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

The Pulse-Echo-Overlap method （PEO method） has now been considered to be the mest adequate method for accurate measurement of the absolute value of ultrasonic wave velocity. For reaching a realizable resoult of its high ablity of accurate time measurement, it is essential to find and implement its delay time corrections, e.g. reflection time delay, diffraction time delay, etc. Because of the unconvenience in practice of the widely used calculation method of reflection time delay, and its imperfection in theory, this paper makes a further investigation.
In this paper, a calculating procedure of the reflection time delay correction is worked out, and is also suggested an experimental determination method for its value by means of double crystals. This paper further suggests a parameter of period increment of zero phase shift △τr, and considers it to be an experimental constant, whose value is about 1.7 ns in p- raetical applications.
Furthermore, this paper suggests a criterion for correct overlap. If it is correctly over-lapped, the slope of the curve of ultrason isc wave trap time to be measured against RF period will equal to - h.