strange readings


I am trying to calibrate my current sensor and i am getting very different results

compared to a wall killawatt and a DMM.

Using some resistive loads all three meters are displaying allmost the same values (range 0.15A and 7A),

but when i measure my laptop the measurements go way off :

-killawatt and the multimeter 0.10A-0.15A

-my sensor 0.20-0.25A

where does this error come from? is there somethig wrong with the multimeter or the killawatt (like not having a true rms value) or is something wrong in my design.

I am also curios to know if anyone else has done some similar tests


glyn.hudson's picture

Re: strange readings


this is caused by the laptop SMPS drawing current in a non-constant way creating a non sinusoidal AC waveform. Check out the photos here:

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