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Adjusting the tunable probe capacitor to get a flat frequency response is called probe compensation. Probe compensation balances the electrical properties of the probe to the particular digitizer you are using. The following figure illustrates that an undercompensated probe attenuates higher frequency signals, whereas an overcompensated probe amplifies higher frequencies.

For the most accurate measurements, always compensate probes for each channel (CH 0 and CH 1) of the digitizer and use them on that channel only. Refer to the probe user documentation for information on how to compensate the probe.

Tip  Frequently calibrating your probe helps ensure accurate measurements from your digitizer.

How to Compensate a Probe

To compensate a probe, complete the following steps:

1. Connect the BNC end of the probe to an input channel of the digitizer, either CH0 or CH1, and select X10 attenuation on the body of the probe tip.
2. Attach the BNC adapter (probe accessory) to the tip of the probe.
3. Connect the SMB100 probe-compensation cable to one of the PFI lines.
4. Attach the probe with the BNC adapter to the BNC female end of the SMB100 cable.
5. Enable the probe compensation signal on the PFI line you selected in step 3. The Scope Soft Front Panel allows control of the probe compensation signal. Programmatic users can call niScope Enable Probe Compensation.
6. Digitize data on the input channel. Adjust the vertical range on the input channel until the signal starts to clip. Then increase the vertical range one step so that it no longer clips to ensure that you use the main dynamic range of the ADC.
7. Adjust the tunable capacitor to make the waveform look as square as possible.
8. For the most accurate measurements, compensate probes for each channel (CH 0 and CH 1) and use them on that channel only. Recompensate when using the probe on a different channel.