Abstract: The present invention relates to a non-electromagnetic wave temperature controller for a heating cable and a method therefor, which can perform heating and temperature detection in a non-electromagnetic fashion without short-circuiting one end of the heating cable that is used in warmers, such as electric floors, electric mats and electric fomentation devices. Furthermore, the present invention relates to a temperature detection non-electromagnetic heating cable and a temperature controller, which can reduce the amount of heat and control temperature without using a separate temperature sensor when the temperature of the heating cable is controlled or an arbitrary portion of the heating cable is overheated, and can prevent a magnetic field from being generated in the heating cable without short-circuiting one end of electrical heating wires and intercept the generation of a leakage electric field.

Abstract: An electric heating element is provided with a durable PTC resistance made at least partially of an iron-based alloy, exhibiting stable characteristics to a temperature of 1500 DEG C. and having a resistance/temperature characteristic curve which substantially increases in a linear manner within a temperature range between an ambient temperature and 1500 DEG C. and can be used for a temperature control. The PCT resistance is provided with an oxidation resistant metallization or is gas-tightly enveloped by a jacket (2, 3, 12), a space between the jacket (2, 3, 12) and the PCT resistance (1,13) being filled with a powder or granules (14) which remove an important gas amount from the space.

Abstract: An electric heating structure of a domestic appliance includes at least one first electric heating track (23) having a positive temperature coefficient and at least one additional electric heating track (27, 28). A control structure (22, 25, 29) is provided for controlling electric power supply to said first and additional heating tracks (23, 27, 28) and is sensitive to the heating of said at least one first heating track (23) for switching on said at least one additional electric heating track (27, 28) in parallel and in addition to said at least one first heating track (23) when said at least one first heating track (23) has been heated to at least a predetermined extent.

Abstract: Disclosed is a heat fusing apparatus for thermally fusing toner that has been transferred to a printing medium from a toner image formed on an image bearing member using an electrophotographic process. Temperature is detected at the surface of a heating element or in the vicinity thereof. If control is performed so as to interrupt supply of power to the heating element based upon result of comparing the detected temperature and a reference value, the amount of current that flows into the heating element is detected and the reference value is changed over in accordance with the result of detection. Further, a pressure roller, which is a rotation member placed opposite the heating element, presses the printing medium against the heating element and transports the printing medium. The state of rotation of the roller is detected and the reference value is changed over in accordance with the result of detection.

Abstract: A solder-joint detection circuit uses a resistive bridge and a differential detector to detect faults in the solder-joint network both inside and outside the digital electronic package during operation. The resistive bridge is preferably coupled to a high supply voltage used to power the package. Resistors R1 and R2 are connected in series at a first junction between the high and low supply voltages and a resistor R3 is coupled to the high supply voltage and connected in series with the resistance of the solder-network at a second junction. The network is held at a low voltage on the die. The detector compares the sensitivity and detection voltages and outputs a Pass/Fail signal for the solder-joint network.

Abstract: The present invention relates to a system and method for controlling electrical heating of an element to maintain a constant electrical resistance, by adjusting electrical power supplied to such element according to an adaptive feedback control algorithm, in which all the parameters are (1) arbitrarily selected; (2) pre-determined by the physical properties of the controlled element; or (3) measured in real time. Unlike the conventional proportion-integral-derivative (PID) control mechanism, the system and method of the present invention do not require re-tuning of proportionality constants when used in connection with a different controlled element or under different operating conditions, and are therefore adaptive to changes in the controlled element and the operating conditions.

Abstract: A temperature-responsive device (14) is provided for an electric heater (2). The heater (2) is located behind a heatable surface and comprises a dish-like support (6) having therein at least one electric heating element (12) having first and second terminal regions, (12A, 12B). An electrical component (18), having an electrical parameter which changes as a function of temperature, is supported inside the heater (2) by an elongate member (16). The elongate member (16) is secured to the heater (2) and extends at least partially across the heater (2). An electrically insulating carrier member (30) is secured to the elongate member (16) at a location externally of the periphery of the heater (2). The carrier member (30) has first and second side edges (32, 38) at opposite sides of the elongate member (16) and is provided with first and second electrically conductive elements (34, 40) accessible at the opposite side edges (32, 38) for electrical connection to the first and second terminal regions (12A, 12B).

