Abstract
A description is given of a technique for measuring the ultrasonic wave velocity in liquids, based upon the measurement of the total phase shift through a liquid path at frequencies in the region of 10 Mc/s. A fixed-path acoustic system is employed and the method is suitable for use over wide ranges of temperature and hydrostatic pressure. The phase difference between a modulated r.f. pulse propagated through the known liquid path and the incident pulse reflected from a solid-liquid interface is determined by cancelling each pulse separately against a continuous-wave signal adjustable in phase and amplitude. From two such measurements at slightly different frequencies the total phase shift in the liquid may be calculated. The technique is capable of very high accuracy and under suitable conditions an absolute accuracy to better than 3 parts in 105 in velocity is obtainable. Measurements of the velocity of sound in water have been made over the temperature range 23-80?C and the results are presented as a fifth-degree polynomial. A value of 1496?58 ? 0?04 m sec-1 at 25?000?C is obtained.
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