Sense point circuit

Abstract

The disclosure relates to a sense point circuit for sensing the active or inactive condition of an electrical path as represented by the conduction or nonconduction of a solid state device in response to an interrogating signal pulse. The sense point circuit comprises an input for receiving the interrogating signal pulses, a solid state switch such as a transistor, and a transformer having a primary coupled across the base and emitter of the transistor and a secondary coupled across the solid state device and an output coupled to the emitter of the transistor. The sense point circuit additionally includes a first resistor coupled between the input and the common junction of the base of the transistor and the transformer primary, and a second resistor coupled between the input of the sense point circuit and the collector of the transistor. When the solid state device is conductive, the primary winding of the transformer provides a substantially short circuit across the base and the emitter of the transistor, to thereby cause the transistor to be nonconductive upon the receipt of an interrogating pulse so that the interrogating pulse is conducted from the input to the output through the first resistor and the transformer primary. When the solid state device is nonconductive, the primary provides a substantially open circuit between the transistor base and emitter to thereby cause the transistor to conduct upon receipt of an interrogating pulse so that the interrogating pulse is conducted from the input to the output through the second resistor and the transistor for providing a second signal. Because the first resistor has a resistance greater in magnitude than the second resistor, the first signal magnitude is substantially less than the second signal magnitude.