Chapter 4
Connecting Signals
4-16
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In NRSE mode, the AISENSE and AISENSE2 signals are connected
internally to the negative input of the AT E Series device PGIA when their
corresponding channels are selected. In DIFF and RSE modes, these
signals are left unconnected.
AIGND is an AI common signal that is routed directly to the ground tie
point on the AT E Series devices. You can use this signal for a general
analog ground tie point to the AT E Series device if necessary.
Connection of AI signals to the AT E Series device depends on the
configuration of the AI channels you are using and the type of input signal
source. With the different configurations, you can use the PGIA in different
ways. Figure 4-4 shows a diagram of the AT E Series device PGIA.
Figure 4-4.
AT E Series PGIA
The PGIA applies gain and common-mode voltage rejection and presents
high input impedance to the analog input signals connected to the
AT E Series 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 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 device. The AT E Series device
A/D converter (ADC) measures this output voltage when it performs A/D
conversions.
+
+
–
–
PGIA
V
m
= [V
in+
– V
in–
]* Gain
V
in+
V
in–
V
m
Programmable
Gain
Instrumentation
Amplifier
Measured
Voltage
