Abstract

Apparatus for detecting and providing a signal from detection indicia that is applied to a substrate such as a controlled document for the purpose of determining the character of the document, the substrate comprising individual substrate members or an elongate relatively continuous substrate member passing through the apparatus at high speed. Speeds of between 10 to 15 linear meters per second are the order of speeds which are contemplated by the invention.The detection indicia on the controlled document comprises an area or areas which are deliberately applied to the document in a manner which renders the detection indicia substantially more conductive than the substrate.Detection is effected by establishing a capacitive element with the aid of a charging electrode passing relative to the detection indicia and in such passage inducing a capacitive charge onto the detection indicia following which movement of the charged detection indicia relative to a sensor electrode establishes a second capacitive element. The charge which remains on the detection indicia as it moves into juxtaposition relative to the sensor electrode tends to leak off through coupling with this sensor electrode. The leakage current is used to provide a signal whose amplitude is detected and to operate certain output means such as indicators, ejectors, counters, or the like which will respond in accordance with the character of the detection indicia, for example, its size.The method of the invention comprises the procedure which is followed using apparatus of the above described type.A modified form of the invention provides means for reducing if not eliminating interference with detection which might be caused by the edges of a controlled document passing through the detecting apparatus.