Campbell Scientific CR1000 Measurement and Control System - Manual (Page 161)

Section 7. Installation
161
7.8.1.5.5 Two-Point Slope Only (Option 3)
Some measurement applications do not require determination of offset. Wave
form analysis, for example, may only require relative data to characterize change.
Case: A soil-water sensor is to be used to detect a pulse of water moving through
soil. To adjust the sensitivity of the sensor, two soil samples, with volumetric
water contents of 10% and 35%, will provide two known points.
The following procedure sets the sensitivity of a simulated soil water-content
sensor.
1. CRBasic example FieldCal Multiplier-Only Demonstration Program
(p. 161)
to
the CR1000.
2. To simulate the soil-water sensor, place a jumper wire between channels
VX1/EX1 and SE6 (3L).
3. Simulate deployment-calibration conditions (output @ 10% = 175 mV, output
@ 35% = 700 mV) in two stages.
a. Set variable mV to 175. Set variable KnownWC to 10.0.
b. Start the calibration by setting variable CalMode = 1.
c. When CalMode increments to 3, set variable mV to 700. Set variable
KnownWC to 35.
d. Resume the calibration by setting variable CalMode = 4
4. When variable CalMode increments to 6, the calibration is complete.
Calibrated multiplier is 0.0476.
CRBasic Example 30. FieldCal() Multiplier‐Only Demonstration Program
'Jumper VX1/EX1 to SE6(3L) to simulate a sensor
Public mV 'Excitation mV Output
Public KnownWC 'Known Water Content
Public CalMode 'Calibration Trigger
Public Multiplier 'Sensitivity
Public Offset 'Offset (Starts at zero, not changed)
Public RelH2OContent 'Relative Water Content
'Data Storage Output of Calibration Data ─ stored whenever a calibration occurs
DataTable (CalHist,NewFieldCal,200)
SampleFieldCal
EndTable
BeginProg
Multiplier = 1
Offset = 0
KnownWC = 0
LoadFieldCal (true) 'Load the CAL File, if possible