USB3.0 Power Monitor (to 1 mV and 0.1 mA) first impressions

[JBeale]

Out of curiousity I got the YZXStudio "USB3.0 Power Monitor" with OLED display, which is on ebay around US$32.  It reads voltage to 1 mV and current to 0.1 mA, also tracking accumulated mAh and mWh. It has a cute scrolling graph mode to show current over time, but unfortunately fixed at +3.0 A max scale, so the resolution is not too useful for <200 mA type loads.  I also have a smaller, cheaper "Matek USB Power Monitor" that has only 10 mV resolution (and maybe 20 or 30 mV accuracy).

The quick summary is that the YZXStudio device does actually justify the number of digits it presents. As far as I can tell, it is off by only a few counts.  I compared voltage and current readings to a 6.5 digit Keithley 196 DMM, last calibrated in 2008 but it reads 9.99985 V on a 10V Geller reference  mfr. in Oct. 2011.  By the way, 1 mV resolution is probably as much as you need in a USB power monitor, as none of the USB sockets in various computers I tried are stable at the mV level. I tested with a separate custom power supply.  I noticed my cheap bench supply is not too stable at the mV level either.

Code: [Select]

USB3 meter Keithley 196 DMM
----------------------
AMPS readout
----------------------
0.1201 0.120083
0.1571 0.157168
0.2246 0.22455
0.4467 0.44685
0.4476 0.44801
----------------------
VOLTS readout
----------------------
4.683 4.68247
5.015 5.0138
5.192 5.1925
5.349 5.34856
5.457 5.4567
----------------------