Campbell Scientific 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bridge Terminal Input Modules - Manual (Page 29)

4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bridge Terminal Input Modules (TIM)
Assume R
D
= R
G
L G
L G
G G L
G L G
R 2R 2R
R R
R 2R 2R
R R R
V
+
+
−
Δ + +
Δ + +
=
4.4.5
Simplify
( )( )
L
G L G G
R
V =
G G L G
2R + 2R R 2R + 2R Δ +
R R R R Δ + Δ
4.4.6
Solve for ΔR
G
/R
G
( ) ⎟⎟
⎠
⎞
⎜⎜
⎛ +
=
Δ
L G R G
R R 4V R
⎝
G R G
R 2V - 1 R
4.4.7
Use the Gauge Factor to calculate micro-strain
⎟⎟
⎠
⎞
⎝
⎛
Ч
Ч Δ
=
GF R
R
G
6 10
με
( )
⎜⎜
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ + ×
=
G
L G
R
R
R
R R
2V - 1 GF
4V 6 10
με
4.4.8
4.4.1.2 Mathematical Lead Compensation Programs
Example Program 4.6. CR9000X ¼ Bridge Strain with zero offset and Lead
Compensation
This program starts with Example Program 4.2 and adds instructions to
mathematically compensate for the leads resistances effects on the Gauge
Factor (sensitivity effect). Added instructions are highlighted.
' Program name: StrainSH.C9X
Public StrainMvperV(3) : Units StrainMvperV = mV_per_V 'Raw Strain dimensioned source
Public Strain(3) : Units Strain = uStrain ‘uStrain dimensioned source
Dim GF(3) 'Dimensioned gauge factor
Public ZeromV_V(3), ZeroStrain(3)
Public ZReps, ZIndex, ModeVar
Public Leadlength(3), Lead_R(3),GF_Adjusted(3),
Public I, LeadRper100ft, Gauge_R
DataTable (STRAIN,True,-1) 'Trigger, auto size
DataInterval (0,0,0,100) 'Synchronous, 100 lapses, autosize
CardOut (0,-1) 'PC card , size Auto
Sample (3,Strain(),IEEE4) '3 Reps, uStrain, Resolution
Sample (3,StrainMvperV(),IEEE4) ‘3Reps,Stain mVolt/Volt, Resolution
EndTable 'End of table STRAIN
DataTable (Calib, NewFieldCal ,10) ‘Table for calibration factors from zeroing
SampleFieldCal ‘User should collect these to his computer
EndTable ‘for future reference
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