NI sbRIO-960x/962x/963x OEM Instructions & Specifications 34 ni.com
Figure 26. Differential Connections for Floating Signal Sources with
Balanced Bias Resistors
Both inputs of the PGIA require a DC path to ground in order for the PGIA
to work. If the source is AC coupled (capacitively coupled), the PGIA needs
a resistor between the positive input and AI GND. If the source has
low-impedance, choose a resistor that is large enough not to significantly
load the source but small enough not to produce significant input offset
voltage as a result of input bias current (typically 100 kΩ to 1 MΩ). In this
case, connect the negative input directly to AI GND. If the source has high
output impedance, balance the signal path as previously described using the
same value resistor on both the positive and negative inputs; be aware that
there is some gain error from loading down the source, as shown in
Figure 27.
PGIA
–
+
–
+
–
+
Floating
Signal
Source
Bias
Current
Return
Paths
AI GND
Input Multiplexers
Measured
Voltage
Instrumentation
Amplifier
AI+
AI–
I/O Connector
Bias
Resistors
(see text)
V
s
V
m
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