so usable.
There are a lot of options for detecting very small angles from vertical. The TalyVel uses a pendulum and LDVTs and is accurate to a second.
At this point I'd use a wire flexure pendulum with 3 or 4 capacitor plates and stops to prevent a short or other damage. One then has the option of a huge number of bridge designs.
One attractive option is to use the capacitors to shift the frequency of xtals. Mix them to a frequency an Arduino can sample and measure the frequencies to determine the angular deviation from vertical.
An aluminum cylinder filled with fine lead shot with an 0.010" hole in the center of rotation and an 0.010" guitar string for a flexure should be robust and sensitive. Calibration by reversal. If you're making a portable device use three small carbide balls for contact points.
Have Fun!
Reg
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Wyler in Swizerland uses a pendulum to build a differential capacitor. It is quite a fancy micro mechanical system.
Check Compendium "The secrets of inclination measurement" (https://www.wylerag.com/fileadmin/pdf/compendium/Compendium_eng%202018.pdf) for further information.
Safran Colibrys has some quite expensive MEMS sensors based on a servo controller to keep the seismic mass in the middle position.
We currently have a project to improve our pcb based, capacitive, fluidic inclination sensors (https://www.hahn-schickard.de/fileadmin/media/Hauptnavigation/Anwendungsberichte/AB_2-axis_inclination_sensor_en_R0.pdf). Within the project we are improving linearity. Hopefully in about 1.5 years there will be a paper with results.
-branadic-
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Dear Reg,
Thank you for the helpful reply!
Sadly, I broke the vial :-( That revealed that the Chinese vial was not fully ground making continuing seem a bit pointless. And I didn't feel like buying UK made vials.
Did the vial break because you soldered to the copper contacts while they were in place on the vial? The ones I have are borosilicate glass (branded PIE, purchased from the UK) which has a low coefficient of expansion, so I thought that soldering directly to them might be OK. But I have not done so yet.
There are a lot of options for detecting very small angles from vertical. The TalyVel uses a pendulum and LDVTs and is accurate to a second.
I own a Talyvel 4, which uses the same mechanism as the earlier Talyvels. It has a resolution of 0.1 arcsec, and according to the specs is accurate to 0.2 arcsec plus 2% of the (absolute value of the) reading. I have calibrated it and can confirm that (at least for angles larger than a few arcsec) it meets these specs.
An aluminum cylinder filled with fine lead shot with an 0.010" hole in the center of rotation and an 0.010" guitar string for a flexure should be robust and sensitive.
I'm not sure that guitar string would be the best choice, as it might have a tendency to stretch. The Talyvel uses beryllium copper (BeCu), also known as copper beryllium (CuBe), beryllium bronze or spring copper, for its support wires. The diameter is fine enough that I suspect it is under a substantial fraction of its yield tension.
I am going to start by reproducing the NASA circuit, and then perhaps experimenting with a capacitance to digital converter.
Cheers,
Bruce
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Because of magnetic forces I would be a bit carefull with a LVDT. It may still show a stable reading, but may be off from the earths magnetic field, if one is not carefull with the shape (a ball should be OK).
With the string it may be important to avoid anything magnetic, as from the shape the string would cause a magnetic force. So normal steel should be out and under high stress / after some cold working some stainless steel versions can show weak magnetism.
The shift in the resonance frequency of crystalls (especially low frequency tuninig forc ones) can be uses to detect variations in gravity but it could be tricky with the direction. The difficulty is not in measuring the frequency, but in the mechanical mounting and getting a stable temperature.
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I was smoothing out the Cu foil and hit the teat :-( Had not got to the solder stage. However, I've used the tape for Manhattan style prototyping on SS PCB and soldering is a non-issue. When the *wire* is hot you're done. Press the wire to the tip, place it in contact with the foil and solder. The foil is such a small thermal mass and so much more conductive that the glass never sees the heat if done properly. An excellent "belt and suspenders" dodge is to leave the foil sticking up where the connection is to be made, solder it and then stick it down.
Rather than speculate, I suggest looking up the material mechanical properties and calculating the relevant stresses and strains of music wire and beryllium bronze wires. As I understand, the TalyVel uses the suspension wires for signal as well. That presents different requirements.
The dominant parameter of a flexure wire is the stiffness. The stiffer the flexure wire, the longer it must be. But it is the product of stiffness and length that matters. Larger wire, longer pendulum. Music wire is available as small as 0.003". That's pretty fine. Naturally, with a draw plate you can go finer. The point of a wire flexure is that, properly designed, it matches the mathematics of a perfectly flexible string suspension. Knife edges, etc not needed.
