Campbell Scientific CR1000KD CR800 and CR850 Measurement and Control Systems - Page 157

Section 7. Installation CRBasic Example 27. FieldCal() Offset Demo Program 'Jumper VX1/EX1 to SE6(3L) to simulate a sensor Public mV Public KnownSalt Public CalMode 'Excitation mV output 'Known salt concentration 'Calibration trigger Public Multiplier Public Offset Public SaltContent 'Multiplier (starts at .05 mg / liter / mV, 'does not change) 'Offset (starts at zero, not changed) 'Salt concentration 'Data Storage Output of Calibration Data -- stored whenever a calibration occurs DataTable(CalHist,NewFieldCal,200) SampleFieldCal EndTable BeginProg Multiplier = .05 Offset = 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(SaltContent,1,mV2500,6,1,0,250,Multiplier,Offset) 'Perform a calibration if CalMode = 1 FieldCal(1,SaltContent,1,Multiplier,Offset,CalMode,KnownSalt,1,30) 'If there was a calibration, store it into a data table CallTable(CalHist) NextScan EndProg 7.8.1.5.3 Zero Basis (Option 4) Case: A non-vented piezometer (water depth pressure transducer) needs its offset zeroed before deployment. Because piezometer temperature and barometric pressure have strong influences on the pressure measurement, their offsets need to be zeroed as well. The relationship between absolute pressure, gage pressure, and piezometer temperature is summarized in the linear equation, pressure = G * (R0 - R1) + K * (T1 - T0) + (S0 - S1) where, G = gage factor (0.036 PSI/digit is typical) R0 = output at the zero state (out of water) R1 = measurement 157