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
  • 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
  • H05B3/146—Conductive polymers, e.g. polyethylene, thermoplastics
• • 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

• the present invention relates to a temperature limiter as well as to a heating device making use of this limiter.
• the term heating appliance brings to mind first of all heating equipment such as radiators, but many other applications require a heat source, in particular food cooking plates.
• Heat on the other hand, can be produced in different ways, using fossil fuels naturally, but more and more commonly using electric energy. For the sake of clarity, the invention will therefore be presented with reference to an electric heater.
• an electric radiator essentially consists of a heating body in contact with the environment, this heating body coating a heating module which ensures the production of heat.
• the heating module is a resistive wire embedded in a heating body made of thermosetting plastic.
• the radiator is often associated with a thermostat which regulates the ambient temperature. During the heating phase, the temperature of the heating body appreciably exceeds the ambient temperature and may even exceed a limit value imposed for safety reasons or to avoid damage to the radiator.
• a temperature limiter is therefore provided, a component similar to a thermostat, but whose function here is to keep the temperature of the heating body below a limit value and not to regulate the ambient temperature.
• temperature limiters including mechanical components such as, bimetallic strips, liquid or gas expansion devices, vapor pressure devices, heat-sensitive waxes, fusible materials or magnetic actuation mechanisms. These components result from the assembly of several elements, at least one of which is mobile. Their manufacture is therefore relatively complex due to the assembly and their reliability is often limited. In addition, they do not lend themselves to strong miniaturization.
• Static components are also known, temperature sensors, such as thermistors with a positive or negative temperature coefficient and thermocouples. These sensors do not suffer from the limitations of mechanical components, but when used as temperature limiters, they require an electronic measurement circuit. The overall size and the cost of the temperature limiter are very significantly affected.
• the present invention thus relates to a temperature limiter of great simplicity and a heating device making use of this limiter.
• a heating device comprising, in a heating body, on the one hand a heating module and on the other hand a temperature limiter to act on the supply of this heating module, the active element of the temperature limiter is made of semiconductor polymer material.
• the polymer material has an electrical resistivity with a positive temperature coefficient, this resistivity being preferably less than 10 _ 1 ⁇ .m at low temperature.
• the temperature limiter consists of a plurality of heat-sensitive dipoles connected in series, each of these dipoles containing the active element.
• these heat-sensitive dipoles have a resistance of less than 2.5 ⁇ .
• the temperature limiter is constituted by a filiform dipole connecting between its ends this active element.
• the active element having a maximum resistance variation when it is traversed by a saturation current
• the temperature limiter is itself designed to be traversed by a current less than one third of this saturation current.
• the heating module has an electrical supply.
• the temperature limiter is connected in series with the heating module, or the temperature limiter is provided to control a switch acting on the supply to this heating module.
• the invention also relates to the temperature limiter, the active element of which is made of semiconductor polymer material.
• FIG. 1 a diagram of a first embodiment of '' a heater
• FIG. 2 a diagram of a second embodiment of a heating appliance
• FIG. 3 a diagram of a filiform temperature limiter.
• the temperature limiter according to the invention is therefore produced by applying two electrodes to a semiconductor polymer material.
• Such a material is formed from a matrix of an organic polymer in which are arranged electrically conductive micro particles, generally carbon black.
• the temperature sensitivity of this material is due to a phase change in the polymer.
• the polymer At low temperature, the polymer has an essentially polycrystalline structure, the conductive particles coming to lodge in the walls in amorphous phase which separate the crystallites.
• the proportion of particles in the material exceeds a so-called percolation threshold such that the conductive particles are in contact or in quasi-contact.
• the material then has a resisitivity close to that of a metal, preferably less than 10 _1 ⁇ .m.
• the amorphous phase of the polymer progresses to the detriment of the polycrystalline phase due to the melting of the crystallites, thus disturbing the conduction network formed by the particles.
• the material past a certain temperature, therefore has a high resistivity. In this case, it is characterized by a positive temperature coefficient.
• a temperature limiter is to limit the temperature of the body in which it is integrated. It is therefore advisable not to distort the temperature measurement by excessive self-heating of the limiter itself. Indeed, although the resistance of the semiconductor material is low at low temperature, it is however not zero, so that when the material is traversed by a current, self-heating by Joule effect occurs.
• the variation in resistivity of the material is considerable in a very narrow temperature range corresponding to the melting of the crystallites of the polymer while it is relatively small outside this range.
• a critical temperature respectively a saturation current
• the temperature limiter exploits the variation in resistivity of the material, so that its set value will preferably be chosen equal to the critical temperature. This choice provides maximum sensitivity.
• the radiator comprises, embedded in a thermosetting plastic heating body, two resistive wires 13, 14 and a thermosensitive dipole 16 in series.
• thermosensitive dipole formed by a pellet of semiconductor polymer material sandwiched between two electrodes constitutes the temperature limiter.
• this dipole has a resistance less than 2.5 ⁇ at low temperature.
• the radiator 20 similar to that previously described, therefore comprises a heating body 21.
• the heating module here consists of three resistive wires 23, 24, 25 connected in parallel on a supply cable AL.
• the temperature limiter here is composed of a plurality of heat-sensitive dipoles 26 connected in series to a measurement cable MES. Again, these dipoles each have a resistance of less than 2.5 ⁇ at low temperature.
• the radiator is designed to operate in association with a control circuit 28 essentially comprising a power relay 29 which connects or isolates a power cable P and the power cable AL of the radiator. This power cable is designed to deliver the electrical energy necessary for the heating module.
• the MES measurement cable is inserted in series on one of the conductors of the COM control supply of the relay In this case, the current passing through the heat-sensitive dipoles can be very low since its sole function is to control the relay 29 or any equivalent switching device.
• the plurality of heat-sensitive dipoles 26 makes it possible to detect local overheating which could be masked if only one dipole was used.
• this sensor is presented as a wire or a strip 31 metallized with a metallic layer 32 having discontinuities 33.
• a thermosensitive dipole is thus defined at each discontinuity.

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• Control Of Resistance Heating (AREA)

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• 2000
  • 2000-01-25 FR FR0000889A patent/FR2804278B1/fr not_active Expired - Fee Related
• 2001
  • 2001-01-25 WO PCT/FR2001/000244 patent/WO2001056332A1/fr not_active Application Discontinuation
  • 2001-01-25 EP EP01903968A patent/EP1250831A1/de not_active Withdrawn

Non-Patent Citations (1)

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