User`s guide

Signal Connections • 21
3.2 Analog Input Signal Connection
The DAQ/PXI-22XX provides up to 64 single-ended or 32 differential
analog input channels. You can fill the Channel Gain Queue to get desired
combination of the input signal types. The analog signal can be converted
to digital value by the A/D converter. To avoid ground loops and obtain a
more accurate measurement from the A/D conversion, it is quite important
to understand the signal source type and how to choose the analog input
modes: RSE, NRSE, and DIFF mode.
3.2.1 Types of signal sources
Floating Signal Sources
A floating signal source means it is not connected in any way to the
buildings ground system. A device with an isolated output is a floating
signal source, such as optical isolator outputs, transformer outputs, and
thermocouples.
Ground-Referenced Signal Sources
A ground-referenced signal means it is connected in some way to the
buildings system. That is, the signal source is already connected to a
common ground point with respect to the DAQ/PXI-22XX, assuming that
the computer is plugged into the same power system. Non- isolated out-
puts of instruments and devices that plug into the buildings power system
are ground-referenced signal sources.
3.2.2 Input Configurations
3.2.2.1 Single-ended Connections
A single-ended connection is used when the analog input signal is refer-
enced to a ground that can be shared with other analog input signals.
There are 2 different types for single-ended connections: RSE and NRSE
configuration. In RSE configuration, the DAQ/PXI-22XX board provides the
grounding point for the external analog input signals and is suitable for
floating signal sources. While in NRSE configuration the board doesn’t
provide the grounding point, the external analog input signal provides its
own reference grounding point and is suitable for ground-referenced sig-
nals.