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| how do you calibrate a dvm with 6.5 digits? |
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| GigaJoe:
yeah been there ... any instability multiplied by x100 , self- heating divider sucks even with 10ppm resistors, noise multiply by x100 ... need rare capacitors at least 600V in serial ... im end up to build 2 fixed sources on 250V and 2 variable 90-200 , 250-350, so you can connect in ser and adjust in overall cheapest solution - get a trusted one , ask performance paper, no adjustment, then do value transfer adjusting against performance report. so target is - to acquired \ build all necessary sources for value transfer. |
| J-R:
Fully calibrating/adjusting any DMM is no trivial task as you'll typically need access to high voltage AC and DC signals. The path I've taken frequently is to use another DMM along side the DMM that needs calibration/adjustment and then carefully dial in the source. For example, I recently needed 1kV DC, which required about an hour of tinkering and waiting for the Spellman DC-DC converter to stabilize, then within about a 5 second window I quickly stored the calibration point while observing the value on another DMM that I had calibration data for. The results are acceptable for a hobbyist, not so much for a volt-nut perhaps. For AC, I use a function generator with a transformer. When that limit is reached, I've been known to insert an amp in between to push the voltage higher. I recently acquired some additional custom transformers to see if I can get better results especially for higher frequencies. I have also acquired some vintage gear that has helped with providing stable sources. The Fluke 515A is pretty handy, although one issue is that it has reduced specs when using a DMM with a 10M input. Another nifty bit of gear is the Advantest R6144. Both took many months of searching to find at a reasonable price point. |
| coromonadalix:
when you have many meters, you make one calibrated and serve as a reference ... but if you do serious stuff .... other than hobbyist you know what to do even if its costly ... |
| David Hess:
--- Quote from: GigaJoe on May 03, 2023, 10:30:36 pm ---yeah been there ... any instability multiplied by x100 , self- heating divider sucks even with 10ppm resistors, noise multiply by x100 ... need rare capacitors at least 600V in serial ... --- End quote --- If the resistor temperature coefficients match, then a string of resistors can be used in an isothermal environment to improve tracking. Using a string makes sure that the voltage and current of each resistor is the same. If the voltage and current is the same, then the power is the same and the temperature of each resistor should be the same. If the voltage coefficients of resistance match, then the resistor string can be tested and verified at low voltage. Noise and instability would be multiplied in any design using a low voltage reference. In a good design the noise and drift from the reference dominates, so that means using a better reference, like a buried zener, or multiple references in series/parallel. While that would be nice, I could change the reference later if it is a problem. |
| GigaJoe:
I'm really had no idea how it goes, so such high voltage source was my first attempt to learn things. at first shot it more less acceptable. would be great if would be some discussion about. |
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