Abstract: A fuser-controlling apparatus for generating a power synchronization signal and detecting a power voltage. The fuser-controlling apparatus comprises a power synchronization signal generation circuit for outputting a power synchronization signal for synchronizing fuser operations with a power voltage, a power voltage detection circuit for detecting a level of the power voltage and for outputting a level of the power voltage, and a control unit for controlling a voltage to the fuser in a phase control manner based on the power synchronization signal and the detected level of the power voltage. The fuser-controlling apparatus can produce a power synchronization signal at the zero-crossing points of the power voltage regardless of the levels and frequencies of the power voltage. Accordingly, the fuser-controlling apparatus can instantaneously perform phase and power controls based on such a power synchronization signal, resulting in improvements to the power factor and flicker characteristics of the system.

Abstract: An improved control device and method is usable with flexible heating wire having a conductive core with a Negative Temperature Coefficient (NTC) layer and a helically wound heater conductor within an insulative outer sheath. The conductive core is coupled to a control circuit, a phase shift relative to the AC power supply being indicative of the temperature of the wire. The nonlinear nature of the NTC layer enhances the detection of local hot spots anywhere along the length of the wire. Precise temperature measurement is achieved by measuring the time differences between two zero crossings and the power to the heater compensates for abnormal use such as bunching of the heater wire. The control of the heater wire is particularly suitable for use with appliances such as heating pads and electric blankets.

Abstract: A temperature and flow rate controlled capillary aerosol generator includes two heating zones optionally separated by a region in which a pressure drop is induced. Power is metered or applied to the downstream, second zone to achieve a target resistance, and therefore a target temperature, while power is metered or applied to the upstream, first zone to achieve a target mass flow rate exiting the second zone. A target temperature is achieved in the second zone to generate an aerosol from the liquid flowing through the generator at the desired mass flow rate.

Abstract: Improved adhesion, electrical connection, and thermal connection between an electrical heater and a wax motor element are obtained by using multiple zones of different adhesives optimized for different properties. The location of the zones and the area of the zones may be a controlled to effect a trade off between different properties and to limit the expression of the conductive adhesive.

Abstract: The present invention relates, in general, to a temperature controller and heating cable used for electric heating bedding, such as an electric blanket, electric papered floor or electric fomentation device, or warmers and, more particularly, to a controller having a safety device, which can immediately shut off the supply of power when the disconnection, breakage or local overheating of a heating cable occurs while preventing the generation of an induced magnetic field and the leakage of an electric field, in warmers, such as simple bedding or fomentation devices that are operated by allowing a user to simply control a heating temperature to a high or low level without measuring the temperature of a separate heating cable. The controller, having a safety device, for blocking electromagnetic waves includes a switch unit, a heating current U-turn and detection unit, a fuse, and a cutting operation unit.

Abstract: A heating structure and its temperature control method having therein a heat generating line and a controller. The heat generating line includes a PTC element and a short circuit line serially connected having an insulating fusible layer separating them. When a user sets a heating temperature, electric current is conducted to heat the PTC element, alternative string wave signals input into an AC phase shaping circuit and an AC phase delay shaping circuit are converted into square wave signals; and by measuring with a microprocessor at a given time the phase shift between the two phase shaping circuits to control the switch of a trigger circuit, the PTC element can keep on heating or reduce its temperature to therefore keep the heat generating line at a predetermined working temperature. The structure is applicable to heat generating devices such as electric ovens and heating blankets etc.

Abstract: A sensor may comprise a first electrode and a second electrode in mutual ionic communication with an electrolyte, a first socket disposed near a rear portion of a sensor element, a first lead disposed in electrical communication with the first electrode and in physical contact with the first socket and configured for electrical communication with a first terminal element, a second socket disposed near the rear portion of the sensor element, and a second lead disposed in electrical communication with the second electrode and in physical contact with the second socket and configured for electrical communication with a second terminal element. The first socket is disposed through at least one of an edge and an end of the sensor element, and the second socket is disposed through at least one of the edge and the end of the sensor element.

Abstract: An information processing assembly includes at least one heater suitable for information processing, and a controller for controlling the at least one heater by at least one of adjusting a power to the at least one heater to match a target power level, and changing a polarity of an electrical current supplied to the heater.

