App-18
IM DL850E-01EN
Appendix
Calculation Example
When Determining the Shunt Resistance (Rs) from the Strain (
ε
)
Given a gauge factor (K) of 2,
Detailed equation (equation B) Rs = R × (1 − ε)/(2 × ε) .........................(6)
General equation (equation A) Rs = R × (1 − 2 × ε)/(2 × ε) ...................(7) Degree of error of 1 to 2%
Desired Strain
ε (μSTR)
Rs Value (Ω) Derived from
the Detailed Equation (6)
Rs Value (Ω) Derived from
the General Equation (7)
R = 120 Ω
R = 350 Ω
R = 120 Ω
R = 350 Ω
1 000
59 940
174 825
59 880
174 650
2 000
29 940
87 325
29 880
87 150
5 000
11 940
34 825
11 880
34 650
10 000
5 940
17 325
5 880
17 150
When Determining the Strain (
ε
) from the Shunt Resistance (Rs)
If we derive ε from equations (6) and (7),
Detailed equation (equation B) ε = 1/(1 + 2 × Rs/R) ..............................(8)
General equation (equation A) ε = 1/{2 × (1 + Rs/R)} ............................(9) Degree of error of 1 to 2%
• When the Bridge Resistance R is 120 Ω
RS Value (Ω)
Strain ε (μSTR) Derived from
the Detailed Equation (8)
Strain ε (μSTR) Derived from
the General Equation (9)
60 000
999
998
30 000
1 996
1 992
12 000
4 975
4 950
6 000
9 901
9 804
• When the Bridge Resistance R is 350 Ω
RS Value (Ω)
Strain ε (μSTR) Derived from
the Detailed Equation (8)
Strain ε (μSTR) Derived from
the General Equation (9)
180 000
971
970
90 000
1 941
1 937
36 000
4 838
4 814
18 000
9 629
9 537