Campbell Scientific CR1000KD CR800 and CR850 Measurement and Control Systems - Page 162
FieldCalStrain Demonstration Program
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Section 7. Installation 'Data Storage Output of Calibration Data ─ stored whenever a calibration occurs DataTable(CalHist,NewFieldCal,200) SampleFieldCal EndTable BeginProg Multiplier = 1 Offset = 0 KnownWC = 0 LoadFieldCal(true) 'Load the CAL File, if possible Scan(100,mSec,0,0) 'Simulate measurement by exciting channel VX1/EX1 ExciteV(Vx1,mV,0) 'Make the calibrated measurement VoltSE(RelH2OContent,1,mV2500,6,1,0,250,Multiplier,Offset) 'Perform a calibration if CalMode = 1 FieldCal(3,RelH2OContent,1,Multiplier,Offset,CalMode,KnownWC,1,30) 'If there was a calibration, store it into a data table CallTable(CalHist) NextScan EndProg 7.8.1.6 FieldCalStrain() Demonstration Program Strain-gage systems consist of one or more strain gages, a resistive bridge in which the gage resides, and a measurement device such as the CR800 datalogger. The FieldCalStrain() instruction facilitates shunt calibration of strain-gage systems and is designed exclusively for strain applications wherein microstrain is the unit of measure. The FieldCal() instruction (FieldCal() Demonstration Programs (p. 154) ) is typically used in non-microstrain applications. Shunt calibration of strain-gage systems is common practice. However, the technique provides many opportunities for misapplication and misinterpretation. This section is not intended to be a primer on shunt-calibration theory, but only to introduce use of the technique with the CR800 datalogger. Campbell Scientific strongly urges users to study shunt-calibration theory from other sources. A thorough treatment of strain gages and shunt-calibration theory is available from Vishay at: http://www.vishaypg.com/micro-measurements/stress-analysis-straingages/calculator-list/ Campbell Scientific applications engineers also have resources that may assist users with strain-gage applications. FieldCalStrain() shunt-calibration concepts: 1. Shunt calibration does not calibrate the strain gage itself. 2. Shunt calibration does compensate for long leads and non-linearity in the resistive bridge. Long leads reduce sensitivity because of voltage drop. 162