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Hall Effect Current Sensor Measurement Fluctuations at low current measurements

  1. Feb 28, 2012 #1
    I was trying to measure DC link current on a switched mode power supply when I came across a quirk of my circuit. I'm using an LEM HX 03-p SP2 hall effect current transducer to measure current. I couple the output node of my current transducer to ground via a 2KΩ resistor. The device's bandwidth is 50KHz and measures a nominal current of 3A. When I try to measure a current that's 10% of the nominal current, I get large voltage swings on the device's output. I've checked that I'm measuring DC link current past any capacitors to avoid large current flows. I'm sampling the DC link current every 250us and am sending an averaged measurement every 1000 samples back to my computer. The picture that I've attached shows the output current measurement for a varying load (sort of distinguishable as discreet load steps (0.8A, 0.2A, 0.18A) in the beginning before going of to a continuously varying regime). I must pointe out that I was conducting this experiment in tandem with a current probe that did NOT show the wild fluctuations that I observed with the transducers. My ADCs are working alright, I tested them with a 50KHz signal. Does anyone have any ideas as to what may be going on? Thanks very much!

    Attached Files:

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