| dev (ppm) temp (deg C) min -42.04121928 8.4112 max 32.44987977 44.5383 diff 74.49109905 36.1271 TC = 2.061917482 |
Granted, a hobbyist does not usually have access to a high quality resistor bridge but that method coupled with an appropriate delta temperature range gives a more accurate and repeatable TCR measurement. I have an ESI 242D (yes, they are very expensive too), one of the most accurate resistor bridges made, the only method which is more accurate than a 242D is a Direct Comparison Current bridge and those are real heavy weights in the price category.
If you want to know more about my resistors you can ask here or I can tell you how to contact me more directly.
I am also not shure if it is a good idea to work with (possibly hand picked) samples which are not easily avaliable from stock of common suppliers.
How can I be shure that this would not give a wrong picture? And how can other hobbyists get those resistors?
There is no 'sweet spot' in resistors,
One more thing, the 'lumpy' TCR curve of foil resistors is inherent in the design, you should have seen the original TCR curves 30 or 40 years ago, it would make you seasick.
You didn't seem to have any problem with testing their sub-standard parts so why are you questioning mine?
I also have some reservations about your ADC test setup as well, from your statements, it sounds like you have to use a lot of math on those 'measurements' due to various influences such as noise, I am very leery of measurement results that use statistics to iron out garbage. It calls into question the results accuracy.
I am not trying to throw cold water on these projects, on the contrary I think they are quite commendable and a valuable teacher but I still question a hobbyist's need for such component performance.
If you want to know more about my resistors you can ask here or I can tell you how to contact me more directly.
The foregoing is standard calibration procedure, you may want to check a resistor's characteristics at something higher than minimum power levels.
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The 801 detector is about average in performance, you can substitute a better null detector such as a Fluke 845A...
...
The Fluke 8508A is an excellent DMM, in many instances I have been able to calibrate Flukes to much better accuracy than the specifications...
...
The ESI 240C and RS925A forms the most important parts of a Kelvin bridge and it is there that your accuracy in resistance readings resides. The power supply is not critical but a good analog null detector is, you are 85% of the way to where you need to be with the two Kelvin bridge components you already have, in conjunction with your Fluke for the higher resistance readings, you are very well set for good accurate readings.
For the measurement on my VHP202Z, I have used an aluminium block (16x16x30 mm³), see photos.
The sensor (black leads) is a precision epcos NTC.
The outer aluminium box serves as an additional thermal shield, to further minimize air draught and thermal imbalances.
Those ppm/K measurements are really very delicate.
To summarize, your current setup suffers greatly from too high heat transfer resistivity, and you should simply add an isothermal aluminium block.
For the measurement on my VHP202Z, I have used an aluminium block (16x16x30 mm³), see photos.
The outer aluminium box serves as an additional thermal shield, to further minimize air draught and thermal imbalances.
But I will not handle with cyrogenic liquids.
On the other side the thermal block will increase the effort for measuring different sizes of resistors.
I already asked myself how you did your 0.3 ppm/K measurement.
I hope you will deliver some details soon:
- temperature range
- temperature gradient
It could be possible that the bond of the metal foil to the ceramic substrate has a time constant regarding hysteresis.
So I think the ramp speed could also have a effect on hysteresis amount even if the temperature sensor is mounted correct.
I have seen such a effect on the LT1236AILS8-5 reference. But on the other side it could be also the temperature sensor mounting.
with best regards
Andreas
In the various threads concerning the voltage divider required for the LTZ1000/A (actually two dividers would help....can anybody guess where the other divider goes?)
Would you accept if I donate a metal slab (might be brass or whichever fitting slab I find) with drills (say 2 mm interval) and a tube of thermal grease?
I took a good look at the LTZ1000/A data sheet and curiously, many of their data sheets will specify resistor characteristics, even down to TCRs, this one is not the case.
..
Another question is: why do I see always a non-linear (convex) T.C. curve?
I think I have to check NTC linearity influence. (and possibly correct the curves).
With best regards
Andreas
Which diameter shall I plan in for the hole?
To Andreas (reply #53)
Thank you for pointing me to those resistor specs, I remember the VHP100 series, as I recall they came out in the late 1980s or 1990. I
...
I see Dr. Frank answered your question about the convex curve, he is mostly right in his answer. Vishays precision foil resistors have two types of curves, sine wave and hyperbolic. The C, K, and Z all have hyperbolic curves, if Vishay actually published readable curves instead of purposely obfuscated curves, you would see the hyperbolic curve. These are the sum of all of the various stress sources working on the foil and Vishay has done a very good job getting them down to a very low level. The design of the internal resistor is more complex than the earlier drawing I showed in another reply.
My luck with VHP202z's
The 10K metal foils of Dr. Frank are between -0.3 ... -1 ppm. My first measured 1K is around 0.9 ppm at 25 degrees.
So what is in between? Of cause not all metal foil alloys will have the same TC so the values might vary from batch to batch.
I suppose if I use the marketing method that Vishay and others use, I could validly claim that my typical TCR is 0 +/-1 PPM/°C since the majority of my resistors fall into that spec and I wouldn't be lying.
In such cases, another trick is to thermally "catch"/absorb the wires also.
That means, to solder the ends of the wires to a pad on the alu block, which is electrically isolated, but thermally coupled to the block.
QuoteI suppose if I use the marketing method that Vishay and others use, I could validly claim that my typical TCR is 0 +/-1 PPM/°C since the majority of my resistors fall into that spec and I wouldn't be lying.
But it's one thing to complain about specs given in datasheets by competitor but to not have an own datasheet of resistors that are fabricated by you for long time. That is somewhat strange, won't you agree?
He posted his specifications sheet, dated 2001, which states "60% of units will be 0+/-1 PPM". That's actually more specific than just the word "typical".
What are the thoughts on resistors made by Burster?
We haven't talked about them yet. They say that they can achieve <2ppm/K with selecting materials and Zeranin, but also do some "meticulous artificial aging procedure".
I've been told that in a quantity of 10 a single resistor (1142) is about 23,13€.
Another option could be Powertron.Powertron - A VPG Brand (http://www.vishaypg.com/powertron/high-precision/)
Powertron - A VPG Brand (http://www.vishaypg.com/powertron/high-precision/)
Do you mean a special series?
On your point about TCR curves and manufacturers always 'lies' about them....I must pose an objection here, at least in my case.
I think I could try removing the oxidation
Interesting, obviously this part is out of spec, even if it is one third of UPW50 in price.
You likely received two resistors from the same production batch,
Almost 20 years ago I measured the temperature coefficients of 10 or maybe 20 bulk metal foil resistors. If I remember correctly the resistors were the old yellow/orange Sfernice. I still haven't been able to find the documents, but I keep on searching...
The beauty of that circuit is that the resistor change in PPM is attenuated at least 100 times.For the ~7V portion, yes. But if you're looking for 10V, there's still a problem to solve that isn't answered in the datasheet.
....
By the way, EDN also published an article (that's a laugh) after mine from Vishay on their resistor 'history', if you'd like to read that I can post the link here as well. Be forewarned though, the published article was somewhat modified from the original before it was published. The original was put together by a Wall Street PR firm and was freely handed out among employees and at shows. Frankly it was full of cock and bull hot air and very little fact, it was exceptionally thin on the history of how the Vishay resistors came to be and the long trek of re-engineering them (time and again) to the point that they are at today. I know, I was around for most of it; I can post a copy of the original for comparison if anyone would like to see it. It is good for a laugh or two and is also as effective as ipecac syrup.
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low T.C. but high hysteresis.
there are no problems directly putting the resistors into the oil bath with their connections, that is a standard procedure when using an oil bath, insulating the resistors causes problems.
Even if the thermal resistance from the metal block to the resistor housing is low, it still can be quite high from the housing to the chip. Seems possible that most of the hysteresis comes from the long thermal time constant and not the resistor itself.
Is it possible to wind Evanohm wire on an old-school mica card? Would there be any advantages or disadvantages to this?
You are correct.
Increasing the sweep time from 3 to 24 hours remarkably reduced the hysteresis of the RS92 resistors, but didn't much affect the Vishay. The speed of the temperature change seems to be important. Interesting...
Do you have any photos of the insides of an SR-104 that you are allowed to post? Also-- how many resistors are in an SR-104? Are they in series, or parallel, or series/parallel? I always wondered exactly how they made such a good resistor...
They are slow to make and go through many cycles of processing, it is far more than winding a wire on a mica card (which, by the way, has absolutely nothing to do with matching thermal expansions, Evanohm is far stronger in tensile strength than mica, mica can't 'stretch' Evanohm if it tried) for long term stability and low TCR.
similar hysteresis
I wonder how much these are going for? Perhaps Digi Key lists them.
similar hysteresis
It would be interesting to test the audiophoolery VAR.
http://www.vishaypg.com/docs/63140/var.pdf (http://www.vishaypg.com/docs/63140/var.pdf)
According to some sources it is just a naked Z201 (probably lacquered). That could give some idea how much the mechanical connection from the rigid housing to the chip affects the hysteresis, compared to a "free" chip and wire connections.
real long term stability (sub ppm pa) like the sr104 can only be achieved be a fully hermetic housing.
real long term stability (sub ppm pa) like the sr104 can only be achieved be a fully hermetic housing.Sorry, but I have to disagree. It depends on the technology and contruction, if the hermetic sealing is necessary or not. It helps only if remarkably reduces some of the main drift mechanisms.
For example the 1 ohm standard designed by the Australian National Measurement Laboratory, a sort of "modern Thomas", can be as stable as 0.01 ppm/year. The construction is open, basically just a perforated metal can.
Another example could be the classic 1 ohm Thomas. A common problem with the very early units is that the hermetic seal starts leaking. That increases the pressure coefficient but the long term drift is necessarily not affected.
for critical resistors earlier fluke units used oil filled resistors, as far as I know current fluke units use hermetic metal can resistors. the 34401 network e.g. is ceramic.
the NML is operated in oil and thats the way to keep humidity away, this is in no way comparable with a resin encapsulated resistor
An SR-104 that is more than a few years old will only drift [typically] about -0.07ppm/yr. This is too small of a drift to measure without some very sophisticated gear [probably, a QHR and CCC]. The drift value in the data sheet only applies to the first few years [typically the first year].A *very* old SR-104 that has an intact hermetic enclosure can drift even less than the -0.07ppm/year.
With the talk of what's inside the ESI boxes, I have to wonder what's inside the high end Fluke calibrators? I would assume very few inherently stable standards, with everything else being compared and compensated in software. Is that how it's done, or do they use banks of near-perfect resistors for both resistance and dividers?
If we throw out the data on the SRX which has nothing to do with the SR-104, and throw out John Lion's self-calibrated value, then we are left with an average of +0.07ppm/year drift.
Humidity sensitivity:
On the other side a volt-nut friend of mine has reported a humidity sensitivity between 5-50ppm for 30% RH change of 8E16 resistors which are similar to the UPW50 wire wound resistors. I hope I will get further information on this topic from him when he is back from his trip.
As for foil resistors, the early designs [and even the newer Z-foil resistors] use high-temperature epoxy to glue the foil to the ceramic substrate.
The new Z1-foil resistors use polyimide to glue the foil to the substrate and to seal the resistor on the top after they are done adjusting it.
...
The solution for foil resistors is to get them in hermetic packages if this kind of shift is important to your design-- or, just buy less expensive PWW resistors from Edwin that minimize this problem.
I have a love-hate relationship with foil resistors. Currently, I am hating them. Tomorrow is another day...
If I am reading your graphs correctly, I believe you are seeing a case of internal condensation effect for the first cold cycle, the condensation being evaporated during the subsequent heating cycle (for the 29th).
Let's see if I have the sequence correct, on the 27th, the resistor had been 'cooked' over night so any humidity inside was minimal for the first test. Rate of temperature change 0.12°C/minute.
On the 29th, resistor had been sitting at room temperature for two days in moderate humidity before testing, resistor showed odd reading. Rate of temperature change 0.3°C/minute.
On the 1st, the same resistor had been sitting at room temperature and similar humidity, the only 'difference' was the rate of temperature change, 0.12°C/minute. Readings appeared about normal.
I have a question or two for you. How many cycles of cold and hot do you do before the resistor rests? Any particular reason why you chose a different rate of temperature change for the second test?
still very interesting results but somewhat confusing. Can you give a brief summary what resistor is best in your measurements?
I think it's still a Work In Progress [WIP], but I too am interested in the "Reader's Digest" version of which [so far] are the best resistors. But then, we have to define what "best" means, but to me, it is excellent TCR and super-stable resistance over time-- but that is because I will not be running the resistors under high power or pulsed power conditions [at least in what I am doing now].
As with many things in the world of engineering, the definition of "best" depends on how you are using the resistor.
I would be interested in what Andreas found with Edwin Pettis' resistors, which appear to be the best of the Evanohm-wire based PWW resistors available.
Andreas, DiligentMinds, branadic
"...it is no way of judging, which resistor technology or brand is better, or best in class..."
<snip>
Therefore, up to now I would not draw such a conclusion, as DiligentMinds did.
<snip>
Hi Dr. Frank,
Sorry, when I posted that I guess I kind of implied that I was basing my conclusions on the work done here in this thread by Andreas. I apologize for that. That isn't what I meant to say.
My conclusions were [and still are] based not only on Andreas' work, but long years of experience and hundreds of hours scouring the available literature for relevant material.
In a private email from Edwin Pettis to me, Edwin complained that many engineers over-spec the resistors they are using in their circuits. I think he is correct. You do not need a super stable hermetically sealed, oil-filled, 0.001% resistor for an LED ballast resistor. Part of the art of electronics is knowing when to specify better parts, and in order to do that you have to know *why* you need a better part. Then, you can use your engineering skills to ask the question: "how good do I need this part to be?" You also need to know what parts are available, and what the environmental effects on each resistor type are. In some applications, you also need to know what the long term drift might be for each resistor type. Without this information, you might get lost in all of the data, and end up specifying the wrong part. In some applications, you would want to know how to accelerate the aging of the resistors and other components in your design so that your design is very stable coming off of the factory floor. There are different techniques for doing this, and not all of them apply to all resistor types [and/or other components].
I too think that the work Andreas is doing is important, and interesting. Andreas, please keep going!
The z series are supposed to be mounted touching the pcb, so if we assume single sided with the copper opposite the component, it will be used about 1 mm from the body.
Hello Frank,
The basic problem with all of measurements is, that you never get some repeatable curves or parts of curves in ALL of your measurements.
Even if you measure slowly, the wires may always be on a different temperature, than the thermal mass and the thermometer.
I don't dig it from your measurements, but all these curves look quite strange, if I recall temperature measurements, and also hysteresis measurements I have done.
Maybe the S102K has a very huge hysteresis, but the 201Z definitely has to have much lower hysteresis (and only for bigger temperature excursions as +/-15°C only)
I propose that I repeat your measurements with my Veltins thermal chambers ;) and see what happens.
Do you remember, what happened to your resistors?
Maybe, that you already have a prepared aluminium box with jacks for the resistor and the sensor?
Otherwise I have to build one.
PS: I may probably measure these two comrades during that session, the left one is also a Z201.
Has yours the same case?
I will prepare a box then.. careful soldering at the end of the wires, with a copper pincer is allowed, I hope?
I also would like to get more insight in your heater/cooler assembly.. One sentence drew my attention.. you mentioned, that you run the fan.. all the time?
Does that imply, that either the thermal heat or sink is always on, also the fan?
Then there might lay the reason..
As I indicated, it's better to leave the system alone w/o forced heating or cooling, and especially no air draught.
My suggestion:
Put some thin foam, say 1 to 5 mm, around every available spot on the isothermal block and try again.
For voltage measurements, that's of course not available, You would have to reverse the DUT manually
Not totally clear, what You Want to measure in this instance.
As you noticed : As you increase the thermal mass, you have lower the slope of temperature accordingly, or phase lag will appear. So : The smaller test system, the better.
Any ideas? Are resistors with welded connections in reality some hidden diodes?
Just dipping into epoxy will not really help. (May only change the time constant).
One way to check your system is to choose different temperature points on the now rounded curves. Approach the point from above or below, however once at the point, stay there for an hour or more.
