Method for measuring the wall thickness of a workpiece by ultra-sound

Apparatus for measuring a wall thickness of a workpiece with an ultrasonic wave, said apparatus comprising:

• means for providing a start signal corresponding to a surface echo of the ultrasonic wave and a stop signal corresponding to a rear wall echo of the wave;
• means including a saw tooth generator for generating a sequence of identical, triangular, saw tooth signals in response to said start signal and a counting-pulse generator for generating counting-pulses indicative of each reversal of the saw tooth signal in response to said start signal and terminating generation of said counting-pulses in response to said stop signal;
• a counter connected to said saw tooth generator for counting said counting-pulses;
• an analog-to-digital converter connected to said saw tooth generator for converting the amplitude of said saw tooth signal present when said stop pulse occurs to a corresponding digital value represented by at least one digital value pulse;
• and
• an adder connected to said counter and said converter for forming a sum from said counting pulses and said at least one digital value pulse, each of said counting pulses defining a constant unit of wall thickness and said at least one digital value pulse defining a fraction of said unit of wall thickness.