Spontaneous and highly accurate ultrasonic temperature measurement system for air conditioner in automobiles

Abstract

This paper presents a microprocessor-based, ultrasonic air temperature sensor system whose output controls temperature adjustment of car air conditioner (AC). Perceived thermal comfort correlates better with temperature of bulk air than temperature measured by conventional in-car temperature sensor. It uses ultrasonic measurement of changes in sound speed in air to determine temperature of bulk air. Changes in sound speed are calculated from phase shift of multi-frequency continuous wave. A 89c51 single-chip microprocessor-based signal generator and phase detector was used to record and calculate phase shift and temperature. Advantages of proposed system are high accuracy, instant detection, wider range and low cost.