So I ran into something interesting today.

I have a hall effect sensor (L18PXXXD15) and I was attempting to measure current of a 30Vrms sine wave across a 50 ohm load. However, when I connected my hall effect on the high side, my signal dropped like 10Vrms. When I measured across the current sense pins, I noticed my missng 10Vrms was there. When I increase frequency, the drop increases and when I lower my frequency the drop decreases.

I switched it to the low side, and I'm able to get my full voltage across the laod, as expected.

Generally speaking for hall effect sensors, does placement matter ? I've only messed around with this one sensor, so I can't say if generally all hall effects are required to be low side, or whether it varies.

Is there something in the datasheet that I should look for that might indicate placement ? There was none that I saw for this particular one.


1 Answer 1


It should make no difference as the sensor just detects the magnetic field emanating from the current-carrying conductor, which is just a piece of metal. It may act like an inductor, however if the sense wire is coiled up for higher sensitivity.

The only thing that I can think of is you may have had a bad connection somewhere that caused the drop as you should be seeing the same thing on both sides of the load.

  • \$\begingroup\$ I'll recheck tomorrow, but I did think it was odd that it would work one way but not entire the other. I was getting a current reading on both, its just that one way caused a significant voltage drop. \$\endgroup\$
    – efox29
    Jan 23, 2015 at 1:20

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