suggestions for high-resolution tiltmeter (inclinometer) sensor?

[rhb]

Here are photos of the mount in my Chinese machinist's level

[rhb]

one more

[metrologist]

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?

[rhb]

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.

[JBeale]

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.

[Conrad Hoffman]

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.

[rhb]

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.

[rhb]

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.

[metrologist]

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.

[ez24]

FYI - Received my two vials which are too sensitive for me (I forgot my trig).  Also got two less sensitive vials.  Pretty fast shipping.

[Conrad Hoffman]

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.

[ez24]

.. differential screw ..

Interesting   

[rhb]

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.

[Conrad Hoffman]

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.

[branadic]

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-

[StillTrying]

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.

[metrologist]

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.

[JBeale]

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.

[Conrad Hoffman]

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.

[branadic]

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 that can be used for this purpose. There are also vial with 3"/2mm available.

-branadic-

[metrologist]

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.

[metrologist]

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.

[ez24]

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

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

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

[StillTrying]

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.

[rhb]

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.