GB2065883A

GB2065883A - Temperature indicating means

Info

Publication number: GB2065883A
Application number: GB8038896A
Authority: GB
Original assignee: Bosch Siemens Hausgerate GmbH
Current assignee: BSH Hausgeraete GmbH
Priority date: 1979-12-20
Filing date: 1980-12-04
Publication date: 1981-07-01
Also published as: IT8026728A0; NL8006275A; DE2951410C2; GB2065883B; YU320680A; SE447506B; YU40244B; FR2472327A1; FR2472327B1; DE2951410A1; IT1134768B; BE886602A; GR72947B; SE8008243L; CH657001A5

Abstract

Temperature signalling means for indicating the heating-up of a cooker hot-plate (not shown), especially a glass ceramic hot-plate, above a predetermined temperature safe for contact (touching) comprises a temperature-dependent switch (20) disposed in the vicinity of and thermally coupled to the hot-plate, and a signal element e.g. a lamp, controlled by the switch. The switch (20) is closely thermally coupled to a heat storage component (12, 13, 14) which is in close thermal connection with a control heater (15) for heating the switch, the heater being actuated when the cooking plate is switched on to heat the storage components to correspond with the heating of the hot-plate. <IMAGE>

Description

SPECIFICATION Temperature signalling means The present invention relates to temperature signal means for providing a signal indicating that the temperature of a cooking plate, especially a glass ceramic cooking plate, is above a predetermined level.

In a known signal device of the aforementioned type (DE-AS 26 27 373), the temperature of a temperature-sensitive switch is, without contact with the glass ceramic cooking plate, closely thermally coupled to the heater of the plate. After the cooking plate has been switched off, the residual heat of the cooking plate heater causes the switch and thus the signal element to be kept in an operative condition until the residual heat has fallen below a predetermined temperature of, for example 500 C. Only then is the signal device switched off.In this manner, a reliable indication of residual heat above a specific temperature is provided after the cooking plate has been switched off, but practice has shown that the switching-on of the signal device often takes place with a long delay, due perhaps to different thermal coupling relationships between heater and cooking surface on the one hand and heater and switch on the other hand and also due to delayed rise of the ambient temperature in the region of the switch. During short-term operation of the cooking plate for, for instance, one to two minutes, the cooking plate surface may reach too high a temperature to be touched, but nevertheless the temperature at the switch is not yet sufficient to actuate it or keep it in the actuated position.

There is therefore a need for temperature signalling means providing a reliable and rapid actuation of a signal element and maintaining the signal output, especially following short-term operation of the cooking plate, until the temperature at the cooking plate surface has fallen sufficiently for it to be safe to touch the surface.

According to the present invention there is provided temperature signailing means for providing a signal indicating that the temperature of a cooking plate is above a predetermined va!ue, comprising a temperature dependent switch to be thermally coupled to such cooking plate, a signal element controlled by the switch, heat storage means closely thermally coupled to the switch, and a control heater to be actuated in conjunction with the cooking plate, the control heater being closely thermally coupled to the heat storage means to transmit heat to the storage means for actuation of the switch.

Temperature signalling means embodying the present invention may have the advantages that the signal element is switched on, virtually without delay directly after switching-on of the cooking plate, through the control heater directly associated with the switch and that the heat emitted by the control heater is stored in the heat storage means so that, especially after short-term switching-off of the heated cooking plate, the signal element remains actuated. Preferably, the control heater comprises a PTC resistor, i.e. a cold-conductor resistor, which causes heating of the switch only in the switched-on phase and thereafter becomes ineffective.

Preferably, the heat storage means comprises a first member directly connected to the switch and a second member clamped to the first member, the control heater being disposed between the members. Advantageously, therefore, the heat storage means switch and control heater are combined into one unit.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Fig. 1 is a plan view of the lower face of a cooking plate provided with temperature signalling means embodying the invention, Fig. 2 is a front view of part of the temperature signalling means, Fig. 3 is a side view of said part of the temperature signalling means, and Fig. 4 is a circuit diagram of the temperature signalling means.

Referring now to the drawings, in Figs. there is shown a glass ceramic cooking plate 1 constituting a support surface and surrounded by a frame 2. The illustrated cooking plate comprises four cooking zones 3, 4, 5 and 6, indicated in Fig. 1 by the covers bearing directly against the lower face of the plate 1, in which electrical radiant heaters are disposed. As indicated by broken lines, the cooking plate may possess an integral, lateral extension which provides a standing area, below which, for example, two heaters 7 and 8 for heating this area 9 are situated. Reference E and A denote operating switches for the cooking plate. A temperature signal device, to be described in more detail with reference to the following figures, essentially consists of a component 10 and a signal element 11 in the form of a lamp.The component 10 is so disposed centrally of and immediately beneath the plate 1 that it is basically at a uniform distance from the individual cooking zones 3 to 6. In the vicinity of the front side of the cooking plate the signal element 11 is so disposed that it is easily visible from outside, for example through the plate 1.

