Campbell Scientific CR6 CR6 Measurement and Control System - Page 225
FieldCalStrain Examples
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Section 7. Installation Scan(10,Sec,1,0) 'CS100 Barometric Pressure Sensor measurement BP_mmHg PortSet(3,1) Delay(0,2,Sec) VoltSE(BaroPressure1,1,mV5000,5,1,0,_60Hz,0.2,600) PortSet(3,0) 'VW Piezometer measurement : Temperature and Pressure AVW200(AVWRC,ComC1,0,200,VW(1,1),1,1,1,1000,4000,1,_60Hz,1,0) 'Calculate digits and degrees C from the VW measurements Digits1 = (VW(1,1)^2)/1000 Temperature1 = 1/(1.4051E-3 + 2.369E-4 * LN(VW(1,6)) + 1.019E-7 _ * LN(VW(1,6))^3)-273.15 '==Field zero points calibration for sensor== 'FieldCal(Function,MeasureVar,Reps,0,OffsetVar,ModeVar,0,Index,Avg) FieldCal (4,Equation_Parameters(),3,0,ZeroFactor(),ModeZero1,0,1,1) 'Calculate Pore Pressure (PSI) using Digits, Temperature and calibration constants Pressure1 = (GF1 * (Digit_ZeroPoint - Digits1) + Temperature1_K * _ (Temperature1 - Temperature_ZeroPoint) _ - (BaroPressure1 - Baro_Zero)*0.014503) CallTable CalFact CallTable Table1 NextScan EndProg 7.9.12.6 FieldCalStrain() Examples Reading List: • Strain Measurements - Overview (p. 64) • Strain Measurements - Details (p. 336) • FieldCalStrain() Examples (p. 225) 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 CR6 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() Examples (p. 213) ) 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 CR6 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 using search terms such as 'micro-measurements', 'stress analysis', 'strain gages', 'calculator list', at: http://www.vishaypg.com Campbell Scientific application engineers also have resources that may assist you with strain-gage applications. FieldCalStrain() shunt-calibration concepts: 225
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