Compensating oscilloscope probes: what does it do and why do it?

Compensating an oscilloscope probe is a simple, and possibly sometimes overlooked, procedure one needs to do in order to ensure they’ve getting the best possible signal from their oscilloscope. I once heard it likened to tuning an instrument. If you don’t tune, you are not going to hear the song correctly. Similar results will happen to your measurements if you do not compensate your probes.

So, what does compensating a probe do? All oscilloscopes have some level of inherent input impedance. You will want to compensate your probe in order to minimize the loading effect on the circuit to be measured. Basically, if the impedance of your probe does not match the impedance of your scope, you will not get accurate readings on whatever it is you are trying to measure.

Most oscilloscope probes will have some form adjustment. The probes we used in class had a potentiometer we could turn with a small driver in order to match the 1 kHz square wave signal generated by the oscilloscope. The goal here was to make our signal look as flat as possible. Any rounding of the waveform’s edges meant we had to adjust further.

Ultimately, what may seem to be a complex procedure is actually quite simple once you figure out how to compensate your particular probe and what the proper signal looks like.

I found this site to be really helpful with visuals showing what a compensated probe signal will look like compared to what an uncompensated signal looks like: Oscilloscope Probe Compensation