2-2
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Chapter 2
Using the PXIe-4310
Signal Connections
Figure 2-1 shows the voltages V
SIG
, V
CM
, and V
ISO
, which are used to describe signal
connections in this section.
Figure 2-1.
V
SIG
, V
CM
, and V
ISO
Signal Connections
V
SIG
is the voltage difference between AI<0..7>+ and AI<0..7>-. This is the desired signal
to be measured. V
CM
is the common-mode voltage with respect to the AI isolated ground,
COM<0..7>, calculated by subtracting COM<0..7> from AI<0..7>-. V
ISO
is the isolation voltage
with respect to the chassis ground of the measurement device.
The analog input channels are floating with respect to chassis ground and each other. If you make
a ground-referenced connection between the signal source and the PXIe-4310 input, make sure
the voltage on the AI+, AI-, and COM connections are within the safety voltage limits to ensure
safe operation. Refer to the
PXIe-4310 Specifications
for more information about Safety
Voltages.
The COM terminal for each channel must be connected to the reference ground of the AI source.
Failure to connect COM results in inaccurate measurements. You can connect the COM terminal
directly to the negative terminal of the source as shown in Figure 2-2 or to an isolated ground of
the source as long as the working voltage specification of the PXIe-4310 is not violated.
To ensure the specified EMC performance, wire the AI+ and AI- signals as twisted pairs and use
the COM as a shield. The COM connection should be made as close to the source as possible to
take advantage of the differential nature of this device.
I
s
ol
a
ted Gro
u
nd
Ch
ass
i
s
Gro
u
nd
+
–
AI+
AI–
COM
AI Ch
a
nnel
+
–
V
S
IG
+
–
V
I
S
O
+
–
V
CM
