WO2001093638A1 - Ameliorations apportees a des elements de chauffage electrique - Google Patents

Ameliorations apportees a des elements de chauffage electrique Download PDF

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Publication number
WO2001093638A1
WO2001093638A1 PCT/GB2001/002372 GB0102372W WO0193638A1 WO 2001093638 A1 WO2001093638 A1 WO 2001093638A1 GB 0102372 W GB0102372 W GB 0102372W WO 0193638 A1 WO0193638 A1 WO 0193638A1
Authority
WO
WIPO (PCT)
Prior art keywords
heating element
thick film
current
cut
temperature
Prior art date
Application number
PCT/GB2001/002372
Other languages
English (en)
Inventor
David Andrew Smith
Robert Andrew O'neill
Original Assignee
Otter Controls Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Otter Controls Limited filed Critical Otter Controls Limited
Priority to AU58651/01A priority Critical patent/AU5865101A/en
Publication of WO2001093638A1 publication Critical patent/WO2001093638A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B1/00—Details of electric heating devices
    • H05B1/02—Automatic switching arrangements specially adapted to apparatus ; Control of heating devices
    • H05B1/0227—Applications
    • H05B1/0252—Domestic applications
    • H05B1/0258—For cooking
    • H05B1/0269—For heating of fluids
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
    • H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
    • H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
    • H05B3/141—Conductive ceramics, e.g. metal oxides, metal carbides, barium titanate, ferrites, zirconia, vitrous compounds
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/78—Heating arrangements specially adapted for immersion heating
    • H05B3/82—Fixedly-mounted immersion heaters
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2203/00—Aspects relating to Ohmic resistive heating covered by group H05B3/00
    • H05B2203/02—Heaters using heating elements having a positive temperature coefficient

