Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Patent
1986-12-29
1988-12-06
Goldberg, E. A.
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
219481, 219448, 219449, H05B 374
Patent
active
047897724
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to infra-red heaters which incorporate at least one infra-red lamp and which are provided with a ballast device.
It is well known to use cyclic energy regulators and multi-position electromechanical switches in order to control the energy output of the resistance element of conventional radiant heaters for use in glass ceramic top cookers. It is also known to use multi-position electromechanical switches to control infra-red heaters which incorporate a number of infra-red lamps. However, the use of multi-position switches requires a number of series and parallel interconnections of the infra-red lamps in order to obtain a usable range of energy outputs and in practice this requires that the infra-red heater incorporates at least three infra-red lamps.
A considerable proportion of the cost of such infra-red heaters is attributable to the lamps. It is therefore desirable to reduce the number of lamps in the heater in order to reduce costs. However, it becomes difficult to provide an effective control of the energy output with a reduced number of lamps.
Multi-position switches become impractical as the number of lamps is reduced and cyclic energy regulators also present a number of problems. For example, the electrical resistance of the filament of infra-red lamps is very low at ambient temperatures and this gives rise to high inrush currents when the lamp is energised which results in a high loading on the energy regulator contacts and can overload the domestic wiring system, thus tripping the protective circuit breaker. Further, an infra-red lamp has a high visible light output which gives rise to a disturbing flashing if the lamp is repeatedly turned on and off. Moreover, when a cyclic energy regulator is at a low setting, for example for simmering, the cycle will consist of a short on-period of full power followed by a long off-period and, due to the fast response of infra-red lamps compared with conventional resistance wire elements, can raise the contents of a cooking utensil to boiling point for a short period followed by a long cooling period instead of giving a continuous simmering condition.
It has also been proposed to reduce the number of lamps by employing an electronic energy regulator, but electronic controls are themselves expensive and can be unreliable in the demanding environment of an electric cooker.
It is an object of the present invention to provide an infra-red heater which incorporates at least one infra-red lamp and which overcomes the above-mentioned disadvantages when used in conjunction with a cyclic energy regulator.
According to the present invention there is provided an infra-red heater for a glass ceramic top cooker, which heater comprises:
a dish;
a base layer of thermal insulating material supported in the dish;
a peripheral wall of thermal insulating material extending around the periphery of the base layer;
a thermal cut-out device;
at least one infra-red lamp extending across the base layer; and
a ballast device electrically connected in series with the at least one lamp.
The heater may be combined with a cyclic energy regulator, which regulator at its full power setting may connect the at least one lamp directly with its power source.
The ballast device may comprise a coil of bare wire in the form of a ballast resistor. The ballast resistor preferably has an electrical resistance approximately half the resistance at operating temperature of the at least one lamp. The ballast resistor is preferably arranged in the peripheral region of the heater. The ballast resistor may comprise two coils of bare wire electrically connected in parallel. The coil comprising the ballast resistor may be straightened in regions where the coil passes adjacent to the at least one lamp.
A further heating element may be arranged adjacent to or around the peripheral wall, a further peripheral wall being provided around the further heating element. The further heating element may comprise an infra-red lamp having a ballast resistor electrically connected in series wit
REFERENCES:
patent: 2614200 (1952-10-01), McNair
patent: 2681973 (1954-06-01), Macoicz
patent: 2959662 (1960-11-01), Crowley
patent: 4535221 (1985-08-01), Holsworth
patent: 4639579 (1987-01-01), Brooks et al.
patent: 4645911 (1987-02-01), Husslein
patent: 4700051 (1987-10-01), Goessler et al.
Goldberg E. A.
Micropore International limited
Walberg Teresa J.
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