I got involved in this as far as I have for two reasons: I'm a professional geoscientist and I was given three 4"/div Chinese vials by a thread participant. I was interested in observing the crustal deformation associated with the water level in the lake a mile from my house. Spending $70+ for a pair of UK vials wasn't a high priority. For workshop use I'm much more interested in a suspension based system. I'll build out an XY system using the Chinese vials just to see how they do. But the crappy quality took the bloom off the project.
The reason that a turned solid aluminum cylinder with a small center hole (over a *short* distance, e.g. 0.1") is that made from round bar stock on a basic lathe it will be as true as you can afford. And not hard to accomplish to 0.0001" with proper practice.
Have Fun!
Reg
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I have not really done much with the bubble-tiltmeter since my last post here. I discovered that the electronic readout has quite good resolution in theory, but the mechanical properties of my glass vial were less than ideal. The resolution of the overall system in my case was determined by some "stickyness" or hysteresis of the bubble, due to the roughness or texture on the inside of the glass vial. Maybe this could be smoothed out by a fixed amount of vibration applied by a speaker or similar transducer, but that adds its own opportunity for uncontrolled offsets and I didn't investigate the possibility.
Separately I also tried measuring the left-right timing of a driven pendulum with optical center detector; timing with Raspberry Pi Pico at 200 MHz. Very high-resolution in theory (output being a frequency ratio avoids some analog pitfalls). It worked but was still somewhat noisy, perhaps due to the optical sensor, and background horizontal earth motion (microseism).
Separately I also tried DC analog optical position sensing of a suspended pendulum using a slit and a split-field photodiode. That works but the optical beam has some scattering by fine particles so it is also a dust meter.
I would imagine the pendulum with capacitive sensing would be very sensitive, although I have not tried it.
As far as I know, all tiltmeters are also horizontal seismometers, so you have to do a lot of low-pass filtering if the system is not already well damped, like a nearly-horizontal fluid bubble probably is.
-john
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Hi Reg,
Thanks for your detailed reply. There are certainly many possibilities, both for sensing and for readout.
Regarded a suspended aluminium cylinder, one possible complication concerns the mechanical "stops" which prevent the cylinder from hitting the capacitive sensing pads or frame. If these are "hard" then each impact will deform both the cylinder and the pads, changing their shape and hence their capacitance and the balance. If they are "soft" then they will also be deformed by impact. This won't change the shape/balance of the pendulum but by changing the distance to the pendulum, it will also influence its capacitance. The fluid bubble sidesteps some of these issues, although as the discussion here has shown, it is not free of hysteresis.
A second issue is the orientation. I am not sure if it is correct to assume that a single wire will return the cylinder to the same orientation, particularly if that wire is very thin. (Even if the cylinder is round to 2.5 microns, that may not be good enough, as we are sensing significantly smaller motions.) The time constant for this might also be very large. And if you suspend the cylinder from multiple wires, that creates other potential issues.
For the record, I wanted to clarify one point:
As I understand, the TalyVel uses the suspension wires for signal as well.
This is incorrect. The Talyvel armature is suspended from five BeCu wires. One is a single strand, and the other four form two "V"s. All five of those (conductive) wires are attached to the internal metal frame of the device at the top end, and to the metal armature at the bottom end. While it is not their primary purpose, they do provide a conductive path between the moving armature and the fixed frame.
The sensing is done via two coils, located on either side of the suspended armature. The inductance of these coils is a function of their separation from the (steel) armature. The wires from each of these coils are entirely independent from the suspension wires, and are connected to the readout via a shielded set of twisted pairs. The two coils are part of a classic bridge circuit, driven by a 3kHz oscillator.
Cheers,
Bruce
PS: for the NASA/spirit vial design I would be grateful for guidance about the size/shape of the two top electrodes. For my PIE vial, the total internal length is about 95mm (3 3/4") and the bubble (when centered) has a length of about 32mm (1 1/8"). The NASA document suggests a rectangular electrode with a length comparable to the bubble, but if I do that, then the capacitance difference will not be a monotonic function of the displacement angle from horizontal. This is because, as the displacement increases from zero, the bubble first moves completely under one electrode (decreasing its capacitance) but then exits the electrode at the far end, increasing its capacitance again. If I make the electrode the same length as the bubble, then the capacitance will be a (roughly) linear function only for a total displacement of +- 16mm from the central position, corresponding to (nominally) +- 24 arcsec.
PPS: a second technical question. Are the CA3039 "diodes" just Si NPN transistors with the base and collector tied together? If so, can I just use (say) a transistor array such as CA3127 for this? If I understand correctly, the matching is desirable so that the offset voltages and junction capacitances are the same (as a function of temperature & forward current, and temperature & reverse voltage respectively). Is that correct?
