ADLINK PXI-2006 - Manual (Page 34)

24 Signal Connections
3.2 Analog Input Signal Connection
The DAQ/PXI-20XX provides 4 differential analog input channels.
The analog signal can be converted to digital values by the A/D
converter. To avoid ground loops and get more accurate measure-
ments from the A/D conversion, it is quite important to understand
the signal source type and how to connect the analog input sig-
nals.
Types of signal sources
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/
PXI-20XX, 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.
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.
Single-Ended Measurements
For single-ended connection, the analog input signal is referenced
to the common ground of the system. In this case, all the negative
ends of analog input channels should be connected to the AIGND
on the connector in-stead of floating. Please refer to the Figure 3-
1.