Airflow monitor

An air flow monitor is a compact sensor for monitoring air and gaseous flows. The air flow monitor is mounted as a stationary sensor directly in the flow to be monitored and works according to the calorimetric or also known as thermal anemometry measuring principle.

Measuring principle

The measuring circuit in an air flow monitor is based on a heated measuring element (thin film element, NTC / NTC thermistor ) which, depending on the version, is completely encapsulated and integrated into the housing and completely enclosed or led out.

The air flowing around the sensor causes the measuring element to cool down. Depending on the working principle, either the degree of cooling (cooling method) or the heating power that is required to regulate the heated element to a constant temperature again (constant temperature method) is used as an indicator for the flow rate.

calibration

Air flow monitors usually have a setting option for the flow speed in order to adapt the sensitivity or switching thresholds to the place of use. Intelligent solutions that calibrate the sensor at the push of a button or potentiometers are common .

weaknesses

The weakness of air flow monitors with this measuring principle lies in the detection and compensation of temperature fluctuations in the medium. These influence the measuring elements and can lead to incorrect switching.

Design

In practical use, air flow monitors in particular with measuring elements protruding from the housing are subject to corrosion , contamination, mechanical stress or offer aggressive media - such as those used in electroplating - to attack. Compact air flow monitors with a completely encapsulated housing are resistant to adverse environmental influences, but are less able to compensate for sudden temperature fluctuations that affect the measuring principle.

literature

• H. H. Bruun: Hot-wire Anemometry: Principles and Signal Analysis (English) . Oxford University Press, 1995.