©
National Instruments Corporation
23
SCC-SG Series Strain-Gauge Modules User Guide
Theory of Operation
This section contains information about Wheatstone bridges and the
different strain-gauge bridge configuration types.
Wheatstone Bridges
All strain-gauge configurations are based on the concept of a Wheatstone
bridge. A Wheatstone bridge is a network of four resistive legs. One or
more of these legs can be active sensing elements. Figure 16 shows a
Wheatstone bridge circuit diagram.
Figure 16.
Basic Wheatstone Bridge Circuit Diagram
The Wheatstone bridge is the electrical equivalent of two parallel voltage
divider circuits. R
1
and R
2
compose one voltage divider circuit, and R
4
and
R
3
compose the second voltage divider circuit. The output of a Wheatstone
bridge is measured between the middle nodes of the two voltage
dividers (V
CH
).
A physical phenomena, such as a change in strain applied to a specimen or
a temperature shift, changes the resistance of the active sensing elements in
the Wheatstone bridge. The Wheatstone bridge configuration is used to
help measure the small variations in resistance that the sensing elements
produce corresponding to a physical change in the specimen. For more
information on strain-gauge Wheatstone bridge configurations, refer to the
section.
You use different Wheatstone bridge configurations for different tasks.
The following sections provide information that should help you determine
what bridge configuration type to use, how it works, and if it is the right
configuration type for your task.
Note
Normally load, force, pressure, and torque sensors are arranged in full-bridge
Wheatstone bridge configurations, similar to strain-gauge full-bridge configurations.
If you are measuring load, force, pressure, or torque use the SCC-SG04/24.
+
V
CH
R
1
R
2
R
4
R
3
V
EX
+
V
EX
–
–
