National Instruments 700 User Manual
Page 27
Signal Connections
Chapter 3
DAQCard-700 User Manual
3-8
© National Instruments Corporation
+
+
+
-
-
-
V
M
Measured
Voltage
Signal
Source
ACH<0..15>
Input Multiplexer
Operational
Amplifier
I/O Connector
3
4
5
18
1, 2
DAQCard-700
AIGND
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-
+
-
V
S1
V
S2
V
S3
Figure 3-3. Single-Ended Analog Input Signal Connections
Differential Connection Considerations (DIFF Configuration)
Differential connections are those in which each DAQCard-700 analog input signal has its own
reference signal or signal return path. These connections are available when the DAQCard-700
is configured in the DIFF mode. Each input signal is tied to the positive input of the
instrumentation amplifier, and its reference signal, or return, is tied to the negative input of the
instrumentation amplifier.
When the DAQCard-700 is configured for DIFF input, each signal uses two of the multiplexer
inputs–one for the signal and one for its reference signal. Therefore, only eight analog input
channels are available when using the DIFF configuration. The DIFF input configuration should
be used when any of the following conditions are present:
•
Input signals are low level (less than 1 V).
•
Leads connecting the signals to the DAQCard-700 are greater than 15 ft.
•
Any of the input signals requires a separate ground reference point or return signal.
•
The signal leads travel through noisy environments.