GB646905A - Improvements in and relating to control apparatus for electric blankets and the like - Google Patents

Abstract

646,905. Control systems for electric blankets. BRITISH THOMSON-HOUSTON CO., Ltd. Aug. 26, 1948, No. 22539. Convention date, Aug. 30, 1947. [Class 38 (iv)] [Also in Group XXXVII] A switch for opening the circuit of an electric blanket at a predetermined time and, if desired, sounding an alarm comprises a clock 2, which may be driven by a spring or (as shown) by a synchronous motor having a coil 4 and magnet 3, the motor also driving a cam 7 through gearing at the rate of one revolution in twelve hours. A spring arm 12 biasses a follower 11 against the cam 7, and carries a permanent magnet 14 on which is mounted a contact 13 which co-operates with a contact 15 on a spring arm 16 to control the blanket heating circuit. The arm 16 is biassed away from the arm 12, but is made of magnetic material so that when a button 17 attached thereto is depressed the contacts 13, 15 are held in engagement, an adjustable stop 19 in a fixed insulating bracket 20 limiting the movement of the arm 16 so as just to permit this engagement. In operation, the position of a cam step 9 relative to the follower 11 is adjusted by manual rotation of the shaft 8 by a knob behind the clock so that a pointer 7a indicates the desired time the blanket circuit shall be opened. When the cam step 9 reaches the follower 11 the arm 12 moves down under its bias and opens the circuit, and the arm 16 raises the contact 15 so that on continued rotation of the cam 7 the contacts 13, 15 do not re-engage. The follower 11 has a magnetic extension 21, which, when the arm 12 moves down to open the blanket circuit, comes adjacent the motor magnet 3 whereby it is vibrated to sound an alarm. This vibration can be prevented by a slidable wedge 22 which, when a knob 23 is pushed in, holds the extension 21 clear of the magnet 3 yet permitting the arm 12 to move sufficiently to open the contacts 13, 15. The blanket is maintained at the desired temperature by a bimetal strip 35 heated by a series coil 33, the strip controlling contacts 34 in the blanket circuit and being adjustable by a knob 36 to vary the blanket temperature. In a modification, Fig. 5, the cam 7b has a raised step 44 which raises the follower 11 just prior to its moving down the step 9, thus causing a contact 39 on the extension 21 to engage an adjustable contact 38 on an extension 37 of the bracket 20 and shunt the heater 33 by a resistance (Fig. 6, not shown). The blanket is thus raised to a higher temperature before it is switched off, so as to provide more warmth in the early hours of the morning.