Co Sensor Calibration - netvox RA08D (S) Series User Manual

7. CO Sensor Calibration
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(1) Target Calibration
Target concentration calibration assumes that sensor is put into a target environment with a known CO
concentration value must be written to Target calibration register.
(2) Zero Calibration
Zero-calibrations are the most accurate recalibration routine and are not at all affected performance-wise by having an available
pressure sensor on host for accurate pressure-compensated references.
A zero-ppm environment is most easily created by flushing the optical cell of the sensor module and filling up an encapsulating
enclosure with nitrogen gas, N2, displacing all previous air volume concentrations. Another less reliable or accurate zero reference
point can be created by scrubbing an airflow using e.g. Soda lime.
(3) Background Calibration
A "fresh air" baseline environment is by default 400ppm at normal ambient atmospheric pressure by sea level. It can be referenced in
a crude way by placing the sensor in direct proximity to outdoor air, free of combustion sources and human presence, preferably during
either by open window or fresh air inlets or similar. Calibration gas by exactly 400ppm can be purchased and used.
(4) ABC Calibration
The Automatic Baseline Correction algorithm is a proprietary Senseair method for referencing to "fresh air" as the lowest, but required
stable, CO -equivalent internal signal the sensor has measured during a set time period. This time period by default is 180hrs and can
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be changed by the host, it's recommended to be something like an 8 day period as to catch low-occupancy and other lower-emission
time periods and favourable outdoor wind-directions and similar which can plausibly and routinely expose the sensor to the most true
fresh air environment.
If such an environment can never be expected to occur, either by sensor locality or ever-presence of CO
to even lower concentrations than the natural fresh air baseline, then ABC recalibration can't be used. In each new measurement period,
the sensor will compare it to the stored one at the ABC parameters registers, and if new values show a lower CO
while also in a stable environment, the reference is updated with these new values. The ABC algorithm also has a limit on how much
it is allowed to change the baseline correction offset with, per each ABC cycle, meaning that self-calibrating to adjust to bigger drifts
or signal changes may take more than one ABC cycle.
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concentration. A target
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emission sources, or exposure
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-equivalent raw signal
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