National Instruments Data Acquisition Device E Series User Manual page 39

Chapter 2 Analog Input
E Series User Manual
The single-ended input configurations provide up to 16 channels
(64 channels on the NI 6031E, NI 6033E, and NI 6071E). The DIFF input
configuration provides up to eight channels (32 channels on the NI 6031E,
NI 6033E, and NI 6071E). Input modes are programmed on a per channel
basis for multi-mode scanning. For example, you can configure the
circuitry to scan 12 channels—four differentially-configured channels and
eight single-ended channels.
With each input mode configuration, you use the PGIA in a different way.
The PGIA applies gain and common-mode voltage rejection and presents
high-input impedance to the AI signals connected to the device. Signals are
routed to the positive and negative inputs of the PGIA through input
multiplexers on the device. The PGIA converts two input signals to a new
signal by taking the difference between the two input signals and
multiplying the difference by the gain setting of the amplifier. The amplifier
output voltage is referenced to the ground for the device. The device A/D
converter (ADC) measures this output voltage when it performs A/D
conversions. Figure 2-2 shows a diagram of the PGIA.
V
in+
V
in–
Instrumentation
Amplifier
+
PGIA
–
V = [V
m in+
Figure 2-2. E Series PGIA
2-6
+
Measured
V
m
Voltage
–
] × Gain
– V
in–
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