Thermal Flow Meter HNF80-B

The HNF80-B thermal mass flow meter utilizes the principle of thermal dispersion, which is a technology with excellent performance and high reliability under harsh conditions. Its typical sensing element consists of two RTDs (platinum RTDs), a velocity sensor and a temperature sensor that automatically compensates for changes in gas temperature. When the two RTDs are placed in a medium, one of the velocity sensors is heated to a constant temperature above the ambient temperature and the other temperature sensor is used to sense the medium temperature.
The gas mass flow rate through the velocity sensor is calculated from the amount of heat transfer through the sensing element. An increase in the gas flow rate increases the amount of heat carried away by the medium. This results in a consequent decrease in the sensor temperature. In order to keep the temperature constant, it is necessary to increase the operating current through the sensor.
The size of this increase is proportional to the flow rate of the medium.