Why is a special Logger Necessary for air quality measurement devices?

One might assume that numerous loggers for recording temperature and similar data already exist. However, the specificity of data loggers for air quality measurement lies in the official values on which limit values are based, typically half-hourly or hourly averages. In the United States, hourly averages are more common, while in Europe, half-hourly averages are standard. Some averages cannot be calculated immediately because they are more easily and accurately determined at a central location. An example of this is an 8-hour rolling average, which recalculates every half hour to reflect the average of the past 8 hours. In this context, averages are often arithmetic means. It is crucial to determine whether an average is valid or invalid.

If a measurement device receives an error signal, such as no airflow, this status signal must be included in the recorded values. However, if such an error status is present, the value should not be included in the average calculation. For instance, if a device or pump overheats, a portion of the average is already compromised. Regulations dictate when a value is valid or invalid, typically decided at the EU level and then implemented in modified forms within individual countries. Additionally, there are agreements among measurement networks in Austria, specifying certain procedures or actions to be handled in a unique manner. The validity of a value can be verified at the measurement network center, where it is also possible to see which and how many individual values are included in the averages.

Measurement devices are delicate instruments. They aim to detect a small portion of air within a cubic meter. However, instead of ingesting the entire volume, they typically sample between half a liter and one liter of air per minute. Detecting this small air fraction is intricate, and minor changes in conditions can easily cause errors. Therefore, functionality tests and verifications are essential. One such test involves providing the device with purified ambient air. The expected reading should be zero; if it deviates, the degree of deviation matters. Minor deviations in the lower decimal range are acceptable, but significant deviations necessitate prompt resolution. A similar check is performed at a test point (span), where a defined amount of gas is generated using this 0-air combined with a dilution or test gas from a bottle. The device then checks if the values align. If the deviation is too great, an external technician with a calibration device must determine whether the device is calibrated wrong or if there is another underlying issue. To automate this verification process, software embedded in the devices is required.