Temperature measurement system based on ultrasonic phase-shift method

The purpose of this study describes an ultrasonic system which can measure air temperature based on the variations of sound speed in the air. Changes of the sound speed are in turn determined by detecting the phase-shift variations of a 40 kHz continuous ultrasonic wave. Phase angle differences between transmitted and received signals are determined by a FPGA digital phase detector and then analyzed in an 89C51 single-chip microcontroller. Theoretical accuracy of measurement is within 0.05 L at an inter-transducer distance of 10 cm. Temperature variations are measured within 10 ins. The main advantages of the temperature measurement system are high resolution, rapid temperature measurement, noncontact measurement and easy implementation.