E1C11 09/14/2010
13:14:4 Page 490
Equation 11.39 and Equation 11.40 yield the remaining values
s min ¼ À0:976 MPa
t max ¼ 0:578 MPa
f ¼ À63:4
COMMENT Other orientations of strain gauge rosettes result in different equations relating
stress and measured strain.
Signal Conditioning
The most common form of signal conditioning in strain gauge bridge circuits is amplifying the
signal using a low noise amplifier. For an amplifier of gain G A , Equation 11.25 becomes
dE 0
E i
¼
G A k dR=R
ð
Þ
4 þ 2 dR=R
ð
Þ
¼
G A kGFe
4 þ 2 dR=R
ð
Þ
%
G A kGFe
4
ð11:41Þ
The simplified form of Equation 11.41 is suitable for all but those measurements that demand
the highest accuracy, and remains valid when dR=R ( 1. A common means of recording strain
gauge bridge circuit signals is the automated data acquisition system. A schematic diagram of such a
setup is shown in Figure 11.18.
Strain
gauge
bridge
Data-acquisition
system
Multiplexer
Amplifier
j = 1
j = 1
j = M
2
j = M
Excitation
voltage
A/D Control Output
Figure 11.18 Data acquisition and reduction system for Example 11.7.
490 Chapter 11 Strain Measurement