Abstract: An apparatus for measuring the thickness of a clad material having an outer mother metal and an inner clad metal. The apparatus includes a transmitter crystal and a receiver crystal of a double crystal angle-type probe which contact the outer surface of the mother metal, for receiving a first echo from the boundary surface of the mother metal and clad metal, and for receiving a second echo from the inner, bottom surface of the clad metal. The apparatus further includes an amplifier for amplifying the echo signals, a detector for detecting the zero-crossing points of the echoes, a zero point determining circuit, a calculator for calculating the periods from a zero point in time to the zero-crossing points, and a calculator for calculating the thickness of the clad material and clad metal based on the calculated periods.

Abstract: Method and apparatus are disclosed for measurement of the thickness of a workpiece by periodically transmitting ultrasonic pulses into a workpiece by means of a probe provided at its front surface with a delay material, receiving ultrasonic echo pulses reflected from the bottom surface of the workpiece, measuring the period of time corresponding to the period of time elapsed from the transmission of each ultrasonic pulse to the reception of its related echo pulse minus the period of time corresponding to the propagation time of the ultrasonic pulse through the delay material which is specified by the setting of a zero-point adjusting circuit, calculating the thickness of the workpiece from such measured time periods, and displaying the thickness value thus calculated on a display.

Abstract: Method and apparatus are disclosed for measuring the thickness of a workpiece by periodically transmitting ultrasonic pulses into the workpiece, receiving ultrasonic echo pulses reflected from the bottom surface of the workpiece, measuring the period of time elapsed from the time of transmission of each ultrasonic pulse to the time of reception of its related echo pulse by counting the number of clock pulses within the time period, counting each of such measured time periods by clock pulses, and deriving from each of such counted time periods and number of clock pulses within the time periods values a signal representing the thickness of the workpiece, wherein the measurement of the elapsed time period is effected with respect to a plurality of successive echo pulses, during which the phase of the clock pulses is caused to be shifted by a predetermined amount of 2 .pi.