Abstract: In order to create a heating device which can operate in different power stages, but only has to be contacted from one side, the invention provides a heating device with at least two plate-like ceramic heating elements, which are electrically contacted on opposite flat sides and on at least one side is provided at least one flat, electrical conductor, in which on one side of the elements there are at least two conductors electrically insulated from one another, each of the conductors being in contact with at least one heating element.

Abstract: The present invention discloses an all disassembleable electric-heating apparatus comprising a shell, a cover, a reservoir installed inside said shell, an electric heater installed inside said reservoir and immersed in the liquid contents of said reservoir in working mode, and control elements including a control box and thermo-elements; wherein, said thermo-elements include electrical elements, said electrical elements are peripherically electric-insulated and sealed, so as to be immersed in the liquid contents of said reservoir in working mode and be taken out for cleaning after use.

Abstract: A flexible body has a conductive resistance pathway which includes conductive resistance flexible strands of material connected in series between two supply bus flexible strands of material, and a temperature dependent variable resistance pathway with temperature dependent variable resistance flexible strands of material electrically connected in series by connection bus flexible strands of material.

Abstract: A surface mountable PTC device includes a PTC layer, first and second electrodes formed on the PTC layer, first and second insulating layers formed respectively on the first and second electrodes, and first and second terminals connected respectively and electrically to the first and second electrodes. Each of the first and second electrodes is formed with a hole. Each of the first and second insulating layers fills the electrode hole in the respective one of the first and second electrodes and is formed with an insulating hole surrounded by the electrode hole. Each of the first and second terminals extends through the insulating hole in the respective one of the first and second insulating layers.

Abstract: An electric heater apparatus for automobiles is disclosed. A sheathed heater (14a) constituting a heat generating member of a heater assembly (14) generates heat by power supplied from a main power supply for generating a DC high voltage through an inverter. A thermal fuse (15) has a temperature detecting element (15a) (low-melting alloy) adapted to fuse when a set temperature is reached. The temperature detecting element (15a) is connected to the power circuit of the sheathed heater (14a) through lead wires (15b, 15c). The thermal fuse (15) is arranged in such a position that the longitudinal direction of the temperature detecting element (15a) accommodated in the casing (17) is coincident with the longitudinal direction of the heater assembly 14, and mounted in surface-to-surface contact with the body (aluminum body (14c)) of the heater assembly (14). Also, the interior of the casing (17) is sealed with a material (such as cement or a silicon caulking material) higher in heat conductivity than air.

Abstract: The present invention is a method for calibrating the temperature of a cooking appliance. It has been discovered that the calibration can vary widely, depending on when during the heating cycle it is performed. In accordance with the principles of the invention, temperature calibration is judiciously performed only when the sensed temperature substantially tracks the actual or calibration temperature of the cooking medium, increasing both accuracy and consistency. Such tracking has been found to occur after the sensed temperature is falling or rising form a detected peak or valley, respectively, while the gradient of the temperature profile is substantially constant.

Abstract: A method for monitoring the condition of a heating element involving installing the heating element in a location and setting the initial composition Ci of the material as a reference baseline at an initial time Ti corresponding to said installation of the heating element. Data is then collected reflecting the subsequent composition Cs of the heating element material after a subsequent time Ts at the installed location and any change in the material composition of the heating element between Ti and Ts is monitored. An alarm is sent when the change reaches a threshold value indicating a possible failure condition. According to one embodiment, an impedance monitor is provided that calculates and compares impedance at the required levels of accuracy to determine changes in material composition. The impedance monitor, or portions thereof can be embedded within a microcontroller for increased portability and functionality.

Abstract: Electric heating apparatus and manufacturing method for an electric heating apparatus, wherein prefabricated constructional units are used. The prefabricated constructional units consist of PTC heating elements fastened to contact sheets by means of a lacquer. This simplifies production and enhances protection against corrosion.

Abstract: An incubator hood for an incubator for premature and newborn babies as well as to a process for regulating the temperature of an incubator hood are provided. The problem frequently occurring in incubator hoods is that the incubator hoods lead to heat losses at the premature and newborn babies and that water of condensation precipitates on the inside of the incubator in such incubator hoods, and this water of condensation obstructs the view and facilitates the growth of microorganisms in the incubator. This can be counteracted by a heated incubator hood. The comparatively complicated regulation processes, which requires the installation of temperature sensors in the incubator hood is avoided by the use of interior heating wires (1) in which temperature-dependent electric resistors (3), preferably PTC resistors with a nominal response temperature of about 37° C., are arranged.

