Campbell Scientific CR9000X Measurement and Control System - Manual (Page 323)

Section 8. Processing and Math Instructions
Parameter Enter STRAINCALC PARAMETERS
Dest Variable to store strain in.
Reps Number of strains to calculate, Destination, source, and zero variables must be dimensioned accordingly.
BrConfig Bridge configuration code for strain gages The bridge configuration code can be entered as a positive or
negative number:
+ code:
V
r
= − 0 001 . ( ) Source Zero
; output decreases with increasing strain.
- code:
V
r
= − − 0 001 . ( ) Source Zero
; bridge configured so output increases with strain
This is the configuration for a quarter bridge using CSI’s 4WFB350 Terminal Input Module (i.e., enter
the bridge configuration code as -1 for 1/4 bridge with TIM.)
Code Configuration
1
Quarter bridge strain gauge : με =
− ⋅
+
4 10
1 2
6
V
GF V
r
r
( )
2 Half bridge strain gauge, one gage parallel to strain, the other at 90 ° to strain :
με
ν ν
=
− ⋅
+ − −
4 10
1 2 1
6
V
GF V
r
r
[( ) ( )]
3 Half bridge strain gauge, one gage parallel to
+ε
, the other parallel to
−ε
:
με =
− ⋅ 2 10
6
V
GF
r
4 Full bridge strain gage, 2 gages parallel to
+ε
, the other 2 parallel to
−ε
:
με =
−10
6
V
GF
r
5 Full bridge strain gage, half the bridge has 2 gages parallel to
+ε
and
−ε
: the other half
+νε
ε
and
−ν
:
με
ν
=
− ⋅
+
2 10
1
6
V
GF
r
( )
6 Full bridge strain gage, one half
+ε
and
−νε
, the other half
−νε
and
+ε
.:
με
ν ν
=
− ⋅
+ − −
2 10
1 1
6
V
GF V
r
r
[( ) ( )]
Source The source variable array for the measurement(s), the input is expected as millivolts out per volt in (the
result of the full bridge instruction with a multiplier of 1 and an offset of 0.
Zero The variable array that holds the unstrained reading(s) in millivolts out per volt in.
GF Gage Factor. The gage factor can be entered as a constant used for all repetitions or a variable array can
be loaded with individual gage factors which are automatically used with each rep. To use an array enter
the parameter as arrayname(), with no element number in the parentheses.
v Poisson ratio, enter 0 if it does not apply to configuration.
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