Epoxy; is that a physical limit, i.e. diffusivity of oxygen & vapor through epoxy well defined? There are tons of different epoxies available. I imagine the epoxies used in electronics are subject to dozens of requirements, diffusivity only one of them.
I thougth more on a tin can case and using ceramic feed through cap's
which could be useable to get the signals in / out of the box.
These cap's are also available with copper / tin legs.
I thought of having a thin metal membrane showing inner pressure. As long as there is over-pressure the metal membrane would bulge out and you'd be safe from in-leakage and . A product someone?
Hi Andreas,
That's very strange..
Is this resistor identical to the Z201, you've sent me, 1k also?
Then I'll do the reversal test on my 3458A also.
Although i can't understand that behaviour.
Frank
Hi Andreas,
That's very strange..
Is this resistor identical to the Z201, you've sent me, 1k also?
Then I'll do the reversal test on my 3458A also.
Although i can't understand that behaviour.
Frank
Do you have x-ray inspection at work or can you take it to a dentist to x-ray it? This might give some (pun intended) insight if it is not available in the datasheet.
Long thread to read. Very nice though :-+
Would it be possible to get all the results in some kind of sheet or selection guide?
It would make it easy to choose a right resistor for the right job :)
Or, make a comparison against a poor mans 0.1% resistor like the RT0805BRD071KL from Yageo?
What do you get extra when paying $10 for a resitor, instead of $0,10?
T.C. as low as < 1ppm/K (thin film 25ppm/K)
T.C. as low as < 1ppm/K (thin film 25ppm/K)
I think Yageo specifies 20ppm/K
Thanks for the comparison. Do you have any idea about the spread of spec. between DUT's?
(Specialy when they sit next to each other on the tape.)
When the resistors are thermo coupled, and used as resistors in a circuit, absolute drift and accuracy is not as important as the spread between devices.
This one, obviously:
http://www.vishaypg.com/foil-resistors/case-studies/study/wekomm_1/ (http://www.vishaypg.com/foil-resistors/case-studies/study/wekomm_1/)
Maybe the internal layout is similar to the Fluke 742A. Attached is a picture of the internals of my 742A-10K.
FYI I'm getting a pretty awesome 10K metrology grade transfer standard soon from Wekomm
2ppm tolerance
Long term stability better then 1ppm / year
Temperature stability better than 0.3 ppm / °C
And they are conservative specs, and they are working on producing 0.001ppm tolerance parts.
For the tolerance, you really meant 0.001% [10ppm], not "0.001ppm", right?
I don't think there is any way to even *measure* 0.001ppm-- well, maybe with a QHR and cryogenic comparator, but I think the leads connecting to the QHR inside the liquid helium Dewar will prevent you from getting to 0.001ppm [because the leads are not superconductors].
So, a "typo" right?
Can you show us a picture of what is "face up" and what is "face down" and which side is closest to your temperature measuring device in each case?
Is this resistor identical to the Z201, you've sent me, 1k also?
Then I'll do the reversal test on my 3458A also.
There exist many Pictures of the ceramic /metal foil chip, with attached leads.. That always looks symmetrical, so no reason for asymmetric thermal behavior.They are symmetrical if you mount them in upright position.
Or, make a comparison against a poor mans 0.1% resistor like the RT0805BRD071KL from Yageo?
What do you get extra when paying $10 for a resitor, instead of $0,10?
Did you consider any SMTs?
Susumu RG and URG are avaliable to 2ppm/C, with URG series being supposedly a higher quality, better aging. Both have some kind of secret inorganic coating. Datasheet: "Unmatched Reliability and Excellent Stability at different environmental conditions".
Thermal cycling is sometimes recommended for removing mechanical stress on sensitive components. Do you have any thought on that based on the measurements?Heating removes humidity from PCB. So the following thermal cycle will get lower hysteresis.
Thermal cycling is sometimes recommended for removing mechanical stress on sensitive components. Do you have any thought on that based on the measurements?Heating removes humidity from PCB. So the following thermal cycle will get lower hysteresis.
Thats an old trick to let voltage references with plastic package look better in the datasheet.
But it will not help you in real life applications. (except when you heat up the whole device).
With best regards
Andreas
Sorry I wasn't clear: what I meant, implications of cycling a whole completed assembled PCB to relief mechanical stress on components?I fear my English is not good enough to understand what you mean.
Sorry I wasn't clear: what I meant, implications of cycling a whole completed assembled PCB to relief mechanical stress on components?I fear my English is not good enough to understand what you mean.
But also a pcb stores humidity and gets dry by thermal cycling for the next measurement cycle.
With best regards
Andreas
About thermal hysteresis and relief by controlled thermal cycling, you might enjoy this : :)
http://www.google.com/patents/US5369245 (http://www.google.com/patents/US5369245)
[...]so everything inside will be on the same temperature +/- a few hundredths of a Kelvin, if the measurement is done slowly enough.
With your measurement septup, it's not likely to happen.
Again : The main thermal conduction path is the leads of the resistor, not the case. You should make a proper thermal contact on the leads, not on the case. Your ugly purple/grey/black/white thick wires are going sink a lot of heat from your resistor, and cause a temperature difference between the resistor element and your measured temperature (on the block) in an order of magnitude which exceed "several milidegrees".
Making a precision thermal system is similar to precision analog electronics. Since you supply the heat from a finite "impedance" source (The conductivity of aluminium between your heater and the resistor), for high precision applications you have to minimize leakage from the resistor to the outside. Make your purple/grey/black/white wire as thin as possible!
Nice thermal contacts via the leads + Small leaks via thin wires and polystyren-like insulation everywhere + A low mass = A fast and precise thermal system.
these ugly cables are really thin, indeed. So they won't transport that much heat.
Sure they will transport some ugly heat! :D
Let's say they're #24 AWG (~0.5mm diameter of pure copper) even if they appear thicker than that. When your chamber is at 50°C, the ambient at 25°C, and there is 30cm of such wire connecting the DUT to something at ambient temp, let's make some simple calculations of what happens :
Thermal conductivity of copper=385W/(mK). Thermal resistance of your two pair of wires : 4 wires * 385 * Pi*0.00025² / 0.3 = 0.001 W/°C <=> 1000°C/W
Thermal resistance of the block-resistor_under_test interface : 2W/°C <=> 0.5°C/W (Very favorable. It's the typical interface resistance of a well mounted power transistor with silicone pad or grease. Or the minimum available junction to case thermal resistance of a TO220 package)
Thermal flux through the resistor interface and the wires = Delta Temp / Rth = 25°C / (1000 + 0.5) = ~25mW
These 25mW cause through the interface a temperature loss of : Tloss = 25mW * 0.5°C/W = 12.5mK
And it's a very very favorable case.
Don't forget that when you add aluminium mass to improve temperature distribution, you decrease the thermal resistance between two points, but you also add thermal capacity. At some point, the "induced" thermal capacity increases beyong what's acceptable, regarding to the benefits of a lower thermal resistance.
From a dimensional analysis point of view, the thermal resistance is a matter of contact/tranverse area, and the thermal capacity a matter of volume. The volume increases with the cube of a dimension of your system, and the tranverse area only with the square. If the figure of merit of your system is Resistance/Capacity, it varies with x^2/x^3 = 1/x ("x" being a dimensions of your system) : Small systems are naturally favored.
At this point, I have to apologize Andreas, for casting doubts on his measurements!
His measurements setup, using a much lesser costly equipment, gave qualitatively same or very similar results, and they were nearly on the same order of noise figures.
Well done, Andreas!
The lead material of the S10XX series is solder coated copper while the Vishay hermetrics are Kovar. I did not look up the lead materials of the other resistors.
The EMF of Kovar - Copper is 40uV/C while solder - copper is somewhere near 1uV/C
The 1uV/C doesn't make me worried but 40uV/C does. Any thoughts on that? Something seen on measurements?
The lead material of the S10XX series is solder coated copper while the Vishay hermetrics are Kovar.
The lead material of the S10XX series is solder coated copper while the Vishay hermetrics are Kovar.
When I have a look at all my VPG Z-Foil resistors, they are all tinned.
I wonder where and why VPG should use Kovar.
Can you share where you saw the Kovar information?
The kovar input leads of the TO-5 package...
Hi Dave,
This one, obviously:
http://www.vishaypg.com/foil-resistors/case-studies/study/wekomm_1/ (http://www.vishaypg.com/foil-resistors/case-studies/study/wekomm_1/)
But not good for the described big temperature range, as the Vishay foil resistors show hysteresis.
custom specific made part, together with a special packaging.
And 0.001ppm stability or uncertainty?
Nope, never... This German engineering GmbH would need a Klitzing Hall standard.
Even the best secondary standard, the ESI SR 104 (which practically has no hysteresis) does not approach that level..
For the tolerance, you really meant 0.001% [10ppm], not "0.001ppm", right?
I don't think there is any way to even *measure* 0.001ppm-- well, maybe with a QHR and cryogenic comparator, but I think the leads connecting to the QHR inside the liquid helium Dewar will prevent you from getting to 0.001ppm [because the leads are not superconductors].
So, a "typo" right?
Lead Material #22 AWG (0.025 Dia) Solder Coated Copper
I looked up a few Vishay metal can hermetics like VHP100 series and the DON't use Kovar! Relieved!QuoteLead Material #22 AWG (0.025 Dia) Solder Coated Copper
Anyways: the results for the Z201 Resistors are ALARMING and i think at this point it we should contact Vishay about this.
I am now thinking about ordering those Audiofoolery naked Zfoils for my Project, since the whole circuit will be hermetically sealed and under transformer-oil anyways.
(Much cheaper then the hermetic zfoils)
Andres, not sure I have seen: the S102 are available in C, K and J where the K alloy should be slightly more temperature stable than C, while J is far behind. You measured the J and it was walking around a lot. But then there are measurements of S102x, x not specified. I think the early S102 later became S102C?
So, have you measured C and K alloys, can you see any difference?
I do not find this alarming. This is only a feature of the resistor which is not specced within the datasheet like humidity sensitivity. (datasheet = advertisement). And you still have the possibility to use hermetically sealed resistors.
Usually you should read between the lines: which parameters that are of concern for your application are _not_ covered within the "datasheet".
If the observer wants to measure the effect of a change in temperature between two points, how fast or slow the external temperature changes is irrelevant, only that the resistor is given enough time to stabilize at the second temperature internally is important. The same thing applies when returning the resistor to the initial conditions. Additionally, the greater the stimulus change, the greater the hysteresis, this is not to say that the hysteresis will be a large value but hysteresis tends to be larger with larger stimulus change.
Dr. Frank, as I recall, the econistors specify 0±3PPM/°C TCR 0°C to +85°C, your batch is out of specification, the 0±5PPM/°C TCR applies above +85°C or below 0°C. Given that they claim a lengthy thermal conditioning cycle (7 days), something or someone got sloppy on production.
after several months now I have found one "typical" (= golden) Z201#6 resistor. (Date code B1305-)
So, how many of these expensive foil resistors do I have to buy to find one that has "typical" performance of 0.05ppm/K ?
Look what just turned up:
My 34470A is currently saying it is 10.000200
Look what just turned up:
..
My 34470A is currently saying it is 10.000200
Hello,
more interesting would be if there are any accuracy specs for the values in the datasheet.
(including ageing)
The absolute value seems to be that what they have read from the 3458A multimeter.
...
With best regards
Andreas
The 3458A delivers 7 decimal places only.
The 3458A delivers 7 decimal places only.
Even if I use the HPIB connection?
The 28 Bit converter should give a total of 8 digits.
With best regards
Andreas
Measurements International has the following brochure...
http://www.mintl.com/media/pdfs/accubridge.pdf (http://www.mintl.com/media/pdfs/accubridge.pdf)
Does this mean all the extra digits (10's of ppb) are meaningless or do they have a useful application?
I have not seen any videos of these in operation so I am guessing they are not as easy to operate as their sales people advertise.
just curious, how much (ballpark) does it costs?
Therefore, if they write 8 digits on their box, they either must have used something else, an ESI SR104, or maybe measured at PTB (what I doubt w/o a thermometer inside), or they are not very serious.
I can assure you they are very serious.
The unit was calibrated at Germany's national standards lab, and from a brief look at the cal documents, tested for drift at 0.5degC intervals over a large range.
They are working very closely with Vishay to get their very best technology and the resistors are custom designed for them. They are not just buying a stock series resistor sticking it in a box and whacking it on a 3458A.
It took many weeks to characterise and calibrate this resistor for me.
And you really paid that price? Are you really goin' volt-nuts?? :-+
I'd like to see that calibration document, please!!
And a picture of that blue cal sticker on the top, that might be the PTB - blue.
These are not standard Vishay parts, they are:Quotecustom specific made part, together with a special packaging.
Wekomm engineering paired the VHA518-7 resistor with carefully selected components to form a transfer standard product.VHA518-7 (= 7 resistors in series)
they do not say just how many of these 'units' were tested, it appears to be just one each and neither one was a 10K unit.
While I have no qualms about the Dutch VSL, I have always found Vishay's proclamations to leave something to be desired.
Look what just turned up:
(https://pbs.twimg.com/media/CARbfQjVIAAjFFo.jpg:large)
(https://pbs.twimg.com/media/CARcBKZVEAAER3v.jpg:large)
My 34470A is currently saying it is 10.000200
Yes, typically Vishay posts incomplete or 'fuzzy' specifications, 'fuzzy' test results or tests that don't even accomplish what they are supposed to do. Vishay has done this for decades and the practice still continues. I know, I've been here for nearly all of it.they do not say just how many of these 'units' were tested, it appears to be just one each and neither one was a 10K unit.
"Vishay typical" ?
While I have no qualms about the Dutch VSL, I have always found Vishay's proclamations to leave something to be desired.The document I linked is Vishay marketing material. Most likely VSL will publish / has published scientific article of their experiments.
For those of us in the know, some of those purported Vishay scientific papers are just plain laughable and inept.
It is solely up to you whether or not you want to believe me or not
When I get a little time, I'll be happy to post some, and yes, my 40+ years does qualify me as an expert whether you accept it or not, I do accept your opinion, you are welcome to it but on the flip side, what qualifies you to say that I am not what I say I am or my opinions are valid or not?
These are not standard Vishay parts, they are:Quotecustom specific made part, together with a special packaging.
http://www.vishaypg.com/foil-resistors/case-studies/study/wekomm_1/ (http://www.vishaypg.com/foil-resistors/case-studies/study/wekomm_1/)QuoteWekomm engineering paired the VHA518-7 resistor with carefully selected components to form a transfer standard product.VHA518-7 (= 7 resistors in series)
VHA518 long term drift measurements against the Quantum Hall by the Dutch Metrology Institute:
http://www.vishaypg.com/docs/63620/63620.pdf (http://www.vishaypg.com/docs/63620/63620.pdf)
VHA518-11 (= 11 resistors in series)
this 1 could be a tough question. why did they choose 23oC as the zero deviation centre temp?
That is a good question. I have some American equiptments datasheets dating from the 60's that specifies the cal temp of 23degrees C, while my Solartron is specced at 20deg.
Well, the GenRad 1444-A was the precursor to the ESI/Tegam/IET-Labs SR-104 10K resistor.
The GR1444A was introduced in 1970($600.00), and was not listed in the 1978 catalog. It appears to be an analog to the ESI SR104 resistor. The earliest mention of the SR104 is in a 1971 ESI242D manual(I didn't try very hard).
Have people published detailed research papers in rebuttal?
I have not researched any of this of course, but putting my skeptical hat on, I find it hard to believe that one of the leaders in the field of precision resistors for many decades produces "laughable and inept" scientific papers.
Mistakes? I'm sure that happens, but "laughable and inept"?
Proof please.
And BTW, proof is not "go read the professional forums" and "Unlike you folks, I've been in the resistor industry for over 4 decades, I have the experience and knowledge which no one else in this forum has an apparent claim to."
/skeptical hat off
After my complaint about this bad performance of the parts, the Vishay representative had to admit that one can not rely on the typical data and on the intended technology characteristics so far, as advertised...and that there is no guarantee from Vishay about these typical characteristics...
