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Measuring DC power using STPM32 evaluation board

Question asked by MacDonald.Tom on Dec 20, 2016

Hello,

 

I am currently developing a device to measure AC or DC current on the same channel, depending on what type of voltage source the end user decides to connect to that channel.

 

We are thinking of using the STPM line of power measurement ICs, and as such we have purchased a STPM32 evaluation board.

 

The board does great with measuring mains power consumption, but I am having difficulty using it to measure DC power consumption.

 

When I try to measure DC current/power/voltage, none of those values are captured.  I am feeding 0.5 amps constant current into a 1.3 ohm load resistor rated for 10 watts.  Here is my test apparatus:

 

DC apparatus

 

and here is what I captured on my oscilloscope (note CH1 and CH2 in above figure to understand which waveform I am measuring on each channel):

 

 

and here is the output to the evaluation board software:

 

 

... and here is the configuration of the STPM32 while taking those measurements:

 

 

Seems like the current through the load and shunt resistor is varying wildly, despite being hooked up to a reliable benchtop power supply...

 

Has anyone got any ideas on what I'm doing wrong, and why the STPM32 isn't measuring the DC voltage and current correctly?

 

I've attached a basic overview of my test procedure if anyone is interested in reading it.

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