GB847130A - Automatic control system for the scanning of workpieces by ultrasonic or like probes - Google Patents

Abstract

847,130. Automatic position control systems. HIRSCHMANN, F. July 21, 1958 [July 22, 1957], No. 23077/57. Addition to 806,606. Class 38 (4). In a system, as in the parent Specification, in which a probe, such as an ultrasonic transmitterreceiver, used in the non-destructive testing of workpieces is maintained in a desired position relative to the workpiece by utilizing an electrical condition of a liquid-filled region between the workpiece and an electrode on the probe to control the position of the probe automatically, capacity is the electrical condition utilized. This capacity may be supplied with current from a high-frequency oscillator and change of current with change in position may effect automatic control through a magnetic amplifier in the same manner as in the parent Specification. If more than one automatic control system is used to position the probe oscillators of different frequencies are used to prevent interaction. Non-conductive workpieces may be provided with a conductive surface layer as in the parent Specification or the workpiece may float on mercury or rest on metal powder. In the two latter cases the permittivity of the liquid should be considerably less than that of the workpiece, but the variation in the position of the probe due to the effect of variation in the thickness of the workpiece may be arranged, by suitable choice of permittivity, to be that required for ultrasonic testing. Alternatively the latter effect may be obtained by utilizing a signal, representative of thickness, from the probe itself to automatically vary the bias of the controlling magnetic amplifier.