Campbell CR800 Series - Fieldcal() Zero or Tare (Opt 0) Example

Section 7. Installation
218
• Offset
• Two-point slope and offset
• Two-point slope only
• Zero basis (designed for use with static vibrating wire measurements)
These demonstration programs are provided as an aid in becoming familiar with
the FieldCal() features at a test bench without actual sensors. For the purpose of
the demonstration, sensor signals are simulated by CR800 terminals configured
for excitation. To reset tests, use the support software File Control
(p. 498) menu
commands to delete .cal files, and then send the demonstration program again to
the CR800. Term equivalents are as follows:
"offset" = "y- intercept" = "zero"
"multiplier" = "slope" = "gain"
7.7.11.5.1 FieldCal() Zero or Tare (Opt 0) Example
Most CRBasic measurement instructions have a multiplier and offset parameter.
FieldCal() Option 0 adjusts the offset argument such that the output of the sensor
being calibrated is set to the value of the FieldCal() KnownVar parameter, which
is set to 0. Subsequent measurements have the same offset subtracted. Option 0
does not affect the multiplier argument.
Example 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. To step through the example, use the CR1000KD
Keyboard/Display or software numeric monitor
(p. 506) to change variable values as
directed.
Calibration Report for Relative Humidity Sensor
CRBasic Variable At Deployment At 30-Day Service
SimulatedRHSignal
output
100 mV 105 mV
KnownRH (desiccated
chamber)
0 % 0 %
RHMultiplier
0.05 % / mV 0.05 % / mV
RHOffset
-5 % -5.25 %
RH
0 % 0 %
1. Send CRBasic example FieldCal() Zero (p. 219) to the CR800. A terminal
configured for excitation 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