During machining or forming processes, the use of coolants, for example, may generate toxic aerosols, smoke or vapours. Extraction systems ensure that these do not escape from the machine. What is very important is to maintain the ideal flow velocity. If the suction is too weak, the dangerous vapours would not be completely extracted. On the other hand, too strong an extraction flow could suck in chips or cooling lubricant which could clog the filter. The flow sensor, which operates according to the calorimetric measuring principle, has been developed especially for this purpose. It is distinguished by a robust full-metal probe that is resistant to aggressive aerosols, vapours and any particles carried in the extracted air. This ensures a long service life of the sensor. The integrated temperature measurement reduces costs and installation complexity, as no additional sensor is required.