EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: Rene on February 25, 2015, 03:18:50 am

Hello,
I am looking at the Rigol DP832 specifications to try to figure out what the voltage and current accuracy of the unit are and it seems pretty straight forward, but just to verify, could anyone tell me if my calculations below are correct or not? I have attached the DP832 specification manual in case it helps.
Basically, according to me:
1) If the output voltage specified by me is 0 volts, then the unit could potentially output any voltage value between 0.020V and +0.020V (can the min value actually be negative?).
2) If the output voltage specified by me is 1 volt, then the unit could potentially output any voltage value between 0.9795V and 1.0205V.
3) If the output voltage coming out of the unit is exactly 0 volts, then the unit readback could potentially be any voltage value between 0.010V and +0.010V (can the min value actually be negative?).
4) If the output voltage coming out of the unit is exactly 1 volt, then the unit readback could potentially be any voltage value between 0.9895V and 1.0105V.
I feel I am doing something wrong because with the highresolution option installed (to go down to millivolts / milliamps) it seems to me like the +/ actual vs display is huge.
Thanks.

That's pretty much correct. There is also the other stuff (regulation rate and noise), but it's small. If you want to see in practice what the accuracy looks like, see this thead (https://www.eevblog.com/forum/testgear/noobdaclinearityinthedp832/).
The 1mV option gives you greater resolution but definitely not better accuracy. Even in practice, this accuracy is quite a bit worse than 1mV. I found (see the thread above) that a freshlycalibrated DP832 gets you about +/10mV across the range with peaks and valleys along the way. There is a significant temperature drift in the multiple mV across the specced range (25 +/ 5C).
The ADC is pretty good though, within a couple of mV across the range.
Note that it is not uncommon at all for the discrepancy between resolution and accuracy to be large. For instance, the highly regarded 6 1/2digit 34401A DMM gives you a bestcase 1yr reading accuracy of 40ppm, which is 40 counts on its display.
So the DP832 spec is not bad. Just be aware that the highresolution option gives you resolution that is substantially smaller than the accuracy.