the linear transducer in order to control the stroke length of the rod 44 the control unit 14 initiates scanning of the pipe by generating the prf signal which is supplied to the high voltage pulsar 76 the high voltage pulsar outputs a single drive pulse for each prf signal received from the control unit 14 the drive pulse is supplied to the ultrasonic transducer 62 causing it to generate a single sound pulse for every drive pulse received reflected signals received by the transducer 62 are supplied to the amplifier circuit 78 which returns the amplified signal to the control unit 14 for analysis a more detailed discussion of the operation of the control unit will now be made with reference first to fig1 which shows a block diagram of the interface circuit 82 the interface circuit includes a clock 100 control logic 102 water column wc counter 104 wall thickness counter 106 and data buffers 108 and 110 the interface circuit receives a prf signal from the computer 80 which is synchronized to the clock signal typically 60 115 mhz generated by clock 100 by a delay circuit in the control logic 102 the control logic then transmits the prf out signal to the ultrasonic transducer 62 the amplifier circuit detects the transmission of the prf out signal as the.