DETERMINATION OF REFLECTION TIME DELAY AND CRITERION OF CORRECT OVERLAP IN ULTRASONIC WAVE VELOCITY MEASUREMENT WITH PEO METHOD

The Pulse-Echo-Overlap method(PEO method)has now been considered as the most adequatemethod for accurate measurement of the absolute value of ultrasonic velocity.For this accurate timemeasurement,it is essential to find the time delay and implement its corrections,e.g.the correction ofreflection time delay,the correction of diffraction time delay,etc.To overcome the inconvenience of thewidely used in practice method of reflection time delay calculation,and its imperfection in theory,a newcalculation procedure of the reflection time delay correction is worked out in this paper,and an experimentaldetermination method for its value by means of double crystal is suggested.This paper further suggests aparameter of the period increment of zero phase shift Δτ,and considers it as an experimental constant,whose value is about 1.7 ns in practical applications. Furthermore,this paper suggests a criterion of correct overlap.If the echoes are correctly overlapped,the slope of the curve of the ultrasonic wave tri