Electronics > Metrology
ACV stuff for HP3456A calibration
tatel:
Looking to calibrate or at least check ACV ranges on a 3456A.
Yeah, I know the manual says to use a F5200+F5205. Well, none of these are even in sight. Moreover, Ohms and DCV have priority to me. And the series of 19 videos about the F5200 from defpom is scary. So I thought it wouldn't happen anytime soon. But...
...I happened to stumble upon a Gertsch RT-7 ratio transformer on ebay and won the bid.
So far I tested it from mains using a variac. It works as expected. Now looking for a more stable AC source. Since Gertsch docs say V=0.35*freq, 350 V max, I guess some variable voltage, variable frequency AC source would come handy. If I'm getting it right, Gertsch RT-7 best accuracy is at 400 Hz, and I guess it would do 1 kHz with no problem. I don't know what would be the max frequency this Gertsch could deliver while maintaining accuracy.
3456A manual asks for up to 250 kHz. I would be more than happy with about 300Vrms at 1 kHz. More frequency would be better of course, but I could easily live without it. I would like to have lower frequencies available however.
So far I have seen some different ways. I would rather follow the one that would allow me to came as close as possible to adjust the ACV ranges. I guess it would also be the most expensive one and that it will require external calibration. In that case I just will allow plenty of time for the project, but would aim to complete it anyway.
Being an ignoramus, I would like to hear some general opinions/ideas about all the approaches I have found. Perhaps it would be wise to go the cheap way while learning and hope some F5200 will come into reach sometime in the future.
First, a couple threads from enut11 and the links he provided, about signal generator+ audio amplifier + reversed mains transformer (I have a Rigol DG800):
https://www.eevblog.com/forum/metrology/an-experimental-ac-voltage-calibrator/msg3840836/#msg3840836
https://www.eevblog.com/forum/projects/diy-variable-ac-voltage-and-frequency-source-for-calibration/msg5552145/#msg5552145
Second, almost the same thing seems to be available from Feelelec. It's said it can work with other AWGs, not just FeelTech:
https://aliexpress.com/item/1005004153177445.html
Third, the DIY ultra low distortion oscillator mentioned by branadic, it seems to have also basic AGC somehow:
https://www.eevblog.com/forum/metrology/ac-voltage-standard/msg3602024/#msg3602024
And last, the SWR200 way, which, if I'm getting it right, will output a sinewave from an integrated zener reference, with AGC and variable frequency using two external capacitors. It would need a DAC and anyway the same amplifier + reversed mains transformer thing I guess. Available from Mouser:
https://eu.mouser.com/ProductDetail/Apex-Microtechnology/SWR200C?qs=TiOZkKH1s2QO3EEJBtAi3w%3D%3D
So what do you guys think?
J-R:
Volt-nut in-training here... Are you trying to calibrate/adjust the HP3456A directly off these outputs or in combination with another calibrated DMM?
My quick opinion is that I don't see how any of the methods listed would provide the desired absolute accuracy alone, but the short-term stability is probably acceptable when used in a transfer standard context and another calibrated DMM.
I have an RT-5 but the problem is that you still need an initial high-precision source and a way to double-check everything. Many times I got an output that wasn't expected, perhaps sometimes due to noise, RF interference, or even just poor accuracy when changing frequencies.
Ultimately I did go the route of a function gen with a transformer, which can get you up a few DMM ranges alone depending, and then for higher voltages/frequencies add an audio amp in between. Then I was able to calibrate/adjust unknown DMMs against known calibrated DMMs no problem. This worked well enough for me since I had multiple calibrated 6.5 digit DMMs and was repairing other 3.5-5.5 digit DMMs. But I think for a 6.5 digit DMM you'd want to just ship it out for a proper calibration.
tatel:
--- Quote from: J-R on August 04, 2024, 09:46:45 pm ---Volt-nut in-training here... Are you trying to calibrate/adjust the HP3456A directly off these outputs or in combination with another calibrated DMM?
--- End quote ---
You might be right, I'm afraid.... Hopefully I will remain as a mild case. My goal is to be where you are telling me. To have a calibrated 6.5 digit max, to calibrate/adjust lesser, 3.5/4.5 devices. Not interested in say, maintaining the standard volt.
IIRC it was also you who told me it would be easier/cheaper to get a calibrated DMM. I can say now you were right, I'll probably expend more money than a brand new 34465 would cost. But where the fun is in that approach?
I don't have any 6.5 calibrated DMM at this moment.
--- Quote ---My quick opinion is that I don't see how any of the methods listed would provide the desired absolute accuracy alone, but the short-term stability is probably acceptable when used in a transfer standard context and another calibrated DMM.
--- End quote ---
Then I'll take the cheap way for now I think... I was wondering about SWR200, but if it can't be good enough, it is what it is.
I'll get that 3456A externally calibrated eventually, but I want to learn more and to get more fun, checking it myself before doing that. I'm gonna collect the toys anyway.
Thank you very much
J-R:
Yeah, collecting and tinkering is a fun part of the hobby. You could go down the rabbit hole of the AC-DC thermal converter?
It will still be interesting to hear what the true experts say on this query, probably will take some time for everyone to weigh in.
Another option: Youtuber atkelar just finished a repair on a Fluke 5100B calibrator and he mentioned his plan was to rent the equipment necessary to calibrate/adjust it.
tatel:
--- Quote from: J-R on August 04, 2024, 11:39:08 pm ---Yeah, collecting and tinkering is a fun part of the hobby. You could go down the rabbit hole of the AC-DC thermal converter?
--- End quote ---
At this moment I would say no...
--- Quote ---It will still be interesting to hear what the true experts say on this query, probably will take some time for everyone to weigh in.
--- End quote ---
I was expecting SWR200 could perhaps be useful, since it's a expensive, hermetic IC which has quite a few useful things in it. At the very least, I was expecting it could give accurate, stable amplitude, and perhaps frequency also. Otherwise I can't see how that price (€320, up to 500 for the selected M variant) could be justified. It makes AD5791 look cheap. But, I guess they could be milking the cow a little bit too much?
--- Quote ---Another option: Youtuber atkelar just finished a repair on a Fluke 5100B calibrator and he mentioned his plan was to rent the equipment necessary to calibrate/adjust it.
--- End quote ---
Well, I got a €200 quote for having that 3456A calibrated. If, after getting the toys and tinkering at will, I become reasonably confident it will pass that calibration, then it will go to the cal lab. To, say, get confirmation I did it right. So far it doesn't look as being really out of whack, but I still have no confidence it's in 90 day specs. Voltage reference and some resistors will do that trip before.
I guess, to calibrate a 5100B is another entirely different can of worms.
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