Campbell CDM-A100 Series, Instruction Manual

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Appendix B. Example Programs
B-4
B.4 Measuring Bonded Foil Strain Gages
The following program example measures four quarter-bridge bonded foil
strain gages using Campbell Scientific 4WFBS350 bridge completion modules
(pn 20592) on DIFF 1-4. Equivalent resistance for each strain gage circuit is
518.52 Ω (2000 Ω in parallel with 700 Ω) and can be found in the
4WFBS350
manual . Due to current sourcing limits, only three strain gages are excited per
excitation channel.
To perform real-time offset corrections, this program uses FieldCal(). Run the
Calibration Wizard in LoggerNet or RTDAQ, and set the zmode variable to
“true”.
Bonded foil strain gages are susceptible to ambient electrical noise. Adjust the
notch frequency parameter (f
N1
) to help reduce this noise. Use the StdDev()
output processing instruction in a data table to see how changing the f
N1
parameter affects the signal output. Graphing the real-time output using
datalogger support software shows if the input noise can be reduced via the f
N1
parameter.
CRBasic Example B-4. Measuring Bonded Foil Strain Gages
'This program measures four 350-Ohm bonded foil strain gages on DIFF channels 1-4.
'4WFBS350 bridge completion modules are used on each channel.
'Declare Variables and Units
Public BattV
Public FCLoaded
Public PTemp_C
Public CReps
Public ZMode
Public QBSSMode
Public CIndex
Public CAvg
Public LCount
Public Strain(4)
Public Vr1000(4)
Public GFAdj(4)
Public BrZero(4)
Public CKnown(4)
Public GFsRaw(4)={2.0,2.0,2.0,2.0}
Units BattV=Volts
Units PTemp_C=Deg C
Units Strain=microstrain
Units Vr1000=mV/V
Units GFAdj=unitless
Units BrZero=mV/V
'Define Data Tables
DataTable (Table1,True,-1)
DataInterval (0,1,Sec,10)
Average (1,Strain(1),IEEE4,False)
Average (1,Vr1000(1),IEEE4,False)
Average (1,Strain(2),IEEE4,False)
Average (1,Vr1000(2),IEEE4,False)
Average (1,Strain(3),IEEE4,False)
Average (1,Vr1000(3),IEEE4,False)
Average (1,Strain(4),IEEE4,False)
Average (1,Vr1000(4),IEEE4,False)
StdDev (1,Strain(1),IEEE4,False)
StdDev (1,Vr1000(1),IEEE4,False)
StdDev (1,Strain(2),IEEE4,False)