Co2meter CM-0155 User Manual - Page 10
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CO2Meter
Figure 7: Filter Installation and Orientation.
We recommend installing the included humidity/particulate filter to ensure the sensing chamber and
pump baffle stays clear and corrosion free.
Theory of Operation
The CO2 sensor inside this device uses non‐dispersive infrared technology to sense, as a function of
transmitted light, the concentration of CO2 in the air. It has been factory‐calibrated to operate within
the specified range and precision.
0‐1% and 0‐30% Units Only
The sensor uses an algorithm called Automatic Background Calibration (ABC) to continuously adjust the
zero‐point to ensure accuracy is maintained. This is required to compensate for sensor drift, which
occurs normally on these units. The primary contributor to sensor drift is the normal and unavoidable
aging of the infrared light source within the sensor.
The ABC algorithm allows the CO2 sensor to dynamically shift its CO2 reading by a constant. It works via
storing the lowest CO2 sample taken over the ABC period and assuming that this low value is equal to a
known value (the target value). It then adjusts the output of the CO2 reading by the delta between
these values. This algorithm does not affect the linearization of the output signal.
For example, the ABC algorithm is enabled by default, with an ABC period of 180 hours, a target value of
400ppm, and a maximum delta of 30ppm. This operates under the principle that a CO2 level in ambient
outdoor air is 400ppm.
The sensor will keep track of the lowest CO2 reading recorded over a period of 180 hours and then
adjust the zero point based on the lowest CO2 level recorded, up to 30ppm at a time, towards that
value.
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