GB2249386A - Cooker hobs - Google Patents

Description

2 2 '+ 4 j _) -:} COOKER HOBS.

This invention relates to cooker hobs and concerns glass ceramic cooker hobs. Glass ceramic cooker hobs are now well known and have an advantage to the user that they present a flat, continuous surface to the user which is relatively easy to clean. The heating positions on the hob are generally indicated by etched or otherwise formed lines on one surface as decided by the hob manufacturer. In practice, that is all that is provided apart from a surface pattern, although it is also possible to obtain hobs which provide a visual indication of which heating portion is on, in the form of an illuminable device to is one side of the hob. For example, in the case of a hob with four heating positions there may be four lamps arranged in a square to one side of the hob and arranged to be illuminated when its associated heating position is on. The heating means is invariably electrically energised and some, such as halogen heaters, will illuminate their associated heating position. An object of the present invention is to provide such a hob with means for indicating which heating position is in use and developments thereof can provide an indication of the magnitude of the power being applied thereto. According to the invention there is provided a glass ceramic cooker hob comprising means for heating the contents of a utensil placed on a predetermined heating position on the hob, means for indicating the heating position comprising a plurality of illuminable devices, and means for energising said illuminable devices. The illuminable devices may be arranged substantially in a circle at or near the periphery of the heating position.

The illuminable devices may, preferably, be light-emitting diodes. The means for energising may be arranged to energise the illuminable devices when power is supplied to the heating means. The means for energising may be arranged to energise the illuminable devices at a first level when no power is supplied to the heating means and at a second level when power is supplied to the heating means.

The means for energising may be arranged to energise the illuminable devices at a variable level in dependence upon the magnitude of power supplied to the heating means. The means for energising may be arranged to energise the illuminable devices in a predetermined sequence and the devices may be illuminated sequentially at a rate dependent upon the magnitude of the power supplied to the heating means. The invention may further include a combination of two or more of the arrangements of the next preceding six paragraphs. Preferably, the heating means comprises an induction heating means. The invention will now be described by way of example with reference to the accompanying drawing, in which: Fig.1 shows a plan view of a glass ceramic hob according to an embodiment of the invention, Fig.2 is a side view of part of the hob of Fig.1 to a different scale, Fig.3 is a circuit diagram of two light-emitting diode (LED) rings for the hob of Fig.l. Fig.4 is a block circuit diagram of another LED drive circuit. Fig.5 is a block circuit diagram of a further LED drive circuit.

Fig.6 is a schematic circuit diagram for a digital indicator for use with the hob of Fig.i.

In the drawings, like parts are given like references.

Referring to Figs.1 and 2, there is shown a glass ceramic hob 10 suitable for use with the usual utensils such as pans (not shown).

Two heating positions 12, 14 are generally defined, in use, by two sets 16, 18 of light emitting diodes 20 mounted below the hob and which when energised shine through the hob 10 as shown.

Two alpha-numeric displays 22, 24 are also provided below the hob and their purpose will be described hereinafter.

Each heating position is provided with a similar heating means, one 26 of which is shown in outline in Fig.2.

The heating means comprises an inductance heater primary coil 26 resiliently mounted on a support bracket 28 by way of spring loaded bolts 30. Means 32 is provided for supplying current to the coil 26.

In use, a utensil of a suitable metal placed on the heating position will act as the secondary and food or other material placed in the utensil will be heated in known manner.

Fig. 3 shows a circuit diagram of an energising means for the LEWs 20 of the heating positions 12, 14.

The circuit 32 comprises a d.c. power supply 34 having input terminals 36, 38 for connection to the 240V a.c.

mains supply and output terminals 40, 42 arranged to supply a 24 volt d.c. supply to the two sets of L.E.D.1s.

Each L.E.D. is coupled in series with a 1 K ohm resistor 21 and the L.E.D./resistor combination for each set is connected in parallel across the d.c. supply, so that as shown they provide a constant level of light through the hob 10 to the user.

Referring now to Fig.4, there is shown a circuit for energising a ring 16 or 18 in a manner dependent upon the power supplied to the associated heating means.

A filtered and smoothed bridge rectifier circuit 44 having input terminals 36, 38 for connection to the 240V a.c. mains has output terminals 46, 48 for connection to the ring circuit 16 (or 18).

Across the terminals 46. 48 is connected a 2.2 K ohm resistor 50 and a 15V zener diode 52 which supplies a stabilised 15 Volt supply to a square wave oscillator circuit shown within the broken line 54 and designed to have a pulse repetition frequency (p.r.f.) of about 300 Hz.

The oscillator comprises an integrated circuit amplifier 56 which could be, for example, one quarter of an integrated circuit type LM.324 (quad voltage comparator) as manufactured by National Semiconductor Corporation (N.S.C.) and is configured to operate as a square wave oscillator. By virtue of a feedback loop comprising diodes 58, 60 and variable resistor 62 the mark-space ratio of the square wave output,can be varied substantially continuously over a wide range. Thus the current through the L.E.D.Os 20 which can be ultrabright L.E.D.'s type HLMP-D105 as manufactured by Hughlett Packard, is controlled by an NPN trarmsistor 64 having its base coupled to the output of the oscillator 54 as shown. The mark-space ratio of the signal applied to the base of transistor 64 and therefore the current to the L.E.D.Os 20 can be varied by variation of the resistance of resistor 62.

