How to Eliminate AC Noise When Measuring DC Signals

Updated Feb 19, 2018

Reported In

Hardware

  • NI-9208
  • NI-9216

Driver

  • NI-DAQmx

Issue Details

I am measuring low magnitude DC signals and am seeing noise from AC signals, such as 50 or 60 Hz power lines running in parallel to my signal wires. How can I filter out this noise?

Solution

AC noise can be filtered out of DC measurements with a low-pass filter. To build a low-pass filter, simply set up the RC (Resistor-Capacitor) circuit shown below. Choose the resistance and the capacitance so that the cut-off frequency is below the frequency of the noise signal you want to reject. The cut-off frequency is computed by: 

Cut-off Frequency = 1/(2 x pi x R x C)

where:
R = resistor value in Ohms
= capacitor value in Farads

Additional Information

If a hardware filtering solution is not desirable, it's also possible to eliminate noise purely in software.

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