GB899124A - Improvements in and relating to ultrasonic testing - Google Patents

Abstract

899,124. Automatic alignment control systems. KELVIN & HUGHES Ltd. Feb. 11, 1959, No. 5280/58. Class 38 (4). [Also in Group XL (c)] An apparatus comprises transducer means for injecting ultrasonic pulses into a body and for receiving the pulses after traversing the body, there being means for deriving a signal indicative of the time difference between the arrival of the received pulses and other pulses which either have traversed a path in the body different from that traversed by the firstmentioned pulses or are reference pulses, and means for using the signal to control the position of the transducer means relative to the body such that the signal is maintained at a minimum value. Pulses from unit 26 feed a transmitter 29 which causes transmitting/receiving probe 10 to inject pulses into the test body. Received pulses are passed via unit 33 to a comparison circuit 48, the pulses being maintained constant in amplitude by A.G.C. 38. If the A.G.C. cannot maintain constant amplitude an alarm system 40 is actuated. A gating circuit 35 allows unit 33 to be operative only during predetermined periods after each transmitted pulse. Pulses from a generator 47 are also fed to the circuit 48, which gives a signal indicative of the time difference between the two sets of pulses fed to it. The signal is fed to a meter 49 and, via an amplifier 50, to a servo-mechanism 51 which moves the probe in such a manner that the signal is maintained at a minimum. Generator 47 may be replaced by a second probe which transmits and receives pulses along a path different from that associated with probe 10, and the probes may operate with transverse, surface or Lamb waves. The invention may be used for automatic control of a manufacturing process. As applied to a welding apparatus, the transducer means and the welding electrode are mounted on a movable carriage. The transducer means are mounted ahead of, and are shielded from, the electrode. A coupling liquid is provided between the transducer probes and the material to be welded, the probes being capable of limited vertical movement by being hinged to the body of the carriage.