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The wire will allso restrore the rotation. If needed one can measure the rotation (e.g. from thermal effecs) too. There is a torsional more of oscillation and the frequency can be relatively low, but for a small system (e.g. < 2 cm diameter) this would not be so extraordinary slow (e.g. < 1 Hz). The air would provide some and possibly enough damping of the oscillations. If really needed magnetic damping (with a permanent magnets on the outside, providing eddy current damping) could be added.
The mechanical stop needs to be taken into account, but I don't think it would be such a bad point. It dones not have to be the same surface as used for sensing. The sensing distance would need to be larger than the mechanical stops, which limits the resolution. Still the resolution of capacitive readout is usually quite good, well OK to see the seismic motion.
One will need some filtering. Today this would be mainly in the digital domain. It would be not just a simple low pass, but also additional suppression of the main resonant modes of the system. I would even go beyound just a classic filter and consider fitting the resonant mode(s) to also take into account a decaying oscillation if needed.
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@branadic: Located at Stuttgart, not too far from artificial (Straßbourg) and natural (Schwäbische Alb) serial offenders regarding seismic activity, I wonder why the inclination measurement experts didn't recommend against getting sensitive measurement devices. ;)You might want to set up one or three geophones (HX711 ADCs do well enough) to evaluate shaking floor.
BR
Hendrik
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Seismic activity never has been a problem in the last 14 years. The only real pita however was when they've started to build ZAQuant next to us, scratching on the rocks in the building pit.
-branadic-
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I put together the first crude model this evening, following the NASA document. Photo attached below. It works exactly as advertised. A few notes:
(1) Since I didn't have a CA3039, I used a CA3127 NPN transistor array with bases tied to collectors
(2) I soldered directly to the copper tape on the glass vial
(3) To shift the output to be roughly zero at the center, I inserted a 2pf trim
capacitor. This was about 1/3 of full range!
(4) I'm driving it with a 10Vpp sinewave at 300kHz
(5) The full range of bubble motion under the top electrodes is +-16mm, which generates approximately +-500mV,
corresponding to +-24 arcsec. So the gain is approximately 20mV/arcsec. I have not measured
or characterized the noise or stability.
Because my vial is much longer than the NASA one, I think it makes sense to shift the top electrodes. I will keep them the same length as currently, but move them towards the ends of the vial so that they just overlap the bubble by (say) 2mm, when the bubble is in the central position. This should give me a broader monotonic range of capacitance versus motion, though will reduce the gain (mV/arcsec) by about a factor of two. Will try that tomorrow.
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Congratulations! Sorry, I didn't visit for a few days.
The music wire flexure is an alternative to a mechanical pivot. There are various refinements to such a suspension and it may be TalyVel are using one of those to constrain motion to a plane. No matter, the principle is the same. I'm simply proposing to do X & Y, rather than just X.
The purpose of the bumpers is to *prevent* damage by restraining the motion of the plumb bob. In particular, kinking the music wire. As for precision, the plumb bob doesn't really matter beyond basic accuracy. Everything is calibrated by reversal.
I don't know about the physical construction of the diode arrays. Your solution works. I do know that the large diode and transistor arrays of the past are highly sought after today. Smaller arrays are still made.
Have Fun!
Reg
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I'm setting up some logging stuff to compare the Talyvel and the NASA tiltmeter outputs over a few days.
I thought that the following might be of interest. For anyone who wants to understand how the circuit works, read this article:
https://aip.scitation.org/doi/abs/10.1063/1.1685975
Here is a screenshot showing the behavior:
The pink line is the voltage at the top junction of the bridge, relative to ground. This is just the oscillator, 10Vpp.
The yellow line shows the voltage at the sense capacitor which is charged by the oscillator when the oscillator is positive. The white curve is the (magnified) difference between these, which is the voltage across the diode that charges this sense capacitor. A positive voltage means that the diode is conducting (forward biased).
