Campbell CR850 - Quarter-Bridge Shunt (Option 13)

Section 7. Installation
165
'//////////////////////////// PROGRAM ////////////////////////////
BeginProg
'Set Gage Factors
GF_Raw = 2.1
GF_Adj = GF_Raw 'The adj Gage factors are used in the calculation of uStrain
'If a calibration has been done, the following will load the zero or
'Adjusted GF from the Calibration file
LoadFieldCal(True)
Scan(100,mSec,100,0)
'Measure Bridge Resistance
BrFull(Raw_mVperV,1,mV25,1,Vx1,1,2500,True ,True ,0,250,1.0,0)
'Calculate Strain for 1/4 Bridge (1 Active Element)
StrainCalc(microStrain,1,Raw_mVperV,Zero_mVperV,1,GF_Adj,0)
'Steps (1) & (3): Zero Calibration
'Balance bridge and set Zero_Mode = 1 in numeric monitor. Repeat after
'shunt calibration.
FieldCalStrain(10,Raw_mVperV,1,0,Zero_mVperV,Zero_Mode,0,1,10,0 ,microStrain)
'Step (2) Shunt Calibration
'After zero calibration, and with bridge balanced (zeroed), set
'KnownRes = to gage resistance (resistance of gage at rest), then set
'Shunt_Mode = 1. When Shunt_Mode increments to 3, position shunt resistor
'and set KnownRes = shunt resistance, then set Shunt_Mode = 4.
FieldCalStrain(13,MicroStrain,1,GF_Adj,0,Shunt_Mode,KnownRes,1,10,GF_Raw,0)
CallTable CalHist
NextScan
EndProg
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7.8.1.6.1 Quarter-Bridge Shunt (Option 13)
With CRBasic example FieldCalStrain() Calibration Demo
(p. 164) sent to the
CR800, and the strain gage stable, use the external keyboard / display or software
numeric monitor to change the value in variable KnownRes to the nominal
resistance of the gage, 1000 Ω, as shown in figure Strain-Gage Shunt Calibration
Started
(p. 166). Set Shunt_Mode to 1 to start the two-point shunt calibration.
When Shunt_Mode increments to 3, the first step is complete.
To complete the calibration, shunt R1 with the 249-kΩ resistor. Set variable
KnownRes to 249000. As shown in figure Strain-Gage Shunt Calibration
Finished
(p. 166), set Shunt_Mode to 4. When Shunt_Mode = 6, shunt calibration
is complete.