Pulse-echo ultrasonic apparatus

An apparatus for measuring the dimension of a workpiece which includes circuit means for periodically transmitting an ultrasonic search pulse into the workpiece and subsequently receiving an echo pulse responsive to the search pulse intercepting an acoustic impedance change, means coupled to said circuit for providing counts commensurate with the transit time of the search pulse traversing the workpiece dimension as determined by a first signal responsive to the transmitting of the search pulse and a second signal responsive to the receipt of the echo pulse, the improvement comprising:

• counting means coupled for receiving the counts responsive to each transit time and accumulating such counts to provide a transit time responsive count;
• a feedback circuit comprising a buffer storage and a divider circuit coupled to said counting means for receiving each transit time responsive count and dividing it by a value c to thereby derive a corrective count and feeding the corrective count to said counting means for updating said transit time responsive count of said counting means, and
• display means coupled for periodically displaying a value responsive to said updated count of said counting means,
• the value c being selected to be greater than the squared ratio of the accuracy of the dimension measured during one transit time interval in units of length to the desired accuracy of the dimension to be determined in units of length.