Start from the second crossing of the pink and yellow curves. At this point there is no current flow through the diode. As the oscillator voltage continues to rise, the diode begins to conduct, and the voltage on the capacitor rises, following behind the oscillator. Eventually the diode swings into full conduction, and charges the capacitor, with about an 800mV drop. After the oscillator peaks, the voltage on the capacitor would remain fairly stable, but then is discharged by the second diode. The article shows that if diode drops are neglected, then in the steady state the two capacitors end up with the same average amount of charge, so that (Vp + Vdc) C1 = (Vp - Vdc) C2, where Vp = 5V, Vdc is the output DC voltage of the circuit, and C1 and C2 are the capacitances of the two sense electrodes. Hence Vdc = (C2 - C1)Vp/(C1+C2). Here the value of C2-C1 can get to about 10% of C1+C2. [attachimg=1]
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I thought that the following might be of interest. For anyone who wants to understand how the circuit works, read this article:
https://aip.scitation.org/doi/abs/10.1063/1.1685975 (https://aip.scitation.org/doi/abs/10.1063/1.1685975)
That's the same link posted two pages ago :)
https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/msg2417991/#msg2417991 (https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/msg2417991/#msg2417991)
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That's the same link posted two pages ago :)
Yes, I know. There were also many other links posted in that part of the thread, but IMO this reference has the clearest and most direct analysis. So I thought it would be helpful to put it alongside the waveforms.
I have a practical question for the experts:
The CA3127 is a 16-pin DIP containing five NPN transistors. The data sheet has the following comment: "The collector of each transistor of the CA3127 is isolated from the substrate by an integral diode. The substrate (Terminal 5) must be connected to the most negative point in the external circuit to maintain isolation between transistors and to provide for normal transistor action."
Currently pin 5 is floating. However I don't know how to "pull it negative". Can someone tell me how I could do this? The largest achievable potential differences in my circuit are 10V, because I have a 10vpp oscillator driving it. Does this mean that I should take an independent 12V voltage source (or would 7v be enough?) and tie the positive terminal to the "ground" of the circuit and the negative terminal to pin 5? Will this back-bias all of the transistors? Is there any way to accomplish this without a separate voltage source? I've also attached a snapshot of the circuit diagram from the NASA publication.
[attachimg=1]
Here is a link to the datasheet: https://www.digchip.com/datasheets/parts/datasheet/235/CA3127-pdf.php (https://www.digchip.com/datasheets/parts/datasheet/235/CA3127-pdf.php)
The comment in question is Note 1 on page 5-2.
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The transistor array would add extra parasitic capacitance. I don't think all 4 diodes need to be matched. It should be enough if the upper and lower 2 diodes are matched. So one could use 2 pieces of SOT23 dual diodes (2 in series each). These are much easier to get and with 2 parts from the same batch the matching may not be so bad. There is little power and thus also need for tight thermal coupling.
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For anyone who wants to understand how the circuit works, read this article: https://aip.scitation.org/doi/abs/10.1063/1.1685975
I'd seriously love to read it but it just brings up a summary, and an offer to download a PDF which requires a subscription. Anyone have the actual document?
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Go to Sci-hub and search for the DOI: 10.1063/1.1685975, or simply paste the link in the search box.
https://sci-hub.st/https://aip.scitation.org/doi/abs/10.1063/1.1685975
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The transistor array would add extra parasitic capacitance.
I don't think all 4 diodes need to be matched. It should be enough if the upper and lower 2 diodes are matched. So one could use 2 pieces of SOT23 dual diodes (2 in series each). These are much easier to get and with 2 parts from the same batch the matching may not be so bad. There is little power and thus also need for tight thermal coupling.
The Harrison and Dimeff paper says "At or near the balance condition, the calculated contribution of the diodes to the dc output voltage is
\Delta V = 1/2 ((V_d1-V_d2) - (V_d3 - V_d4))
which suggests the need for temperature tracking at least by pairs and preferably by all four diodes. In the experimental tests the circuit includes a commercially available diode-quad assembly with a temperature tracking specification of \Delta V_d <5.0 mV for -55°C< T<l00°C."
Here \Delta V is the change in the DC output level due to a change in the diode forward voltage drops, V_d1 and V_d2 are the forward drop diode voltages in the upper half of the circuit, and V_d3 and V_d4 are the same in the lower half.
So as you say, it's enough to ensure that diodes 1 and 2 track each other, and that diodes 3 and 4, track each other in forward voltage drops as the ambient temperature changes. Note also that there is virtually no power dissipation in this circuit, so the diode temperature is primarily tracking the changing ambient temp.
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You can ameliorate the lack of monolithic arrays by mounting tempco selected devices to a common heatsink and then holding the temperature as stable as possible. You can also fix that and many other shortcomings in post-processing.
What is the use case? Geophysics or engineering? I'm familiar with both.
In the non-TalyVel pendulum sensor department, consider a 0.003" music wire flexure with a turned cylinder suspended from it with HDPE stops to prevent excessive displacement. With 3 silicon carbide ball feet and 3 adjustable capacitor plates, a measuring system can be set up which will resolve very small angles. Initial setup is by rotation through all 3 positions on a well leveled surface plate to place the capacitor plates in the proper locations relative to the pendulum.. After that, calibration is by reversal in the field on an almost level surface.
