How do you display a current waveform in an oscilloscope?

Answer 1

There are 3 methods.

1. Get a current probe, made specifically for the oscilloscope.

2. With a single-ended (normal) scope probe, measure the voltage across a small-value (i.e. 0.1 Ohm 1%) resistor, with one side at ground potential (also known as a "low" side current measurement).

3. If a low-side measurement is not possible, use a differential measurement using 2 probes. Again, place a small value resistor in line with the current you wish to measure, and use the tips of the probes, only. Set the vertical inputs to channels 1, and 2, and use a math function (or a switch setting) to invert channel 2, then add ch1+ ch2.

WARNING: the oscilloscope must be rated to handle common mode voltages at least as high as the voltage that exists on the current-sense resistor with respect to ground, otherwise you'll blow out the vertical amps in the scope. That's why high-side current measurements are not done too often. You must also be careful in handling the probes around the higher voltages in a high-side current measurement.

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Answer 2

That is one of the best descriptions I have ever read for doing current measurements with a scope.

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