Abstract: Transducer means mounted on a moving head produce test signals which modulate an FM transmitter on the moving head. A stationary FM receiver has demodulation means including a toggle flip-flop supplied with an FM signal corresponding to the transmitted signal, preferably an IF signal. The flip-flop changes state when its input passes through a threshold level and yields a rectangular wave output, and preferably also the inversion thereof. Short pulses are produced at edges of the rectangular wave, as by differentiation. The short pulses are applied to a sawtooth generator, preferably of the constant charging current type, to produce sawtooth waves whose amplitude and duration are proportional to the periodicity of the pulses. The sawtooth waves are filtered and the output applied to apparatus for processing and indicating variations in the object being tested.

Abstract: An interface signal gate and received interface and flaw signals are displayed by a cathode-ray tube on respective sweeps from a first sweep generator having coinciding baselines. The gate as displayed is adjustable in height, width and position to enable the operator to select the desired interface signal. When adjusted so that the height of the interface signal exceeds the gate height, a trigger signal is produced which controls a second sweep generator to display flaw signals occurring after the interface signal. Sweeps from the second generator are displaced from the sweeps of the first generator, as displayed, and alternately display received signals and a flaw signal gate which is adjustable in height, width and position to select flaw signals above an adjustable threshold level for indication, etc. Received signals and interface and flaw signal gates are continually displayed on predetermined sweeps from the two sweep generators.

Abstract: Apparatus is described including means for generating short driving pulses for an ultrasonic transducer which are of selectable PRF and highly stable. A multi-stage amplifier for received signals comprises emitter-follower transistors of approximately unity gain coupled by step-up transformers. Expanded sweeps for a cathode-ray tube (CRT) display are produced from initial ramps synchronized with the driving pulses, and supplied through a variable attenuator to a limiter. Signal gates of adjustable position and width are produced from the sweeps and maintain their relative positions with respect to the sweeps during expansion. A threshold control circuit is gated to yield output signals for an alarm, etc. when received signals within the gate exceed an adjustable threshold level, and also produces a display signal gate for the CRT which accurately indicates the displayed echo amplitude required to actuate the threshold circuit.