Full-Bridge Type Iii; Figure 4-14. Full-Bridge Type Iii Measuring Axial And Rejecting Bending Strain; Figure 4-15. Full-Bridge Type Iii Circuit Diagram - National Instruments NI PXI-4220 User Manual

Full-Bridge Type III

© National Instruments Corporation
This section provides information for the full-bridge strain-gauge
configuration type III. The full-bridge type III only measures axial strain.
Figure 4-14 shows how to position strain-gauge resistors in an axial
configuration. Figure 4-15 shows the full-bridge type III circuit wiring
diagram.
(+ )
R
2
(+ )
R
4
(– )
R
3

Figure 4-14. Full-Bridge Type III Measuring Axial and Rejecting Bending Strain

A full-bridge type III configuration has the following characteristics:
• Four active strain-gauge elements. Two are mounted in the direction of
axial strain with one on one side of the strain specimen (top), the other
on the opposite side (bottom). The other two act together as a Poisson
gauge and are mounted transverse (perpendicular) to the principal axis
of strain with one on one side of the strain specimen (top), the other on
the opposite side (bottom).
• Compensates for specimen temperature variation.
• Rejects bending strain.
• Compensates for the aggregate effect on the principle strain
measurement due to the Poisson's ratio of the specimen material.
• Compensates for lead resistance.
Sensitivity at 1000 µε is ∼ 1.3 mV
•

Figure 4-15. Full-Bridge Type III Circuit Diagram

(– )
R
1
R
4
Axial
R
3
/V
out
(– )
R
1
+
V –
+
EX
V
CH
–
(+ )
R
2
4-17
Chapter 4 Theory of Operation
R
2
Bending
input
EX
(+ )
R
4
(– )
R
3
NI PXI-4220 User Manual
R
1