Campbell Scientific CR6 CR6 Measurement and Control System - Page 218
FieldCal Slope and Offset Opt 2 Example
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Section 7. Installation BeginProg 'LOAD CALIBRATION CONSTANTS FROM FILE CPU:CALHIST.CAL 'Effective after the zero calibration procedure (when variable CalMode = 6) LoadFieldCal(true) Scan(100,mSec,0,0) 'SIMULATE SIGNAL THEN MAKE THE MEASUREMENT 'Zero calibration is applied when variable CalMode = 6 ExciteV(U11,SimulatedSalinitySignal,0) VoltSE(Salinity,1,mV5000,U1,1,0,15000,0.05,SalinityOffset) 'PERFORM AN OFFSET CALIBRATION. 'Start by setting variable CalMode = 1. Finished when variable CalMode = 6. 'FieldCal(Function, MeasureVar, Reps, MultVar, OffsetVar, Mode, KnownVar, Index, Avg) FieldCal(1,Salinity,1,0,SalinityOffset,CalMode,KnownSalinity,1,30) 'If there was a calibration, store calibration values into data table CalHist CallTable(CalHist) NextScan EndProg 7.9.12.5.3 FieldCal() Slope and Offset (Opt 2) Example Most CRBasic measurement instructions have a multiplier and offset parameter. FieldCal() Option 2 adjusts the multiplier and offset arguments such that the output of the sensor being calibrated is set to a value consistent with the linear relationship that intersects two known points sequentially entered in the FieldCal() KnownVar parameter. Subsequent measurements are scaled with the same multiplier and offset. Case: A meter measures the volume of water flowing through a pipe. Multiplier and offset are known to drift, so a two-point calibration is required periodically at known flow rates. The following procedure adjusts multiplier and offset to correct for meter drift as shown in the calibration report below. Note that the flow meter outputs millivolts inversely proportional to flow. Table 38. Calibration Report for Flow Meter SimulatedFlowSignal KnownFlow SimulatedFlowSignal KnownFlow FlowMultiplier FlowOffset At Deployment At Seven-Day Service 300 mV 285 mV 30 L/s 30 L/s 550 mV 522 mV 10 L/s 10 L/s -0.0799 L/s/mV -0.0841 L/s/mV 53.90 L 53.92 L 1. Send CRBasic example FieldCal() Two-Point Slope and Offset (p. 219) to the CR6. 2. To place the simulated flow sensor in a simulated calibration condition (in the field a real sensor would be placed in a condition of know flow), place a 218
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