A high accuracy ultrasonic system for measurement of air temperature

This paper introduces an ultrasonic measurement system to determine the mean temperature of the air between source and receiver. The system uses measurement of changes in the local speed of sound in the air to determine the temperature of the air. The changes in the speed of sound are determined by multi-frequency continuous wave frequency modulation (MFCWFM) techniques. This paper present a simple but efficient algorithm based upon phase shifts generated by three ultrasonic waves of different frequencies. To confirm concept feasibility, two low cost 25 kHz ultrasonic transducers were positioned face to face and used to transmit and receive ultrasound. Frequency modulation of the 25 KHz carrier frequency was used to transmit three frequencies; 25kHz, 1 kHz and 100 Hz. The proposed method can give a more accurate measurement of temperature than the time of flight (TOF) and phase shift (PS) methods. The range accuracy was found to be 0.070C. The main advantages of this system are high resolution and ease of implementation.