Chapter 3
Signal Connections
3-6
©
National Instruments Corporation
How you connect analog input signals to the PCI-1200 depends on how you
configure the PCI-1200 analog input circuitry and the type of input signal
source. With different PCI-1200 configurations, you can use the PCI-1200
instrumentation amplifier in different ways. Figure 3-2 shows a diagram of
the PCI-1200 instrumentation amplifier.
Figure 3-2.
PCI-1200 Instrumentation Amplifier
The PCI-1200 instrumentation amplifier applies gain, common-mode
voltage rejection, and high-input impedance to the analog input signals
connected to the PCI-1200 board. Signals are routed to the positive and
negative inputs of the instrumentation amplifier through input multiplexers
on the PCI-1200. The instrumentation amplifier 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 PCI-1200 ground. The PCI-1200 ADC measures this output voltage
when it performs A/D conversions.
All signals must be referenced to ground, either at the source device
or at the PCI-1200. If you have a floating source, you must use a
ground-referenced input connection at the PCI-1200. If you have a
5
0 to 1.99951 V
10
0 to 999.756 mV
20
0 to 499.877 mV
50
0 to 199.951 mV
20
0 to 99.975 mV
Table 3-3.
Unipolar Analog Input Signal Range Versus Gain
Instrumentation
Amplifier
Measured
Voltage
V
m
= [V
in+
- V
in-
] * GAIN
V
in–
V
m
V
in+
+
–
+
–
