Improvements in electrical control systems

摘要

1,103,546. Automatic temperature control systems. WILD BARFIELD Ltd. March 3, 1965 [March 6, 1964], No.9583/64. Heading G3R. In a furnace temperature control system of the type comprising an operating coil 1 for varying the heat supply consequent upon the opening or closing of contacts 2 whose operating coil (not shown) is supplied by a main thermocouple (not shown) in the furnace, a safety arrangement comprising members 3...10 is provided to prevent the furnace from exceeding a predetermined temperature should contacts 2 fail to open, the arrangement thereafter functioning to control the furnace at its normal predetermined temperature. Thermocouple 4 and operating coil 5 are chosen to produce operation of contacts 3 at the same temperature as for contacts 2, but contacts 3 are normally maintained closed by energization of a relay 8 (through push button 10 and holding contacts 9) which opens a contact 7 to insert a bias resistance 6 in series with coil 5 and so increase its temperature setting. Permanent closure of contacts 2 produces opening of contacts 3 when a predetermined excess temperature has been reached and consequent shorting of resistor 6 to allow members 3, 4, 5 to subsequently control coil 1 at the normal furnace temperature setting. Warning devices may be included, and protection against low temperature conditions or failure of coil 1 and/or associated apparatus is envisaged. The circuit of Fig.1 may be modified by omitting the normal temperature control members, i.e. main thermocouple, contacts 2, and using the safety arrangement to heat the furnace up to a predetermined excess temperature and then maintain it at a predetermined lower temperature, Fig. 2 (not shown). Application of the invention to potentiometer bridge type control systems is discussed, and mention is made of arrangements in which the bias resistor is inserted in the safety circuit instead of being cut out, when a predetermined temperature has been reached.