EEVblog #835 - Wekomm Resistance Standard Part 2

Part 2 of an impromptu play with Dave's Wekomm 10K Transfer Resistance Standard.
Was the Keithley DMM7510 multimeter the culprit in the discrepancy in the thermal response?
Dave finds out with the help of a thermal chamber.

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[NickMoore]

Never before have I been so interested in the measurement of a 10k resistor.

[redsquirrelftw]

We need to get audiophiles in on this concept, perhaps there is a market for oven controlled audio cables, so the entire length of the cable is kept at a stable temperature, to keep a steady resistance.

[AmRadPodcast]

I enjoy the videos on things we take for granted, like resistors or taking seemingly simple measurements. There's always more to uncover. Nice one Dave.

[andytroo]

the undershoot could be because of a pool of un-mixed warm air somewhere in the room, so the first thing the aircon does is to mix the air in the room resulting in a (small; that's a few tenths of a degree) temperature rise.

[bfx]

Dave thx for nice video. It's also example why is 7.5 DMM  little overkill for hobbyist's :)
One suggestion try to short DMM to "0 ohm" and measure during few days.

[CoolMusicToMyEars]

Your Noise might come from the Fluorescent Lights, But I be honest Dave, if you use far better cables, use guard if Keithley has it to the Resistor case, isolate from anything that the case might touch,
Use Raychem PTFE Insulated Silver Plated Copper Twisted Pair, Silver plated Copper Screen, outer Tufnel Coating, use one for sense & one for Input, spades Gold plated copper Spades, crimped on each end of lead,
You might need an EMC Sniffer Probe to look at the area for noise pickup, use mass in the thermal chamber for better stability, Don't forget you have plated test connectors nickel which is not that good for good mesurements,
I would love to see a Solartron 7081 DMM thats really great for its age :) or a Datron 1081 if you use better cables far better results,

[questionmark]

Thank you, Dave, for letting us participate in this truly fascinating two part test. Super interesting and please keep doing this sort of videos!
Cheers
Mark

[patsullivan]

If the A/C uses duct work, the air in the duct might be getting hot when the A/C is off, so when you kick it on that warm air is blown out. And the air near the ceiling is warmer than near the floor, so circulating air in the room might increase the temp at your meter slightly, when the A/C is first kicked on.

[Captain__Obvious]

Don't call it quits, build that neutrino detector!

[PeterWalkerHPc]

You obviously need to invest in some audiophool unobtanium plated leads, connectors, enclosures and whatnot.

[esnam]

The last two videos are really neat and intersting. Thank you very much Dave.

[ChipGuy]

Can't remember this chamber in action since you moved out of your garage. Finally it gets used for something awesome!

[bytefree]

15:00 what about the heat put in the lab by the "thermal chamber". Not a big ammount but is near to the DMM and little things ... just add up. The DMM is faster picking up temperature-related variations than the resistor. You also mention the undershoot of the reference (or something) when the aircon kicked on, so, any chance that this cycling is happening inside the DMM ?. I would submit the resistor to the PTB ...

[GadgetReviewVideos]

Down the rabbit whole, lol. I agree some of the cycling is the thermal chamber but I also wonder if you were to measure the rpm of the fan in the keithley if the fan RPMs change slightly according to the internal temp monitor on the meter? As your aircon changes the ambient air if the speed of the fan changes inside the meter to compensate?

Also, did "Santa" bring a new tripod so no more sudden dips on the camera?

[Zadster]

I would be tempted to measure the temperature of the inside of the oven, to rule out (or otherwise) that AC noise. Maybe log it versus the temperature of the Keithley instrument too.

[wgm-engx]

Thanks for putting in the time Dave. This is very interesting. I always wondered about calibration sources and what is used to calibrate those sources and what calibrate those sources and so on.

[bigmacmike]

merry chrismas dave thanks for a very interestering year of videos mate

[JerryWalker]

Totally agree with reburneI see this a lot and it is generally caused by the mismatched materials in the leads / instrument terminals. This can contribute large affects at these measurement levels.The sudden dips when switching on the air con may just be the leads changing temp quickly compared to the meter terminals.

[bernik]

What you are seeing there are likely thermocuple effects of the connections. The resistor might not be able to change in temperature so fast but the banana terminal certainly can. Try breathing on banana jacks and you will see it. My Keithley 2002 can certainly see it.

[Phil_L_]

At this level of precision, does humidity start to have any effect at all? Presumably the AC will be drying the air out in the lab as well as cooling it down.