Campbell Scientific CR800 and CR850 Measurement and Control Systems - Manual (Page 156)

Section 7. Installation
156
Scan (100,mSec,0,0)
'Simulate measurement by exciting channel VX1/EX1
ExciteV (Vx1,mV,0)
'Make the calibrated measurement
VoltSE (RH,1,mV2500,6,1,0,250,Multiplier,Offset)
'Perform a calibration if CalMode = 1
FieldCal (0,RH,1,Multiplier,Offset,CalMode,KnownRH,1,30)
'If there was a calibration, store it into a data table
CallTable (CalHist)
NextScan
EndProg
7.8.1.5.2 Offset (Option 1)
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 23. Calibration Report for Salinity Sensor
Parameter
Parameter at
Deployment
Parameter at 7-Day
Service
mV output 1350 mV 1345 mV
KnownSalt (standard
solution) 30 mg/l 30 mg/l
Multiplier 0.05 mg/l/mV 0.05 mg/l/mV
Offset -37.50 mg/l -37.23 mg/l
RH reading 30 mg/l 30 mg/l
1. Send the program in CRBasic example FieldCal Offset Demo Program
(p. 156)
to the CR800. An excitation channel has been programmed to simulate a
sensor output.
2. To simulate the salinity sensor in deployment-calibration conditions (30 mg/l
standard solution), place a jumper wire between channels VX1/EX1 and SE6
(3L). Set variable mV to 1350. Set variable KnownSalt to 30.
3. To simulate the deployment calibration, change the value in variable CalMode
to 1 to start calibration. When CalMode increments to 6, offset calibration is
complete. Calibrated offset will equal -37.48 mg/l at this stage of the example.
4. To continue this example and simulate an offset-drift condition, change
variable mV to 1345.
5. To simulate 7-day, service-calibration conditions (30 mg/l standard solution),
set variable KnownSalt to 30.0. Change the value in variable CalMode to 1 to
start calibration. When CalMode increments to 6, 7-day, service-offset
calibration is complete. Calibrated offset will equal -37.23 mg/l.