T.C. measurements on precision resistors

[dietert1]

The difference of the measurements appears to be a linear TC in branadics measurements, while you seem to have only the curvature without any significant linear term. I mean your measurements show small positive deviations in the middle and small negative deviations at the extreme temperatures. Could there be thermal EMF in branadics measurement? Did you also use Kelvin clamps? Can anybody tell which material the wires of those resistors are?

Regards, Dieter

[branadic]

No thermal EMF issues, it's the behavior of the resistor. Still measurements on 1k resistor are running, but it shows a more curvature shape with its zero point close to ~35°C. Will post results once the measurement finished.

-branadic-

[branadic]

Here is HCZ1k0000T, with some weird behavior from 10 to 25°C. a=-0.01306  b=1.02755 c=-0.19573

-branadic-

[Andreas]

Hello Branadic,

For me it looks like you had a ageing drift/hysteresis during the run-up phase.
This seems to be gone after reaching 60 deg C.
So I guess when you repeat the measurement the hysteresis will be much lower.

with best regards

Andreas

[dietert1]

Probably the time scale of the upper plots is seconds, so there seems to be some kind of overshoot/relaxation with a time scale of 100 to 200 seconds. This would be typical for thermal EMF when using point contacts that conduct well, but no heat.
Since i am close: With rainy weather you might want to use desiccant when cooling down to avoid humidity. In my office the dew point limit would be 14 + 3 = 17 °C.

Regards, Dieter

[mimmus78]

Here is HCZ1k0000T, with some weird behavior from 10 to 25°C. a=-0.01306  b=1.02755 c=-0.19573

-branadic-

I 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 ...

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[dietert1]

Andreas: The measurements below 25 °C happened after coming back from 60 °C.
mimmus78: HCZ1k0000T is a Vishay hermetic resistor.

Regards, Dieter

[mimmus78]

Andreas: The measurements below 25 °C happened after coming back from 60 °C.
mimmus78: HCZ1k0000T is a Vishay hermetic resistor.

Regards, Dieter

Well I had this 1ppm effect after a jump of 20° and almost zero when doing 5° steps. This was a vhp101.

When using "not sealed" resistor the effect was much bigger. If you search in past post on this topic you can find I already showed this effect and we all discussed about this ... I have to search if I made other measurements on the sealed ones.

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[branadic]

In my measurements each value has a distance of about 4s (NPLC 100), so the temperature profiles I'm driving are quite slow. However, I'm currently repeating a measurement on this particular device and reduced maximum temperature to 60°C.

-branadic-

[branadic]

Repeated the measurement in the range of 10...60°C without touching the setup. It looks different know, though I will play with slower and continuous temperature slope next. I also received 1k and 20k HCZ resistors today.

-branadic-

[MegaVolt]

This behavior may result from very good thermal insulation of the resistor from the housing. When the temperature of the resistor itself lags far behind the temperature of the case.

About the same as the charge and discharge of an RC chain begins and ends at one point. But it goes in two different ways.

[branadic]

Repeated the measurement with the slowest temperature slope possible on the TEC controller, which is 0.1K/min. Gives a slightly different picture and hysteresis. I indeed could increase the time for the plateau, however the resistance seem to follow the temperature change without lag, as can be seen in upper subplot.

-branadic-

[TiN]

Now we talking. I would also coverge temperature sweep to the same start and end value, so you can estimate hysteresis and induced shift in resistor this way.
Many PWW resistors (from all manufacturers) exhibit a shift after temperature cycle, which can take hours-days to recover.

Also one thing that confusing on your graph - lack of X axis units on top plot  . I discourage using sample counts, as it does not give any indication of test time duration.

[dietert1]

Resistance measurements like this are difficult when it comes to the last ppm. I mean whatever you do, you are measuring against the temperature stability of another resistor. I would really check very carefully what are the ambient temperature variations and what are the specs of my resistance meter. If the resistance meter has 1 ppm/K and the ambient temperature variation is 1 °C during that scan of several hours, the last ppm is lost. A heuristic check would be repeating cycles to see whether the measurement and its conclusions about hysteresis etc. are reproducible.
By the way, today i got an Alpha Electronics HCZ500R00T. From the first measurements the resistance curve looks similar, i mean a parabola with a maximum at about 28 °C.

Regards, Dieter

PS: Since we don't have anything better than a HP 3456A, i wired a bridge using four resistors in a SR1010 12 x 1K standard resistance box. So i have 3.3 V on the DUT and a resolution of 0,1 uV. But i have seen 2 ppm drifts from a mere 0.3 °C ambient temperature change. Need to mount a temperature sensor into the SR1010.

[branadic]

I already repeated the measurement and values are similar also in the second run.

First run: a=-8.345312561203197e-03   b=6.205501661826067e-01  c=-8.774558142298194e+00
Second run: a=-9.258042270128818e-03  b= 6.813891181729642e-01  c=-10.81120835213617e+00

I also implemented ambient sensor readout in the snake script, but didn't plot the values for it.

-branadic-

[dietert1]

While my measurements aren't yet complete, they show a similar "hysteresis" effect with rising temperature, of about -3 ppm size. The size seems to depend on the scan speed. With decreasing temperature i also got a nice parabola.
Don't know whether these resistors are of any value, with unexpected deviations/drifts of 3 ppm. Also i am wondering what may be the physics behind the "hysteresis" effect. Maybe a 2-phase system inside, similar to a heat pipe?

