Low velocity thermal anemometer with precise, digitally controlled temperature compensation

Air temperature changes are an important source of uncertainty in velocity measurement using thermal anemometers, therefore, such anemometers require thermal compensation. Low velocity thermo-anemometers (LVTAs) are used for measuring air velocity in rooms where the air temperature can vary considerably. In this paper, we present a novel circuit of digitally controlled anemometer bridge and its application in the LVTAs. This circuit allows for precise digital change of the resistance and temperature of the velocity sensor depending on the air temperature. The heat transfer from the sensor to the air is analyzed considering the changes in the resistance of the velocity sensor and the impact of temperature on the air thermal conductivity and viscosity. Based on this analysis, the LVTA temperature compensation method is developed. We propose a method to control the temperature of the velocity sensor so that the output voltage of the LVTA is independent of changes in air temperature.