Chapter 4
Connecting Signals
4-8
ni.com
Figure 4-2.
Programmable Gain Instrumentation Amplifier (PGIA)
In NRSE mode, signals connected to ACH<0..15> are routed to the positive
input of the PGIA, and AISENSE is connected to the negative input of the
PGIA. In DIFF mode, signals connected to ACH<0..7> are routed to the
positive input of the PGIA, signals connected to ACH<8..15> are routed to
the negative input of the PGIA, and AISENSE is not used.
Caution
Exceeding the differential and common-mode input ranges distorts the input
signals. Exceeding the maximum input voltage rating can damage the device and the
computer. NI is
not
liable for any damage resulting from such signal connections.
The maximum input voltage ratings are listed in the
Protection
column of Table 4-3.
AIGND is an AI common signal that is routed directly to the ground tie
point on the devices. You can use this signal for a general analog ground
tie point to the device if necessary.
Note
AIGND is not connected to the negative input of the PGIA in single-ended mode
unless it is connected to AISENSE with an external wire.
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 signal
that is the difference between the two input signals multiplied by the gain
–
Instrumentation
Amplifier
–
Measured
Voltage
V
m
+
+
PGIA
V
in+
V
in–
V
m
= [V
in+
– V
in–
]* Gain
