The WSERD air flow monitor is suitable for monitoring fans, control dampers, humidifiers and electric heating registers in accordance with DIN 57100, Part 420 and for use with DDC systems. The air flow monitor works according to the calorimetric principle. The heat extraction by the air flow is measured and converted into the switching value. The sensor contains a heating element and two temperature sensors. A microcontroller controls the heating and measures the temperature differences. It calculates the air flow velocity from the stored calibration curves and transmits the value serially to the control unit. Here, another microcontroller determines the switching behavior of the two relays from the default values of the setting controllers. It is mounted on the duct using the mounting flange included in the scope of delivery.