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Why do some sensors show “0” / a negative value?

The electrochemical sensors (such as nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide(CO), and ozone (O3)) have been calibrated before installation. However, short-term deviations in measurement values may occur due to climatic shocks (e.g., significant fluctuations in temperature or humidity when windows are opened). These deviations can manifest as values that are too high, too low, or even negative. Negative values are filtered in the smartphone app and web app and correctly output as “0.” However, for diagnostic purposes and automatic calibration, negative values are internally used and stored on the device’s webpage and in the data files on the air-Q memory card. They are also output during direct data retrieval, for example, through various smart home systems.

This temporary effect does not need to be further considered. The values correct themselves after a short period of time.

Persistent “0” or negative values in the electrochemical sensors indicate an incorrect calibration of the zero line. This means that the baseline/zero line of the respective sensor is shifted, causing it to display values that are too low. The air-Q, therefore, has its own functions for automatic calibration. Calibration can be expedited through manual calibration.

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