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| Reference PCB for Calibrating DMM's |
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| wasedadoc:
--- Quote from: JenniferG on November 24, 2022, 05:45:26 pm ---.... take some Royal Ohm 1 cent metal film resistors (1%) , say like 3 of them, to my local electronics store and see if they'd kindly measure them for me on a calibrated scope. --- End quote --- Think again. Scopes are rarely if ever calibrated to anywhere near the accuracy of a decent meter. And as for a local electronics store having one calibrated and maintaining its calibration - more chance of seeing pigs fly overhead. |
| tautech:
This is the proper tool if you are serious about a reference check: https://dmmcheckplus.com/ |
| Gyro:
--- Quote from: wasedadoc on November 24, 2022, 06:26:51 pm --- --- Quote from: JenniferG on November 24, 2022, 05:45:26 pm ---.... take some Royal Ohm 1 cent metal film resistors (1%) , say like 3 of them, to my local electronics store and see if they'd kindly measure them for me on a calibrated scope. --- End quote --- Think again. Scopes are rarely if ever calibrated to anywhere near the accuracy of a decent meter. And as for a local electronics store having one calibrated and maintaining its calibration - more chance of seeing pigs fly overhead. --- End quote --- Yes, a typical DSO is 8 bit resolution, an expensive one 12 bits, I even have an old picoscope ADC216 that manages a whole 16 bits up to 333ksps. Your local ectronics store will have the 8 bit - a $3 DMM [Edit: or Harbour Freight giveaway in the US?] has better resolution and accuracy. |
| Kleinstein:
The cheap boards are no way near as good to calibrate the GDM8251 (5.5 digit meter). For calibration one tends to need a significant better reference / meter. The cheap references from China are at best a quick spot check for one maybe 2 ranges and over time a crude test for dirft. Usually the DMM would still be more stable than the ref., but as long as the result is good, there is no need to ask which one is drifting. One may (still have to check if the ranges line up OK) use the 5.5 digit meter together with an only somewhat stable source (but larger range to check most ranges) to check a 3.5 and maybe 4.5 digit handheld meter, at least in some ranges. The AC part can still be tricky and so is a suitable AC source. |
| alm:
If you want to adjust one of the meters, then you also need to study if you can adjust just a single range at a time, or if you need to adjust all ranges before you can save. Even if you are forced to adjust just the DCV ranges, that still means having a stable 100V and 1000V (or whatever the correct points are). For meters where you can adjust a single range at a time this is no problem. At least some Keithley bench DMMs require adjusting all ranges and functions before it will save the adjustments. So having a reference to adjust a single range doesn't do you much good then. |
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