Abstract: A method and device for limiting and/or controlling the surface temperature of a hob having a ceramic cooking surface. The hob is heated by an energy source which includes a temperature limiter with a variable switching temperature. The switching temperature of the temperature limiter is varied during a cooking procedure according to a redetermined switching temperature-time profile.

Abstract: A heating system including a power supply and a heating element for conducting a current from the power supply. A temperature sensing device is adopted to detect a temperature of the heating element, and a switch is connected in a circuit containing the power supply and the heating element to switch the current on or off. Further, a microprocessor produces a pulse-width-modulated signal as a function of the detected temperature, where the pulse-width-modulated signal drives the switch.

Abstract: A flexible body has a conductive resistance pathway which includes conductive resistance flexible strands of material connected in series between two supply bus flexible strands of material, and a temperature dependent variable resistance pathway with temperature dependent variable resistance flexible strands of material electrically connected in series by connection bus flexible strands of material.

Abstract: A method and heating device for heating a liquid, particularly useful for removing liquid condensate from cooling devices, by wetting a heating plate with the liquid and controlling the electrical power supply to maintain the heating plate at a the predetermined temperature above the boiling point of the liquid, such that when the heating plate is not wetted by the liquid, the electrical power supply to the heating plate is automatically maintained at a relatively low value, but as soon as the heating plate is wetted by the liquid, the electrical power supplied to the heating plate is automatically increased until the liquid is completely evaporated. The heating plate is heated by one or more PTC thermistors in which the electrical resistance increases with temperature to automatically maintain the predetermined temperature. Besides evaporating liquid condensate, the heating device is described for use in many other applications including steam generation, space heating and plastic molding.

Abstract: An electrical heater utilizes negative temperature coefficient material (NTC) and current imbalance between live and neutral ends of the heater to simultaneously protect the heater from the hot spot and mechanical intrusion into the heating cable. The NTC layer, separating the heating wire and current leakage conductor, becomes electrically conductive at the temperatures above 60° C., thus “leaking” the current to earth. The hot spot is detected by measuring the current imbalance between line and neutral connections of the heating cable. The mechanical intrusion into the heater, such as cable or insulation damage, water or sharp metal object penetration, is also simultaneously measured by the same current imbalance measuring system such as Ground Fault Circuit Interrupter (GFCI). The optional return conductor and metal foil/mesh hot spot detection shields cancel electromagnetic field. The heater may contain positive temperature coefficient (PTC) continuous sensor to control the temperature in the heater.

Abstract: An improved water heater for use in spas, hot tubs, pools, hydrotherapy pools, bath tubs, and similar bodies of water used indoors, outdoors, or both indoors and outdoors are used for both therapeutic and recreational purposes. The water heater uses heating element technology know as thick film on substrate comprising resistive elements bonded to the outer dry surface of a pipe to heat the pipe which in turn heats the water flowing therethrough. The heater is highly efficient due to the direct contact of the wet heating surface with the water and provides a smooth seamless inner heating surface by eliminating the need to pass electrical leads into the wet region of the heater. This virtually eliminates the risk of leaks in the water heater due to bulkhead fittings. The invention further eliminates the need for a heating element to be contained in the inner wet region of a spa heater, thereby reducing the risk of corrosion.

Abstract: A heater effectively uses a current controlled fan motor in series with a resistance heating arrangement. The fan motor preferably is wound with a gauge of wire to appropriate for the relatively high current provided to the fan motor. This arrangement is effectively used to adjust the fan speed to match the heat output when the heating arrangement has variable heat output. More desirable operating characteristics are achieved without increasing costs and fan motor manufacturing savings are realized. The portable heater preferably produces heat at different outputs and the current used to power the resistance heating arrangement is used to power the fan motor.

Abstract: An optical communication module includes an optical radiation source as well as control circuitry to control the temperature and the power emitted by he optical source. In order to permit soft start-up of the source while avoiding undesired wavelength variations, the optical source is pre-heated before being caused to emit optical radiation. This may be effected by initially heating the optical source to an initial temperature using the thermoelectrical conditioner associated therewith as a heater and subsequently causing a partly under-threshold current to flow through the source, thus causing the source to be heated while still emitting negligible optical power.

