Adaptive Measurement Control of a Thermal Flow Sensor

In the present work, an adaptive gain switching control strategy and a digital temperature compensation technique are integrated with a hot-thermistor anemometer to achieve sensor speed and accuracy improvement. The limitation of the Wheatstone bridge technique for temperature thermistors is compensated to achieve accuracy improvement. The feedback control gains are adapted to the particular range of airflow rates to achieve faster response. Simulation results have confirmed the response speed and accuracy improvement with the proposed digital sensor system. The proposed design has been implemented, and experiments have been conducted. Compared to an original thermal flow sensor with analog circuit, the measurement speed is significantly improved at low airflow rates with adaptive feedback control gains implemented in the prototype digital sensor system. The developed digital sensor system possesses desirable features such as a direct interface to the computer through a serial port, easy change of operational parameters and sensor configurations, and energy conservation, as well as simpler control design with the use of Pulse Width Modulation (PWM) to control the probe heater power.