National Instruments SCB-68 - Manual (Page 37)

Chapter 3 Connecting Signals
© National Instruments Corporation 3-9 SCB-68 Shielded Connector Block User Manual
Single-Ended Connections for Floating Signal
Sources (RSE Input Mode)
Figure 3-4 shows how to connect a floating signal source to a channel on
the DAQ device configured for RSE input mode.
Figure 3-4. Single-Ended Input Connections for Nonreferenced or Floating Signals
Single-Ended Connections for Grounded Signal
Sources (NRSE Input Mode)
To measure a grounded signal source with a single-ended configuration,
configure the DAQ device in NRSE input mode. The signal is then
connected to the positive input of the DAQ device instrumentation
amplifier, and the signal local ground reference is connected to the negative
input of the instrumentation amplifier. The ground point of the signal
should, therefore, be connected to AISENSE. Any potential difference
between the DAQ device ground and the signal ground appears as a
common-mode signal at both the positive and negative inputs of the
instrumentation amplifier, and this difference is rejected by the amplifier.
If the input circuitry of a DAQ device were referenced to ground, in this
situation (as in the RSE input mode), this difference in ground potentials
would appear as an error in the measured voltage.
Measurement Device Configured in RSE Input Mode
PGIA
–
+
–
Floating
Signal
Source
V
s
I/O Connector
AIGND
ACH
+
Instrumentation
Amplifier
Measured
Voltage
V
m
–
+
*Not all devices support RSE input mode.
AISENSE*