National Instruments E Series - page 47

Chapter 4 Signal Connections
 National Instruments Corporation 4-11 DAQCard E Series User Manual
the PGIA in different ways. Figure 4-2 shows a diagram of your
DAQCard PGIA.
The PGIA applies gain and common-mode voltage rejection and
presents high input impedance to the analog input signals connected to
your DAQCard. Signals are routed to the positive and negative inputs
of the PGIA through input multiplexers on the DAQCard. The PGIA
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 ground for the DAQCard.
Your DAQCard ADC measures this output voltage when it performs
A/D conversions.
You must reference all signals to ground either at the source device or
at the DAQCard. If you have a floating source, you should reference
the signal to ground by using the RSE input mode or the DIFF input
configuration with bias resistors (see the Differential Connections for
Nonreferenced or Floating Signal Sources section later in this
chapter). If you have a grounded source, you should not reference the
signal to AIGND. You can avoid this reference by using DIFF or NRSE
input configurations.
Figure 4-2. DAQCard E Series PGIA
-
Instrumentation
Amplifier
-
Measured
Voltage
Vm
+
+
PGIA
Vin+
Vin-
Vm = [Vin+ - Vin-]* Gain