Regards, Dieter

[Andreas]

Hello,

with hermetically metal foil resistors I can only think of the bond between ceramics and the metal foil as reason for the hysteresis.
Usually this is some kind of epoxy and most probably threre is some creeping effect.
Normally the hysteresis is removed over night.
Size of the hysteresis is dependant on min/max excursion of the temperature and also the temperature gradient.

with best regards

Andreas

[bsw_m]

Designer of AJAX metal foil resistors confirms the presence of this effect.
To reduce this effect in their resistors, it sinteres(weld) the foil with the substrate. And does not use glue.

with best regards

Alexey

[branadic]

Andreas, what you mean by "removed over night"? You mean it recovers?

-branadic-

[Andreas]

Hello,

yes usually it recovers. At least on repeated measurements.

This may not be valid for large temperature excursions or for the "first time".
I usually am doing only around +/-15 deg around 25 deg C.

with best regards

Andreas

[dietert1]

Yes, i also saw a + 4 ppm drift while keeping the resistor at 37 °C after the last scan. But i don't trust that completely, because during the night our lab has a certain ambient temperature profile, which may be part of the story.
The plot shows the end of the scan (steep part of red curve at 0,2°C/minute) and then an almost constant oven temperature during the night. At about 6:00 movement starts in lab, with clearly visible ambient temperature crosstalk. Will repeat measurement with temperature monitoring of the reference resistor box in the SR1010.
Anyway, the ambient temperature decay after 0:00 is smooth many hours, while the resistor drift/relaxation has a time constant of about 45 to 50 minutes.

Regards, Dieter

PS: Since TC of the resistor under test is negative at 37 °C, the + 4 ppm drift is NOT caused by delayed heating. During the scan i have seen the resistor follow faster than the temperature sensor in the oven.

[FriedLogic]

This plot is from the start of my current test of the Alpha HCZ 1K and 10K resistors, and there is quite a noticeable fall in the resistance of both. (The 2 wire wound resistors in that test had much greater falls and a greater TC, and the 2 VHP100's VHP101's from hifi-szjxic fell very little, but had a higher TC - I don't know how typical all that is)

The oven for the reference VH201Z VH102ZT 10K had been on for the winter, but off for the summer. It had been on for a few days at the start of this test, but the resistance is clearly still falling a little - although part of that fall is likely due to the room temperature falling and affecting the meter. Over the next 2 weeks it fell another 4PPM or so.

Size of the hysteresis is dependant on min/max excursion of the temperature and also the temperature gradient.

I suspect that most of what gets termed as hysteresis is just the stressing and relaxing that happens with changes in temperature, humidity, etc. Continually cycling the temperature is one test, but running them at certain temperatures for longer times might give a better idea of how the stressing and relaxing proceeds, and make an interesting comparison for step or ramp cycles, load tests, etc.

[dietert1]

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.

Is anything known about a constructive difference between VHP and HCZ resistors? Are they using a different glue to fix the foil?

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.

Regards, Dieter

[FriedLogic]

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.

(Slightly late reply...)
   I wasn't thinking of that sort of simulation at all. It's just that in the limited tests that I've done, the effect of simply running at a particular temperature for an extended period can be a lot more important than the TC. At least separating out temperature and humidity would be useful for some resistors.
   It's worse for new components. Page 9 of the design guide at:
http://www.texascomponents.com/pdf/TXCCBMFDesignGuide.pdf
gives some example plots. The 500+ hour settling times are not too dissimilar to some other components like LS8 versions of an LT1027 and LCT6655. The reference VH102ZT in the oven at about 45°C took around a month to get to the point where I don't see it drifting down in resistance, even although the oven was powered for months over winter, and the room was mostly 24°C+ during the summer. The plots in the design guide don't show convergence, which seems to fit with both the PMO info that I've seen mentioned and another extended settling time if the temperature increases again, but I've not checked the extent to which that happens.
   I could probably reduce the temperature a bit to be more realistic, and I really need to test low temperatures too. Running extended tests at different temperatures would help to show how much the cold-to-hot changes reverse after the temperature is reduced again for these resistors, and what temperature changes are needed for lasting effects.

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.

   For an LTZ1000, that's a particular solution for a particular hysteresis problem. I would expect that there are some hysteresis issues with resistors which are roughly similar and do respond to temperature cycling, but there are a lot of other things going on too.
   Even in the LTZ1000 case it's just an attempt to get rid of an issue caused by a temperature change, not some way to improve the performance.
   I noticed that Dr. Frank mentioned using temperature cycling for foil resistors that had been given large temperature changes, which does look a generally similar case, but I didn't see any details.

   As far as I understand it, the 'Post Manufacturing Operations' on resistors are designed to replicate extended use in particular conditions, but they're more complex. There are various comments on that for different resistor types earlier in this thread, and page 15 of the design guide above also has some info. I'd like to get some more info on PMOs, but I've not seen many details.

[3roomlab]

found 2 interesting pdf

1) a TEC based "resistance standard"
1ohm–10 kohm high Precision transportable Setup to calibrate Multifunction Electrical instruments
P.P. Capra and F. Galliana
nevermind where you are going, it carry its own active "environment"

2) Analysis of the voltage coefficient of high value standard resistors
G. Boella, F. Galliana

according to the article, the measurement of the humidity change took them some 1 year. applying different voltage at different humidity levels presents a different VC. it looks like unless you have a guildline, best to keep those Gohm thingies inside a "dessicated box" and monitor the humidity ... must be some plastics/epoxy

motto : kill the ambient TC and murder the humidity

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"

the voltage coefficient have some further interesting readings thru the KATRIN experiment (measuring a neutrinio mass). the many nos of pdfs are few hundred pages. but tracing thru the pages and links we find that somewhere along the manufacturing of the precision voltage divider for high kV sense, wirewound resistors are dropped because they are "no longer manufactured" (looks more like all precision resistor factories are acquired by vishay ops!), and are replaced by special order 600v VHA518-11 pre-aged. (master_patrik_herud page 20.pdf)