Chapter 4 Analog Input
NI USB-621x User Manual 4-36 ni.com
Using the DAQ Assistant, you can configure the channels for referenced
single-ended or non-referenced single-ended input modes. Refer to the
Configuring AI Ground-Reference Settings in Software section for more
information about the DAQ Assistant.
Connecting Analog Input Signals on
USB-6215/6216/6218 Devices
You can connect the USB-6215/6216/6218 directly to a variety of devices
and other signal sources. Make sure the devices you connect to the
USB-6215/6216/6218 are compatible with the input specifications of the
module.
When connecting various sources to the USB-6215/6216/6218, you can use
differential, single-ended, or a combination of single-ended and differential
connections.
Note Yo u must always connect AI GND to a local ground signal in your system using a
low impedance connection. If you leave AI GND unconnected, you cannot ensure that
AI <0..31> are within 10 V of AI GND, and your measurement may be unreliable.
Taking Differential Measurements
To attain more accurate measurements and less noise, use a differential
measurement configuration. A differential measurement configuration
requires two inputs for each measurement. The AI <0..31> description in
Table 3-1, I/O Connector Signals, lists the signal pairs that are valid for
differential connection configurations with USB-621x devices.
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