Three-terminal controller for fiber glass bushing

Abstract

A bushing controller circuit for regulating the current flow through a fiber glass bushing to thereby control the temperature of the molten glass being drawn into fibers is disclosed. The bushing temperature is measured by a plurality of thermocouples which produce an average temperature reading that is used to control the power fed to the bushing. The bushing controller circuit is a three-terminal device connected across two sections of the bushing to regulate relative current flow in the two sections, in order to control the amount of fiber produced by each section. The bushing controller circuit includes a pair of timing circuits which operate in response to the polarity and magnitude of a control signal, produced at a remote control panel, to control the conductivity of a corresponding pair of current control devices connected across respective sections of the bushing. A reset circuit produces a signal corresponding to the zero crossing of the input AC power to synchronize the timing circuits.