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How to recalibrate a CO2 sensor?

Sensors in an HVAC environment

Sentera CO2 sensors do not require manual recalibration. They use an intelligent calibration algorithm to automatically recalibrate themselves once they are installed. This feature eliminates one of the biggest concerns surrounding CO2 sensing: sensor drift and routine maintenance for recalibration.

Virtually all gas sensors are subject to some sort of drift, including CO2 sensors. The degree of drift is partially dependent on the use of quality components and good design. But even with good components and excellent design, a small amount of drift can still occur in the CO2 sensor. This may ultimately result in the need for a sensor to be recalibrated. Such manual recalibration process is simple but it is time consuming and therefore it can turn into a significant expense if recalibration is required frequently. Thanks to the intelligent recalibration algorithm, the sensor service life is extended and significant (maintenance) cost savings can be realised.

How does the automatic recalibration algorithm work?
The microprocessor of the sensor remembers the lowest CO2 concentration that occurred during the past 24 hours. This low point is assumed to be the outside CO2 level. The sensor is smart enough to discount periodic elevated readings that might occur if, for example, a space was exceptionally used 24 hour per day. Once the sensor has collected 14 minimum CO2 levels, it performs a statistical self-analysis. If the analysis concludes that there is sensor drift, a small correction factor is made to the sensor calibration to compensate the drift.

It is important to notice that Sentera CO2 sensors are designed for applications where spaces are periodically unoccupied for 4 hours per day or more so that indoor CO2 concentrations can drop down to typical outside levels.

If a Sentera CO2 sensor is applied in an application that is unlikely to see regular outdoor CO2 concentrations, then the self-calibration algorithm should be deactivated. This can be done via Modbus Holding Register 40. By default, the self-calibration algorithm is enabled.