Patent ID: 6504387
Filing Date: 2003-01-07
Classification: G01D

Abstract:
An item detection/inspection arrangement comprising at least four capacitor plates arranged together in at least two pairs of opposing or generally opposing plates, forming at least two capacitive cells, to provide, in use, at least two intersecting electric fields, items passing through said fields, in use, producing respective signals/pulses dependent on the changes of capacitance for the pairs of plates, and processing means for producing from said signals/pulses, detection/inspection data for said items;wherein one plate of each pair is a sense plate having a voltage induced thereat by the driving, in use, of drive plate means formed by at least said opposing or generally opposing plate of the pair; wherein the drive plate means comprises at least one further capacitor plate, said opposing or generally opposing plate and said further plate being on respective sides of a transducer providing said intersecting electric fields, in use, said further plate being on a side of the transducer at an angle of 90Â° or greater to respective sides of the transducer on which are said sense plate and said opposing or generally opposing plate; and wherein the capacitor plates are formed from electrically conducting material on the inner surface of an insulating layer, which layer has its outer surface formed with electrically conducting material, said electrically conducting material of said outer surface, in use, being at a voltage which provides a screen to shield a sensing area of the transducer from items outside said area.