Switch assembly and circuit for electrically heated bedcovers

摘要

A switch assembly includes a pair of pushbuttons such as 13, each manually depressible to close contacts 15, 16 or 17, 18, and each also having a flange 26, Fig. 2 (not shown), engaging a U-shaped contact member 19 to open contacts 19b, 20, acting as a safety switch. The switch assembly controls the circuit for an electric bedcover heated by a heating resistance 38. Contacts 15, 16 are closed by depressing pushbutton 13 to initially energize relay coil 36 to close relay switch 37 which remains closed under normal conditions. Overheating causes a layer 15 of material normally insulating to become conducting and allow current flow between conductors 43 and 44, thus lowering the voltage to coil 36 and causing relay switch 37 to open. Closing of contacts 17, 18 by the other push-button (Fig. 2, not shown), shunts relay coil 36 and opens relay switch 37 manually if required. Whenever a push-button is depressed, the safety switch contacts 19b, 20 open first to interrupt the heater circuit before the contacts 15, 16 or 17, 18 close. Each pushbutton is guided for movement in the housing 10 by a projection 28 on push-button 13, moving in a guide groove 31.