Chapter 4
Analog Input
©
National Instruments Corporation
4-7
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 4-3, channel 0 is configured in differential mode, and channel 1 is
configured in RSE mode.
Figure 4-3.
Enabling Multimode Scanning in LabVIEW
To configure the input mode of your voltage measurement using the DAQ
Assistant, use the
Terminal Configuration
drop-down list. Refer to the
DAQ Assistant Help
for more information about the DAQ Assistant.
To configure the input mode of your voltage measurement using the
NI-DAQmx C API, set the
terminalConfig
property. Refer to the
NI-DAQmx C Reference Help
for more information.
Multichannel Scanning Considerations
M Series devices can scan multiple channels at high rates and digitize the
signals accurately. However, you should consider several issues when
designing your measurement system to ensure the high accuracy of your
measurements.
In multichannel scanning applications, accuracy is affected by settling
time. When your M Series device switches from one AI channel to another
AI channel, the device configures the NI-PGIA with the input range of the
new channel. The NI-PGIA then amplifies the input signal with the gain for
the new input range. Settling time refers to the time it takes the NI-PGIA to
amplify the input signal to the desired accuracy before it is sampled by the
