CR1000 Manual - Campbell Scientific

Section 7. Installation
"offset" = "y‐ intercept" = "zero"
"multiplier" = "slope" = "gain"
7.8.1.5.1 Zero or Tare (Option 0)
Zero option simply adjusts a sensor's output to zero. It does not affect the
multiplier.
Case: A sensor measures the relative humidity (RH) of air. Multiplier is known to
be stable, but sensor offset drifts and requires regular zeroing in a desiccated
chamber. The following procedure zeros the RH sensor to obtain the calibration
report shown. Use the external keyboard / display or software numeric monitor to
change variable values as directed.
Table 22. Calibration Report for Air RH Sensor
Parameter
Argument at Deployment
mV output 1000 mV 1050 mV
KnownRH (desiccated
chamber)
0 % 0 %
Multiplier 0.05 % / mV 0.05 % / mV
Offset -50 % -52.5 %
RH reading 0 % 0 %
Argument at 30-Day
Service
1. Send CRBasic example FieldCal Zeroing Demonstration Program (p. 155) to the
CR1000. An excitation channel has been programmed to simulate a sensor
output.
2. To place the simulated RH sensor in a simulated-calibration condition (in the
field it would be placed in a desiccated chamber), place a jumper wire between
channels VX1/EX1 and SE6 (3L). Set variable mV to 1000. Set variable
KnownRH to 0.0.
3. To simulate a calibration, change the value in variable CalMode to 1 to start
calibration. When CalMode increments to 6, zero calibration is complete.
Calibrated Offset will equal -50% at this stage of this example.
Figure 48: Zero (Option 0)
4. To continue this example and simulate a zero-drift condition, change variable
mV to 1050.
154