Web break detector with adjustable scanning head

摘要

A system for detecting breaks in a web moving through a predetermined area including a scanner head assembly having an infrared emitter, optical filtering and an adjustable receiver for detecting the presence or absence of reflecting infrared radiation from an object within the scanner path. The scanner control system provides a power source for the emitter which pulsates at a predetermined frequency and low duty cycle, a receiver circuit incorporating selective filtering, and a phase-locked detector loop tuned to the emitter frequency for optimum selectivity and performance in the face of varying ambient light conditions. A scanner head having a linearly adjustable operating range is employed for tailoring the system to a wide range of web locations and conditions.