Abstract: A power control system for an electric cooktop. The power level is set by a knob connected to a potentiometer. Potentiometer information is digitally communicated by a controller over a serial communication bus to a power unit. The power unit communicates power level display information back to the controller over the same serial communication bus. The display information is displayed as numbers on a digital display by the controller. The power unit controls a heating element of the cooktop according to the potentiometer information. A second potentiometer can be added to control a second heating element by operating as a slave to the first controller. Further, multiple heating elements can be controlled by a single potentiometer by dividing the angular rotation into multiple segments or ranges.

Abstract: A method for controlling power to an electrical load using dual pulse width modulation (PWM) to minimize in-rush current to the electrical load, such as a heater element. An output from a power source, supplying an alternating current, is modulated by a first PWM control signal to provide a first modulated power level to the electrical load. The first modulated power level is modulated by a second PWM control signal to control power supplied to the electrical load at the first modulated power level. The first PWM control signal operates to control the number of half cycles of current in order to provide one-third, two-thirds or full cycle power. The second PWM control signal operates to define a duty cycle and period for providing the power defined by the first PWM control signal to the electrical load.

Abstract: A heating system having an electrical heating conductor arrangement which is integrated into a flexible heating body that can be connected to a supply voltage by a connecting cable and has a first conductor and an adjacent second conductor, placed in series with the first and separated from it by an insulating device, having a heating circuit formed by the heating conductor arrangement and further elements, including a control element for a heating current. A control circuit is connected to the control member for affecting the heating current and regulating the temperature. Monitoring is extended because the insulating device has a resistance characteristic which decreases with temperature.

Abstract: Heating of a functional unit is started by a control device. An actual temperature or a parameter dependent on the actual temperature is monitored during, and optionally before and after the actual heating of the functional unit. A characteristic feature of the time course of the actual temperature or of the parameters dependent on the heating temperature, which determines the phase transition of water, serves for the evaluation and control of the heating. Analysis of the characteristic features is used to control the heating power of the heating elements. Threshold values and further factors such as proportionality factors for the controller, for example, are determined depending upon significant characteristics. The threshold values and factors are also particularly used for a subsequent starting of the heating using the corresponding analysis and control.

Abstract: Air heater with PTC heating element with semiconductor switch, the semiconductor switch (5) without the housing being located in the heating tube (9) in the immediate vicinity of the PTC heating element (15).

Abstract: An airfoil temperature control arrangement includes a resistive heater element. A plurality of detectors allow a controller to gather resistance information at various intervals along the resistive heater element. Determining the resistance of the corresponding portions of the heater element allows the controller to utilize a known relationship between resistance and temperature for the material selected to make the resistive heater element. In one example, a nickel alloy or other material having a high coefficient of resistance is chosen to provide the controller with the ability to determine a temperature for each portion of the heater element. The determined temperature information is used, for example, to monitor whether any portion of the heater element has become delaminated from the airfoil surface.

Abstract: A combined sensor arid heating element includes a sensor mat having several active regions interconnected by flexible connection strips. The flexible connection strips each include two carrier foils laminated together having contact arrangements arranged in the active regions at the inside of the carrier foils. Each flexible connection strips further include a heat conductor directly applied to an outer side of one of the carrier foils.

Abstract: A control unit (3) for controlling an electric household appliance, e.g. a refrigerator, is connected in series with a positive temperature coefficient (PTC) resistive unit (4) which, when supplied with electric current, generates sufficient heat to activate a thermally activated actuating element (6) for selectively turning on/off respective auxiliary switches (9) of the electric household appliance. The thermally activated actuating element (6) includes a temperature-deformable element (7), e.g. a bimetallic plate, the deformation of which is transmitted by kinematic links (10) to a camshaft (8), the cams (12) of which cooperate with the auxiliary switches (9) of the electric household appliance to selectively turn on/off the auxiliary switches (9).

Abstract: An improved air data sensing probe de-icing system that provides for dramatically increased reliability and lifespan, utilizing solid-state heating elements that are electrically connected in parallel and having inherent temperature control, where each of the heating elements are able to provide full system power in the event of failure of one of the heating elements such that system redundancy and de-rating is achieved.

