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return (À or LOW) line and ground (GRD) at the DAS board. The differential-ended connection is
less prone to common-mode voltage errors. But if the measured voltage exceeds the board’s CMV
range limit specification, it can be damaged.
Special Signal Conditioning Modules
Signal conditioning modules exist for different transducer applications. They connect between the
transducer and the data-acquisition module. For example, resistance bridge modules allow the direct
interfacing of strain gauges or other resistance sensors through an on-board Wheatstone bridge, such
as depicted in Figure 7.24. There are temperature modules to allow for electronic thermocouple cold
junction compensation that can provide for signal linearization for reasonably accurate (down to
0.5
C) temperature measurements.
Data-Acquisition Triggering
With DAS boards, data acquisition or equipment control can be triggered by software command,
external pulse, or on-board clock. Software-controlled triggers can send TTL-level pulses to
external devices for synchronization, activation, and control.
G
Gauge 2
Gauge 1
Gauge 4
Gauge 3
S3
4
S
2
S
R
R
R
+
–
E supply
E i
Channel 1
Channel 1
Amplifier
A/D
M
u
l
t
i
p
l
e
x
e
r
I
n
t
e
r
f
a
c
e
P
C
b
u
s
Figure 7.24 A strain-gauge interface. Gauges are connected by wires to the interface.
292 Chapter 7 Sampling, Digital Devices, and Data Acquisition