Voltage monitor for alternating current power system

摘要

A voltage monitoring device for an AC power distribution system utilizes a liquid crystal optical shutter device capacitively coupled between a conductor of the system and electrical ground such that the transparency of the optical shutter device to light varies with the system voltage level. A light source projects a light beam through the optical shutter device to a light detector such that the output of the light detector is dependent on the system voltage. A control circuit responsive to the output of the light detector provides an output signal when the system voltage falls outside of a predetermined operating range.