Chapter 4
Signal Connections
©
National Instruments Corporation
4-13
PCI-4451/4452/4453/4454 User Manual
stage converts two input signals to a voltage that is the difference between
the two input signals multiplied by the gain setting of the amplifier. Your
PCI-4451/4452 A/D converter (ADC) measures this voltage when it
performs A/D conversions.
Connection of analog input signals to your PCI-4451/4452 depends on the
configuration of the input signal sources. For most signals, you use a DIFF
configuration and simply connect the signal to +ACHx (where x is the
PCI-4451/4452 channel) and the signal ground (or signal minus,
as appropriate) to
−
ACHx. However, if a signal has a high output
impedance (greater than 1 k
Ω
) and is floating, you can use an SE
configuration and tether the signal minus to AIGND to reduce
common-mode interference. You can make the DIFF and SE connections
through the BNC-2140 accessory.
♦
PCI-4453/4454
Figure 4-5 shows a diagram of your PCI-4453/4454 analog input stage.
Figure 4-5.
Analog Input Stage of the PCI-4453/4454
The analog input stage presents high input impedance to the analog input
signals connected to your PCI-4453/4454. Signals are routed to the positive
inputs of the analog input stage and their returns to AIGND through a
common-mode choke. Your PCI-4453/4454 A/D converters measure these
signals when they perform A/D conversions.
+
–
Differential
Buffer
Common-Mode
Choke
Calibration
Multiplexer
1 M
AIGND
1 G
0.047 µF
DC/AC
Coupling
Analog-
Lowpass
Filter
A/D
Converter
+ACH
X
AI_SHLD
X
Gain = 0 dB