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| Do most 6.5 digit DMMs measuring amps in the noise? |
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| ballsystemlord:
I rewatched Dave's video on how to choose a DMM and applied the info to the amperage of DMMs. Here: At offset 35:30 he talks about accuracy and says to use the formula, 10/counts * 100 == % to determine what the minimum accuracy of your scope should be. Now if we apply that to a 6.5 digit DMM: (10/1200000)*100 == 0.00083 . Then if we go over to the fine list of Bench DMMs here: https://www.eevblog.com/forum/testgear/multimeter-spreadsheet/ We see that most of them 0.05-0.03 or higher for the amperage range of the DMMs. So, is it just me, or do most 6.5 digit DMMs measure amps in the noise? Thanks! EDIT: Actually, it looks like they measure voltage in the noise as well... |
| Kleinstein:
The formular for the accuracy is a rought guide, usually for the DC voltage as the easiest case. It still is not a strict requirement and does not fully apply to very high resolution ones. The current measurement is more tricky and is usually less accurate for 3 reasons: 1) the heating of the shunts 2) the need to measure relatively small voltages like in the 100 mV range 3) the difficulty to get proper 4 wire contacts with shunts in series as the usual configuration. So it is quite normal to see a lower accuracy for current and rarely a reduced number of digits. More digits than accuracy can still be useful, especially at the lower end of the range. Things have also changed over time: just the resolution got cheap with SD ADCs. Noise is a 3rd parameter to look at for the quality. The expectations are a bit different for a 6 digit meter compared to a 2000 count meter. For the lower resolution one usually wants hardly any visibler noise or peak to peak noise less than 1 LSB. For the higher resolution ones usually 1 LSB RMS noise and thus a 6 times high limit is considered the usual benchmark. |
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