How to Adjust Oscilloscope Probe Compensation

Oscilloscope probes are an essential extra to any oscilloscope, but to get the best performance from the probe and hence the scope, the probe compensation must be correctly adjusted.

Errors in the the scope probe compensation adjustment will result in very noticeable errors when making measurements, so it is absolutely necessary to get the compensation adjustment right.

This video describes which oscilloscope probes need compensation adjustment and why this is needed. The video also shows how to adjust the scope probe compensation and details of the correct tools.

Understanding why scope probe compensation is needed, helps see the need for accurately compensating probes each time they are used. It can also help explain the reasons for gaining poor results on the occasions when anyone forgets to compensate the probe.

There are many different varieties of oscilloscope probe, but the type most commonly used is the passive voltage probe. Of these the x1 or times one probe provides a straight through connection and this enables the input impedance of 1 Mohm to be seen at the probe tip. (There are some 50 ohm probes but these are used for specialist RF applications and are not particularly common).

The times ten probe or x10 probe has a series 9 Mohm resistor and gives an overall input impedance of 10 Mohms, although this is at DC and low frequencies. As the frequency rises the scope input capacitance increasingly affects the input impedance.

To give a flat response a compensation capacitor is added in the probe. This is adjusted to give the correct potential divider effect. If the probe is under compensated then square waves will appear rounded and if over compensated a square wave will have overshoot on the leading edge.

Getting the oscilloscope probe compensation right will enable waveforms to be seen accurately and accurate measurements to be made.

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