Prok Devices manufactures AC Voltage Relays. LVM- Series (UV&OV) is a micro controller based voltage monitoring and supervision relay for polyphase system. It can monitor both under and over voltage conditions in the system. Both under and over voltage conditions are associated with definite time tripping characteristics. It has wide setting range for OV&UV settings and also wide range of operating time on the occurrence of fault condition. Relay provides wide range of time delay for healthy resumption of the operating voltage condition. Working principle: all the line voltages are monitored and sensed simultaneously using three independent scale down potential transducer This low level AC signal is subjected to signal condition, which includes surge suppressors and harmonic filter. The filtered signal is fed to the ADC of the industrial grade PIC micro controller. When the sensing voltage level exceeds the user set value for under or over voltage, the relay gives an output signal in the form of relay change over.