Photo-control device employing thermal relay

Claim 1

A THREE TERMINAL PHOTO-CONTROL DEVICE HAVING A PAIR OF TERMINALS CONSTRUCTED AND ARRANGED FOR CONNECTION TO A SOURCE OF ALTERNATING POTENTIAL, A THERMAL RELAY INCLUDING A RESISTANCE HEATER HAVING A PAIR OF ELECTRODES CONNECTED ACROSS SAID PAIR OF TERMINALS AND A NORMALLY CLOSED THERMALLY RESPONSIVE MEMBER CONSTRUCTED AND ARRANGED TO CONNECT ONE OF SAID PAIR OF TERMINALS TO A THIRD TERMINAL, AN IMPEDANCE MEANS IN CIRCUIT BETWEEN SAID ELECTRODES AND SAID PAIR OF TERMINALS, A DIODE CONNECTED IN A FIRST SENSE ACROSS SAID ELECTRODES, A CONTROLLED RECTIFIER HAVING A GATE ELECTRODE AND HAVING ANODE AND CATHODE ELECTRODES CONNECTED IN AN OPPOSITE SENSE ACROSS SAID ELECTRODES, A PHOTO-SENSITIVE RESISTOR AND AN IMPEDANCE CONNECTED IN SERIES ACROSS SAID ELECTRODES, THE GATE ELECTRODE OF SAID CONTROLLED RECTIFIER BEING CONNECTED TO THE JUNCTION BETWEEN SAID PHOTO-SENSITIVE RESISTOR AND SAID IMPEDANCE TO PROVIDE A GATE POTENTIAL INVERSELY RELATED TO THE LEVEL OF AMBIENT ILLUMINATION, SO THAT SAID RESISTANCE HEATER WILL BE SHORT-CIRCUITED WHEN THE LEVEL OF AMBIENT ILLUMINATION FALLS BELOW A PREDETERMINED VALUE WHEREBY SAID THERMALLY RESPONSIVE MEMBER WILL CLOSE TO CONNECT THE ONE OF SAID PAIR OF TERMINALS TO SAID THIRD TERMINAL.