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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 measurements from the A/D
conversion, it is quite important to understand the signal source type and
how to connect the analog input signals.
3.2.1
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, transformer outputs, and
thermocouples.
3.2.2 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 4.
Figure 4: Single-Ended connections
