How to (re)calibrate a CO2 sensor?
All gas sensors experience a certain degree of drift over time, including CO2 sensors. Even with high-quality components and robust design, small deviations can occur, eventually requiring recalibration. Manual recalibration is straightforward but time-consuming and can become costly if needed frequently. Sentera CO2 sensors avoid this issue thanks to their built-in Automatic Baseline Correction (ABC) algorithm, which extends sensor lifetime and minimizes maintenance.
Automatic recalibration algorithm
In normal indoor environments, Sentera CO2 sensors operate fully maintenance-free. The ABC algorithm continuously monitors the lowest CO2 concentration measured over each 24-hour period and assumes this value corresponds to outdoor ambient levels. After collecting several minimum values, the sensor performs a statistical self-check. If drift is detected, a correction factor is applied to restore accuracy. The sensor will work accurately when it is exposed to typical outdoor CO2 levels (±400 ppm) for several hours at least once per week.
However, when the sensor is installed in a location where CO2 levels never drop to ambient — such as 24/7 occupied rooms, hospital rooms, or security offices — the ABC algorithm should be disabled via Modbus Holding Register 40. In such cases, manual recalibration is required.
Manual Recalibration
When automatic recalibration is not suitable, the sensor can be recalibrated manually on regularly basis. The more often the sensor is recalibrated, the more accurate the readings will be.
The simplest approach is to ventilate the room (simply open a window) until CO2 concentrations return to outdoor baseline levels, then enable the automatic recalibration function for a few hours.
Alternatively, the sensor can be temporarily moved to an area where CO2 levels reliably fall to ambient values. After recalibration, the sensor can be returned to its original location.
