System for detecting multiple superposed sheets

摘要

A system is for detecting the passage of multiple sheets along a feed path. The system includes a sensing station (12) through which the feed path passes and which has a light emitter (48) and an optical sensor (50) arranged to sense light transmitted from the light emitter through an item comprising a single or multiple sheet present at the sensing station. The optical sensor (50) provides a voltage output whose magnitude is dependent on the intensity of the transmitted light received by the optical sensor. This output is applied to the first input (58) of a log ratio amplifier (60). A voltage representative of the output of the optical sensor when no item is present at the sensing station (10) is applied to the second input of the amplifier (64). The output of the amplifier (60) is applied to data processing means (52) which then determines whether a single or multiple item is present at the sensing station. This system can be used in place of more complicated and expensive multiple sheet detect systems such as those incorporating co-operating rollers.