Campbell Scientific CR1000 Measurement and Control System - Manual (Page 154)

Section 7. Installation
154
"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
Argument at 30-Day
Service
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 %
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.