The thermal mass flow meter operates on the thermal diffusion principle; this technology is renowned for its excellent performance and high reliability even under harsh operating conditions. Its typical sensing elements consist of two resistance temperature detectors (RTDs) – one serving as a velocity sensor and the other as a temperature sensor that automatically compensates for variations in gas temperature. When these two RTDs are immersed in the medium, the velocity sensor is heated to a constant temperature difference above the ambient temperature, while the other temperature sensor measures the temperature of the medium. The mass flow rate of the gas flowing through the velocity sensor is calculated based on the amount of heat transferred by the sensing elements. As the gas velocity increases, the amount of heat transferred by the sensor to the medium increases; consequently, more power must be supplied to the sensor. The power required to heat the RTD by the electronic unit is directly proportional to the mass flow rate.