So the new standard from Weekom should be observed very critical also..
If they are "typical" characteristics, then, well, there is no guarantee! Either a spec is typical or it is guaranteed.
If it's typical and doesn't meet spec, bad day for you.
If it's guaranteed and doesn't meet spec, bad day for Vishay!
FWIW I've been assured that the resistor in the Wekomm standard is a custom part and hand selected. So in theory, no matter how bad Vishay's standard production spread is, it's possible to pick the good ones.
Dr Frank, it may also be that the "good ones" are cherry picked for important customers while us mortals end up without those golden ones ???
Besides the fact that the Wekomm part in my opinion is way overpriced (even when considering its calibration), one should put things in perspective. The SR104 is a true primary standard (historically at least, today it is rather Quantum Hall of course). A resistor standard based on VPG hermetic foil resistors is both pretty stable (I can confirm Dr Franks stability data based on cal data) and has a low TC (0.2ppm/K is not bad, I have seen SR104s with similar and higher TCs). Compare this to the not really cheap Fluke standard resitors, and you will see that this is a very good alternative to the SR104s and Flukes out there, given its price. Nobody considering to buy a SR104 would seriously consider the Wekomm anyways, it is adressing another market in my opinion, more a competiton to Fluke.
I think the Wekomm resistor is meant as a "secondary transfer standard", to compete with the likes of the Fluke 742A series [which they are discontinuing].
Question : Manganin alloy naturally offers "parabola" shaped resistance/temperature curve, with a perfect zero slope near 25°C. Produced since May, 1893 (Wikipedia said). Some of you pointed out that at this time it's impossible to find a resistor with such characteristics, even from the best manufacturers like Vishay. Since the material is available for more than a century, I don't understand why this performance isn't achievable today. Is it about manganin manufacturing related issues (Soldering)? Did I miss something?
Snip*If you want to double your accuracy, you have to more than double your price
I have supplied resistor networks to customers with the recommendation that they wrap a piece of copper tape snugly around the resistors
I believe the concept, known universally as "passive heat-pipe technology"
you came here with a superiority complex....and then made wild, bogus claims about things like "heatpipe" technology....which your device clearly does NOT employ.
We can start with claims about your miraculous "heatpipe" technology.....how about claims of somehow bending the laws of physics, to improve Ti's technology? Face it, the ref you are selling simply proves the quality of Ti's REF102C package...DESPITE your best efforts to corrupt it's implementation.....
It is about 4000 times more efficient at moving heat than a similar sized copper bar might be-- and is much lighter as well.
The effective thermal conductivity varies with heat pipe length, and can approach 100 kW/(m?K) for long heat pipes, in comparison with approximately 0.4 kW/(m?K) for copper.
After a long journey I picked up some resistors from local customs office today.
5 days from Grand Junction to San Francisco
2 days from San Francisco to East Coast
2 days to Germany
and finally after nearly one week intensive customs treatment I could pick them up.
Hello 3roomlab,
pricing for the 0.1% 3 ppm/K standard tolerance which I ordered is on the LTZ1000 thread:
https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg602719/#msg602719 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg602719/#msg602719)
So its comparable to that what you will pay for UPW50 or 8G16 resistors from RS / Farnell in small quantities.
But with the service that you can get every individual resistor value.
Shipment was around +11% for the 33 resistors with USPS.
And import tax (=VAT) adds +19% on the total in germany.
With best regards
Andreas
Andreas, do you normalize all measurements to 25C? I should use the same as you 8)
first results from Ultrohm Plus resistor (UP805) 1K #1 0.1% +/- 3ppm/KSo your has about -1.1ppm/C while mine has something like +0.7ppm/C at this temperature range :-DMM
shipment date 1510 (not printed on device).
@Andreas:
You should probably move the sense wire closer to the body of the resistor-- Edwin's spec is 3/8-inch I think [but check the data sheet]. Copper has about 4000ppm/K TCR, and because this is a lower value resistor [1K?], this might affect your data a little bit [and certainly in the sub-ppm range].
I'm not believing the hysteresis, I think that there is a time lag between what temperature the resistor is at and the reading from the temperature sensor. I could be wrong, but if you sweep the temperature slower and pulse the drive current on the resistor [and sensor if it takes current] only while taking a reading, then I think they will track better.
That said, I think Edwin's resistors are showing very well so far... Time for me to order some...
The cal sheet for my Wekomm standard
http://www.eevblog.com/files/WekommResistanceStandardCalSheet.pdf (http://www.eevblog.com/files/WekommResistanceStandardCalSheet.pdf)
The leads are oxygen free copper, tinned.
The epoxy uses a hardener, the manufacturer recommends room temperature curing but also specifies a 60°C bake if time is short. The epoxy sealant on the end uses an epoxy based color ink which does recommend a short bake @ 121°C for two hours or 150°C for 15 minutes, this colored epoxy is the same stuff used for printing on the resistors. I'm curious, why do you ask?
I have seen the comments on hysteresis or not. I do not believe they are time lags. For example the Z #7, the difference in temperature domain is at maximum around five degrees between up / down. It is imo very unlikely that you have such a big temperature difference with the type of setup and slow ramp that you have. Could you simply stop the cycle at mid point, both up and down, let it stabilize for an hour to see if the effect is still there or not?
The cal sheet for my Wekomm standard
http://www.eevblog.com/files/WekommResistanceStandardCalSheet.pdf (http://www.eevblog.com/files/WekommResistanceStandardCalSheet.pdf)
Kalibriercentrum Bayern. Not a primary lab, but very high capability. Volt/ohm nut friendly???
Well, my experience, pretty expensive, and thus not volt/ohmnut friendly in my view. I did a search some time ago in Germany for calibration of 10k and 10V standards. Got many quotes and found that ESZ is pretty cost efficient for both (ISO certificates), and when asking for an ISO certificate they can certify accuracy limits below 0.5ppm for both, so I use them for my standards. And: I can drive by and drop off my standards and pick them up, thats good too (and from time to time have a little chat with the lab guys). For thermal converters I use Testo, because they have an automated procedure, so very good accuracy and at the same time cost efficient because few labor hours involved. RF power I do at Rohde/Schwarz, acceptable prices and they can adjust the EEPROM in their power heads.
These are all the calibrations I need.
If there were any relatively 'easy' tweaks that could be done to improve the performance, don't you think Linear Tech or Fluke would have already discovered them after all this time?
If there were any relatively 'easy' tweaks that could be done to improve the performance, don't you think Linear Tech or Fluke would have already discovered them after all this time?
Hello Edwin,
perhaps they have already discovered some tweaks. But they have to earn money with their products. Some tweaks may be so time consuming that they will not get paid for that.
For me its a challenge to find out how the components work in ppm ranges. And to see how far can I go with self made equipment to create stable references.
With best regards
Andreas
If there were any relatively 'easy' tweaks that could be done to improve the performance, don't you think Linear Tech or Fluke would have already discovered them after all this time?
Hello Edwin,
perhaps they have already discovered some tweaks. But they have to earn money with their products. Some tweaks may be so time consuming that they will not get paid for that.
For me its a challenge to find out how the components work in ppm ranges. And to see how far can I go with self made equipment to create stable references.
With best regards
Andreas
Could the Z201 resistor be humidity sensitive so that the pre-aging process have dried the resistor? In that case the cold cycle will fasten the recovery I guess. I have never tested Z201 resistors but my S102 resistors have seasonal variations that I guess comes from humidity changes.
The hysteresis itself is very low at this sample.
But in the cold phase the previous curve is never met on the 2nd time.
So there is a large ageing drift of 3.6 ppm within 3 days
So probably the pre-ageing procedure (load life) had introduced
a larger hysteresis which will need several temperature cycles to wear out?
I just want to say THANKS! for sharing al your hard work.
Thanks for this work Andreas.
This might be a moot point since I think you said you are only going after "relative" measurements, but even so:
I have never, ever witnessed the UltraOhm (or Vishay hermetics) changing at ~2ppm over a few days, and we've never seen any humidity issue with his product. This maybe in a previous post (forgive me) but what is your measurement technique, and how are you confident that you can actually measure down below into the 1~2ppm area - and how are you characterizing your equipment noise floor before every test? I notice you have an astonishing number of digits in your measurement math values also. Normally we will only work the math out to only the real physical significant digits of measure. I am not questioning your final results, I was just wondering how you characterize the true noise floor of your technique. For instance: When you calculated the value drift of 2 or 3 ppm over a couple days when measuring values, do you think you could have been observing your own equipment drift? And how do you prove or disprove that? Do you cross-check with a "real" resistance standard other than a single Vishay to measure against?
as it only as good as the supplied voltage reference driving it.Since I am comparing ratios only instead of voltages the voltage reference cancels out.
What I see in the photo: 1. Soldered connections - if you are not very, very careful to keep those soldered joints at exactly the same temperature, you will measure thermal drifts, not resistance drifts.
When we are doing precision resistance tests of a component, normally the pressure contact points in the test jig are measured and apply a known, very repeatable clamping force on the test leads in an isothermal fashion and typically in a dry nitrogen atmosphere (or at measured humidity) during the test run.Do you have a photo of the setup? Would be interesting. Perhaps I can adapt some ideas for my measurements.
Typically all of these together might push you out of well out of the capability of measure into the sub 2 or 5ppm area, even for relative measurements.For absolute measurements you are right: I simply cannot prove it in lack of a suitable standard resistor.
I found some rather interesting information from the NIST about the ohm, concerning the quantum ohm standard, it can only be read with an uncertainty of 0.2PPM at best, no matter what national lab in the world it is, all agree on this uncertainty. Furthermore, this uncertainty is not included in calibration certificates as it is understood by all labs that it is there, all uncertainties provided on the certificate of calibration are in addition to this 0.2PPM.
The quantum ohm can be realised with uncertainty of parts per billion, but it is not the same as the SI ohm. The ~0.2ppm is between the quantum ohm and the SI ohm.
Bottom line: Bridges are really your best friend here for any serious discussion of resistor TC.
On a slightly different subject, I calibrated one of my 3458As recently, and it starts up with an error message: 'calibration: secure required'. obviously i had to unsecure the meter by entering the pass code wehn doing the cal. but how do i set secure again. the manual is not very helpfull, and somehow i do not manage to get that resolved. Not the frirst 3458A I calibrate, but somehow I fixed that last times (year ago or so), and do not recall how. must have just pressed some buttons intuitively, does not work this time, issue drives me nuts.
Also the curves with reversed polarity are visibly different. So I think some more tests and improvements of the measurement setup are needed. The noise also looks quite large to me - I would expect less noise in a well shielded setup.
So I might be helpful to read the humidity data as well.
From the pictures at the beginning of the thread, the rather long unshielded and dangling wires don't look very good. They may cause EMI problems, by operating as an antenna. Also they make the effect of reversing the polarity questionable, as moving the cables may also change thermal gradients. As a thermal cycle is rather slow, it might be better to do the polarity reversal more often within a cycle (e.g. every 30 seconds - to really separate possible thermal EMF problems.
FYI I'm getting a pretty awesome 10K metrology grade transfer standard soon from Wekomm
2ppm tolerance
Long term stability better then 1ppm / year
Temperature stability better than 0.3 ppm / °C
And they are conservative specs, and they are working on producing 0.001ppm tolerance parts.
"Teardown anytime soon", you are aware that opening the standard will not only invalidate the warranty but it will also invalidate the calibration certificate as well, not to mention any accidental damage possibly caused while opening it.
But there are always risks. In this case the manufacturer probably underestimated the possibility that someone points out that their product is basically a $50 component in a box with a $4000 price tag.
At 10K, my 242D system is accurate to 0.2 PPM as calibrated against an SR104, I also have the same 0.2 PPM uncertainty as everybody else.
...
As to the claim of 0.001 PPM, pure nonsense, they can't measure to that accuracy, no national primary lab in the world can measure to that accuracy, the uncertainty will likely be reduced to 0.1PPM in the proposed 2018 standards but that is still a factor of 100 over 0.001 PPM. Any one who makes such a silly claim is suspect and is not worthy of consideration. Any serious metrologist would laugh at such a claim.
From what I've seen and read on this blog site, I very likely have the most accurate resistance measurement system of anybody here. DVMs are NOT considered standards under any definition, just check with your National Primary Calibration Laboratory and they will tell you the same thing. Even the 3458A is not considered a standard under any measurement conditions, they are not used as standards by any metrology lab I know of.
At 10K, my 242D system is accurate to 0.2 PPM as calibrated against an SR104, I also have the same 0.2 PPM uncertainty as everybody else. That gives me a 5:1 accuracy ratio when comparing a resistor (standard or otherwise) over the range of 120R0 to 1Meg, accuracy begins to drop off above and below that range. Therefore I am barely accurate enough to test the Wekomm standard under the required specifications. While I have a resolution of up to 0.0001PPM, it has no bearing on the accuracy. A National Lab must be able to to maintain a 10:1 accuracy ratio. Under these requirements I do not see anyone on this blog (unless unknown to me) that has the required measurement system to verify the Wikomm 10K standard or even make an accurate measurement of it.
Even with an older 242D and 'used' standards, you are still looking at a good $20,000 USD plus traceable calibration requirements.
Manual study time (even though its 100% out of my budget)
Curious, I did not underline all of that!
In the modify window, the wayward underlining is not showing up at all. Just a minor annoyance, sorry folks.
[u]accurate[u] [u]
...
...
...
[/u]
@Edwin G. Pettis
So you are telling us, that this document
http://www.kalibriercentrum.de/pdf/DAkkS_Urkunde_Bayern.pdf (http://www.kalibriercentrum.de/pdf/DAkkS_Urkunde_Bayern.pdf)
is basically rubbish ?
Wow.
My German isn't as good as it used to be, but which items on the calibration facility list disagree with E G Pettis' posting?
The capability of the lab relies on their (decades old) GenRad 1444A-10kOhm standard, which is the predecessor of the IET / ESI SR-104. This is an ultra stable artefact, much more stable than the usual SR-104, and which has been calibrated many times directly at the PTB, so its stability of about 0.01ppm/yr. has been characterized since a long time.
There is obviously a demand by the NMIs, especially our PTB, for more stable working-standard resistors, than these Thomas type 1 Ohm and the SR-104, which are mostly too unstable to reach the 1e-9.. 1e-10 comparison region of the QHE and CCC bridge.
The Wekomm resistor, when a precise thermometer and T.C. characterisation will be implemented in the future, is a candidate to improve these standard resistors by orders of magnitude regarding stability.
A typical SR104 drift rate is approximately +0.07 ppm per year. Magnitudes better would really be something!
In a document I posted earlier the VSL measured their Vishay VHA518-11 resistors against the Quantum Hall. The Wekomm uses the VHA518-7 which is the same type except there are only 7 bulk metal foil chips instead of 11 inside the hermetic can.
The two resistors measured by the VSL showed drift rates of 0.4 and 1.9 ppm/year. And most importantly the drift rate it is not (yet) predictable.
Even if Vishay had some magic to improve the stability that much, why would they share that secret only with a small German toy train manufacturer?
why would they share that secret only with a small German toy train manufacturer
To eliminate the thermocouple voltages I make a AC excitation of the resistor divider.
Many metrology grade platinum thermometers use the same technique.
Do you use a simple voltage divider or a wheatstone bridge?
what about using something like picostrain instead of an ADC? They are used for weightscales measurements and have high resolution, ENOB up to 18.9bit. I was thinking of PS081. Maybe you want to check this way to measrure your resistors?
4 channels? Don't you use a LTC2400? (Several ones maybe?)
Hello Branadic,
perhaps it would be worth a try.
But I do not see how I can do a 4 wire measurement with such a device.
In my case the wiring resistance (and T.C. of wiring) cannot be neglected.
Do you have soldered break out boards for these devices?
(my hand soldering will not create reliable connections for the QFN package)
With best regards
Andreas
Aaaaaaah... Ok! Now I understand why you said your measurements take long. I'm convinced this is a great idea to measure on the 4 channels to compensate for various wires losses and drifts, but you miss the possibility of true ratiometric operation (With excitation/output voltage being measured synchronously and not sequentially) that can be brought by a single differential input + reference ADC.
