Campbell Scientific CR6 CR6 Measurement and Control System - Page 216
FieldCal Offset Opt 1 Example
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Section 7. Installation Scan(100,mSec,0,0) 'SIMULATE SIGNAL THEN MAKE THE MEASUREMENT 'Zero calibration is applied when variable CalMode = 6 ExciteV(U11,SimulatedRHSignal,0) VoltSE(RH,1,mV5000,U1,1,0,15000,0.05,RHOffset) 'PERFORM A ZERO CALIBRATION. 'Start by setting variable CalMode = 1. Finished when variable CalMode = 6. 'FieldCal(Function, MeasureVar, Reps, MultVar, OffsetVar, Mode, KnownVar, Index, Avg) FieldCal(0,RH,1,0,RHOffset,CalMode,KnownRH,1,30) 'If there was a calibration, store calibration values into data table CalHist CallTable(CalHist) NextScan EndProg 7.9.12.5.2 FieldCal() Offset (Opt 1) Example Most CRBasic measurement instructions have a multiplier and offset parameter. FieldCal() Option 1 adjusts the offset argument such that the output of the sensor being calibrated is set to the magnitude of the FieldCal() KnownVar parameter. Subsequent measurements have the same offset added. Option 0 does not affect the multiplier argument. Option 0 does not affect the multiplier argument. Case: A sensor measures the salinity of water. Multiplier is known to be stable, but sensor offset drifts and requires regular offset correction using a standard solution. The following procedure offsets the measurement to obtain the calibration report shown. Table 37. Calibration Report for Salinity Sensor Parameter At Deployment At Seven-Day Service SimulatedSalinitySignal output 1350 mV 1345 mV KnownSalintiy (standard solution) 30 mg/l 30 mg/l SalinityMultiplier 0.05 mg/l/mV 0.05 mg/l/mV SalinityOffset -37.50 mg/l -37.23 mg/l Salinity reading 30 mg/l 30 mg/l 1. Send CRBasic example FieldCal() Offset (p. 217) to the CR6. A terminal configured for excitation has been programmed to simulate a sensor output. 2. To simulate the salinity sensor in a simulated-calibration condition, (in the field it would be placed in a 30 mg/l standard solution), place a jumper wire between terminals U1 and U2. Set variable SimulatedSalinitySignal = 1350. Set variable KnownSalinity = 30. These variables are preset by the program. 3. To start a simulated calibration, set variable CalMode = 1. When CalMode increments to 6, offset calibration is complete. The calibrated offset will equal -37.48 mg/l. 4. To continue this example and simulate an offset-drift condition, set variable 216
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