In order to guarantee the quality of plastic pipes and provide data for automatic control of extruding process of the plastic pipes

it is necessary that the wall thick ness of plastic pipes is measured on-line. The paper studies the signal processing of the wall thickness by ultrasonic measurement. By means of the anal-ysis of the echo signais from time domain and frequency spectrum and considering the measurement procision

we put forward the properties that the signal process-ing circuits shoukl have and design of the circuits

which have been verified by ex-perimental data.