An equilateral triangle template that ensured all 3 measurements had the balls consistently placed would be all one needed for calibration. But that's not geophysical observational kit. The vials are better for that with good quality vials.
It just occurred to me that a simple fixture which would take a vial and then automatically test it for accuracy is actually not all that hard. A 3D printed plastic mount with a pair of copper foil strips on the vial contact surface would do. Then you just need a very small angular adjustment mechanism and data acquisition.
Have Fun!
Reg
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So one could use 2 pieces of SOT23 dual diodes (2 in series each). These are much easier to get and with 2 parts from the same batch the matching may not be so bad.
Could you suggest a specific part or parts to me? Most important is that (1) at fixed current, the difference in forward offset voltage is a constant function of temperature and (2) that the difference in reverse bias capacitance is a constant function of temperature.
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You can ameliorate the lack of monolithic arrays by mounting tempco selected devices to a common heatsink and then holding the temperature as stable as possible. You can also fix that and many other shortcomings in post-processing. What is the use case? Geophysics or engineering?
Agreed that temperature dependence can be removed in postprocessing, but would prefer to minimize it at the source as much as possible.
I'm mainly interested in surface plate mapping. So bandwidth from DC to 0.5 Hz would be fine.
Consider a 0.003" music wire flexure with a turned cylinder suspended from it with HDPE stops to prevent excessive displacement.
I am going to concentrate on the vials for now, thanks. Have you computed the rotational period and damping time for the configuration that you suggest? In my applications I need to move the sensor every few seconds. So I need something that damps down in a couple of seconds.
It just occurred to me that a simple fixture which would take a vial and then automatically test it for accuracy is actually not all that hard. A 3D printed plastic mount with a pair of copper foil strips on the vial contact surface would do. Then you just need a very small angular adjustment mechanism and data acquisition.
That's very close to what I have already. My vials were delivered in a 3d printed case, and if you look at my earlier photo, you'll see that I'm using that as a mount, for the moment. It's adequate for testing purposes.
Cheers,
Bruce
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So one could use 2 pieces of SOT23 dual diodes (2 in series each). These are much easier to get and with 2 parts from the same batch the matching may not be so bad.
Could you suggest a specific part or parts to me? Most important is that (1) at fixed current, the difference in forward offset voltage is a constant function of temperature and (2) that the difference in reverse bias capacitance is a constant function of temperature.
The specs usually don't specify the matching, but usually it is quite good. The temperature dependence is usually proportional to 1.12 V - V_f. Voltage matching also implies TC matching. The parameters to look for are more low capacitance, not too much leakage and no too much Trr (e.g. < 200 ns) .
The obvious candidate would be BAV99 in the version with series connection.
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The obvious candidate would be BAV99 in the version with series connection.
I just ordered 30, cost was 2.90 Euros, including shipping.
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LoL!
Aside from geophysical monitoring, surface plate mapping is my other application of interest.
I assumed that the pendulum properties would be determined during construction. I think once per second is rather optimistic. Bubbles don't settle quickly.
I happened to come across the bag of diode arrays a few days ago, so I may build the basic NASA circuit using the crappy Chinese vials.
I just realized that my HP 4284A reads to 0.01 femtoFarads. Now to find something that will hold the vial safely.
Have Fun!
Reg
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The best of those Rieker devices have a resolution/accuracy of about 0.05 = 1/20 degree. In this thread, we are talking about inclinometers that can measure and resolve 0.1 arcseconds. That is 1/(60 x 60 x 10) = 0.000028 degree. In other words, the most sensitive of the devices made by Rieker miss the target by more than a factor of a thousand.
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Yes, I just have to give it a try.
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On a mechanics forum a while ago there was a discussion on how to build a Wyler Niveltronic like tilt meter.
My thought was: Could a 1 um/m tilt meter be built using a off the shelf signal processing frontend? Without any analog tinkering at all?
The idea was to build a magnetically damped pendulum and replace the LVDT by a capacitive sensor. Assuming 15 mm sensor diameter and 100 um nominal air gap, this gives a capacity of around 15 pF. For an effective pendulum length of 40 mm, 1 um/m tilt translates into 40 nm sensor change. 100 um/40 nm= 2500, so a 12 bit resolution seems sufficient.
Searching for usable frontends resulted in the PCap04 - all other capacitive sensor interfaces seem to require floating sensors, while I wanted the pendulum to be grounded. Working with the PCap04 proved to be a nightmare - I found the documentation truly miserable and working with this chip it lots of guesswork, trial and error and reverse engineering of the eval kit operation (and some code snippets floating around).
