YOKOGAWA SL1400 - Page 572

App-22
IM 701240-01E
• 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
Appendix 10 Shunt Calibration of the Strain Module