Experimental Research On The Ultrasonic Thermometer

Aiming at the deficiency of traditional temperature measuring instrument, a high-precision ultrasonic thermometer whose measuring resolution is better than 0.001 ℃ has been developed. The temperature measurement is realized by using corresponding relation of ultrasonic wave propagation velocity and medium temperature, which means detecting the change of the ultrasonic wave velocity to do precise measurement of temperature. When the ultrasonic propagation distance is certain, precision measurement of propagation time in the medium can obtain the ultrasonic velocity, according to which the temperature can be indirectly calculated.This paper is aiming at developing a high-precision ultrasonic thermometer, with resolution better than 0.001 ℃. The design of ultrasonic thermometer is completed after analyzing the principle of ultrasonic temperature measuring systematically. The Ultrasonic thermometer consists of temperature sensors, ultrasonic drive circuit, ultrasonic echo signal processing circuit and interface circuit.The functional realization of a ultrasonic thermometer is completed by two parts, namely, hardware circuit and software algorithm. In the aspect of hardware, ultrasonic drive circuit, ultrasonic echo signal receiving circuit and high-speed data acquisition system is designed. And the FPGA is the core of whole hardware circuit, including main functions: combined with DDS technology to produce ultrasonic drive signal, make high speed sampling of ultrasonic echo signal with high resolution A/D conversion circuit and store the sampling data in internal RAM memory area built on FPGA, and do data processing for the sampling data of RAM memory.Software algorithm includes feature wave search algorithm and software subdivision interpolation algorithm. Feature wave search algorithm is used for the analysis and comparison of sampling data stored in RAM memory, and finding out the biggest feature wave with maximum amplitude in the echo signal. Software subdivision interpolation algorithm can process the sampling data of feature wave and calculate the ending time of propagation time.To ensure the precision measurement of ultrasonic propagation time, high resolution A/D conversion circuit and linear interpolation algorithm are adopted, which combines the hardware circuit and software algorithm organically, meanwhile, hardware circuit based on the FPGA makes the data be quickly handled, and ensures temperature measurement has good real-time performance.It has been verified by experiment that measurement precision of ultrasonic propagation time is better than a nanosecond level, which has further verified the design program of ultrasonic thermometer and laid a solid foundation for developing high precision ultrasonic thermometer.