Ceramaspeed Limited

Micropore International Limited

Richard Charles Scott

George A Higgins

Alfie L Grasso

Apparatus is described for controlling an electric heater incorporating at least one electric heating element (2A, 2B, 2C) and energized from a single voltage alternating current supply (8). The apparatus includes a control knob (15) for manually selecting any one of a predetermined number of power settings for the heater from the voltage supply (8), the power settings varying progressively between a minimum power setting and a maximum power setting. The apparatus further includes a controller (10) adapted and arranged to supply to the electric heater within a predetermined constant time interval in each power setting a first dissipated power level and a second dissipated power level. The first dissipated power level comprises a first selected proportion of half cycles in a predetermined number of half cycles of the voltage supply and the second dissipated power level comprises a second selected proportion of half cycles in a predetermined number of half cycles of the voltage supply. In a plurality of power settings the second selected proportion is different to the first selected proportion. There is no more than one change between the first and second dissipated power levels within the predetermined constant time interval.

Apparatus for controlling an electric heater energized from a single

An electric heating method is described for use with a glass-ceramic top cooking appliance. A first sensor coil is provided in a heater associated with a first heating element and a second sensor coil is provided associated with a second heating element, the first and second sensor coils being adapted to provide first and second electrical output signals respectively. Changes in the first and second electrical output signals are monitored resulting from placement and removal of a metallic cooking utensil on and from the cook top and the ratio of change in the first electrical output signal to change in the second electrical output signal is determined. The first heating element is energised alone in accordance with a first predetermined value, or a first predetermined range of values, of the ratio, resulting from placement of a cooking utensil on substantially only an area of the cook top above the first heating element. Both the first and second heating elements are energised together in accordance with a second predetermined value, or a second predetermined range of values, of the ratio, resulting from placement of a cooking utensil on an area of the cook top above both the first and second heating elements.

Electric heating method

A radiant electric heater arrangement is provided for connection to a dual voltage supply which provides a first alternating current supply voltage and a second alternating current supply voltage higher than the first. The arrangement includes a heater having at least one heating element and a manually operable multiple discrete position switch means for manually selecting in sequence a predetermined number of discrete different power settings for the at least one heating element from the voltage supply. The arrangement further includes control means co-operating between the switch means and the supply whereby in each position of a first sequential series of discrete positions of the switch means the at least one heating element is selectively energisable from the first supply voltage in such a way that at least one selected proportion of half cycles in a predetermined number of half cycles of the first supply voltage is or are arranged for application to the at least one heating element, and further whereby in each position of a second sequential series of discrete positions of the switch means, following the first sequential series, the at least one heating element is selectively energisable from the second supply voltage in such a way that at least one selected proportion of half cycles in a predetermined number of half cycles of the second supply voltage is arranged for application to the at least one heating element. In this way a stepwise increase in power output from the heater is obtainable in operation from one position of the switch means to the next through the first and second sequential series of switch positions.

Radiant electric heater arrangement

A method is described of processing an electrical signal output from a sensor coil located in an electric heater for use under a cook top in a cooking appliance. The sensor coil is employed to operate a switch to switch on and off a heating element in the heater in accordance with placement and removal of a cooking utensil on and from the cook top. The sensor coil is arranged in the heater within magnetic influence of the electrical heating element, the heating element comprising a material which is ferromagnetic below and substantially non-ferromagnetic above a predetermined temperature within an operating temperature range of the heater. The occurrence of an increase in output signal level from the sensor coil is detected and closure of the switch is effected. Subsequently, the occurrence of a decrease in output signal level from the sensor coil is detected and opening of the switch is effected. The switch is opened for a predetermined period and closure of the switch means is subsequently effected unless within the predetermined time period a further decrease in output signal level, consecutive with the previous decrease in output signal level, is detected.

Cooking utensil detection method

A radiant electric heater (10) has two coiled resistance wire heating elements (22,24) each connected to one terminal (N) of a power supply via respective rectifiers. These rectifiers are each made up of two like-poled arms of a bridge rectifier (34) connected in parallel, and they are arranged to allow current through one heating element (22) on positive-going half-cycles of the power supply waveform, and through the other heating element (24) on negative-going half-cycles. The elements are rated for continuous power dissipation under these circumstances. A PTC thermistor (36) is connected between the ends of the heating elements connected to the rectifiers. Optionally an NTC thermistor (40) can be connected in series with the PTC thermistor. Upon initial energization the PTC thermistor is a near short-circuit, so current flows through both heating elements on both polarity half-cycles, dissipating twice their rated power. The elements increase in temperature more quickly than if they were initially energized at only their rated power, so the visible response of the elements to energization is faster. Meanwhile the PTC thermistor increases in resistance owing to self-heating, thereby removing the short-circuit after a few seconds, reducing the power dissipation in the elements to its normal level and protecting them from excessive operating temperatures.

Radiant electric heaters

An electric heater assembly for a glass ceramic top cooker includes a plurality of electric heating elements, a thermal cut-out device incorporating a first set of contacts for controlling the supply of electric current to at least one of the heating elements, and a relay associated with the thermal cut-out device and incorporating a second set of contacts for controlling the supply of electric current to at least another of the heating elements. In the event of the thermal cut-out device detecting a first predetermined temperature the first set of contacts moves from a first position to a second position causing the second set of contacts to move from a first position to a second position and in co-operation with the second set of contacts connects the heating elements in a lower power configuration or cuts off the supply of electric power to the heating elements. When the thermal cut-out device subsequently detects a second predetermined temperature lower than the first predetermined temperature the first set of contacts moves from its second position to its first position causing the second set of contacts to move from its second position to its first position thus connecting the heating elements in their original configuration.

Electric heater assemblies

A power control arrangement for controlling the power output of a plurality of resistive heating elements (9a, 9b) comprises a multi-position switch (S1, S2) for connecting the heating elements in series and in parallel, a zero voltage switch (4), AND-gate (5), clock pulse generator (6), shift register (7) and semiconductor device (8) such as a trail which cooperate to vary the duty cycle applied to the heating elements in both serial and parallel modes.

Power control for multiple heating elements

An electric radiation heater assembly for a glass ceramic top cooker includes at least one heating element having a substantial positive temperature coefficient of resistance, such as an infra-red lamp. A resistive assembly is electrically connected in series with the at least one heating element for suppressing surges of electric current due to the low initial resistance of the heating element. Switch means is operable a time interval of at least thirty milliseconds and preferably about 1/2 second after a supply of electric power to the heater is energized so as to reduce the combined electrical resistance of the heating element and the resistive assembly.

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Stourport-on-Severn, United Kingdom

Richard Charles Scott