Control system for light output of fluorescent tube - uses loop circuit containing up-down counter to provide successive correction signals for power control circuit

摘要

A photocell receives light from a fluorescent tube to be controlled. The photocell output is amplified and applied to an analogue-digital converter. A digital comparator with a reference voltage input has positive and negative outputs which provide inputs for NAND gates. The positive signal is clocked into the count input (24) of a counter while the negative signal is applied to the count down input. A clock circuit controls the converters and controls the counter through a timing circuit. A digital-analogue converter receives successive correction signals from the counter to control a power circuit for the supply to the tube. The clock defines the number of corrections per second.