Hi Andreas,
there is no possibility for 4 wire measurement, because the measurement principle is that one after another resistor is used to form a RC circuit with the same capacitor and discharge time is measured with a Time-to-Digital Converter with ps resolution.
I have the evalkit available at work with serveral measurement modules (high resolution module, standard module, wheatstone module), no seperate breakout board.
If you are able to fabricate a pcb I could solder the QFN package for you.
Regards, branadic
The LTC2410 might be a slightly better ADC. At such a slow temperature cycle, I don't thing the rate of measurement is already critical - for a faster data rate and thus less final noise, one could in principle use 2 ADCs to measure both voltages (differential) simultaneously with periodic swapping of the ADCs - that is having two max4052.
If you want to read up an an AC resistance bridge here is a manual of a LR400
http://www.lakeshore.com/ObsoleteAndResearchDocs/LR400.pdf (http://www.lakeshore.com/ObsoleteAndResearchDocs/LR400.pdf)
no schematic is given, but a rather detailed description is there.
I was debating on bidding on one earlier in the year, it was a parts unit that appears to have been in a barn.
I did not bid, it was sold.
Who said that? :)
http://www.linear.com/solutions/1365 (http://www.linear.com/solutions/1365)
I don't understand why it won't work with a 12.5k reference resistor and a 10k resistor under test. A LTC2440 (And others ADCs from the same family) accept 0...5V differential on the reference pins. Only the input is limited to -Vref/2 to +Vref/2.
This simple circuit will not fully compensate for the wire resistance. So it may work for an RTD but not for very precise measurements.
The only annoying wire resistance comes from the wire between the reference resistor and the resistor under test. The others are fully compensated if you connect the IN and Ref pins close enough to the resistors.
Hello
Absolutely not, this is the same problem for strain gauges for example. You can lower the excitation voltage using a little series resistor, see my schematic (This resistor = 1k).
Andreas: You might have considered this already but - Another "Gotcha!"
Just something to check.
I have never, ever measured drift like that on any UltraOhm PWW (measured using a real bridge) over a year,
ADC noise on the LTC2404 part you are using is not always perfectly random white noise - as you will soon be learning. Also- watch your Vref. It seems the drift data noise has gone up with increasing resistance - highly suspicious. That means something is probably wrong in measuring technique in your measuring jig itself.By the way I am using the LTC2400 (not the LTC2404 which relative similar) together with a MAX4052A/MAX4051A multiplexer.
Another item: you are not sure how well your reference resistor is temperature stabilized.Stay on the carpet:
maybe measure a 10k/ 10k LTC5400 ratio part for a reality check (these will get you a known ratio in ppm area guaranteed). LTC5400's will have more shot noise than PWW but are a cheap way to do a basic reality check on your system.
SUGGESTION: Order an LT5400-1. That will give you a couple pairs of 10k / 10k to work with with a guaranteed matching ratio of 1ppm TC (1ppm is an outlier, typical we see is maybe 0.2 to 0.3ppm TC).Hello,
You are comparing a S & H voltage on ADC inputs to the noise in Vref....and you're not even close yet.
Andreas, you are wrong:SUGGESTION: Order an LT5400-1. That will give you a couple pairs of 10k / 10k to work with with a guaranteed matching ratio of 1ppm TC (1ppm is an outlier, typical we see is maybe 0.2 to 0.3ppm TC).You seem really have no clue: A sigma delta converter does not have a S & H.
You are comparing a S & H voltage on ADC inputs to the noise in Vref....and you're not even close yet.
There is a continuously integration of input and VREF or GND.
Driving the Input and Reference
The analog input and reference of the typical delta-sigma
analog-to-digital converter are applied to a switched capacitor
network. This network consists of capacitors
switching between the analog input (VIN), ground (Pin 4)
and the reference (VREF). The result is small current spikes
seen at both VIN and VREF. A simplified input equivalent
circuit is shown in Figure 15.
Andreas, you are wrong:
See LTC2400 datasheet:QuoteDriving the Input and Reference
The analog input and reference of the typical delta-sigma
analog-to-digital converter are applied to a switched capacitor
network. This network consists of capacitors
switching between the analog input (VIN), ground (Pin 4)
and the reference (VREF). The result is small current spikes
seen at both VIN and VREF. A simplified input equivalent
circuit is shown in Figure 15.
switched capacitor = S&HAndreas, you are wrong:
See LTC2400 datasheet:QuoteDriving the Input and Reference
The analog input and reference of the typical delta-sigma
analog-to-digital converter are applied to a switched capacitor
network. This network consists of capacitors
switching between the analog input (VIN), ground (Pin 4)
and the reference (VREF). The result is small current spikes
seen at both VIN and VREF. A simplified input equivalent
circuit is shown in Figure 15.
And what has this to do with a S&H cirquit?
The Ceq referred to in the figure is not a parasitic capacitor, it is the equivalent of the distributed capacitors in the "internal switched capacitor network".
Please note the use of the term 'sampling' in the above paragraph, by definition, a switched capacitor network is a sample and hold circuit without doubt. Much older integrating ADCs also used switched circuits but the signal was integrated for a complete measurement cycle, not truly sampled even though the input was not being integrated constantly because of the auto-zero cycle, it did not constitute a sample/hold circuit.
Andreas,
I can't find anything on a ADA4538 except that it is an alternator and I don't think that is what you are using.
Maybe the internal layout is similar to the Fluke 742A.
Maybe the internal layout is similar to the Fluke 742A.
There are high resolution internal photos of the Wekomm resistor in this Daves video, from 5:17.
I don't know how to extract the photos from the video...
And resistors are VHA518-7 http://www.vishaypg.com/docs/63625/63625.pdf (http://www.vishaypg.com/docs/63625/63625.pdf)
VHA518 datasheet http://www.vishaypg.com/docs/63120/hzseries.pdf (http://www.vishaypg.com/docs/63120/hzseries.pdf)
According to information from Vishay datasheet VHA518-11 with PMO seems to be better option. Maybe Wekomm needs to to make some selection from Vishay batches...
What is interesting, that on first photo are wires and resistor soldered and on third photo wires are crimped to resistor.
Wire seems to be PTFE insulated and stranded silver coated. I have no idea why they used stranded wire instead solid copper. Any ideas?
VPG on their case study paper (http://www.vishaypg.com/foil-resistors/case-studies/study/wekomm_1/) state it's VHA518-7, with having Dipl.-Ing Guido Weckwerth, CEO, wekomm engineering GmbH as author :)
PTFE insulation is very important for low leakage
I found my notes of that talk, so silver coated wire should be better than pure copper because of thermal voltages.
Actually no, because the insulation resistance of the binding posts dominates. And there is no real need for the the on board PTFE insulators either. The printed circuit board could have been simply divided into two pieces and mounted directly to the binding posts. Air is an excellent insulator. And that way you also get rid of the wire inductance and a number metal-metal connections (source of thermal EMF).
Copper-Copper <0.3 µV/°C, Copper-Silver 0.5 µV/°C. But most important is to minimize the number of joints and make them thermally equal.
I think in this case using exotic materials has been more important than thinking the whole picture and doing the math.
You are right, but these binding posts are also highly insulating, and extremely expensive, as Guido told me.
Also don't forget, that Dave has got a prototype, only WEKOMM knows how the devices were built nowadays.
I'm still collecting information & measurements.
Sorry to say, but when we talk about this specific product you sound more like a business partner rather than the scientist familiar to all of us.
So far this is just a $50 resistor in a box with a $5000 price tag. No data of any kind, just sellers vague promises of the exceptional performance. Somehow reminds me of the high-end audio business.
BMF resistors have been used as transfer standards in primary metrology for decades. Especially in AC/DC metrology because of their excellent AC behaviour compared with wire wound resistors. The 10^-8 short term stability mentioned is achievable using off the self BMF resistors without any special treatment or black magic.
My point is that at the moment I see nothing to justify the astronomical price tag. The metrology business is very conservative and for a reason. The equipment are expensive not because of the material cost, but because someone has done the hard, expensive and time consuming work for you. The scientific proof of performance is what you pay for, not some technology or fancy look. From that perspective I think that Wekomm with their marketing first approach has started from the wrong end.
I don't tolerate that at all, and expect your apologies!
You obviously make some wrong assumptions about WEKOMM and their resistors, even so imputing dubious business behaviour to them. Instead of also bringing them in discredit w/o good reasons, I propose that you contact Guido Weckwerth directly for details.
Please give a valid reference of the MBF standard resistor you mentioned, which is assumed to have 1E-8 stability, on what scale ever.
Maybe some very good SR104 or similar PWW based standards may have this capability, on the order of < 1e-7 maybe, but these are also extremely costly, although their obvious BOM cost may be a fraction of that only.
@Itz2000:
No claims. Just facts.
I attached some documents from our german National Standard Institute PTB. They qualify our resistors as primary transfer standards.
@Theobel:
Long term drift if measured by comparing a resistor directly against the Cryogenic Hall Standard for some days. That tells us the drift with a resolution of 10^-10
Dr. Schumacher from PTB developed main parts of the Cryogenic Hall Standard and some mathematical methods for deriving some quite reliable long term drift from these measurements. We specify a max yearly drift of 1ppm, but up to now all resistors were way better than that.
We did not yet reach the good behaviour of an old SR104, they are extremely good. But we are working on that.
At the time being our resistor is better than most of those of our competitors.
Oh, and for example try to load a Fluke 421A-1? with 1A (makes 1Watt power) and do the same with our resistor. Ours drifts max 10ppm and comes back to it's original value better than 10^-8. That lead to the construction of a second resistor type, being capable of heavy loads. That one drifts about 0.8ppm at this load.
Guido
No claims. Just facts. I attached some documents from our german National Standard Institute PTB.
They qualify our resistors as primary transfer standards.
... off the shelf Vishay hermetic foil resistor which is specified to drift less than 2ppm in 6 years, or .3ppm/year for <100 euros?
A new SR104 costs about the same as the Wekomm.
Why then would Fluke sell their 421A resistors if those off the shelf resistors are way better in all respect ?
And this is the "high load" resistor, being tortured in the PTB lab ....Do you also have some pictures of the PTB lab equipment, measuring this reference resistor?
QuoteA new SR104 costs about the same as the Wekomm.Yes ... and is specified with a drift of 2ppm/year. Have you ever bought one the last five years and verified that drift ?
Do you really think you could start a business in this field just by claiming?
Quote... off the shelf Vishay hermetic foil resistor which is specified to drift less than 2ppm in 6 years, or .3ppm/year for <100 euros?
Have you ever checked that ???
And this is the "high load" resistor, being tortured in the PTB lab ....Do you also have some pictures of the PTB lab equipment, measuring this reference resistor?
What equipment are they using?
(https://www.eevblog.com/forum/projects/t-c-measurements-on-precision-resistors/?action=dlattach;attach=184688;image)
Thanks for the high resolutions pictures, it is really a pleasure, looking at them.
Sure ... basically the PTB are using a Fluke Transconductance Amplifier controlled by a Wavetek calibrator to generate the power. Then they have a range extender from MI (that blue box you can spot) to measure the current via a reference resistor (in the silver box). That is compared to the current through the bigger resistor.
The smaller 1Ohm resistor is used as a short to keep the current flow constant, when the bigger resistor is not loaded. That just helps stabilize the transconductance amplifier.
If you have a known accurate reference (and its uncertainty), within the parameters that apply to your DVM, you can still get a ratio that will be a bit more accurate than your DVM's actual accuracy as set out in the Keysight paper. Just be very careful of noise pickup, ratio modes are quite sensitive to it and even with a filter on, you can expect an additional drop in actual ratio accuracy because of it. A ratio is made up of two independent readings made at two different times (sequentially), even if the linearity of the ratio mode were perfect, the readings would still have error attached to them. According to the engineers at Keysight, that could double the error of the readings.sorry i deleted the question
The other option /besides hermetic resistors/dividers) that may be more stable is dividers in one package. This way the humidity impact affects both resistors on the substrate (made from the same material) the same way and one would expect a more symmetrical behaviour.That's the idea. I have ordered some VHD200 from Vishay that both hermetic and in the same package.
The bottom socket will soldered onto a PCB and I'll find some way to firmly attach the top one before making fly wires to the side of the PCB. ^-^
Hello,The reversal seems to be a good idea but it doesn't work in reality, they allow one way insertion only.
Perhaps you can reverse orientation (upside down) for the upper connector and use a 2nd PCB.
While surfing this thread about 'ugly' wires, 'ugly' heat, I thought there may exist a 2-wire socket for one lead. I then went thru my stuff and found out a kind of socket that allow the leads go through and insert to another socket at the bottom as well. This will make 4 wire connection required.
The bottom socket will soldered onto a PCB and I'll find some way to firmly attach the top one before making fly wires to the side of the PCB. ^-^
Although Vishay is notorious deceiving people in the datasheets for tempco, they do have guarantees for some of their hermetic packages for shell-life of 2ppm/6yr, which is THE most important factor for voltage standards that worth trying out, and seems no other WW manufactures say something about the aging even close.The other option /besides hermetic resistors/dividers) that may be more stable is dividers in one package. This way the humidity impact affects both resistors on the substrate (made from the same material) the same way and one would expect a more symmetrical behaviour.That's the idea. I have ordered some VHD200 from Vishay that both hermetic and in the same package.
Hate to ruin your day, but these don't seem to be consistent in production in regards to TCR tracking. If you order a big batch, you may find that some of them TCR track very well, while the others maybe not so much. In addition, there is no guarantee that they will age together.
For a much better ratio resistor set that actually will track, contact Edwin Pettis-- he can make you a set that are made from the same resistance wire that comes off of the supply reel one after another. This will ensure that the two resistors track very well, and they should age together. I suggest placing several wraps of copper tape around each resistor individually, then wrap those together with several more turns of copper tape. This will help keep the resistors at the same local temperature. If one of the resistors ends up being much smaller than the other, Edwin may suggest that the smaller one be placed in a smaller package-- this will help with tracking. With this method, it is possible to get near zero TCR tracking coefficient.
It would be interesting to put your same experiment inside of another box that has a few large bags of desiccant to see if you get the same overnight shift in value.
Interesting. I wonder if the greater thermal mass of the desiccant packs was responsible for the difference, and not humidity. How do we test this?
The ZVAR has from my side of view no advantage over a Z201 resistor in precision application (which was my hope). The hysteresis behaviour is even worse. And they are very fragile. The ageing is undefined.
The precision film resistors also have their place-- they have relatively low current noise [than carbon or carbon-film] and are good at the higher frequencies-- even better at high frequencies than VPG foils because the resistors are so thin. But they are at the bottom of the list if you are looking for the best long-term stability [Exception: Ta2N [Tantalum Nitride] film resistors, which can have excellent long term stability, but only "good" TCR unless highly selected].That's very informative. One thing I'd like to ask is base on this:
TaN resistors are for example Vishay NOMCA ,are you sure they are using nichrome ones?Thanks for the info. The only thing I'm sure of is 7001 were using Vishay TDP1603 resistor networks. There are a lot of TDP1603 resistor networks in Fluke 8508A as well, but, Fluke seems using better resistor networks(Vishay 1446) around the reference board:
http://www.vishay.com/docs/60117/nomca.pdf (http://www.vishay.com/docs/60117/nomca.pdf)
I'm pretty sure that both the 7001 and the CERN reference use the 'A' version of the LTZ...Nope.
Well on the CERN reference, there is a 10V output and a 10mA output. Obviously, the 10mA is derived from the 10V, and so the 10V will have less than 1ppm/year drift, and the voltage to current converter will add a small amount of drift, totaling up to <= 1ppm/year.And now is much later than the CERN reference, no one has designed a 10V reference with specification better than 1ppm/year.
The CERN reference was designed much later than the 7001, so I'm assuming that the designer learned some things along the way to make it better.
As a ballpark, humidity and temperature variations create about 100 ..500 ppm of change.
Usually, Thin Film were not tested and specified for Shelf Drift, as this technology makes no sense for longterm stability.
Foil resistors have a drift comparable to PWW, I'd guess, and as specified, as these are real bulk material type resistors, not comparable to thin or thick film technology.
