GB780559A - Improvements in or relating to electrical control systems for heating means - Google Patents

Abstract

780,559. Control systems for heaters. COLLIER, R. Nov. 10, 1955, No. 32199/55. Class 38 (4). The temperature of heater 5, such as a hotplate energized from a source 6, is controlled by an adjustable thermal cycling switch 14 which causes periodic energization of an electromagnetic switch 7 having contacts 8 in the heater circuit and having its operating coil 9 supplied from a low-voltage source 11 and rectifier 10 over the contacts of the cycling switch, there being a further switch 12, 15, responsive to the temperature of the vessel, or the like, being heated, having contacts in series with the cycling switch and coil 9 so as to de-energize the contactor upon the vessel reaching a predetermined temperature and prevent further heating until the temperature of the vessel falls below the predetermined value. As shown, any one of four temperature-responsive switches 12, set to operate at different temperatures and having a common contact 15, may be selected by a two-gang switch 13 having contacts so interconnected that when one of the higher temperature settings is selected, say switch position LF, the temperature-responsive switches having lower settings, say those operative when switch 13 is set to positions B, S or W, short-circuit the cycling switch 14, so that the heater quickly heats up to the maximum temperature obtainable from position B of switch 13, whereupon the cycling switch becomes effective to regulate temperature over the range extending up to the response temperature of the switch 12 selected at position LF of switch 13. A pilot lamp 23 may be provided. The contactor 7 may be replaced by a solenoidcontrolled gas valve in the case of a gas-heated hot-plate. Specification 760,296 is referred to.