Patent ID: 6285094
Filing Date: 2001-09-04
Classification: G08C

Abstract:
A self-powered, current-loop controller for controlling a process variable, said controller comprisinga first light-emitting diode for indicating the presence of and controlling direction of electric current flow in said controller;a first zener diode for regulating voltage levels of said current;a pair of transistors, each for controlling current flow between an on position and an off position, and for controlling on-off signal outputs;at least one resistor for converting said current into a first voltage signal;a second zener diode for regulating a set point voltage signal;a first voltage comparator for comparing said first voltage signal to said set point voltage signal, and for controlling operation of said transistors such that when said first voltage signal exceeds said set point voltage, said first voltage comparator turns one of said transistors to said off position thereby causing said current to flow through an associated LED for visual indication and through an associated opto-isolator for controlling said process variable;a third zener diode for compensating for voltage drop across one of said transistors; andvoltage shifting means for shifting voltage level at the base of said transistors to a level at which said transistors are operable.