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National Instruments Corporation
25
SCC-68 User Guide
Use single-ended input connections if the input signal meets the following
conditions.
•
The input signal is high-level (greater than 1 V).
•
The leads connecting the signal to the device are less than 3 m (10 ft).
•
The input signal can share a common reference point with other
signals.
Differential input connections are recommended for greater signal integrity
for any input signal that does not meet the preceding conditions.
Non-Referenced Single Ended (NRSE
)
Refer to the NRSE connection considerations described in the
M Series
User Manual
or the
E Series Help
. If you have SCC modules installed in
the SCC-68, the following cases should also be noted.
Grounded Signal Sources
If you have SCC modules installed in the SCC-68, differential
measurements are recommended over NRSE measurements. When you
have SCC modules installed, connect AI GND to AI SENSE. If you
connect the ground of the signal source to AI SENSE, you are also shorting
it to AI GND. Connecting the ground of the signal source to AI GND
introduces a ground loop and ground-loop-induced errors. Figure 16 shows
this measurement error.
Figure 16.
Ground-Referenced Signal Connected in NRSE Mode
Not Recommended
Ground-Referenced
Signal
AI GND (Pin 67)
AI
AI SENSE (Pin 62)
SCC-68
DAQ Device
NRSE Mode
+
–
+
–