Initially I had a more complex sensor arrangement in mind, but decided to simply put the pad on a PCB. Whether this can be made accurate to 40 nm remains to be seen. The PCB is mounted to the frame via a magnetic kinematic mount (three balls, six cylinders), providing at least in theory a precisely constrained mount without adding any torque onto the PCB (which certainly would result in creep of the FR-4). The kinematic mount consists of six dowel pins that are glued into slots on the PCB and three balls on the tip of micrometer heads. To aid achieving an even 100 um air gap, three auxiliary sensors are placed around the center sensor.
Currently I have a simplified setup where I can set a fixed position via a reference plate. After much trial and error the PCap04 gives useable results and I am achieving an RMS error of less (not much) than 40 nm, with lots of drift (which I assume is thermal and is no wonder given my setup). So for now it seems to work and I am waiting for the completed pendulum assembly.
For calibration the idea is to put the device on a precision granite beam and support it using gauge blocks. This way I should be able to set the tilt in increments of 10 um/m. If linearity with this is OK and noise good enough, I think it should achive 1 um/m, although I have no direct means of verifying that. Drift will be interesting... to be seen.
The final test will be trying to measure the topology of a surface plate and comparing it to its calibration certificate. This will also define the required drift stability - I'd assume this can be done in 15 minutes so this is the time frame for stability. For machine leveling required accuracy will be lower.
As I said this is kind of a fun project. I have nothing in my workshop requiring (even remotely) that precision - my lathe sits on rubber bumpers. It's really to find out how far you can push an off the shelf frontend without diving into analog design.
- Martin
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Short update. Mechanics arrived (friend of mine did these, precision scraped functional surfaces) and so far looks good. RMS noise of the sensor is below the required 1 um/m, although not by a huge margin.
Next step will be to build a test jig that can tilt the assembly by defined amounts. Easiest would be just to put a bunch of 50 nm shims below one side (just kidding).
Current plan is to use two precision ground plates and tilt them using a differential micrometer in addition to a piezo stack. Of course this will not give me precise reference angles, but for this I'd have to invest in metrology grade ($$$) reference instruments like an interferometer and a climate controlled lab on its own foundation.
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Trying to understand how that works, and couldn't figure what pendulates, and where, and relative to which plane. Googled 'Wyler Niveltronic' and it only returns marketing pitch flyers with specs and applications.
Do you have any link that describes the basic principles for that method of measuring the tilt, please?
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Wyler Niveltronic (AFAIK) uses a pendulum where tilt is measured using a LVDT. Can't find an inside image right now. Obviously their LVDT signal conditioning is low noise and stable enough, a hassle I wanted to avoid using a capacitive distance sensor.
See the annotated image on my sensor. It's really just a pendulum with the sensor PCB besides it. Air gap is only 100 um so you don't see it in the picture.
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Voltage matching also implies TC matching. The parameters to look for are more low capacitance, not too much leakage and no too much Trr (e.g. < 200 ns) .
The obvious candidate would be BAV99 in the version with series connection.
Pulling this forward to 2023, there are 4-diode versions of BAV199, BAV99 etc in 6 pin SOT363 & SOT26 packages, which allow this to be done in one package.
That give you two choices on wiring.
I'm guessing left-right matching matters more than up-down matching, so the pairs would be used left-right.
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One more update. 50 nm shims proved to be unobtainium, instead I got a differential adjuster head. 25 um per revolution, 1 um/500 nm divisions. Mounted this in a plate together with two conventional micrometer heads. Most difficult in this was to buy the precision machined plates here in Switzerland and to cut the 1/4-80 fine thread for the DM22 adjuster.
(https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/?action=dlattach;attach=1940481;image)
Setup is still not optimal, it should be on a half ton granite slab in the basement instead of sitting on my wobbly wooden desk. But together with the adjuster graduation, one gets a very good idea on short term stability and noise.
A 1 um step on the adjuster gives an angle of (170 mm baseline) 1.2 arcseconds, which is 6 times higher than the target 1 um/m 0.21 arcseconds.
(https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/?action=dlattach;attach=1940487;image)
In the graph, you can see three steps: First two 1 um and then one 500 nm adjuster step. Noise judged visually is around 100 nm p-p. The PCAP04 is set to 2 samples/s, so with a 10x averaging (5 s settling time) one could reduce this further. BTW the ratio between adjuster step and actual distance at the pendulum is 170/40 mm, so the 100 nm p-p noise is actually 24 nm at the PCB. Not too shabby, I'd say. How much of this is coming from the PCAP04 and how much is air turbulence or vibration of the building remains to be seen. I need to finish the display module so I can close the housing and put this on a concrete basement floor.
