Glow switch relay for blanket overheat control switch

Claim 1

An overload protection circuit for an electric blanket having a heating means and a sensing means which has a resistance that decreases with increasing temperature; the sensing means being located in said blanket in proximity to said heating means and electrically coupled in parallel with said heating means, comprising means for energizing said blanket, an electronic tube filled with ionizable gas which comprises a cathode, an anode, a cathode-anode path coupled in series with said sensing means and a temperature-sensitive movable arm having a control electrode thereon, said arm being positioned in a first position when said gas in said tube is deionized so that said cathode and said control electrode are spaced apart a predetermined distance, said predetermined distance being such that ionization of said gas will result when said blanket is energized and a potential is applied across the cathode-control electrode path of said tube if the resistance of said sensing means is above a predetermined minimum value, said arm moving from said first position to a second position following ionization of said gas to hold the cathode and the control electrode in contact with each other until said blanket is de-energized or until the resistance of said sensing means decreases below said minimum value, said circuit further comprising control means coupled to said tube and having a pair of overload contacts coupled in series with said heating means; said control means being constructed to control the opening and closing of said overload contacts in accordance with the position of said movable arm and means coupled to said tube to apply a potential across said cathode and said control electrode when said blanket is energized.