Chapter 3 Connecting Signals
DAQCard-700 User Manual 3-6 ni.com
The DAQCard-700 instrumentation amplifier applies common-mode
voltage rejection and presents a high-input impedance to the AI signals
connected to the DAQCard-700. Signals are routed to the positive and
negative inputs of the instrumentation amplifier through input multiplexers
on the DAQCard-700. The instrumentation amplifier converts two input
signals to a signal that is the difference between the two input signals
multiplied by the gain setting of the amplifier. The amplifier output voltage
is referenced to the DAQCard-700 ground. The DAQCard-700 ADC
measures this output voltage when it performs A/D conversions.
Single-Ended Mode (RSE)
Although the instrumentation amplifier on the DAQCard-700 is actually
bypassed in RSE input mode, the effect of this mode is the same as if
signals connected to ACH<0..15> were routed to the positive terminal
of the instrumentation amplifier and the negative terminal of the
instrumentation amplifier were connected to the analog ground reference
of the DAQCard-700. Thus, the voltage measured by the DAQCard-700 in
RSE input mode is the difference between an input signal and the
DAQCard-700 analog ground reference.
Differential Mode (DIFF)
In DIFF input mode, signals connected to ACH<0..7> are routed to the
positive input of the instrumentation amplifier, and signals connected
to ACH<8..15> are routed to the negative input of the instrumentation
amplifier. Thus, the voltage measured by the DAQCard-700 in DIFF input
mode is the difference between two of the input signals.
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