As a ballpark, humidity and temperature variations create about 100 ..500 ppm of change.
Usually, Thin Film were not tested and specified for Shelf Drift, as this technology makes no sense for longterm stability.
Foil resistors have a drift comparable to PWW, I'd guess, and as specified, as these are real bulk material type resistors, not comparable to thin or thick film technology.
Thanks, I would think though that foil resistors are also some type of metal film, so as long as they are not hermetic I would expect a similar aging drift behaviour as with metal film. And I would expect wirewound to be lower. Also, I would rather expect 10 to 50ppm/year drift for metal film/foil (shelf life/low power; not temperature drift/extremes), otherwise a 0.05% better resistor would not make much sense. Do you have any specific data supporting 500ppm/year?
Shelf drift, just laying around in a regular room environment, tends to have the lowest drift numbers because it is the easiest environment to live in for a resistor, no power, relatively small temperature range, no on/off cycles. ... Precision wire wounds can vary as well depending on construction, as a general range many are in the 20-35 PPM/year but some can be lower. As a general rule Ultrohm Plus are spec'd at <10 PPM/year but can achieve much lower drift rates. I have some 200 ohm resistors that I made for Bob Pease several years ago which I have been keeping an eye on (spares), they have drifted less than 5 PPM over the years (that was about 7 years ago). This drift can be influenced by value and environment to some small degree, I usually spec a conservative <10 PPM/year in most cases, it is usually less but most of the data I have is just feedback from customers who do track such data.
- 2 pieces of Teflon tubes where the resistor leads are inserted
I get from eBay. They are used somewhere in 3D printers. If you search for Teflon tubes you should find it.- 2 pieces of Teflon tubes where the resistor leads are inserted
Hello,
from where did you get this?
With best regards
Andreas
when I compare this with my own UPW50 measurements the behaviour is quite different:
I usually have a "lag" between temperature change and resistance. This gives the typical hysteresis opening around the middle of the temperature extremes. Over night the resistance returned around to the middle of the opening.
On the other side I never had temperatures above 45 deg C.
Hello,
I think it is better to solder the connections instead of using grabbers.
with best regards
Andreas
| # | °C | avg. resist. - sam. | abs ppm - dt | ppm/°K - dt |
| -- | -- | ------------------- | ------------- | ------------ |
| 00 | 25 | 20011.229886 ? 021 | | |
| 01 | 25 | 20011.236979 ? 019 | +000.35 +0 | |
| 02 | 30 | 20011.703395 ? 022 | +023.31 +5 | +04.66 +5 |
| 03 | 30 | 20011.703168 ? 019 | -000.01 +0 | +04.66 +5 |
| 04 | 35 | 20012.125043 ? 021 | +021.08 +5 | +04.22 +5 |
| 05 | 35 | 20012.120768 ? 019 | -000.21 +0 | +04.17 +5 |
| 06 | 50 | 20013.388645 ? 022 | +063.36 +15 | +04.22 +15 |
| 07 | 50 | 20013.374047 ? 019 | -000.73 +0 | +04.18 +15 |
| 08 | 50 | 20013.363585 ? 020 | -000.52 +0 | +04.14 +15 |
| 09 | 30 | 20011.460479 ? 019 | -095.09 -20 | +04.75 -20 |
| 10 | 30 | 20011.463921 ? 019 | +000.17 +0 | +04.75 -20 |
| 11 | 30 | 20011.472355 ? 020 | +000.42 +0 | +04.72 -20 |
| 12 | 60 | 20014.381990 ? 021 | +145.40 +30 | +04.85 +30 |
| 13 | 60 | 20014.352014 ? 021 | -001.50 +0 | +04.80 +30 |
| 14 | 60 | 20014.339421 ? 019 | -000.63 +0 | +04.78 +30 |
| 15 | 30 | 20011.333014 ? 021 | -150.21 -30 | +05.01 -30 |
| 16 | 30 | 20011.346870 ? 020 | +000.69 +0 | +04.98 -30 |
| 17 | 30 | 20011.356837 ? 019 | +000.50 +0 | +04.97 -30 |
| 18 | 30 | 20011.361145 ? 020 | +000.22 +0 | +04.96 -30 |
| 19 | 30 | 20011.368689 ? 019 | +000.38 +0 | +04.95 -30 |
| 20 | 30 | 20011.375579 ? 019 | +000.34 +0 | +04.94 -30 |
| 21 | 30 | 20011.379270 ? 020 | +000.18 +0 | +04.93 -30 |
| 22 | 30 | 20011.384615 ? 020 | +000.27 +0 | +04.92 -30 |
| 23 | 30 | 20011.390463 ? 019 | +000.29 +0 | +04.91 -30 |
| 24 | 30 | 20011.391643 ? 021 | +000.06 +0 | +04.91 -30 |
| 25 | 30 | 20011.399790 ? 020 | +000.41 +0 | +04.90 -30 |
| 26 | 30 | 20011.401468 ? 019 | +000.08 +0 | +04.89 -30 |
| 27 | 30 | 20011.403340 ? 020 | +000.09 +0 | +04.89 -30 |
| 28 | 30 | 20011.406747 ? 019 | +000.17 +0 | +04.88 -30 |
| 29 | 30 | 20011.413715 ? 020 | +000.35 +0 | +04.87 -30 |
| 30 | 30 | 20011.406163 ? 019 | -000.38 +0 | +04.89 -30 |
| 31 | 30 | 20011.410265 ? 020 | +000.20 +0 | +04.88 -30 |
| 32 | 30 | 20011.412707 ? 014 | +000.12 +0 | +04.87 -30 |
| 33 | 30 | 20011.411674 ? 023 | -000.05 +0 | +04.88 -30 |
| 34 | 30 | 20011.412410 ? 021 | +000.04 +0 | +04.87 -30 |
| 35 | 30 | 20011.415800 ? 019 | +000.17 +0 | +04.87 -30 |
| 36 | 30 | 20011.417324 ? 021 | +000.08 +0 | +04.87 -30 |
| 37 | 30 | 20011.418275 ? 020 | +000.05 +0 | +04.87 -30 |
| 38 | 30 | 20011.417811 ? 019 | -000.02 +0 | +04.87 -30 |
| 39 | 30 | 20011.417795 ? 020 | -000.00 +0 | +04.87 -30 |
| 40 | 30 | 20011.415679 ? 019 | -000.11 +0 | +04.87 -30 |
| 41 | 30 | 20011.411685 ? 020 | -000.20 +0 | +04.88 -30 |
| 42 | 30 | 20011.412853 ? 019 | +000.06 +0 | +04.87 -30 |
| 43 | 30 | 20011.406068 ? 019 | -000.34 +0 | +04.89 -30 |
| 44 | 30 | 20011.404360 ? 020 | -000.09 +0 | +04.89 -30 |
| 45 | 30 | 20011.398074 ? 019 | -000.31 +0 | +04.90 -30 |
| 46 | 30 | 20011.392920 ? 020 | -000.26 +0 | +04.91 -30 |
| 47 | 30 | 20011.392633 ? 003 | -000.01 +0 | +04.91 -30 |Hello Alex,
are you shure that you are not below the dew point
at 16 deg C and below when doing the measurement.
Or why is the resistance first rising and then going down?
With best regards
Andreas
I'm looking to get a small benchtop incubator/oven to start doing some TC measurements! Anyone know of any, fairly decent, cheap units available on the market? :popcorn:
>> For me its not clear: what effect do you mean with "end cycle hysteresis"?
"end cycle hysteresis" is the resistance change measured after one or more thermal cycles.
If you get the following example you can see that at beginning (step 2) resistance was 20011.70 ohm circa.
After the temperature going up and down two times resistance was 20011.39 ohm circa (step 47).
So the resistor has lost 15ppm after thermal cycling.
@Alex Nikitin
That's very odd to me, never expected this to be the case.
From charts it seems you are measuring stability of the Keithley 617 and not of resistor :-)
Anyway this little histeresys (if always recovered) is almost ininfluent within a ltz1000 circuit.
... I don't see a tolerance on the resistors nor any tolerance code so what tolerance these have is anybody's guess.Standard tolerance code "B" = 0.1%
Most of the old Ultronix resistors I have are somewhat tighter in tolerance and much smaller in size.
Remember also that the 3458a isn't really the best way...Indeed, even though actually pair of K2002's used for measurements above.
I would run the test again, but measure the performance at how these are actually used in your LTZ: Measure the ratio of output voltage 12.5k/1kI think this is great summary of the next test, using my fresh acquired K6221. :-DMM
Remember, it's going to take at least 100ppm change in heater resistor RATIO to change the Vref output of LTZ by 1ppm...Great reminder to anyone playing with LTZ-REFs, I just mark this bold here for future lurkers. Indeed good point. :-+
I would also suggest putting your resistors under bias for at least 24~48hrs before testing, especially after shipping. You don't know how cold or hot that shipping container got during transit - and any precision resistor will need some thermal stress recovery time under bias before you can measure true performance.100% true.
1K resistor behave normally and almost linear, other than about -10ppm shifts after each cycle.
However 12.5K one have positive tempco till around 32-35c, reversing to negative right after.
Resistance shift after first run was -27 ppm, and -13 after second run.
Make me think to bake these resistors for some good amount of hours and coat them afterwards to get more predictable behaviour.QuoteI would also suggest putting your resistors under bias for at least 24~48hrs before testing, especially after shipping. You don't know how cold or hot that shipping container got during transit - and any precision resistor will need some thermal stress recovery time under bias before you can measure true performance.100% true.
Once again, (read reply 713 above) I do use the same wire to make both of the heater resistors, therefor they have by default the same TCR. The TCR of the wire cannot be changed by any operating temperature, not even +150°C. The apparent TCR can be made to look higher by external stress if applied directly to the wire, this is not a change in wire TCR nor can it change the polarity of the TCR. I cannot stress enough the difficulties of measuring PPM (or sub-PPM) quantities, there are many artifacts that can affect the readings. Again, the only reliable method of reading PPM quantities of resistance is with a high quality resistance bridge of sufficient accuracy and uncertainty. Any other method brings additional uncertainties to the measurement process whether known or unknown. I know the capabilities of my resistance systems, their accuracy and uncertainties. The accuracy and uncertainty varies to some degree with the actual value in question. I cannot measure a 10 ohm resistor to the same degree of accuracy as I can a 10K resistor because of system limitations and I know what those are.
Calculated values made from measurements with unknown uncertainty errors are not acceptable, calculations does not enhance the original accuracy and uncertainty of the measurement, ask a high grade calibration lab about that. Whether using a 3458A (freshly calibrated) or a Keithley K2002 (or similar) does not equate to a high performance resistance bridge. All these posted readings I have seen have never quoted an uncertainty factor (likely greater than 2 PPM), the readings are apparently taken at face value, errors and all. Every reading has an uncertainty, often from multiple sources (you don't know accurately, the temperature to 5 decimal places or even 3 decimal places), this cannot be ignored.
While these measurements can be used as a rough basis for comparison, this cannot imply actual accuracy of the measurements without the actual accuracy and uncertainty declared. None of the equipment mentioned here are capable of the accuracy implied, whether calibrated or not, the uncertainty of said measurements easily exceeds the implied accuracy. Yes, you can compare 'relative' measurements but that still leaves wide open the actual accuracy involved and uncertainty (a real question is, relative to what? At best, that means itself which is virtually meaningless). The world of PPM is filled with unknowns and uncertainties unless you're the NIST (or equivalent), a fact you cannot get around.
I can read a 10K resistor on my 242D bridge to at least 10 digits, it may even repeat a reading to 9 or ten digits, that doesn't change the fact that the accuracy is within 1 PPM and the uncertainty is 0.5 PPM, that absolutely means the accuracy stops at the 6th decimal place and anything beyond that is essentially useless, it cannot be used to enhance the reading by math.
I understand the premise being pursued here, it can be fun and educational but it is a requirement of science to maintain accuracy of statements and measurements, state the known accuracy of your equipment if known or if it is unknown, and uncertainty involved and view the data in that light, it is of little use to compare unknown quantities, particularly when these quantities are being claimed in PPM. As Bob Pease would say, that is just sloppy work.
a lab with access to JJ-array (measurement uncertainty ~0.3ppm, which is about the best possible we can expect anywhere)
Dr. Frank: I won't argue with you on your results heater resistor ratio influence - but from a customer test we did 5~6 years ago on 10ea LTZ1000ACH - in a lab with access to JJ-array (measurement uncertainty ~0.3ppm, which is about the best possible we can expect anywhere) - we found the datasheet is closer to being correct. We found the heater resistor -ratio- had to change at least 103~105ppm to deliver a solid >1ppm change on output voltage, at 25° ambient, PWW 3ppm TCR resistors, mounted on our 1.5oz copper board design inside our application enclosure with semi-insulated LTZ can. Again this is one of those measurements where all environmental elements comes into play. Your mileage may vary.
Even if we take your more conservative estimate of an LTZ Vref delta attenuation factor of 76 lower than the heater resistor ratio change - these resistors will be fine for most applications - especially given the fact the basic LTZ stability as ppm drift is down in the mud when it comes to most real lab's measurement capability (Usually better labs are at 2ppm uncertainty for voltage). It all depends on the expected operating temperature range of your final application.
The take-away here is that for a typical LTZ 7V datasheet circuit - expensive Vishay's won't buy you much of anything in terms of overall profitable cost / performance benefit, and that foil will always get you a bit more noise over PWW's (although that noise effect is difficult to measure on LTZ output, but is there).
while cnt <= 400000:
if (cnt < 3000):
meter2510.deduct_tmp(28)
if (cnt >= 3000) and (cnt <= 6000):
meter2510.deduct_tmp(40)
if (cnt >= 6000) and (cnt <= 9000):
meter2510.deduct_tmp(20)
if (cnt >= 9000) and (cnt <= 12000):
meter2510.deduct_tmp(30)
if (cnt >= 12000) and (cnt <= 16000):
meter2510.deduct_tmp(40)
get_THP() # Read Temp, RH, Press from BME280 sensor
meter2510.get_data()
k10v = k4.get_data()
k16v = k6.get_data()
732B cal'd directly against Fluke Everett's JJA in January and they reported a measurement uncertainty of 0.06 µV/V.
Quote from: CalMachine732B cal'd directly against Fluke Everett's JJA in January and they reported a measurement uncertainty of 0.06 µV/V.
That is measurement uncertainty, but your final 732B uncertainty at your site is higher, because it's sum of all uncertainties and 732B stability. Per 732B spec your end uncertainty at the box connector is +/-0.36 ppm/30 days, or +/-0.86 ppm/30 days or 2.06ppm/year assuming that there was no output change due to shipping, and conditions of your lab and Fluke's calibration facility are exactly the same.
Yes, I know this. He had made the claim that 0.3 PPM was the best uncertainty you were going to find from a lab with access to a JJA. I provided a case of a lab with a JJA of having much much less uncertainty. In NO way was I trying to insinuate that was my uncertainty.....
Quote from: CalMachine
Yes, I know this. He had made the claim that 0.3 PPM was the best uncertainty you were going to find from a lab with access to a JJA. I provided a case of a lab with a JJA of having much much less uncertainty. In NO way was I trying to insinuate that was my uncertainty.....
About 0.35ppm uncertainty is the typical advertised specified limit -at- Fluke, and that includes the uncertainty of transfer between their lab to and from NIST. They can also to tighter tolerance measures if you pay for it. You won't have that uncertainty after the 732b gets shipped to you - every transfer adds uncertainty. I know they have 732b's shipping to and from NIST and other JJ-array labs almost continuously - and newer methods involve shipping "Compact" Josephson junction array equipment to inter-compare the JJ-Arrays. That's what it takes to get into fractional ppm world and NIST traceability.
That is not the same as their lab measurement resolution, which is usually finer-grained than uncertainty - they are just telling you what their equipment reading was...and that will have a specified uncertainty of the absolute value, before they shipped the Vref to you.
Even the manufacturers of JJ-Array will give you these measurement uncertainty specs if you order a new JJ-Array, with very good uncertainties in the 10's of nV range on 10V scale. This gets better with the newer JJ-Array 10V chips. But in the 0.2~0.3ppm uncertainty on a voltage measure is considered very good for typical alignment to another lab without a government budget.