Abstract: A glass or glass ceramic cooking top 1 has on its underside 6 at least one heating unit 7. The heating unit 7 is in flat, heat-conducting contact with the underside 6, and contains an electrical resistance heating element exhibiting PTC behavior, the temperature in zone 3 being limited to a desired value without the use of a temperature limiter.

Abstract: Emissivity of a substrate is measured at least before the substrate is heated, heating operation of the substrate is controlled under a heating condition corresponding to the emissivity, and the substrate is processed.

Abstract: A negative temperature coefficient thermistor includes a thermistor element containing a transition metal oxide as a main component; internal electrodes disposed in the thermistor element; and external electrodes, electrically connected to the internal electrodes. A method for manufacturing such a thermistor includes providing green ceramic sheets for forming the thermistor element; applying a conductive paste for forming the internal electrodes onto some of the green ceramic sheets to form internal electrode layers; stacking the green ceramic sheets and the green ceramic sheets with the paste to form a green compact; firing the green compact to obtain a fired compact; and forming the external electrodes.

Abstract: The invention relates to an electrically and thermally conductive adhesive composition for cementing together at least one metallized (e.g. aluminized or silvered) surface of a positive temperature coefficient (PTC) element to at least one metallic (e.g. aluminum) electrode, in the manufacture of PTC thermistor devices which are potentially capable of operating in a working temperature range not less than ?55° C. to +300° C. and for at least 30,000 hours. The composition comprises, as the adhesive component, a curable silicone (e.g. silicone rubber) prepolymer, as well as finely divided silicon carbide and finely-divided silicon, and preferably also a finely-divided metallic powder.

Abstract: A temperature control system for reducing flicker in an electrical resistance heater comprising: an electrical resistance heater divided into at least two electrical loads and; a source of electrical power for repetitively supplying electrical power to each of the at least two electrical loads at successive different time sub periods within a predetermined time period, wherein the sum of the power supplied to the at least two electrical loads is equal to the total power supplied to the electrical resistance heater during the predetermined time period.

Abstract: A heating element made from flexible circuit technology with a single contiguous heating zone for uniform heating or multiple temperature heating zones is described. These flexible heating elements can conform to three dimensional object surfaces with irregular shape. The heating element's overall flexibility and its thickness (in the region of 10 mils) allow for heating many object shapes in an efficient, compact and light-weight manner. Each thermal sensor or thermostat is used to regulate each heating zone and provide a unique temperature setting. A thermostat can be mounted directly on an object's metallic surface. In addition, using diodes connected to the flexible heating element is described here to allow the use of two or multiple voltage sources. The technique permits one heating element to be powered from either AC or DC sources with comparable heating characteristics from both.

Abstract: U.S. Ser. No. 2002009312A cooking appliance having an electric resistance heater is connected to a multiple phase external power source and includes a system for compensating for whether the cooktop is connected to 240V split phase system wherein the two phases are 180° out of phase with each other or a 208V three phase system which has two phases that are only 120° out of phase. In particular, the cooktop includes a system for distinguishing whether the multiple phases of the external power source are 180° out of phase such that the electric resistance heater is compensated against whether it is connected to a three phase external power supply.

Abstract: A temperature control apparatus for an exhaust gas sensor can promptly heat the exhaust gas sensor with an electric heater up to an activation temperature while preventing thermal shock damage thereof due to water immediately after engine starting. Energization of an electric heater arranged near an exhaust gas sensor is controlled by a CPU cooperating with a ROM through a switching element. A low voltage is supplied for evaporation of the water by a first preheater immediately after engine starting, and enhanced preheating is subsequently carried out by a second preheater for preventing thermal shock on the exhaust gas sensor. Thereafter, a heating controller performs automatic control with a proper activation temperature of the exhaust gas sensor being made as a target. The temperature controlled by the first preheater is set to such a temperature level at which rapid cooling damage of the exhaust gas sensor due to the water will not be caused but the water can be evaporated.

Abstract: A heating system having an electrical heating conductor arrangement which is integrated into a flexible heating body that can be connected to a supply voltage by a connecting cable and has a first conductor and an adjacent second conductor, placed in series with the first and separated from it by an insulating device, having a heating circuit formed by the heating conductor arrangement and further elements, including a control element for a heating current. A control circuit is connected to the control member for affecting the heating current and regulating the temperature. Monitoring is extended because the insulating device has a resistance characteristic which decreases with temperature.