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PXIe-5111 Compensating Passive Probes

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    Last Modified: August 31, 2018

    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.
      spd-note-note
      Note  

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

    The PXIe-5111 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. Connect the ground clip of the probe to the ground terminal on the front of the oscilloscope.
    3. Contact the tip of the probe to the 5 V square wave terminal on the front of the oscilloscope.
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      Note  

      The probe compensation signal at this terminal is activated by default on the PXIe-5111. You can disable and re-enable the signal in InstrumentStudio with the Probe Compensation options in the instrument header menu ( ) in the upper-right corner of the panel or programmatically in NI-SCOPE with Probe Compensation Signal Stop and 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. Set the Vertical offset to 2.5 V.
      4. 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.
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    Tip  

    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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