Normally you will have a 734 unit with at least three other references at your location, and as soon as you get the freshly cal'd 732b back form Fluke you add that to your existing pool and immediately compare with your existing pool members and start running the numbers to see if you see drift in the just-received unit or any of the other three - and then you make a decision on which ref to send in next.
You are always looking at the measured drift vs. the predicted drift to see how your Vref is settling in. Older units are generally much better performers than brand-new units.
Normally on a new 732b you'll run cal cycles every 6 months or sooner until you begin to see it settle down and you can detect a predictable drift rate - and then you can go longer in between cal checks.
If you do all that religiously your lab will eventually have about 2~3ppm real measurement uncertainty capability, traceable back to NIST. Add more cal'd 732b's to increase confidence and lower uncertainty.
Lots of docs at Fluke site that explain in better detail.
3458a's - as good as they are - aren't really considered a shippable transfer standard. They can be used as a short term, in-lab voltage measure transfer though, within limits - especially if their drift rate is fairly stable and known.
Hi MisterDiodes,
there were four people in the LTZ thread, who virtually did the same measurement, like you, I assume, i.e. modifying these both resistors by some percentage, and measuring the LTZ1000 output deviation.. this varied from 74 (Andreas) to 105 (somebody on bbs38hot).
So 74 was worst case.
I just mentioned that, because even using these worst case T.C. numbers, the effect and the optimizing of the resistors T.C. are of 2nd order importance only ..
The residual T.C. will always be below 0.05ppm/k, and may be disappointingly too high, if you set your money on expensive ultra - low - T.C. Vishays, or T.C. matched sets.
The LTZ itself, i.e. up to now undisclosed / not yet explained effects, will play an important role, so a T.C. trimming to << 0.05ppm/K might be accomplished otherwise, e.g. by this T.C. compensating resistor
What interests me, in this context, how did you characterize the T.C. of your LTZ1000 devices, as most of the gear accessible to us amateurs has much higher T.C.?
Do you know a possibility to accomplish that, say trimming to 0.01ppm/K , w/o the aid of a JJA standard?
Frank
Since this is much worse than expected, it might be worth using a different setup / meter or check a different known good resistor of similar value.
In theory there is even the possibility to allow for an external measurement of the set-point voltage and if needed maybe correct for the effect of a possible drift of the divider. Detecting a 100 ppm drift in a divider ratio is easy compared to a 1 ppm drift in an reference voltage.
If I am reading your chart correctly, once your TECBOX reaches temperature 40°C and stays at that temperature, the resistors should also level out and stay constant once they reach thermal equilibrium. Why are there slants in the resistor tracks when the temperature is apparently constant? Is it just too late in the evening for me or am I missing something?
Plotting resistance over temperature, ambient temperatur, humidity and dew point could help to identify the different influences of your measurements.
Dew point was calculated by the Magnus formula: https://www.wetterochs.de/wetter/feuchte.html (https://www.wetterochs.de/wetter/feuchte.html)
Hello, I have a question, I believe it is appropriate for this topic. Excuse me if it is duplicate, however the topic has already 30+ pages.
We use in our products resistors from Nicrom (http://www.high-voltage-resistors.com/), parts are from HVC BT series and 200.3 BA series. Product catalog (http://www.nicrom-electronic.com/Catalog_2004.pdf) should explain it.
The reason is 0.1% accuracy and 10/15ppm/°C.
The problem is that Nicrom is not responding for weeks/months and it is not possible to source parts from them.
Can anybody advise me alternative source of high-resistance resistors with such low tempco ? We can omit accuracy by parts selection or calibration.
My colleague found out Ohmcraft manufacturer and their SM HVC (http://www.ohmcraft.com/uploads/SM_HVC.pdf) series looks good, but not exactly as good as Nicrom.
Any advice on high resistance resistor manufacturers please ?
There are two:
HVC-2010-20M-BT .... 20M, 2.2kV, 0.5W, 0.1%, 10ppm/°C, -5ppm/V
200.3-100M-BA-R .... 100M, 20kV, 3W, 0.1%, 15ppm/°C, 0.3ppm/V
Is it possible to make these resistors with these parameters ?
The time it takes to reach equilibrium for humidity depends on the temperature and likely only a little on air movement. The slow part is usually the diffusion in the plastics.You are correct, my bad.
In the LTZ1000 circuit there is a good chance that the circuit part with the resistors get slightly warmer than room temperature. A 10 C temperature rise corresponds to about a reduction of RH by a factor of 2. This also reduces the possible range of humidity variations.This is also my findings. But my LTZ1000 design in an alubox with a well-insulated LTZ have just a couple of degrees C rise on the resistors. If the temperature is higher one drawback is that you might get more drift and if the unit is off a long time it will absorb moisture that during the first day or weeks after start will desorb giving a long “warm-up” period. But as said before this will normally be a minor problem for the resistors for the LTZ.
For 10V refs in plastic packages I have somewhere else showed this with data from boxes with average internal temperatures of about 23C respectively 36C. For a seasonal variation of about 40%RH I had for REF102 about 20ppm at 23C and 10ppm at 36C and for LT1236 about 24ppm at 23C and 12ppm at 36C. For the AD587 I had only 4-6ppm at 23C for four samples and around 1-3ppm at 36C for five samples but one sample had 9ppm (at 36C). In another test with six AD587LN with different date codes I got very different humidity sensitivities. Think I have shown this before also but don´t remember so well. All these were DIP-8 in sockets (on FR4 boards).
I have also tested a few SMD versions at the same time. For the SMD they were mounted on SMD to DIP adapters from Aries (Farnell). For the REF102 the DIP8 and SMD results were very similar. For the LT1236 the SMD was much better, only about half of the drift. For the AD587 the SMD was about 6ppm at 36C for two samples so worse than most of the DIP8’s. That Maxim says that SMD is worse than DIP’s might be because of MAX674. I had one sample in SMD (no DIP) in the 36C box and the seasonal variation for that was more than 20ppm! After a power down (controlled) for three weeks it started 40ppm higher (measured after 1 and 3hours) but after a couple of weeks it was back on track again.
For any precision reference, you need hermetically sealed devices. Metal can or ceramic. Plastic is useless to even validate, they will drift considerably due to humidity/environmentals.
And next, if you have the choice, burried ceners.
Another interesting part of the story: We expect the PWW resistor to have a -higher- TCR and a fairly long thermal response time lag compared to film, but a couple of other effects we look for also besides the usual Temp. / Humidity / Pressure effects:
1. Noise. The film resistor datasheets are a bit sketchy on this one; it's better to measure on your own. The PWW will have the lowest noise down to DC - usually right at theoretical thermal minimum for resistance value. The metal film and chip-scale diffused resistors are doomed to have more noise - even the foil-to-lead attach points can be a problem.. It is interesting to look at how much more noise comes from certain film designs, and to what substrate the foil has been bonded. If the foil has been laser-trimmed we've seen various effects from the foil edge thermal damage and slag debris that's left over. And so on.
I have to ask how much noisier at low frequencies (0.1-10Hz) a standard LTZ design will be if I use thin film resistors as SMD RN73, PCF0805 or ERA6 (Digikey, Mouser etc) or through hole like PTF56 or other similar to the ones HP uses in the 3458A?
Precision wire wounds are the only resistor technology that can very close to the theoretical thermal noise limits as calculated, all other resistors are higher, not just my opinion, it has been proven by Universities independently.
One reason to validate plastic is that they are used much more often than metal/ceramic. [...]
Lars
Wow, send that guy back to remedial soldering class <grinning>, if the wire weld isn't broken, it should still measure good.
One reason to validate plastic is that they are used much more often than metal/ceramic. [...]
Lars
Have you attempted to use any kind of conformal coating to reduce the humidity sensitivity in your experiments?
Or does no coating exist that acts as a 100% humidity barrier?
The usual way to measure the excess noise of resistors is by using a bridge circuit of 4 equal resistors, so that the AC amplifier does not see an DC voltage applied to the resistors.
So you have the PET fan blowing directly on the switch card box ... ummm I don't like.
Have you considered if this can cause weird EMF problems?
What are those connectors you are using for the resistors.
Pyta: You probably want to send those GR's back for inspection, or double check the setup. We received a batch last month, the 120's are all running in spec for TC at about 2.5 ~ 3 ppm TC. Never seen them that whacko.
When you run those screws down on the leads, do you have a spring-loaded tensioner-spreader plate between the screw and lead (so you get a consistent, repeatable clamping force) - or is the screw just directly pressing into the lead and extruding / deforming it? We've seen that problem before. It looks like the other resistors were behaving, approximately.
Hello,
Wow: what a effort to measure one batch of resistors.
Just one question: the y-axis on the diagram is marked as ppm/K ?
Or should it be ppm
with best regards
Andreas
Photos part 4 + sample measurements.
Now You see why I had problems with two of my LTZ 1000 boards which used 120ohm 8G16D resistors.
P.S.1. I don't use temperature ramping. I set cretain temperature and I wait for an hour for temperatures to equalize. Then I start measurements.
P.S.2. The project wouldn't be finished without software work done by Mr. Zbigniew K. Thank You!
Photos part 4 + sample measurements.
Now You see why I had problems with two of my LTZ 1000 boards which used 120ohm 8G16D resistors.
P.S.1. I don't use temperature ramping. I set cretain temperature and I wait for an hour for temperatures to equalize. Then I start measurements.
P.S.2. The project wouldn't be finished without software work done by Mr. Zbigniew K. Thank You!
The LTZ circuit runs ok now, but I doubt, that even 10ppm/K makes a difference. The drift 'attenuation factor' for the 120 Ohm is about 800, if I remember correctly.
Frank
In the LTZ1000 circuit the drift attenuation is about 100 for the 120 Ohms and the divider.Hello,
| T['C] R_fluke_P1 [ohm] R_fluke_P0.5 [ohm] 15 1.9993265E+4 9.9965340E+4 20 1.9993420E+4 9.9965880E+4 25 1.9993547E+4 9.9966300E+4 30 1.9993652E+4 9.9966630E+4 35 1.9993739E+4 9.9966850E+4 25 (check after 24h) 1.9993545E+4 9.9966290E+4 |
But obviously: there is no free lunchAndreas I also was thinking at this but after the 60°C phase even if I was leaving the resistors in desecant it maintain the same behavior (I used an aspirine tabs tube to keep the resistors well dry and "hermetically sealed" with some more desecant inside).
the night following the first measurement the resistor drifted about 10 ppm at constant temperature.
and the following cycles have gone worse and worse .....
And each night another (fortunately decreasing) upward drift.
so the last measurement on 70K#3 does no longer look good.
#3 on last measurement: +/-7 ppm "open" hysteresis
box T.C. around 1 ppm/K and 31 ppm drift over 6 days.
So the largest part of the hysteresis is humidity related.
A baking brings somewhat better values. (drying Epoxy is shrinking).
But the baking also shifts the value of the resistor.
When the resistor is left around room temperature the Epoxy is swelling again by taking air humidity.
So the drift goes into reverse direction.
with best regards
Andreas
humidity is the most plausible explanation that I found.
(since time constant is several days).
Of course it could also be some relaxation/creeping effect.
Now conformal coat the resistors and see what changes.
humidity is the most plausible explanation that I found.
(since time constant is several days).
Of course it could also be some relaxation/creeping effect.
Actually, we've found humidity might not be all to blame here - and of course you've ruled out drift in your measurement system (we are always comparing to a known SR-104 Rref standard to help negate equipment drift):
1. Try testing your resistors in a controlled saturated salt solution atmosphere. I'd let them run at least a 30 days at 70% and again for another 30 days at 10% humidity. That will give you some idea of what's going on. Now conformal coat the resistors and see what changes.
2. For voltage dividers, it's always better to run the divider on a test PCB in about the same physical arrangement as the final design. It's also very important to realize the resistors need to be under typical bias condition and typical thermal flow situation as your application - in other words just testing the resistors on a DMM is not the same thermal flow characteristic you're looking at for the real divider.
Another test is to run the resistor divider set under oil, and yet another is to measure the water absorption rate of your components on a sensitive lab scale. This usually takes a month or two (or longer) oven dry out in the oven - get a baseline weight, and then a month or two exposed to a humidity controlled atmosphere, and see what the mass change was. The wire itself on a PWW doesn't care about humidity, but you might see some stress issues from the bobbin - but this tends to stabilize over time.
You'll probably find that the resistance drifts a bit early on, but as the component stress-relieves itself it will become more stable over time - and not as much will be attributed to humidity as you first thought, maybe. It all depends on how the resistor is constructed.
What we've found is that running the divider under actual bias conditions and several thermal cycles for at least a few weeks will let you see the system stabilize.
Normally we would not see major changes over a few days time on a well-relaxed PWW divider, so you might be looking at something else. You do see some yearly drift of course but if you spec the PWW divider resistors to have the same or similar TC you should see a relatively stable divider in RATIO TC, which is what you want normally. You don't usually care too much about the absolute value of each resistor drifting - but be aware of this effect in balanced differential amps, since sometimes that absolute value change can sneak in to cause trouble even if the ratio TC is fairly steady.
The only way to get rid of this is to use materials that are immune to humidity such as metal, glas and ceramics which ends up in hermetic packages.
But it's not humidity only, there are a lot of materials that exibit gas in some way.
You can get some epoxies that are quite immune to water - depends on how much you want to pay.
Good. Details and setup? Do tell.
Why would you expect zero TC from VPG H/HZ? :) They are specified at 2ppm at best, which your number confirm well with margin. :-+
Why would you expect zero TC from VPG H/HZ? :) They are specified at 2ppm at best, which your number confirm well with margin. :-+
I just measured a 9K9850 VHP202Z at -1.3ppm/K. What a bummer. Now I understand what they mean by "0.2 +/- 2 ppm/C". That means it could be as bad as 2ppm/C.
Any idea how much copper wire can be stable?
Inviato dal mio ONEPLUS A5010 utilizzando Tapatalk
There are published designs of copper wire based temperature sensors with better than 10mK stability, so in absence of strong thermal shocks a better than 50ppm long-term stability should be possible.
Copper is ok also from a EMF point of view as resistors leads are also of copper if I'm not wrong. Or not?Any idea how much copper wire can be stable?
Inviato dal mio ONEPLUS A5010 utilizzando Tapatalk
There are published designs of copper wire based temperature sensors with better than 10mK stability, so in absence of strong thermal shocks a better than 50ppm long-term stability should be possible. In the practical case of this 3.3 Ohm compensation resistor it's potential instability is reduced by 1/3000 times ratio to the main resistor value, so should not be a problem.
Cheers
Alex
Hi all,
we X-rayed some PWW resistors today. Here is what the 8G16D from Rhopoint looks like. You can fairly see the strain-relief construction, but also how they try to decrease inductance, two seperate winding sets with opposite winding direction.
-branadic-
May I ask here, what the cost is for two kx sets of Mr. Edwin G. Pettis resistors to germany incl. tax, customs fees, sending, packing, approximately to germany?Hello,
Sorry, have absolutely no plan for that :-[
Thanks.
Hello,
some results of my brand new VHP101 & VHP202Z, I'm afraid there is only 20% chance you will get an almost zero TC resistor from the batches your order or so. |O
Hello,
some results of my brand new VHP101 & VHP202Z, I'm afraid there is only 20% chance you will get an almost zero TC resistor from the batches your order or so. |O
I just measured a 9K9850 VHP202Z at -1.3ppm/K. What a bummer. Now I understand what they mean by "0.2 +/- 2 ppm/C". That means it could be as bad as 2ppm/C.
What about x-ray of a 12k econistor, in comparison?
@ MisterDiodes
If you have a contact to G.R. please let me know, I wasn't able to find one on the web.
-branadic-
In fact, we do not know the cause of the failures, you latched onto bending as the cause, it was just one of several possibilities I mentioned.
To use such an exceedingly small sample as the basis for a claim of a high failure rate is just plain absurd.
since you're not qualified to do the analysis, you must accept the fact that the cause remains unknown.
