©
National Instruments Corporation
25
SCC-SG Series Strain-Gauge Modules User Guide
A quarter-bridge type II has the following characteristics:
•
One active strain-gauge element and one passive, temperature-sensing
quarter-bridge element (dummy gauge). The active element is
mounted in the direction of axial or bending strain. The dummy gauge
is mounted in close thermal contact with the strain specimen but not
bonded to the specimen, and is usually mounted transversely
(perpendicular) to the principle axis of strain.
•
This configuration is often confused with the more commonly used
half-bridge type I configuration, with the difference being that in the
half-bridge type I configuration the R
3
element is active and bonded to
the strain specimen to measure the effect of Poisson’s ratio.
•
Completion resistors provide half-bridge completion.
•
Compensates for temperature.
•
Sensitivity at 1000
µε
is
∼
0.5 m
V
OUT
/
V
EX
input.
•
Used with the SCC-SG03. Dummy gauge R
3
provides quarter-bridge
completion.
Half-Bridge I
This section provides information for the half-bridge strain-gauge
configuration type I. The half-bridge type I measures either axial or
bending strain.
Figure 19.
Half-Bridge Type I Measuring Axial and Bending Strain
A half-bridge type I has the following characteristics:
•
Two active strain-gauge elements. One is mounted in the direction of
axial strain, the other acts as a Poisson gauge and is mounted
transversely (perpendicular) to the principal axis of strain.
•
Completion resistors provide half-bridge completion.
•
Sensitive to both axial and bending strain.
•
Compensates for temperature
•
Compensates for the aggregate effect on the principle strain
measurement due to the Poisson’s ratio of the specimen material.
R
3
(– )
R
4
(+ )
R
4
(+ )
(– )
R
3
Axial
Bending