The control shaft of the resistor 62 is connected physically to the user's power control (not shown) for the induction heater which would normally be mounted on the front panel or near the top of the hob, such that as the heating power is increased the current through and therefore the brightness of the L.E.D.'s increases in is sympathy therewith, for example, the illumination can be increased or decreased in a manner somewhat analagous to that of a gas ring. Thus, the user has an immediate. indication of the power to be dissipated in a utensil placed on the associated heating position. Referring now to Fig.5, there is shown a circuit for energising a ring 16 or 18 in a manner dependent upon the power supplied to the associated heating means. The 15 Volt d.c. output from rectifier 44 is coupled to a variable p.r.f. square wave oscillator shown within the broken line 70 and comprising an amplifier 72, which may be one fourth part of an integrated circuit type LM.324, connected as shown to provide a square wave output variable between 0.1Hz and SHz. The output of the oscillator 70 is coupled to the input of a divide by 10 circuit 74, which may be an integrated circuit type C.D.4017 (decade counter/divider) as manufactured by N.S.C. Each of the ten L.E.D.Is 20A to 20J in a ring is coupled by way of serial resistors 76, 78 respectively between the positive and negative d.c. lines to energise the L.E.D. Is to a "half bright" level of illumination. Each of the L.E.D.'s 20A to 20J in the ring is also coupled to an associated NPN transistor SOA to 80J which is effectively arranged in parallel with associated resistor 78A to 78J. The base electrodes of the transistors are coupled to appropriate outputs of the divider 74. In use when power is supplied to the associated heater 26, the output of the oscillator 70 is coupled by way of the divider 74 sequentially to the transistors 80A to 80J which are switched on in turn effectively to short circuit the associated resistor 78 and increase the current through and therefore the brightness of the associated L.E.D., "full brightness".

Thus, when the heating power is off the L.E.D.1s are all illuminated at "half brightness" and when heating power is supplied, the L.E.D.Is are illuminated at "full brightness" and-sequentially around the ring at a frequency dependent upon p.r.f. of the oscillator 70. By coupling the adjustment control of the variable resistor 82 which controls the p.r.f. of oscillator 70 to the user's power control for the heater the p.r.f. can be varied so as to increase with increase in heating power.

Thus, as the power is increased the L.E.D.s are fully illuminated sequentially around the ring at a rate which increases with increase in power to give the user an immediate indication of the heat to the transferred to the contents of a utensil placed on the heating position. Referring now to Fig.6 there is shown a block circuit diagram of a digital indicator for use with the invention. Means, such as a current transformer 84 arranged around the current supply lead 86 to the induction coil 26, is provided to generate a voltage across resistor 88 dependent upon the heating current. The voltage developed across resistor 88, which can conveniently be 1 volt for each amp flowing in line 86, is coupled by way of a 50 ohm impedance coaxial cable to the input of a voltage measuring device, such as an analog to digital converter or a digital voltmeter 90 having a three digit display 92. The display 92 can be arranged to display the converted voltage as 0 - 100 (another as 0 - 9) or any other convenient manner. The display 92 which can typically be a L.E.D. display can be mounted beneath the glass ceramic hob to be visible thereto to the user. The current transformer 84 could typically be a No.27 Ferrite Bead (Ferronics 11-122-B) wound with 25 turns of No. 30 enamelled wire.

other alpha-numeric displays can be provided to-provide information useful to the user, including a clock, a timer which can count up from zero, a timer which can count down to zero from a preset time and so on. A timer could additionally be used to control the power to a heating position during a cooking operation and switch off the current to the heating coil at the end of the present period.

Claims (1)

1. CLAIMS.

   1. A glass ceramic cooker hob comprising means for heating the contents of a utensil placed on a predetermined heating position on the hob, means for indicating the heating position comprising a plurality of illuminable devices, and means for energising said illuminable devices. 2. A hob according to claim 1, wherein the illuminable devices are arranged substantially in a circle at or near the periphery of the heating position. 3. A hob according to claim 1 or 2, wherein the illuminable devices are light-emitting diodes. 4. A hob according to claim 1, 2 or 3, wherein the is means for energising is arranged to energise the illuminable devices when power is supplied to the heating means. 5. A hob according to claim 1, 2, 3 or 4, wherein the means for energising is arranged to energise the illuminable devices at a first level when no power is supplied to the heating means and at a second level when power is supplied to the heating means. 6. A hob according to any one of the preceding clains, wherein the means for energising is arranged to energise the illuminable devices at a variable level in dependence upon the magnitude of power supplied to the heating means. 7. A hob according to any one of the preceding claims, wherein the means for energising is arranged to energise the illuminable devices in a predetermined sequence and the devices are illuminated sequentially at a rate dependent upon the magnitude of the power supplied to the heating means.

   4 8. A hob according to any one of the preceding claims, comprising an illuminable information display means and means for illuminating said display. 9. A hob according to claim 8, wherein the display means comprises alpha or numeric or both alpha and numeric characters. 10. A hob according to any one of the preceding claims, wherein the heating means comprises an induction heating means.

   11. A glass ceramic cooker hob substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

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