Chapter 4
Signal Connections
PCI-4451/4452/4453/4454 User Manual
4-12
www.ni.com
Analog Input Signal Connections
♦
PCI-4451/4452
The analog input signals for the PCI-4451/4452 are +ACH<0..3>,
−
ACH<0..3>, and AIGND. The +ACH<0..1> signals are tied to the two
analog input channels of your PCI-4451; the ±ACH<0..3> are tied to the
four analog input channels of your PCI-4452.
Caution
Exceeding the differential and common-mode input ranges distorts your input
signals.
AIGND is an analog input common signal that connects directly to the
ground system on the PCI-4451/4452. You can use this signal for a general
analog ground tie point to your PCI-4451/4452 if necessary, but connecting
AIGND to other earth-connected grounds is not recommended. AIGND is
not directly available if you are using a BNC-2140 accessory.
Figure 4-4 shows a diagram of the analog input stage of your
PCI-4451/4452.
Figure 4-4.
Analog Input Stage of the PCI-4451/4452
The analog input stage applies gain and common-mode voltage rejection
and presents high input impedance to the analog input signals connected
to your PCI-4451/4452. Signals are routed directly to the positive and
negative inputs of the analog input stage on the device. The analog input
+ACH
x
–ACH
x
AIGND
Calibration
Multiplexer
DC/AC
Coupling
20 dB
Attenuator
Analog
Lowpass
Filter
Differential
Amplifier
+
–
Gain = 0 dB
Gain = 10 dB
Gain = 20 dB
Gain = 30 dB
Gain = 40 dB
Gain = 50 dB
Gain = 60 dB
Gain = 0 dB
Gain = –20 dB
f
c
= 3.4 Hz
1 G
Ω
1 G
Ω
900 k
Ω
100 k
Ω
100 k
Ω
900 k
Ω
0.047
µ
F
0.047
µ
F
A/D
Converter
AIGND
