Author Topic: Do most 6.5 digit DMMs measuring amps in the noise?  (Read 663 times)

0 Members and 1 Guest are viewing this topic.

Offline ballsystemlordTopic starter

  • Regular Contributor
  • *
  • Posts: 248
  • Country: us
  • Student
Do most 6.5 digit DMMs measuring amps in the noise?
« on: October 16, 2023, 04:59:51 pm »
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...
« Last Edit: October 16, 2023, 05:01:25 pm by ballsystemlord »
 

Online Kleinstein

  • Super Contributor
  • ***
  • Posts: 15151
  • Country: de
Re: Do most 6.5 digit DMMs measuring amps in the noise?
« Reply #1 on: October 16, 2023, 05:41:33 pm »
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.
 
The following users thanked this post: Performa01


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf