What Are AC and DC Coupling?

Updated May 2, 2018

Reported In

Hardware

  • Multifunction I/O Device
  • C Series Multifunction I/O Module
  • PXI Analog Input Module
  • NI-9229
  • NI-9225

Issue Details

In the Datasheet for my product, I see a section titled Input Coupling, and it is specifies AC or DC. What are AC and DC coupling?

Solution

AC coupling consists of using a capacitor to filter out the DC signal component from a signal with both AC and DC components. The capacitor must be in series with the signal. AC coupling is useful because the DC component of a signal acts as a voltage offset, and removing it from the signal can increase the resolution of signal measurements. AC coupling is also known as capacitive coupling.

DC coupling allows both AC and DC signals to pass through a connection. When using DC coupling, no additional capacitor is added to filter the signal.
 
 

Additional Information

To AC couple a signal with an NI DAQ(Data Acquisition) device, insert a capacitor in series with the signal, between the positive lead of the signal and the positive analog input channel on the DAQ device. Wire the negative lead of the signal directly to the corresponding negative analog input channel. This removes the DC component from the signal, which centers the AC signal at 0 volts. Please see the below figure for more detail.

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