How to Measure Current With an Oscilloscope


Measuring current with oscilloscope is useful for measuring constant voltages, the information an oscilloscope can give you is far more valuable. An oscilloscope can display waveforms of voltage changes over time which are then interpreted to provide important electrical information such as frequency, rise and fall times, etc.

To measure current with an oscilloscope you will need to use a probe with a shunt (or equivalent) resistance. The probe ground must be connected to the circuit ground and the tip of the probe must be connected to a point on the current waveform to be measured. Some scopes offer special functions to make this easy. For example the Rigol 1054z has a “De-Skew” function which automatically corrects for the propagation and phase delay caused by the shunt probe, to allow the true power to be calculated.

Current Insights: Mastering Measurement Techniques with an Oscilloscope

Once you have the voltage reading on the screen, you can then calculate the current using Ohm’s law. You can also use the MATH function of the scope to add or subtract two current waveforms together. Many manufacturers offer current probes which connect directly to the oscilloscope without the need for a separate interface box. These usually come with degaussing and Auto-Zero controls which will remove any DC offset from the probe when no current is present.

For more advanced applications you can also build your own current probe by adding a DC hall sensor to a standard 1 ohm current sense resistor. This gives you a much better sensitivity than the typical 1 ohm shunt used in current probes supplied with most scopes.

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