Seems like you US guys do have a serious problem with factual criticism. We could have done a factual analysis on how the failure showed on the resistor and what could be done to prevent such failures in future (one of the things we do for many companies almost every day), but instead you act like your US ego was flawed. Reminds me of your current president, time for a tweet. :palm:
-branadic-
Got a statement on those 12k resistors:
"...Since an order was in process to manufacture 18K resistors a quantity was utilized to create 12K resistors from the 18K resistor by stripping one side of the bobbin. This practice has been suspended going forward..."
This explains why the 12k are looking like they do. I was also offered a replacement.
-branadic-
Hello,
first measurement on a PTF56 (Vishay) metal film resistor. (PTF561K0000BZEB)
http://www.vishay.com/docs/31019/ptf.pdf (http://www.vishay.com/docs/31019/ptf.pdf)
Intention was to use them as a better version of my INL adjustment cirquit for my ADCs (currently built with 25ppm/K resistors)
So long term drift is not a issue. But short term drift (T.C.) is annoying with my changes in lab temperature.
Result:
T.C. around 1.3 ppm/K (5 ppm/K according to data sheet) not bad for $1.5 a piece in small quantities.
Hysteresis around +/-2 ppm but most of it seems to be ageing drift in warm cycle.
I will cycle the first resistor for some days to see if the drift stabilizes. (just being curious if they could be used for a LTZ too).
with best regars
Andreas
What happens due to phisical stress to those resistors?
I'm currently looking at the SEI RTAN series of tantalum-nitride resistors. Same thing: after a 400-hour bake at 125C, the tantalum-pentoxide layer is thickened about as much as it ever will be, resulting in a resistor that will be almost as good as a secondary standard. These have TCR down to 10ppm/K, but those a are about 4X the price of the 25ppm/K ones-- so buy a 25ppm one with a value that is twice what you need, and then find two (after the bake cycle) that will cancel each other for an almost zero TCR. Those are very low in cost, but there is a lot of labor in the selection process. The end result should be good enough for an LTZ reference. Bonus: these totally ignore humidity; so no humidity effect on their performance at all. ;)
What happens due to phisical stress to those resistors?
I'm currently looking at the SEI RTAN series of tantalum-nitride resistors. Same thing: after a 400-hour bake at 125C, the tantalum-pentoxide layer is thickened about as much as it ever will be, resulting in a resistor that will be almost as good as a secondary standard. These have TCR down to 10ppm/K, but those a are about 4X the price of the 25ppm/K ones-- so buy a 25ppm one with a value that is twice what you need, and then find two (after the bake cycle) that will cancel each other for an almost zero TCR. Those are very low in cost, but there is a lot of labor in the selection process. The end result should be good enough for an LTZ reference. Bonus: these totally ignore humidity; so no humidity effect on their performance at all. ;)
Is this the paper?
https://www.researchgate.net/publication/234454148_Stability_of_Tantalum_Nitrides_Thin_Film_Resistors (https://www.researchgate.net/publication/234454148_Stability_of_Tantalum_Nitrides_Thin_Film_Resistors)
Typical annoying data sheets that don't mention anything that they do not want to talk about.
What is missing is the voltage coefficient. It can be a big factor in film resistors.
Vishay sell a mil-spec Tantalum Nitride resistors that are 0.5ppm/V. That is still a 5ppm shift at 10V - definitely an issue for metrology. This is where wirewound are superior.
If voltage coefficient is not defined for the RTAN resistors, then there is a good chance it is worse. I did see a Welwyn graph that was showing that for two different types of film they tested, film resistors with gold terminations had a much bigger voltage coefficient then lead-silver connections.
As far as the voltage coefficient goes, thin-film resistors are going to be the same as metal-film, and those are pretty good.I gather thin film resistors have a typical voltage coefficient less then 2ppm/C which is probably good enough to ignore most of the time, but for precision resistors, it would be handy to know whether it is 2ppm/V or 0.5ppm/V like the Vishay resistors.
so the xray really did change the ppm drift? or it is a coincidence?
I will ask dumb questions, this specification is 100% certified
Moar resistor tests.
Edit: all of these resistors are on their way to Andreas. I am very interested to see how his measurements compare!
Hmm, or perhaps not, if a PPM is relative to the ratio itself...
That's the real beauty of the LTZ circuit!
My advice is to don't over-spend on LTZ resistors - because it may not make any difference to your lab equipment and your measuring ability. Remember that even multiple 732's on hand will get you down to a few ppm measuring of absolute value of a Vref, and anything below that is just pure uncertainty - if an -accurate and traceable- absolute Vref value is important to you.
...
By the way -
If you really want to test resistors correctly, here's a nice kit for a fraction of the "new" price. If you haven't seen how a precision resistor oil bath works, here's an example:
https://www.ebay.com/itm/Measurements-International-Automatic-DC-Resistance-Bridge-Complete-System/282828252605? (https://www.ebay.com/itm/Measurements-International-Automatic-DC-Resistance-Bridge-Complete-System/282828252605?)
...
So calling for 50 Ohms source resistance is completely bullshit:
the chip would not work at higher temperatures with such a desing flaw.
with best regards
Andreas
If you really want to test resistors correctly, here's a nice kit for a fraction of the "new" price. If you haven't seen how a precision resistor oil bath works, here's an example:
https://www.ebay.com/itm/Measurements-International-Automatic-DC-Resistance-Bridge-Complete-System/282828252605? (https://www.ebay.com/itm/Measurements-International-Automatic-DC-Resistance-Bridge-Complete-System/282828252605?)
You cannot get the accuracy of a 9975 with a hammon divider, thats why I use the 9975.Why not? Fluke manage 0.2ppm with this method.
Also keep in mind, it is not just the Hammon divider transfer accuracy, it is also the transfer accuracy of the meter used that contributes.The only meter needed to calibrate the Hamon divider is a microvolt null meter. It is not that hard to make a null meter with a 0.1 microvolt accuracy. You can even eliminate thermal voltages by having the divider powered by a voltage that reverses at perhaps 30 Hz. The null meter can be run as an AC meter for the final adjustment.
Mmmm, 0.1 microvolt accuracy is easy? Please, do tell. Perhaps you confuse accuracy and resolution.The accuracy needed is 0uV +/- 0.1 uv and that can be using AC with a bandpass filter if getting 0.1uV with DC is a problem. The resolution is hopefully less then 0.1uV.
Mmmm, 0.1 microvolt accuracy is easy? Please, do tell. Perhaps you confuse accuracy and resolution.The accuracy needed is 0uV +/- 0.1 uv and that can be using AC with a bandpass filter if getting 0.1uV with DC is a problem. The resolution is hopefully less then 0.1uV.
A couple of things on the bias current. The null meter does not need to have a high impedance - 100K is probably fine. 1M is fabulous. Even 10K is usable but the sensitivity will be down. That helps a bit. Secondly you can feed the Hamon divider and 2:1 divider while calibrating with slow AC instead of DC and use capacitor coupling. This reduces the leakage current to the capacitor's current. Third, for this kind of purpose, I would make a small battery powered galvanometer rather then go through the extreme lengths HP has to go to in floating the 3458A inputs. For the AC source, I would probably use something like a centre tapped mains transformer - provided the windings matched well.
This standard divider uses stable 20V (from a 5440B) for excitation of the Wheatstone Bridge, and a Null reading of 0.5µV then is sufficient for about 0.1ppm accuracy of the 10:1 divider, and about 0.2ppm for the 100:1 divider.
Therefore, the Null detector has to have a resolution of about 0.1µV, but it also needs to be quiet (noise free) enough, that's the correct and much more important criterion.
The bias current also needs to be as low as possible, below 1pA.
Both criterions are not at all easy to meet.
You might successfully use a high grade DVM like the 3458A.
Better results are achieved by means of the classic FLUKE 845AB/AR.
If you don't use stable precision resistors for the Hamon divider and the Wheatstone bridge, the whole effort is useless, because otherwise the whole divider drifts too much during calibration mode, already.Yes - you have to have resistors that you have proven stable over the amount of time you are measuring and that have no voltage coefficient - so precision wirewound resistors are perfect. You could possibly slow down thermal effects by putting all the Hamon resistors in an oil bath and then insulating it. You have to check the resistors for drift with maximum applied voltage. The ideal would be to have all the resistors used in the divider to be made with the same wire. If you made the divider with 10 identical resistors, you could actually pick the single low resistor that was closest to the average coefficients of the other 9 resistors. This will minimize drift when a high voltage is applied to the divider.
The transfer of resistance using 10 similar resistors (100:1 transfer), e.g. with the IET labs SR1010 series is less accurate. Besides its transfer accuracy (1ppm + 0.1uOhm) there are two measurements necessary, comparing the standard and the DUT with the SR1010 resistance. As a consequence, sqrt 2 times the transfer accuracy of each of teh two measurements of the ohms meter used adds. So the transfer is 2ppm-ish accurate, at best.The SR1010/MT is built a little differently from the SR1010. It can do a 0.1ppm transfer at 100:1 and 10:1. The temperature coefficient however is 1ppm/C so to get the 0.1ppm transfer, you have to watch the room temperature variation and the time taken for the transfer.
#1 (one dot on the top) 27.02.2018
Box: 1.10 ppm/K (including noise)
LMS: -0.95 ppm/K @ 25 deg C (but very linear T.C.)
Box LMS 0.95 ppm/K (without noise)
#2 (2 dots on the top) 28.02.2018
Box: 1.12 ppm/K
LMS: -0.96 ppm/K @ 25 deg C (linear)
Box LMS: 0.96 ppm/K
#3 (3 dots on the top) 01.03.2018
Box: 0.47 ppm/K
LMS: -0.31 ppm/K @ 25 deg C (curvy)
Box LMS: 0.35 ppm/K
VHP202Z, 120R, #1, #2, and #3
Results: roughly -0.9, -1.0 and -0.4 ppm/C.
If we had a third independant measurement, with a third independant setup, giving the same results, would you still doubt them?If you want, I can do the third run.
And isn't it true to characterise a component, even though it might behave somewhat different within a given circuit? Is the component supplier characterizing the component within your circuit? No, he's characterizing the component as it is and chanes are it might behave different in it's final application, don't you agree?
-branadic-
If we had a third independant measurement, with a third independant setup, giving the same results, would you still doubt them?Even 10 measurements with incorrect data on 10 different setups would not make up for 1 correct measurement :).
Even 10 measurements with incorrect data on 10 different setups would not make up for 1 correct measurement :).
#3 (3 dots) from 01.03.2018
-0.57 ppm/K linear regression coefficient for the ratio
#3 (3 dots) reverse mounted (with the 1K resistor towards VRef and the 12K5 resistor to ground) from 02.03.2018
-0.71 ppm/K linear regression coefficient for the ratio (normalized to 12.5/1)
Does anyone have any information on the ageing drift of typical 1% metal film resistors?
Time to start buying some salts!
I do not think that you want to have that nasty stuff (creeping almost everywhere) near of your precision equipment.
But i cant really see the thermal-lag-effect you mention. ???
Interesting , but inside of an enclosure you won't (or shouldn't) see rapid temperature shifts. Especially if you thermally lag the box with insulation inside.What you can get is effects from different amounts of self heating when a current is going through a resistor. If you have a 1ppm/C resistor, and you put enough current through it to raise it by one degree, you get a 1ppm shift. When you do the same to a -5ppm/C resistor and a 5ppm/C copper compensating wire, you can get up to 5ppm shift with the same current. Even if the resistor and the wire are in thermal contact, there will still be a heat gradient from the resistor to the wire.
| Resistor | Value | Tempco spec | Number | Measured tempco | Datalog chart |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 1 kΩ | +/-5 ppm/°C | 12 | -0.96 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 9 kΩ | +/-5 ppm/°C | 9 | +2.18 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 20 kΩ | +/-5 ppm/°C | 7 | -2.26 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 5 kΩ | +/-5 ppm/°C | 10 | +2.99 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 100 kΩ | +/-5 ppm/°C | 1A | +1.71 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 18 kΩ | +/-5 ppm/°C | 8 | +3.59 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 200 kΩ | +/-5 ppm/°C | 2 | +3.20 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 24 kΩ | +/-5 ppm/°C | 5 | -1.28 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 100 kΩ | +/-5 ppm/°C | 1E | +0.74 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 22 kΩ | +/-5 ppm/°C | 6 | +3.80 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 100 kΩ | +/-5 ppm/°C | 1D | +2.75 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 500 kΩ | +/-5 ppm/°C | 3 | -2.03 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 25 kΩ | +/-5 ppm/°C | 4B | -1.06 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 100 kΩ | +/-5 ppm/°C | 1B | +3.69 ppm/K | |
| Caddock TF020R (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeTF.pdf) | 25 kΩ | +/-5 ppm/°C | 4A | -0.58 ppm/K |
(with one combined to check idea of action in two opposite TCR resistors in series).
1A + 1C = 0.02 ppm/C
9 + 4B = 0.03 ppm/C
10 + 4B = -0.12 ppm/C
10 + 4A = 0.17 ppm/C
1E + 7 = 0.24 ppm/C
9 + 4A = 0.28 ppm/C
9 + 5 = -0.34 ppm/C
1E + 5 = 0.35 ppm/C
2 + 3 = -0.39 ppm/C
11A + 4A = -0.42 ppm/C
12 + 4A = -0.42 ppm/C
11B + 4A = -0.43 ppm/C
1E + 4B = 0.44 ppm/C
1E + 1C = -0.47 ppm/C
8 + 7 = 0.51 ppm/C
9 + 7 = -0.88 ppm/C
9 + 12 + 4B = 0.00 ppm/C
2 + 1D + 3 = 0.01 ppm/C
9 + 11B + 4B = 0.01 ppm/C
1E + 5 + 7 = -0.01 ppm/C
8 + 4B + 7 = 0.01 ppm/C
1A + 12 + 1C = 0.02 ppm/C
1A + 11B + 1C = 0.02 ppm/C
1A + 11A + 1C = 0.02 ppm/C
9 + 11A + 4B = 0.02 ppm/C
1A + 4A + 1C = -0.03 ppm/C
6 + 1E + 1C = -0.04 ppm/C
1A + 4B + 1C = -0.06 ppm/C
1E + 4B + 7 = 0.07 ppm/C
1A + 10 + 1C = 0.09 ppm/C
9 + 10 + 5 = 0.10 ppm/C
1A + 9 + 1C = 0.11 ppm/C
6 + 5 + 7 = 0.12 ppm/C
1A + 5 + 1C = -0.12 ppm/C
2 + 1A + 3 = -0.12 ppm/C
10 + 12 + 4A = 0.13 ppm/C
1E + 4A + 7 = 0.13 ppm/C
1E + 8 + 1C = -0.13 ppm/C
6 + 8 + 1C = -0.13 ppm/C
10 + 11A + 4B = -0.13 ppm/C
10 + 11B + 4B = -0.14 ppm/C
10 + 11B + 4A = 0.14 ppm/C
10 + 12 + 4B = -0.15 ppm/C
10 + 11A + 4A = 0.15 ppm/C
8 + 4A + 7 = 0.15 ppm/C
9 + 4A + 4B = -0.15 ppm/C
1E + 4B + 5 = 0.17 ppm/C
2 + 1B + 3 = 0.17 ppm/C
8 + 5 + 7 = -0.18 ppm/C
1A + 7 + 1C = -0.19 ppm/C
| Resistor | Value | Tempco spec | Number | Measured tempco |
| Caddock TF020R 4B + 9 + 12 | 35 kΩ | 3S | Calculated by cell : 0.00 ppm/K | -0.19 ppm/K (https://xdevs.com/fres_caddock_t6/) |
| Caddock TF020R 4A + 10 | 30 kΩ | 2S | Calculated by cell : 0.17 ppm/K | -0.17...+0.30 ppm/K (https://xdevs.com/fres_caddock_t6/) |
| Caddock TF020R 1A + 1C | 200 kΩ | 2S | Calculated by cell : 0.02 ppm/K | -0.24 ppm/K (https://xdevs.com/fres_caddock_t7/) |
| Keithley 2001 R354 | 100 MΩ | +8 ppm/K ? (https://xdevs.com/fres_caddock_t7/) | ||
| Keithley 2001 R366 PTF65 T16 | 1 MΩ | -2.87 ppm/K (https://xdevs.com/fres_caddock_t7/) | ||
| Keithley 2001 R365 PRC HR175N 0.1% | 78.7 kΩ | +2.70 ppm/K (https://xdevs.com/fres_caddock_t7/) | ||
| Keithley 2001 R358 PRC HR125N | 7.15 kΩ | +3.07 ppm/K (https://xdevs.com/fres_caddock_t8/) | ||
| Caddock 1737 network element | 89.982 Ω | -1.70 ppm/K (https://xdevs.com/fres_caddock_t8/) | ||
| Edwin PWW 70K | 70.006 kΩ | +1.80 ppm/K (https://xdevs.com/fres_caddock_t8/) |
VHP202Z, 70k, #1, #2, #3
Results: about -0.55ppm/C, -0.6ppm/C, and -0.45ppm/C.
