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  3. Why do some sensors show “0” / a negative value?
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  2. General
  3. Why do some sensors show “0” / a negative value?
  1. Home
  2. General
  3. Why do some sensors show “0” / a negative value?

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

The electrochemical sensors for nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO) and ozone (O3) are pre-calibrated. Nevertheless, deviations can occur.

These are expressed in values that are too high or too low, including negative values. However, negative values are output as “0” in the smartphone app and web app. However, negative values are used internally for diagnostic purposes, e.g. for calibration – these are output on the air-Q device website.

Persistent “0” or negative readings from the electrochemical sensors indicate incorrect baseline calibration. This means that the baseline / zero line of the sensor in question is shifted and it shows values that are too low.

The air-Q therefore has its own functions for automatic calibration. This works optimally when there are no major changes in the climate during the calibration phases. The calibration can be speeded up by performing the calibration manually.

See here: How do I perform a manual calibration?

For a short time, climatic shocks can lead to negative values (e.g. strongly fluctuating temperature or humidity when opening the windows). This temporary effect need not be further considered.

Furthermore, some sensors have cross-sensitivities (e.g. the sulfur dioxide (SO2) sensor reacts negatively to alcohol. This means that the presence of alcohol reduces the sensor reading and can even lead to a negative value.

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