GB1093459A - Ultrasonic thickness measurement - Google Patents

Abstract

1,093,459. Ultrasonic thickness measuring. DR. J. U. H. KRAUTKRAMER GESELLSCHAFT FœR ELEKTROPHYSIK. Aug. 1, 1966 [Aug. 4, 1965], No. 34367/66. Heading H4D. In an ultrasonic pulse-echo system for indicating reduction of the wall thickness of a test specimen below a prescribed minimum value, an ultrasonic delay line is used to define the open time of a time gate which closes immdiately before the expected arrival of the rearsurface echo from a specimen wall of the said minimum thickness and an alarm is actuated if the rear-surface echo from the test specimen falls within the open time of the gate. In the embodiment of Fig. 6, an electrical pulse corresponding to the front-surface echo received from a specimen by a conventional pulse-echo instrument 12 is selected by unit 13, passed through electrical delay line 15 (providing a fixed delay at least equal to the duration of the front surface echo) and opens gate 20. The electrical pulse is also converted into an ultrasonic pulse, delayed, and reconverted to an electrical pulse in components 16, 17, 18 respectively, constituting a piezo-electric or magnetostrictive delay line, and the reconverted pulse closes gate 20. The reception of any rear-surface echo within the open time of the gate 20 is detected by coincidence stage 21 and causes actuation of alarm 22, actuation of the alarm by the front-echo pulse being prevented by the delayed opening of gate 20. By thus comparing the transit time of an ultrasonic pulse through the wall of the specimen with the gate-open time defined using the ultrasonic delay line, it is stated that thickness measurement accuracy is improved over known systems in which the comparison is made with a purely electronically produced gate interval subject to variations due to temperature effects, operating voltage and ageing of component parts. The ultrasonic delay component 17 may take the form of interchangeable cylinders of various thicknesses to suit the thickness to be measured, and may be of the same material as the test specimen to permit direct comparison of thickness. In a modification, delay line 15 is dispensed with and a tapping on the ultrasonic delay component 17 provides the fixed delay for the gate-opening pulse. Details of known ultrasonic pulse-echo thickness measuring systems (Figs. 1 to 5, none shown), are given.