Measuring Constant Voltage Only Shows Peak Structure

Updated Jan 31, 2020

Reported In

Hardware

  • PCI-6115

Driver

  • NI-DAQmx

Issue Details

I try to measure a constant voltage. Instead of constant value, I only measure a short signal spike, when I change the voltage.

Expected Signal:

Measured Signal:

Solution

For many DAQ cards and modules of NI, you can set the input coupling.
Check if you configured your hardware to use AC coupling.
Since AC coupling cancels constant voltages, you will only see voltage changes.

Additional Information

If your device is set to DC coupling, check you cabling for high-pass filters, which also work like a differentiator.