ADLINK PXI-2208 - Manual (Page 41)

Signal Connections 29
3.2 Analog Input Signal Connection
The DAQ-/DAQe-/PXI-2204/2205/2206/2208 card 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 values
by the A/D converter. To avoid ground loops and get more accu-
rate measurements from the A/D conversion, it is important to
understand the signal source type and how to connect the analog
input signals.
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, trans-
former outputs, and thermocouples.
Ground-Referenced Signal Sources
A ground-referenced signal means it is connected in some way
to the building system. That is, the signal source is already
connected to a common ground point with respect to the DAQ-
/DAQe-/PXI-2204/2205/2206/2208 card, 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.
Input Configurations
Single-Ended Connections
A single-ended connection is used when the analog input sig-
nal is referenced to a ground that can be shared with other
analog input signals. There are two types of single-ended con-
nections: RSE and NRSE. In RSE configuration, the DAQ-/
DAQe-/PXI-2204/2205/2206/2208 card provides the ground-
ing point for the external analog input signals and is suitable for
floating signal sources. In the NRSE configuration the board
does not provide the grounding point, the external analog input
signal provides its own reference grounding point and is suit-
able for ground-referenced signals.