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
(Vx1,SimulatedSalinitySignal,0)
VoltSE
(Salinity,1,mV2500,1,1,0,250,0.05,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.
Example 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 31.
Calibration Report for Flow Meter
CRBasic Variable
At Deployment
At Seven-Day Service
SimulatedFlowSignal
300
mV
285
mV
KnownFlow
30
L/s
30
L/s
SimulatedFlowSignal
550
mV
522
mV
KnownFlow
10
L/s
10
L/s
FlowMultiplier
-0.0799
L/s/mV
-0.0841
L/s/mV
FlowOffset
53.90
L
53.92
L
1. Send CRBasic example
FieldCal() Two-Point Slope and Offset
(p. 219)
to the
CR1000.
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
Summary of Contents for CR1000
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