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I'm a little late chiming in here, but... I have a Taylor Hobson Talyvel electronic level. From the spec sheet it can reliably read 0.1 arc second. Mine has been around a bit, so maybe is still good to 0.2 arc second or so. The sensing head is about a 3" block, with maybe a 5" wide base. If you stick one human hair under one end, it goes off-scale. The sensing mechanism is pendulum suspended by 5 TINY thinner than a hair wires. It hangs between two inductive sensors that are wired into some kind of AC bridge. Damping is provided by a magnet that acts on an aluminum plate at the side of the pendulum. When unlocked, the pendulum is only free to swing maybe 1-2 mm between the sensors.
Jon
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Jon, do you have a pitcture of its innards? Would be interesting!
But well, the whole point of this exercise was to find out if simply placing a $5 sensor on a PCB could achieve the same accuracy as a Niveltronic or Talyvel, which both (to my knowledge) use differential inductive transducers (LVDT). Looking back, figuring out how the pcap device works took such an effort (due to the miserable documentation) that at least design wise there's not much saving.
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The only info I know of is given in their compenium:
https://www.wylerag.com/fileadmin/pdf/compendium/Kompendium%20deutsch%202018.pdf (https://www.wylerag.com/fileadmin/pdf/compendium/Kompendium%20deutsch%202018.pdf)
The theory of operation is given on page 21 and 38. Looking into it, the sensitivity is specified to 10 µm/m aka 2 arcsec, while repeatability is specified to be 1 μm/m.
I agree, that the documentation of the PCap is hard and most of the really interesting details took me years to figure out myself, which eventually made it into my PhD thesis. However, since then we made huge progress with capacitive sensors in general, but also our capacitive two-axis inclination sensor. We recently finished a project, in which a process was developed to improve its linearity.
-branadic-
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I agree, that the documentation of the PCap is hard and most of the really interesting details took me years to figure out myself, which eventually made it into my PhD thesis. However, since then we made huge progress with capacitive sensors in general, but also our capacitive two-axis inclination sensor. We recently finished a project, in which a process was developed to improve its linearity.
-branadic-
The PCap devices are somewhat strange. I guess initially developed by acam in Studensee, then acquired by ams and then going to Sciosense in the Netherlands? Does not really feel like a successful product. Maybe they gave it a final chance before discontinuing the whole line. At least they are available at Mouser or Digikey, but I would not trust those in a product development. Also, there are near zero other projects to be found on the internet using the PCap devices. Little wonder given how time consuming it is to reverse-engineer them in order to compensate for missing docs.
Found this interesting paper most likely using a PCap device https://www.hahn-schickard.de/fileadmin/media/Hauptnavigation/Anwendungsberichte/AB_2-axis_inclination_sensor_en_R0.pdf (https://www.hahn-schickard.de/fileadmin/media/Hauptnavigation/Anwendungsberichte/AB_2-axis_inclination_sensor_en_R0.pdf)
I would assume your PhD thesis is public? Would you share a link? Thanks!
- Martin
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The PCap devices are somewhat strange. I guess initially developed by acam in Studensee, then acquired by ams and then going to Sciosense in the Netherlands? Does not really feel like a successful product. Maybe they gave it a final chance before discontinuing the whole line. At least they are available at Mouser or Digikey, but I would not trust those in a product development. Also, there are near zero other projects to be found on the internet using the PCap devices. Little wonder given how time consuming it is to reverse-engineer them in order to compensate for missing docs.
Well, that all happened right after the founder of ACAM, Mr. Braun, passed away. It is and all their other ICs are however a successful product(s), although you obviously don't see them in everyday devices.
Found this interesting paper most likely using a PCap device https://www.hahn-schickard.de/fileadmin/media/Hauptnavigation/Anwendungsberichte/AB_2-axis_inclination_sensor_en_R0.pdf (https://www.hahn-schickard.de/fileadmin/media/Hauptnavigation/Anwendungsberichte/AB_2-axis_inclination_sensor_en_R0.pdf)
Yes, in the latest versions of this sensor we are using the PCap devices ;)
I would assume your PhD thesis is public? Would you share a link? Thanks!
No, it's not public, hence why I can't share a link nor the IP how to properly use the PCaps at their full capability, which I already wrote took me years to figure out. But I can tell you, once understood how to write your own firmware and how to deal with the raw measurement values the PCap is an amazing powerful device. No, I'm not getting any money for that statement, it's just my experience from multiple different and current sensor projects using this/these device(s).
-branadic-
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No, it's not public, hence why I can't share a link nor the IP how to properly use the PCaps at their full capability, which I already wrote took me years to figure out. But I can tell you, once understood how to write your own firmware and how to deal with the raw measurement values the PCap is an amazing powerful device. No, I'm not getting any money for that statement, it's just my experience from multiple different and current sensor projects using this/these device(s).
