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Basic Information about AC and DC Coupling



Hardware: Multifunction DAQ (MIO)

Problem:
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.

To AC couple a signal with an NI data acquisition (DAQ) 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.


Figure 1: Capacitor added between Device Under Test and Data Acquisition Device

Please refer to KnowledgeBase 3I8B6NN8: AC, DC, or GND Coupling on a Physical Channel if you want to check if your device has built in AC coupling.

For more details about AC and DC coupling and how it can affect your signal, read White Paper: AC and DC Coupling.

Related Links:
Product Documentation: Specifications Explained: NI Multifunction I/O (MIO) DAQ
KnowledgeBase 3I8B6NN8: AC, DC, or GND Coupling on a Physical Channel
Tutorial: AC Voltage RMS Measurements
White Paper: AC and DC Coupling

Attachments:





Report Date: 01/06/1999
Last Updated: 05/23/2017
Document ID: 1H59Q2W3

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