Definitions

  • This invention concerns improvements relating to electric heating elements and more particularly relates to the protection of thick film heating elements against overheating.
  • the invention will be described in the following by reference to heating elements for liquid heating vessels such as kettles and hot water jugs for example, but it is to be appreciated that the invention is susceptible of wider application.
  • overtemperature protection devices designed to disconnect the heating element from its power supply in the event of the element temperature rising above a predetermined level, for example as a result of the kettle or jug being switched on without first being filled with water.
  • overtemperature protection devices have commonly comprised bimetallic elements which are juxtaposed with the heating element so as to be responsive to its operating temperature, the bimetal causing a switch to operate to disconnect the heating element from its power supply when the heating element temperature as sensed by the bimetal rises to a predetermined level deemed to be representative of an overtemperature situation.
  • fusible materials to protect heating elements against overtemperatures, the fusible material melting at a predetermined temperature and causing a set of contacts to open to disrupt the supply of electricity to the heating element.
  • Proposals have also been made to incorporate a current carrying fusible component into the manufacture of a heating element, the fusible component melting when exposed to a heating element overtemperature situation and disrupting the current path through the heating element.
  • a thick film heating element which has between adjoining track sections a bridging portion formed of a glass, ceramics or glass ceramics material which exhibits a resistivity which is negatively temperature dependent such that above a certain temperature the track portion in question operates as a thermal fuse, the leakage current between the adjoining track sections increasing to such a level as to generate sufficient heat to vaporise the respective parts of the heating element track and thereby disable the heating element.
  • a thick film electric heating element has a portion of such a glass, ceramics, or glass ceramics material included in its track and the track is so configured that, upon overheating of the element causing the electrical resistance of said portion to fall, the current in the track increases to such an extent as to trip an associated current sensitive device without causing destruction of the element.
  • a thick film heating element has a track section extending in parallel with the main heating track and a narrow gap in the parallel track is bridged by a patch of glass, ceramics or glass ceramics material as is employed in the arrangement of WO-A-9739603.
  • the power supply to the heating element is through a current-sensitive thermal cut-out of the type used in DC motor protection, for example a Q or B3 control switch as manufactured and sold by us.
  • the resistance of the patch decreases thus connecting the parallel track section in parallel with the main track section and thereby reducing the overall resistance of the heating element and causing the current through the cut-out to increase to such a level as ' to cause the cut-out to operate.
  • an arrangement of PTC (positive temperature coefficient of resistance) and normal heater tracks may be positioned close to the patch so that as the temperature rises the power density close to the patch increases as compared to the remainder of the heating element.
  • PTC positive temperature coefficient of resistance
  • normal heater tracks may be positioned close to the patch so that as the temperature rises the power density close to the patch increases as compared to the remainder of the heating element.
  • this problem can be overcome or at least substantially reduced by use of a very short NTC material track of great width which enables the necessary low values of track resistance to be obtained.
  • Figure 1 is a schematic showing of a thick film heater track including a parallel track section having a gap bridged by a patch of glass, ceramics or glass ceramics material of the kind described in WO-A-9739603;
  • Figure 2 shows how the responsiveness of the Figure 1 arrangement can be enhanced by means of a PTC track section
  • Figure 3 is a graph showing power output as a function of temperature for the PTC and normal track sections of Figure 2;
  • Figure 4 is a schematic showing of an alternative thick film heater track employing a short and wide NTC track section
  • Figure 5 is a circuit diagram corresponding to the arrangement of Figure 4.
  • Figure 6 shows a graph of circuit resistance and current as a function of temperature for an exemplary thick film heating element according to Figure 4.
  • a thick film heating element 1 which has a main track section 2, which extends between conductors 3 and 4, and a parallel track section 5 having a small gap therein which is bridged by a patch 6 of glaze of a glass, ceramics or glass ceramics material of the kind described in WO-A-9739603.
  • the whole heating element 1 is supplied through a thermal cut-out (not shown) of the type used in DC motor protection - for example a Q or B3 control.
  • a thermal cut-out (not shown) of the type used in DC motor protection - for example a Q or B3 control.
  • the glaze patch 6 will be heated by the surrounding tracks and will start to conduct electricity. This will effectively connect the track section 5 in parallel with the main track section 2 and lead to a reduction in the overall resistance of the element and a rapid increase in the current used by the element which causes the generation of more heat. If the thermal cut-out has been calibrated to just carry the normal operating current of the heating element, this increase in current will cause the cut-out to operate, thereby disconnecting the power supply from the heating element.