Here I extended each run to multiple ramps, eventually settling on three ramps up and down, at 5min/C, with 30min plateaus at the top and bottom of each run.
Additionally, I added a "Savitsky-Golay" smoothing filter (raw data in light blue, filtered value in dark blue). Thanks to Conrad Hoffman for mentioning this filter! https://www.eevblog.com/forum/metrology/data-smoothing-excel/ (https://www.eevblog.com/forum/metrology/data-smoothing-excel/)
No, not groups of four--but how about parallel combinations?
(I would have expected a result which was some kind of average of the two)
Why that: we have small changes on the 2 resistors so in first order we actually get the difference in T.C. for the divider.
Any resistor operating at true 'shelf life" conditions as defined by Vishay would really have to be at -zero- power, and I can't think of a good use case for that.
Why is it suddenly zero power , when used as working standard at home? Private households don't apply magic, and resistor still powered by DMM current source, even used alone...
VPG in their data sheets (some VHP) defines shelf life identical with less than 10mW load. Aging is driven by environmental effects and by power applied. They consider 10mW low enough to make no difference to shelf storage.
Mister Diodes, could you please elaborate on how you burn-in the assembled boards you mentioned? I've tried looking up Post Manufacturing Operations but I'm coming up dry.
Every mW power dissipation is going to affect 1000hr drift by up to 0.5ppm and affect temp by about 0.1C
Did Vishay suggest that the additional drift is (mostly) a result of the 0.1C temperature elevation alone or due to some ageing mechanism triggered by the current flow, independant of temperature? What might that be - electromigration? That would, with my very limited knowledge in this area, be surprising given the much lower current density (j) compared to thin film resistors (approx 100x thicker). My understanding is that you'd expect electromigration rates around j^2 or 10,000x higher for thin film (but that also significantly depends on the composition of the resistive element) and I don't believe that thin film resistors are anywhere near that bad.
There's no way that 0.1C alone could cause that much drift given that Lymex and Dr Frank have seen long term drifts better than the datasheet (typical?) of < 2ppm/6 years and there's no way they could have maintained the temperature to << 0.1C over long periods! (Of course you did say 'up to 0.5ppm' which may apply to resistance values significantly different to their's).
The datasheet power derating graph from 70C to 125C implies .37C/mW which is significantly different to the above. Is the 0.1C the temperature rise of the BMF element itself or the metal can and thus measurable without dismantling the part?QuoteOh - and that VC they say is essentially zero on the standard datasheets? In reality you find out that's more like a 3ppm/V on some of their VHP and Z-Foil ratio resistors on values over 1k.
Shock! Surely you're not suggesting that Vishay's datasheet (< 0.1ppm/V) is anything but 'Legal, decent, honest and truthful' (the UK Advertising Standards Authority's mission statement)? I expect the 'values over 1K' exception is clearly detailed in the microdot at the end of the disclaimer section. ::)
Shock! Surely you're not suggesting that Vishay's datasheet (< 0.1ppm/V) is anything but 'Legal, decent, honest and truthful' (the UK Advertising Standards Authority's mission statement)? I expect the 'values over 1K' exception is clearly detailed in the microdot at the end of the disclaimer section. ::)
Because this is a critical application, all calculations and manufacturer expected drift rates, expected MTBF, etc. must be included for review as part of "deliverables acceptance inspection" by customer.
Yeahhhh, well, not really :-DD These customers have a lot at stake and that means they make sure everyone they buy from has to show it's done right...and that means a paper trail for every part, every procedure.
Oh - and that VC they say is essentially zero on the standard datasheets? In reality you find out that's more like a 3ppm/V on some of their VHP and Z-Foil ratio resistors on values over 1k. Head's up if you're using these on an application where the resistor sees variable bias - say for the input of an ADC front end or similar. That's why went back to a sealed PWW resistor for that location - for virtually no VC effect!.
That's always the big question - because changing the bias point can give you a VC change, but that also causes a temp change...which could make the end result better or worse, depending on actual TCR at that operating point and at your thermal flow.That definition of the VC is odd: in the formula it kind of assumes the resistance would linearly change with voltage. However then they use the delay for getting a self heating effect and this would cause an effect proportional to V² instead. No wonder they get odd numbers.
But there is one defined measurement method way which actually has an interesting hidden use on Vishay datasheets.
Vishay measures VC using the old MIL-STD-202-309.
In a very condensed nutshell:
The VC is computed as VC = (R-r)100 / 0.9Er.
R= Resistance at continuous working voltage, r=resistance at 0.1 * Rated Working Voltage and E = Rated Continuous working voltage.
You apply 0.1 Rated working voltage and let resistor come to equilibrium in your circuit and grab a measure on "r"...then apply your continuous rated working voltage for no more than 1/2 second in any 5 second interval...Grab your "R" measure as quick as possible during that max 1/2 second pulse...as close to the beginning of the pulse as possible, before the majority of heating comes in.
Run the numbers and that's how Vishay measures VC.
The interesting part is that Vishay claims that there is no VC below 1k resistance value on their foils (which is not exactly true). The reason they can get away with that is because MIL-STD-202-309 was only defined for resistors of value 1k and over... :)
Take that for what it's worth. Vishay BMF parts are not necessarily bad, in fact they can be very good. The problem is you always have to lift the veil on their datasheets.
CAme across this: http://www.conservationphysics.org/satslt/satsalt.php (http://www.conservationphysics.org/satslt/satsalt.php)
Time to start buying some salts!
Sensor #1 (NaCl): 82.9% humidity
Sensor #2 (MgCl2): 48.4% humidity
Sensor #2 (NaCl): 80.0% humidity
Sensor #1 (MgCl2): 51.1% humidity
Hello,
again some PTF56 resistors 10K0 (5ppm/K in data sheet) =
PTF5610K000BZEB / PTF10KDCT-ND from DigiKey.
All values again like the 25K2 measured below 2 ppm/K as box T.C.
and there is virtually no hysteresis visible.
Pictures of some examples covering the whole range of T.C. + the overview sheet
With best regards
Andreas
Would you please post a CSV file of the PTF56 data?see above below the overview pictures
Would you please post a CSV file of the PTF56 data?see above below the overview pictures
I want to find the form of the polynomial.
What you have provided in the overview and the CSV file version is an approximation based on an assumption that the T.C. is a straight line.
Once I have the correct polynomial form I can generate a random set of resistors and determine how many measurements are needed to calculate the change in the voltage of a divider over a specified temperature range. This is an afternoon's work if I have your actual measurements.you are loosing yourself in a dream world in generating artificial data.
Edit: I digitized a few points from 10k#8.
Hello,
sorry your wording is difficult to understand at least for me as a non native speaker.
I never could imagine that you really want me to take my precious hobby time to grab out all the data.
Up to now you cry for data without telling what you really want to do.
Now with the pictures I get the image that you want to solve a problem that is long solved on my side
every time I draw a LMS curve it is actually a 3rd order polynom.
2nd order does not fit in all cases and 5th order usually does not improve the result.
What you have provided in the overview and the CSV file version is an approximation based on an assumption that the T.C. is a straight line.
No, the 25 deg C value is actually the linear (1 st order) coefficient of the 3rd order polynominal.
Interestingly the 2nd order coefficient is around 0.032 +/- 10..15% on this batch of the PTF56 resistors.
So the 25 deg C value is a good measure for the fitting.
Once I have the correct polynomial form I can generate a random set of resistors and determine how many measurements are needed to calculate the change in the voltage of a divider over a specified temperature range. This is an afternoon's work if I have your actual measurements.you are loosing yourself in a dream world in generating artificial data.
Reality will differ: in the PPM range you have to treat every resistor as a individual.
Edit: I digitized a few points from 10k#8.
attached the normalized result of 1 minute averages of deviation from 25 deg C value (in ppm) over temperature difference to 25 deg C in (deg C)
(ignore the first 3 lines they are only the instruction for my solver).
good luck
Andreas
...
For a resistor constructed from a ceramic tube and metal end cap soldered to the tube, the hysteresis should exhibit a threshold effect. Small temperature changes will deform the tube, solder and cap within the elastic range. So if the original temperature is restored, the resistance will return to the original value. Once the stress reaches the elastic limit of the solder, plastic deformation of the solder will take place.
...
...
For the PTF56: I am not shure if he has really end caps as I am missing the "bubbles" on each side.
...
Andreas
The fact you are seeing almost no hysteresis has me intrigued.
Hello branadic,
my kitchen boss sent me a big dislike. :--
But I am shure we will find a solution.
Snail mail sent.
what if you redo the measurement cycle by putting the resistor in a tiny tub of mineral oil (or melt it into wax?)? will that exclude humidity?
what if you redo the measurement cycle by putting the resistor in a tiny tub of mineral oil (or melt it into wax?)? will that exclude humidity?
Hello,
I am pretty shure that (pure white) mineral oil will help against humidity.
With wax (which one) I am not shure if it will be really tight.
But I fear I will not do this experiment as I am looking for resistors that I can use afterwards in a LTZ cirquit.
And even the thermal grease to remove after the first measurements was a mess that I do not want to repeat.
with best regards
Andreas
according to my compulsive FEMM simulation disorder
Thanks for the simulation, very interesting ! :-+
In order to exploit your disorder, I have some questions:
- Can you explain in detail what your picture shows?
- What are the blocks on the right side?
- Which are the leads with associated leakage (I see branches on both the left and right sides, or is this an axial resistor)?
- What are the materials you assumed for the sleeves, encapsulation, leads and resistor body?
- What thermal sources/loads did you assume?
Unfortunately my reference resistor is not stable enough for long term tests with only a few ppm drift over a year.
This soviet made P331 is of the .01% class (don't know over which temperature range that applies) and well aged.0.01% at 20 degrees. Works in oil or other silicone fluid.
guenthert,I know next to nothing about materials. All I can say is that it has the colour of steel (more or less -- the white balance in the picture above is off) and isn't (strongly) ferromagnetic.
Is it possible to determine the type of metal used in the binding posts? I have wondered about those resistors and what was used to make them. Are the posts silver plated or possibly ferrous?
Thanks a bunch. Wished I'd be able to read Russian though.Ask what is interesting I will translate :) I think it will be easier for me to type in Russian and translate into Google.
Apparently the foil material has positive TC and the ceramic substrate shrinks with rising temperature, compressing the resistive element. They don't tell numbers though.
Can the experts tell whether those Z-foil voltage divider parts are made with one substrate or with two substrates?I'm no expert but AFAIK these are separate resistors.
Hello,
I am missing the thermometer for the "measurement thread"
with best regards
Andreas
Here is a measurement of a hermetically sealed 10k ± 0.01% AE resistor (https://de.farnell.com/alpha-electronics/hcz10k000t/widerstand-10k-0-01-300mw-radial/dp/2611649) spec'ed with ±1ppm/°C, linear t.c. is 1.4275ppm/K,
Here is HCZ1k0000T, with some weird behavior from 10 to 25°C. a=-0.01306 b=1.02755 c=-0.19573I had the same behavior in some of my measurements ... I also think (as Andreas) this is hysteresis. Some resistor like vishay ermetic doesn't show it. Try to increase temperature more slowly and it should not appear ...
-branadic-
Andreas: The measurements below 25 °C happened after coming back from 60 °C.Well I had this 1ppm effect after a jump of 20° and almost zero when doing 5° steps. This was a vhp101.
mimmus78: HCZ1k0000T is a Vishay hermetic resistor.
Regards, Dieter
Size of the hysteresis is dependant on min/max excursion of the temperature and also the temperature gradient.
But how can we arrive at a predictive model from such measurements? Even if you measure "all" ambient conditions like temperature, humidity, air pressure you may have delayed contributions (typical with heat conduction), integrators, differentiators and nonlinear effects and so on. Did you ever try to fit a model that (roughly) predicts the behaviour of such resistors? I think in order to do that one should define certain key tests to isolate parameters like the TC curve, one by one.
For tools that got magnetized we have a demagnetizer in our lab, which works by imposing magnetic field cycles of decreasing size. Maybe one should try that to force the resistor into a state where it no longer drifts. I think this is the idea behind that Pickering patent.
additional NIST article which is lost in their own server, but printed this page using google cache.
NIST pubid 9237 page 11
"wirewounds have no voltage coefficient"
Is the ultimate solution to have precision components in a vacuum...
1) a TEC based "resistance standard"
1) a TEC based "resistance standard"
Would the 2PPM over 6 years that Vishay quote for some of their resistors mean that their standard processing for them is effectively a specific one for optimizing the drift for zero load and room temperature?
Would the 2PPM over 6 years that Vishay quote for some of their resistors mean that their standard processing for them is effectively a specific one for optimizing the drift for zero load and room temperature?
I found that paralleling resistor on channel 3 and 8 can give a decent reference. Any suggestions on that?
However, noone knows how things change after soldering them to a board, I agree with you.
-branadic-
For higher temperature PT1000 may not be that good anymore, as isolation gets increasingly difficult.Leakage of current inside the Pt1000 element? How?
even if just brieflyHahaha, sadly it wouldnt help if I cant keep it in that state for at least an hour to get a good reference :P
MAX1978 looks like a nice IC, a little on the expensive side perhaps...
Can it be amplified externally if you need more than 3 amps, I wonder...
Can you explain a little how your comment relates to "T.C. measurements on precision resistors"?
I currently measure on NOMCA1603 networks. I ran into some issue before, as I use a zero force socket. Obviously the socket was not able to reliable break through the oxide on the leads, which resulted in strange t.c. curves. So with a bit of flux and an almost clean solder tip I had to break the oxide, now I get more reasonable results. Here is a first view on a first samle. The t.c. seems to be almost linear.
Edit: Calculated some first values
R1: 4.333ppm/K
R2: 5.452ppm/K
R3: 4.983ppm/K
R4: 4.667ppm/K
R5: 6.072ppm/K
R6: 5.409ppm/K
R7: 5.986ppm/K
R8: 4.823ppm/K
-branadic-
Hi everyone,
By accident I came across this wonderful article Temperature coefficient compensation of standard resistance (Beta coefficient compensation) (http://bbs.38hot.net/thread-167995-1-1.html) by lymex on bbs.38hot.net and thought I give it a play to compensate the t.c. of the formentioned resistor by using a proper sized NTC with serial resistance, some copper wire plus adjustment resistor.
-branadic-
Does the epoxy NTC turns the circuit to humidity sensor with unpredictable behavior.
Beta was compensated with a parallel circuit of 5 meg resistor in series with a glass encapsulated NTC
How ceramics pouder or balls react to moisture? How long will take to go the moisture away?
This time could be reduced by improving the thermal transfer inside the case. I was thinking about filling the case with ceramic balls (3-4 mm in diameter) or ceramic pouder, thermally conductive but electrically insulating.
Hello,
it would be interesting to see also the rising temperature.
This would show wether the resistor has some hysteresis (or if the temperature sensors have not the right temperature = position or a time lag).
with best regards
Andreas
Mhm,
if you now put the temperature on the X-Axis and the ppm on the y-Axis there should be a large difference at the temperature extremes.
32 degrees -5 vs -10 ppm
21 degrees -17 vs -8 ppm
if I see it right.
The 26 degrees remain stable at +10 ppm
with best regards
Andreas