Campbell CR1000 User Manual

Section 7. Installation
intersects two known points sequentially entered in the FieldCal() KnownVar
parameter. Subsequent measurements are scaled with the same multiplier.
FieldCal() Option 3 does not affect offset.
Some measurement applications do not require determination of offset.
Frequency analysis, for example, may only require relative data to characterize
change.
Example Case: A soil-water sensor is to be used to detect a pulse of water moving
through soil. A pulse of soil water can be detected with an offset, but sensitivity
to the pulse is important, so an accurate multiplier is essential. To adjust the
sensitivity of the sensor, two soil samples, with volumetric water contents of 10%
and 35%, will provide two known points.
Table 32. Calibration Report for Water Content Sensor
CRBasic Variable At Deployment
SimulatedWaterContentSignal
175 mV
KnownWC
10 %
SimulatedWaterContentSignal
700 mV
KnownWC
35 %
WCMultiplier
0.0476 %/mV
The following procedure sets the sensitivity of a simulated soil water-content
sensor.
1. Send CRBasic example FieldCal() Multiplier
(p. 221) to the CR1000.
2. To simulate the soil-water sensor signal, place a jumper wire between terminals
VX1 and SE1.
3. Simulate deployment-calibration conditions in two stages as follows:
a. Set variable SimulatedWaterContentSignal 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
SimulatedWaterContentSignal 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 43. FieldCal() Multiplier
'This program example demonstrates the use of FieldCal() in calculating and applying a
'multiplier only calibration. A multiplier calibration compares the signal magnitude of a
'sensor to known standards. The calculated multiplier scales the reported magnitude of the
'sensor to a value consistent with the linear relationship that intersects known points
'sequentially entered in to the FieldCal() KnownVar parameter. Subsequent measurements are
'scaled by the multiplier.
221

Campbell CR1000 Specifications

General

Power Requirements	9.6 to 16 VDC
Data Logger Operating System	CRBasic
Memory	4 MB
Analog Inputs	16 single-ended or 8 differential
Analog Input Resolution	13 bits
Analog Input Range	+/-2.5V
Digital I/O	8
Pulse Counters	2
Communication Ports	RS-232
Operating Temperature	-25°C to +50°C
Pulse Channels	4