  • Figure 1 shows a basic track layout incorporating the parallel sensor track 5 with a break, with conductive glaze 6 covering the break, and bunching of the main heater tracks 2 to raise the local power density is also shown.
  • the track material of the sensor track 5 is selected to give a suitable resistance which will cause the cut-out to operate, but will not cause any mains protection to operate.
  • Fig 2 shows the addition of a PTC branch 10 to the main heater track 2 to cause a raised power density at high temperatures
  • Fig 3 shows a graph of power output against temperature for each of the branches, showing the power increase in the non PTC branch.
  • Any type of current sensitive cut-out could be used, and it may provide for manual reset, either mechanical or electrical.
  • FIGS 4 to 6 show a further embodiment which takes an alternative approach.
  • the reduction in resistance of the glaze in the first embodiment is very similar to the natural behaviour of an NTC resistor, except that in an NTC resistor it occurs more slowly and generally at a lower temperature.
  • a glaze which needs to exceed 400 or 500°C in order to operate could be unsuitable, as such high temperatures would possibly overstrain the rest of the heating element and furthermore there would be a need for considerable thermal insulation of the heating element from the appliance body in which the heating element was mounted and there would be similar implications for any seal that was provided between the heating element and the appliance body.
  • Figures 4 to 6 show a proposal to use two concentric ring conductors joined by an NTC area. NTC materials tend to have a very high resistivity, so having a short track (defined by the spacing between the conductors) of great width (defined by the length of the conductors) will allow the necessary low values of track resistance to be obtained.
  • the thick film heating element 20 has a schematically illustrated main track portion 21 which may take any convenient form and there is additionally provided a short and wide NTC track section 22 consisting of parallel arcuate conductors 23, 24 which are bridged by NTC material 25.
  • the NTC track section 22 is connected in parallel with the main track portion 21 across power supply terminals 26 and 27 with a current sensitive thermal cut-out 28 provided in series with the NTC track section 22 as shown in Fig 4 or more preferably in series with the overall heating element as shown in Figure 5.
  • a ballast resistor 29 may, if necessary, be provided.
  • a boil control 30, for switching off the heating element in response to boiling of liquid in an associated vessel may also be provided as shown in Figure 5.
  • the precise layout of the NTC track section in this embodiment will depend on the materials used. It may be formed as a single almost complete circuit, or it may be divided into a number of shorter arcs, to give the necessary total width and length. For typical NTC materials, a fall in resistance of 11 times may be expected with a 150°C temperature rise, increasing to a fall of 26 times at 250°C rise. Such a material also has a fall in resistance of about 4 - 5 times at boiling point. By the use of suitable values a stable heating element current may be obtained up to boiling point, with a rapid increase in current thereafter.
  • the overall track resistance of these two in parallel will rise from 19 Ohms at 20°C to 19.7 Ohms at boiling, but will fall above boiling to 7.8 Ohms at 250°C.
  • Such a heating element would have a nominal power of 3kW, and could be controlled by a B3 current sensitive cut-out set around 50°C, which would break the resulting 30 Amps in less than 8 seconds.
  • the current would rise very rapidly in practice, due to the unstable nature of the NTC resistance, and it would be expected that the cut-out would trip much more quickly than this, thus avoiding the tripping of any mains circuit protection.
  • Fig 6 shows a graph of circuit resistance and current versus temperature for the embodiment of Figure 4 for a particular set of values suitable for a 2.4kW heating element.
  • Rm, Rmain is the main track resistance
  • Rs, Rsensor is the sensor (NTC) track resistance
  • R is the overall element resistance.
  • the temperatures in the graph work backwards from 250°C for convenience of calculation, so 230 is 20°C and 150 is 100°C. Such an arrangement would allow a section of the NTC part to be exposed before the main track, thus giving a measure of protection against operation of a water heating appliance for example on a slope.
  • the circuit resistance falls and the current increases sharply above a predetermined temperature.
  • a significant advantage of the present invention is not only that a thick film heating element can easily be protected by means of a simple and relatively inexpensive current sensitive cut-out, but also that the current sensitive cut-out does not have to be mounted on the heating element or, indeed, anywhere near it if necessary.
  • the ability to provide slope protection in a kettle is an incidental benefit.
  • the ability to operate with a remote current sensitive device would allow the use of a thick film heating element in appliances other than kettles, where a complex control/connector such as our X4 is not needed, and allow the thermal control to be mounted elsewhere, such as on a control panel or circuit board.
  • the cut-out were a manual reset, then the reset button may be placed at some convenient place, where it can be made accessible.
  • the invention can be applied to appliances such as washing machines and tumble dryers, where the heating elements are generally mounted in inaccessible locations.
  • a tumble drier does not (as a rule) contain water, the heating element is still subject to overheating as a result of blocked airflow filters.
  • Figure 4 could possibly be constituted by a glass, ceramics or glass ceramics material as employed in the embodiments of Figures 1 and 2.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Food Science & Technology (AREA)
  • Resistance Heating (AREA)
  • Control Of Resistance Heating (AREA)

