Ultrasonic measurement of sound velocity in liquids which automatically eliminates temperature dependence

This paper describes the workings of a new ultrasonic technique for measuring sound velocity in liquids which relies on a phase difference method to automatically eliminate the dependence on temperature. This technique uses a very simple circuit system which deals only with continuous sinusoidal waves and consists entirely of analog circuits. Its validity and usefulness was verified experimentally using NaCl solutions as test-liquid specimens. The design method was derived by analyzing the temperature-compensation circuit, and a temperature-compensation factor for NaCl solutions was derived from the equation for ultrasonic velocity in sea water. A compensation circuit which has a specific value of 34.2 deg//spl deg/C over a range of 25.0/spl deg/C/spl plusmn/2.0/spl deg/C was designed. This value was consistent with the experimental value of 34.0 deg//spl deg/C. The system with compensation circuit was applied to NaCl solutions of varying concentrations and was shown to yield 0.01% accurate velocity determination, independent of temperature variations of /spl plusmn/1.0/spl deg/C at approximately 25.4/spl deg/C.