Campbell Scientific 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bridge Terminal Input Modules - Manual (Page 44)

4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bridge Terminal Input Modules (TIM)
Subtracting the unstrained (zero) result from the strained result gives V
r
:
g D
g
g g D
g g
unstrained strained
r R R
R
R R R
R R
Vin
Vout
Vin
Vout
V
+
−
Δ + +
Δ +
= ⎟
⎠
⎞
⎜
⎝
⎛
− ⎟
⎠
⎞
⎜
⎝
⎛
=
4.5.4
( ) ( )
g D g g D
g D
R R R R R
R R
+ × Δ + +
Δ ×
=
The terminal input module is selected so that R
D
= R
g
; Substituting R
g
for R
D
:
38
V
R R
R R R
R R
R
R
R R r
g g
g g
g g g
g
g g
=
R R R R
g g
g g g
⋅
+ + ⋅ +
=
Δ ⋅
+
Δ
=
+
Δ
Δ Δ Δ ( ) 2 4 2 ( ) 4 2
4.5.5
Solving for strain:
( )
g r g g
R V R R Δ = Δ + 2 4
g
R R
r g r g
V R V Δ = Δ + 2 4
V R R V R
r g g r g
= Δ − 2 4 Δ
( )
r g r g
V R V R 2 1 4 − Δ =
4
1 2
V
V
R
R
r
r
g
g
−
=
Δ
4.5.6
Strain is calculated by dividing equation 4.5.6 by the gage factor. The units are
converted to microstrain by multiplying by 10
6 uS/S.
( )
με =
⋅
−
=
⋅
4 10
1 2
10 6 6
V
GF V
R
GF R
r
r
g
g
Δ
4.5.7