14
IM 701957-01E
• Detailed Equation
(1): Basic Equation of Wheatstone Bridge
(2): Equation when turned ON
(3): Equation of combined resistance R'
(4): Since R
1
to R
4
are equal, we represent
them as R
(5): Basic equation of strain
E:
Bridge voltage
V
0
:
Bridge output voltage
R
1
to R
4
: Bridge resistance (except, R
1
=R
2
=R
3
=R
4
)
Rs:
Shunt resistance (shunt resistance you wish to derive)
R':
Combined resistance when the relay is turned ON (R'=R//Rs)
V
0
=E
×
(R
1
×
R
3
–R
2
×
R
4
)/{(R
1
+R
2
)
×
(R
3
+R
4
)}
When shunt calibration is ON,
V
0
=E
×
(R
1
×
R
3
–R'
×
R
4
)/{(R
1
+R')
×
(R
3
+R
4
)}
R'=R
2
//Rs
R
1
=R
2
=R
3
=R
4
=R
Also, from the basic equation of strain,
V
0
/E=K
×
ε
/4
If V
0
/E and R
1
to R
4
are cancelled out from (2), (3), (4), and (5),
Rs=R
×
(1
–
K
×
ε
/2)/(K
×
ε
)
(Equation B): Detailed equation used to calculate
the shunt resistance (no error)
E (Bridge power supply)
R
4
R
1
V
0
R
2
R
3
Rs
6 Calibrating Using a Shunt Resistor