Abstract

L'invention concerne un élément de chauffage de film épais utilisé avec une bouilloire électrique. Cet élément est doté d'une section de piste principale et d'une section de piste lui étant connectée en parallèle. La section de piste parallèle possède un espace recouvert par un pont de verre, de céramique ou de vitrocéramique qui présente une élévation marquée de la résistance électrique avec une température augmentant au-dessus d'un certain niveau. Un coupe-circuit sensible au courant contrôle le courant passant par l'élément de chauffage et coupe le circuit lorsque, en réaction à la surchauffe de l'élément, son courant s'élève comme conséquence de la résistance du matériau recouvrant l'espace dans l'élévation de la piste parallèle. Selon une autre configuration, on peut utiliser un autre matériau CTN à la place du verre, de la céramique ou de la vitrocéramique. Ce matériau CTN est disposé entre deux conducteurs parallèles allongés qui sont connectés respectivement aux conducteurs des terminaux de l'alimentation électrique de l'élément de chauffage de film épais. Les deux configurations mentionnées permettent d'éteindre un élément de chauffage de film épais en surchauffe, avant que celui-ci ne soit durablement endommagé.
PCT/GB2001/002372 2000-05-30 2001-05-24 Ameliorations apportees a des elements de chauffage electrique WO2001093638A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU58651/01A AU5865101A (en) 2000-05-30 2001-05-24 Improvements relating to electric heating elements

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0013116.9 2000-05-30
GB0013116A GB2363046B (en) 2000-05-30 2000-05-30 Improvements relating to electric heating emlements

Publications (1)

Publication Number Publication Date
WO2001093638A1 true WO2001093638A1 (fr) 2001-12-06

Family

ID=9892625

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2001/002372 WO2001093638A1 (fr) 2000-05-30 2001-05-24 Ameliorations apportees a des elements de chauffage electrique

Country Status (3)

Country Link
AU (1) AU5865101A (fr)
GB (1) GB2363046B (fr)
WO (1) WO2001093638A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103584729A (zh) * 2013-11-09 2014-02-19 李高升 一种玻璃电热水壶底部远红外线电热膜的电极连接结构

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2454009A (en) * 2007-10-26 2009-04-29 Kenwood Ltd Electrically heated domestic water vessels
US7777160B2 (en) * 2007-12-17 2010-08-17 Momentive Performance Materials Inc. Electrode tuning method and apparatus for a layered heater structure
NL2001283C2 (nl) * 2008-02-13 2009-08-14 Otter Controls Ltd Verwarmingselement en vloeistofhouder voorzien van een dergelijk verwarmingselement.
CN109640417B (zh) * 2019-01-24 2022-02-18 广西桂仪科技有限公司 一种平板厚膜发热器及其制备工艺

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0335617A2 (fr) * 1988-03-25 1989-10-04 THORN EMI plc Limitateur de courant pour éléments chauffants à couche épaisse
WO1997039603A1 (fr) * 1996-04-18 1997-10-23 Strix Limited Elements chauffants electriques
WO1999002080A1 (fr) * 1997-07-11 1999-01-21 Strix Limited Receptacles chauffant des liquides et dispositifs de reglage adaptes

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2069800A (en) * 1980-02-15 1981-08-26 Marconi Co Ltd Ovening of circuit components
JPH07160132A (ja) * 1993-12-01 1995-06-23 Canon Inc 加熱装置
GB9423900D0 (en) * 1994-11-26 1995-01-11 Pifco Ltd Improvements to thick film elements
GB2307629B (en) * 1995-11-20 2001-01-10 Strix Ltd Electric heaters

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0335617A2 (fr) * 1988-03-25 1989-10-04 THORN EMI plc Limitateur de courant pour éléments chauffants à couche épaisse
WO1997039603A1 (fr) * 1996-04-18 1997-10-23 Strix Limited Elements chauffants electriques
WO1999002080A1 (fr) * 1997-07-11 1999-01-21 Strix Limited Receptacles chauffant des liquides et dispositifs de reglage adaptes

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103584729A (zh) * 2013-11-09 2014-02-19 李高升 一种玻璃电热水壶底部远红外线电热膜的电极连接结构

Also Published As

Publication number Publication date
GB2363046A (en) 2001-12-05
GB0013116D0 (en) 2000-07-19
AU5865101A (en) 2001-12-11
GB2363046B (en) 2005-01-26

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