In the specification sheet for your DAQ device, there is an Analog Input Characteristic called Input Coupling.
Some basic information about this specification can be could in Specifications Explained: NI Multifunction I/O (MIO) DAQ - Coupling
This specifies whether your device supports AC, DC, or both types of input coupling.
- AC Coupling: 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: 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. The DC-coupled configuration is usually best if the signal source has only small amounts of offset voltage, less than ±100 mV, or if the DC content of the acquired signal is important.
- Software Select Coupling: Some NI devices are hardware configurable to use either AC coupling or DC coupling on a channel by channel basis. You can configure the input coupling type per channel using the Input Coupling DAQmx Channel Property node .
: If your signal is entirely DC content, ensure you use DC coupling. Otherwise your entire signal content will be removed and will look like a grounded 0 V signal.