Patent ID: 6693420
Filing Date: 2004-02-17
Classification: G01D

Abstract:
Control apparatus comprising at least one electrically-conductive target portion (12), and a position sensor in the form of an electromagnetic device (14) arranged in proximity with the said at least one electrically-conductive target portion (12) to provide a signal indicative of an attribute of the position of that portion relative to a portion of the electromagnetic device (14), and control means (16) connected to receive such a signal from the electromagnetic device (14) and to respond in dependence upon that signal, in which the electromagnetic device (14) comprises electrically-conductive coil means (28), electrical pulse generating means (32) connected to the coil means (28) to deliver electrical pulses thereto, and measuring means (38, 54) also connected to the coil means (28) to measure the voltage or other electrical parameter across the coil means (28) at a predetermined time interval after each pulse characterised in that the electromagnetic device (14) is a pulse induction device (14), so that, subsequent to a pulse, the decay of the voltage or other electrical parameter across the coil means (28) is slowed in relation to what it would have been had the electrically-conductive target (12) been absent, and in that the measuring means (38, 54) are such as to provide a measure of the voltage or other electrical parameter across the coil means (28) at a time when that measure would have been substantially zero had the target (12) been absent, so that the excitation energy has died away.