The component 10 in Fig. 1 is illustrated as a detail in Figs. 2 and 3. The component 10 comprises a heat storage component 12 consisting of an upper shell-like part 13 and a lower shell-like part 14. The parts 13 and 14 are aluminium extrusions, the part 1 3 being very thick-walled and having a substantially greater volume and therefore greater thermal storage capacity than the part 1 4. Situated in the space formed between the parts 1 3 and 14 is a control heater in the form of a bar-shaped PTC resistor tablet 15, i.e. a resistor with a high positive temperature co-efficient which when connected to a source of substantially constant voltage attains a certain resistance such that the current flow through it causes sufficient heat dissipation to balance the heat losses at that temperature.Two electrically conducting contact plates 1 6 and 17 are arranged to bear against the mutually opposed side faces of the tablet 1 5 and possess terminal elements 18 projecting out of the heat storage component. Between the contact plate 1 7 and the part 14 there is disposed an electrically insulating intermediate layer 19.

The component 10 also comprises a temperature-dependent, commercially available type of switch 20, which contains corresponding switch contacts, for example in conjunction with a bimetallic contact, and terminal elements 21 for connection to electrical conductors. The switch 20 possesses a stud-like plug 22 which is engaged in a corresponding bore in the part 13 so as to exactly defining the position of the switch 20 with respect to the thermal storage component 12. The individual parts are resiliently clamped together by a clamping stirrup 23 to form a single component or unit, this clamping stirrup 23 being mounted at one end of the switch 20 and bearing resiliently at the other end against the base of the part 14.

Fig. 4 shows the circuit of the described signal device. A signal circuit 24 is connected to mains terminals Mp and R and contains in series the switch 20, set for example to a switching temperature of 500 C, and the signal element 11.

In Fig. 4, the unit 10 according to Figs. 1 to 3 is indicated by dashed lines. The circuit also includes a heat circuit 25, which can be connected via operating switches associated with the individual cooking zones 3 to 6 or by signal switches 26 to the mains terminal R and additionally is connected to the mains terminals Mp. A indicator lamp 27 is provided to signal the cooking position operation.

Finally, a further temperature-dependent switch 28 is associated with the standing area 9 according to Fig. 1 , which switch is set, for example, to a switching temperature of 500C and which is disposed underneath the cooking plate or standing area in the region of one of the standing area heaters and in parallel connection to the signal circuit 24.

If one or more of the cooking zone heaters or standing area heaters is or are set in operation, then the control heater is simultaneously energized via the switch 26, causing the resistor tablet 1 5 to immediately heat the switch 20 until it switches. The heat emitted from the control heater is stored in the heat storage component 12 so that, even if the cooking plate heating is switched off after a short time, the switch 20 remains in the actuated position and continues to cause a signal output. If the cooking plate or standing area continues in operation the control heater is rendered ineffective by the PTC resistance effect. The switch 20, by contrast, continues to be held in the actuated position by the relatively high ambient temperature now present underneath the cooking plate. After all of the heaters of the cooking plate have been completely shut down, the last-mentioned ambient temperature gradually decreases, the switch 20 opening and interrupting the signal circuit at a predetermined temperature of, of example, 500 C.

Claims

1. Temperature signalling means for providing a signal indicating that the temperature of a cooking plate is above a predetermined value, comprising a temperature dependent switch to be thermally coupled to such cooking plate, a signal element controlled by the switch, heat storage means closely thermally coupled to the switch, and a control heater being closely thermally coupled to the heat storage means to transmit heat to the storage means for actuation of the switch.

2. Temperature signalling means as claimed in claim 1, wherein the switch heat storage means and control means are combined into a constructional unit.

3. Temperature signalling means as claimed in either claim 1 or claim 2, wherein the control heater comprises a PTC resistor.

4. Temperature signalling means as claimed in any one of the preceding claims, the heat storage means defining a cavity housing the control heater.

5. Temperature signalling means as claimed in claim 4, the heat storage means being made of aluminium.

6. Temperature signalling means as claimed in either claim 4 or claim 5, the heat storage means comprising a first member directly connected to the switch and a second member clamped to the first member, the control heater being disposed between the members.

7. Temperature signalling means as claimed in claim 6, wherein at least said first member of the first and second members is provided with a recess.

8. Temperature signalling means as claimed in either claim 6 or claim 7, wherein the control heater comprises a PTC resistor and two contact plates which are each provided with an electrical terminal and disposed between the resistor and the adjacent surface of a respective one of the first and second members.

9. Temperature signalling means as claimed in claim 8, comprising an electrically insulating layer disposed between the resistor and one of the first and second members.

10. Temperature signalling means as claimed in any one of the preceding claims, comprising a clamping member clamping the heat storage means to the switch, locating means being provided to locate the switch relative to the heat storage means.

11. Temperature signalling means as claimed in claim 10, the locating means comprising a plug and socket coupling.

12. Temperature signalling means as claimed in any one of the preceding claims, wherein the signal element comprises an incandescent lamp.

13. Temperature signalling means as claimed in any one of the preceding claims in combination with cooking apparatus comprising a cooking plate and associated switching means, the temperature signalling means comprising a heating circuit which includes the control heater and is connectible to a current source by the switching means.

14. A combination as claimed in claim 13, the temperature signalling means comprising at least one further such switch, signal element and control heater.

15. A combination as claimed in claim 13, wherein the cooking plate comprises a plurality of cooking zones and the switch, heat storage means and control heater of the temperature signalling means are combined into a unit which is disposed directly beneath the cooking plate and at substantially the same distance from each of the cooking zones.

1 6. A combination as claimed in either claim 13 or claim 15, the cooking plate having a standing area heatable by heating means, and the temperature signalling means comprising a further temperature dependent switch which is disposed in the region of said heating means and connected in parallel with a circuit including the firstmentioned switch.

17. Temperature signalling means substantially as hereinbefore described with reference to the accompanying drawings.