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PXIe-5163 Compensating Passive Probes

    Last Modified: June 13, 2019

    Compensating passive probes increases the accuracy of your measurements by matching the capacitance of your probe to the capacitance of a particular oscilloscope input channel.

    Before beginning this procedure, complete the following:

    • Set up your oscilloscope in a compatible chassis;
    • Install a version of NI-SCOPE compatible with your oscilloscope on your system; and
    • Configure a panel and layout in InstrumentStudio to include your oscilloscope.

      For more information on using InstrumentStudio, refer to the InstrumentStudio Manual.

    The following equipment is required for this procedure:

    If using the Oscilloscope Probe Compensator
    • Oscilloscope Probe Compensator (NI part number 786983-01)
    If connecting the probe directly to the oscilloscope PFI
    • A 50 Ω SMB (f)-to-BNC (f) cable, such as the SMB-100 (NI part number 781449-01)
    • A probe tip–to-BNC (m) adapter

    The PXIe-5163 can output a 1 kHz square wave that you can use to compensate passive probes.

    To compensate a passive probe, complete the following steps:

    1. Connect the BNC end of the probe to an input channel of your oscilloscope.
    2. Depending on your connection method, connect the probe tip to the oscilloscope:
      • Oscilloscope Probe Compensator
        1. Connect the SMB end of the Oscilloscope Probe Compensator to the PFI connector of the oscilloscope that generates the probe compensation signal.
        2. Connect the ground clip of the probe to the ground terminal.
        3. Contact the tip of the probe to the square wave terminal.
      • Direct connection to PFI
        1. Connect the SMB end of the SMB (f)-to-BNC (f) cable to the PFI connector of the oscilloscope that generates the probe compensation signal.
        2. Attach the BNC adapter to the tip of the probe.
        3. Connect the probe tip via the BNC adapter to the BNC end of the cable.
    3. Enable the probe compensation signal:
      Option Description
      InstrumentStudio In the instrument header menu ( ) in the upper-right corner of the panel, select Probe Compensation»Enabled.
      NI-SCOPE Call Probe Compensation Signal Start.
    4. In InstrumentStudio, configure the settings of the input channel to which you connected the probe.
      1. Set the channel to On to display the signal.
      2. Set the Input impedance of the channel to 1 MΩ.
      3. Match the Probe attenuation setting to the setting on your probe.
    5. Adjust the vertical range on the input channel until the signal starts to clip and then increase the vertical range by one step so that it no longer clips. This process ensures you are using the maximum dynamic range of the ADC.
    6. Examine the digitized signal and adjust the tunable capacitor on the probe. The probe is correctly compensated when the waveform appears as square as possible:
    Once compensated, the probe conveys signals to the input channel accurately, without artificially attenuating or amplifying frequency components of the signal.

    For the most accurate measurements:

    • Compensate probes for each channel of the oscilloscope;
    • Use a compensated probe only with the channel you used to compensate it; and
    • Compensate your probes frequently.

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