I am not sure why they invented their own DSP in that chip. Sure, you can do all kinds of processing, but why not simply expose the CDC/RDC fully via registers and let some external microcontroller do it? This way the user would not have to mess with barely documented assembly innards.
Even having the DSP, I am not sure what the benefit of using it would be. As far as I can see if you use the standard firmware, all it does is calculate the Cx/C0 ratios and do the averaging. For me this is fine, whatever correction I will use (for the time being a linear scaling factor) will be calculated in a STM32 processor, in plain C using float variables, with proper debug support.
Of course, if you are forced by whatever reason (cost?) to have a single chip version, you could make a sensor with PDM output and linearization for whatever sensor you attach to it, but I somehow can't imagine that this chip ever will find its way in such a price sensitive application.
Do you know if there is still anyone left from the original developers who knows how this chip works? Or is all Sciosense inherited was a mask set for production?
BTW nice work with the dual axis fluid sensor! It reminded me of my first ever sensor project ages ago, where I attempted to build an electrolytic inclination sensor for cave surveying. I used a chamber glued together from acrylic glass, with some vodka as fluid. Leaked of course. I would guess for your sensor, main problems were fluid properties (wetting/capillary effect at boundaries), stability and probably topmost fluid staying inside the cavity and not evaporating.
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Just out of curiosity, how much does the PCap sensor costs, or at least its price range for a 1pcs order?
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I am not sure why they invented their own DSP in that chip. Sure, you can do all kinds of processing, but why not simply expose the CDC/RDC fully via registers and let some external microcontroller do it? This way the user would not have to mess with barely documented assembly innards.
Reason is that you can implement your linearization algorithm into it, beside many other things you could do with it, that I can't comment. If you don't need that ability I highly recommend writing your own firmware that simply reads all the raw data from the measurement registers and shift them into the result registers. That's all I can say about it.
Do you know if there is still anyone left from the original developers who knows how this chip works? Or is all Sciosense inherited was a mask set for production?
Yes, all the developers are still there. ;)
BTW nice work with the dual axis fluid sensor! It reminded me of my first ever sensor project ages ago, where I attempted to build an electrolytic inclination sensor for cave surveying. I used a chamber glued together from acrylic glass, with some vodka as fluid. Leaked of course. I would guess for your sensor, main problems were fluid properties (wetting/capillary effect at boundaries), stability and probably topmost fluid staying inside the cavity and not evaporating.
Thanks. Getting everything fluid tight and selecting the right fluid was indeed one of the challenges, beside many others. Making the sensor linear was another one for example.
Just out of curiosity, how much does the PCap sensor costs, or at least its price range for a 1pcs order?
It's not a commercial product just yet, there are still some challenges that we are working on together with partners, so I can't put a price tag on it.
-branadic-
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Finally getting somewhere.
(https://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/?action=dlattach;attach=1945761;image)
Sensor PCB is working fine, I added the display with a very basic UI. It shows two pages, a first one for parallel adjusting the PCB (using the adjustment sensors on the PCB) to its nominal 100 um air gap.
On a second page it shows the inclination in um over the baseline (currently 170 mm, the width of my "calibration" setup, later 1000 mm) with an offset zero and calib factor adjustment knob.
With this I think the core functionality is implemented. The rest will be some UI polish, nonvolatile storage of calibration and maybe offests, finishing the mechanics (3D printed housing for display module) and such.
1 um/m stability will be tough. I'll have to implement like a 5 s window averaging for this to work.
Just out of curiosity, how much does the PCap sensor costs, or at least its price range for a 1pcs order?
In case you meant the sensor chip itself: Search on Mouser for example for pcap04. Current 1pc price is around CHF 5.90.
Thanks. Getting everything fluid tight and selecting the right fluid was indeed one of the challenges, beside many others. Making the sensor linear was another one for example.
Why bother with linearity? As long as it's somewhat monotonous, you can linearize that easily enough. I used a piecewise cubic hermite interpolator for this on a different capacitive sensor, https://ch.mathworks.com/help/matlab/ref/pchip.html (https://ch.mathworks.com/help/matlab/ref/pchip.html) - works very well.
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Why bother with linearity? As long as it's somewhat monotonous, you can linearize that easily enough. I used a piecewise cubic hermite interpolator for this on a different capacitive sensor, https://ch.mathworks.com/help/matlab/ref/pchip.html - works very well.
I would agree for a one-axis sensor, but as it's a circular spirit level things are way more complicated than you think. ;)
-branadic-