Campbell Scientific CR800 and CR850 Measurement and Control Systems - Manual (Page 157)

Section 7. Installation
157
CRBasic Example 27. FieldCal() Offset Demo Program
'Jumper VX1/EX1 to SE6(3L) to simulate a sensor
Public mV 'Excitation mV output
Public KnownSalt 'Known salt concentration
Public CalMode 'Calibration trigger
Public Multiplier 'Multiplier (starts at .05 mg / liter / mV,
'does not change)
Public Offset 'Offset (starts at zero, not changed)
Public SaltContent '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 * (R
0
– R
1
) + K * (T
1
– T
0
) + (S
0
– S
1
)
where,
G = gage factor (0.036 PSI/digit is typical)
R
0
= output at the zero state (out of water)
R
1
= measurement