National Instruments NI 6238 - Manual (Page 33)

Chapter 4 Analog Input
© National Instruments Corporation 4-7 NI 6238/6239 User Manual
Caution The maximum input voltages rating of AI signals with respect to AI GND (and
for differential signals with respect to each other) and earth/chassis ground are listed in the
Maximum Working Voltage section of the NI 6238/6239 Specifications. Exceeding the
maximum input voltage or maximum working voltage of AI signals distorts the
measurement results. Exceeding the maximum input voltage or maximum working voltage
rating also can damage the device and the computer. Exceeding the maximum input voltage
can cause injury and harm the user. NI is not liable for any damage or injuries resulting
from such signal connections.
AI ground-reference setting is sometimes referred to as AI terminal
configuration.
Configuring AI Ground-Reference Settings in
Software
You can program channels on an M Series device to acquire with different
ground references.
To enable multimode scanning in LabVIEW, use NI-DAQmx Create
Virtual Channel.vi of the NI-DAQmx API. You must use a new VI for
each channel or group of channels configured in a different input mode. In
Figure 4-6, channel 0 is configured in differential mode and
aignd_vs_aignd reads the internal analog input ground-reference of the
device.
Figure 4-6. Enabling Multimode Scanning in LabVIEW
To configure the input mode of your current measurement using the DAQ
Assistant, use the Terminal Configuration drop-down list. Refer to the
DAQ Assistant Help for more information on the DAQ Assistant.
To configure the input mode of your current measurement using the
NI-DAQmx C API, set the terminalConfig property. Refer to the
NI-DAQmx C Reference Help for more information.