Precise measurement of metallic tube dimensions - involves use of obstacles in ultrasonic path to determine coupling medium propagation velocity

摘要

Highly precise measurements of internal and external dimensions of metallic tubes are obtained from measurements of time intervals of ultrasonic pulses. A coupling liquid matches the impedances of transmission elements to the measured object but its temperature affects the speed of sound. This problem is overcome by determining the speed of propagation. A metallic tube (2) whose internal and external dimensions are to be measured is located in a coupling medium such as water between a pair of ultrasonic probes (Ea, Eb). Two obstacles (10, 12) are placed between one probe (Ea) and the tube and one obstacle (14) is placed between the tube and the other probe (Eb). Time intervals of the echos (20, 23, 25, 27) relative to the distance apart (D) and their distances (d1, d2) from the tube permit electronic processing circuits to calculate the tube dimensions.