System for measuring the wall thickness of an object

Apparatus for measuring wall thickness of an object by ultrasonic energy, the apparatus including a transducer for transmitting ultrasonic energy into a front wall of an object and receiving echo signals from the object, a transceiver coupled to the transducer for energizing the transducer to transmit periodic pulses of ultrasonic energy and for processing the echo signals received by the transducer to derive a signal indicative of the wall thickness of the object from a time interval between received echo signals, wherein the improvement comprises:

• a discriminator circuit adapted to select a set of three successive echo signals as caued by reflections from a rear wall of the object from among a group of received echo signals received in response to each transmitted pulse of ultrasonic energy;
• a converter circuit coupled to the discriminator circuit for converting the time intervals between each set of three successive echo signals into a first pulse train indicative of the time interval between the first and second echo signal of the set and a second pulse train indicative of the time interval between the second and third echo signal of the set, said converter circuit including level control circuitry adapted to maintain the relative detection point of each echo signal of each set substantially the same;
• a comparator coupled to the output of the converter circuit for comparing each first pulse train with the corresponding second pulse train;
• and
• a processor circuit for producing a signal which effectively contributes to a measuring result representative of the wall thickness of the object only when the respective first and second pulse trains are substantially matched to each other.