GB634660A - Improvements in or relating to electrical control devices - Google Patents

Abstract

634,660. Automatic temperature control systems. SANGAMO WESTON, Ltd. March 4, 1947, No. 6176. Convention date, June 21, 1946. [Class 38 (iv)] [Also in Group XXXVII] In an electric relay control apparatus, variations between two limits of applied current are made to effect the energization or de-energization of a load circuit. Separate relays 2, 3, Fig. 1, corresponding to the " low " and " high '' limits of regulation are employed for controlling a circuit 32, 33 which may control the power supply to a furnace. The " low " relay 2 comprises a moving coil 4 carrying an arm 5 having an iron rider 6 which co-operates with a magnetized contact 7, the " high " relay 3 being provided with similar parts 4<1>-7<1>. When the " high " limit is reached relay 3 closes contacts 61, 71 which are then held locked magnetically. The control circuit 32, 33 is thereby closed and a solenoid 14 energized to reset, by means of bell-crank levers; the " low relay 2, and operate a transfer switch 16 by moving an arm 17 from contact 19<1> to 19, both of which ara magnetized to hold a contact 20 in its set position. Thereafter, if the low limit is reached the relay 2 is operated in a similar manner and the relay 3 reset to open the control circuit 32, 33. Both relays are enclosed in single case 1. In a modification (Fig. 2, not shown), separate relays in different cases are employed, the transfer switch being outside the casings and operated by a separate auxiliary relay, energization of which is controlled in accordance with movement of the instrument pointers. In a further embodiment, Fig. 3, a single pointer 61 operates between fixed contacts 63, 63<1>, and the resetting mechanism com prises aT-arm 64, operated by solenoids 69, 69<1> and bell-crank armatures 70, 70<1>. In this embodiment the pointer is reset immediately after making the " high " or " low " contact. Specifications 429,177, 432,100 and 440,665, [all in Group XXXVII], are referred to.