PROCESS AND DEVICE FOR ULTRASONIC MEASUREMENT OF TRANSIT TIME IN LIQUIDS OR SOLIDS BY THE PULSE REFLECTION METHOD

摘要

In a process for ultrasonic measurement of transit time in liquids or solids by the pulse reflection method, a test head (24) emits a shock wave pulse which traverses an approach section (22), partly penetrates the test object (pipe 20), and is partly reflected at the surface of the latter. An echo start signal is derived from this entry echo which is reflected into the test head from this surface or from a reflection of the beat from the back surface (start echo), and used to start the transit time measurement (echo start) which is stopped by a subsequent start echo (wanted signal 68) when the amplitude of the latter exceeds an adjustable threshold value (e.g. 62). The magnitude of the threshold value associated with the echo start signal is varied over time to match the variation in amplitude over time of the start echo. The threshold value is high during a first threshold (58) of variable magnitude and then decreases linearly in accordance with a predetermined function within a variable time-interval to a second threshold (62) of variable magnitude.