Why my NI PXIe R Series Oscilloscope Showing Incorrect Measurement?

Updated Oct 24, 2019

Reported In

Hardware

  • PXIe-5171

Driver

  • NI-SCOPE

Issue Details

I have connected my NI PXIe 5171 Oscilloscope with general lab function generator. Currently, I am generating simple Sinusoid waveform. However, I am unable to see the correct readings.
 

Solution

This type of issue arises majorly because of impedance mismatch. NI PXIe-5171 supports only single value as its input impedance, which is 50 Ohms. If the output impedance of function generator is different from 50 Ohms, the maximum power shall not be transferred to the sink device (NI PXIe-5171) in accordance with Maximum Power Transfer Theorem.
This may cause the signal to look attenuated as well as the shape of high frequency signals will appear distorted.
 

Additional Information

For other devices which support variable input impedances, property nodes can be used to select the correct input impedance values. For further specification, please consult the datasheet for each NI PXIe Oscilloscope.