Safety cutout for electric blanket - has two variable and two constant resistances forming Wheatstone bridge unbalanced at preset temperature

摘要

The safety cut-out automatically disconnects the supply to the electric blanket at a pre-set temperature. It comprises a Wheatstone bridge formed by two resistances (1, 2), their values increasing with temperature, and two resistances (3, 4) whose values remain constant. The supply (5, 6) is connected to two opposite terminals (7, 8) of this bridge. The remaining two terminals (9, 10) form a circuit with a negative resistance (11) and a heating resistance (12), the latter opposite a bimetal strip contact (13, 14, 15). The temperature increase causes an unbalance in the bridge, generating a secondary current and heating the bimetal strip. This strip distorts and breaks the supply to the blanket.