FR2574612A1 - HEATING ELECTRICAL DEVICE, IN PARTICULAR COVERAGE AND HEATING MATTRESSES - Google Patents

Abstract

THE INVENTION RELATES TO A HEATING ELECTRICAL DEVICE. IT RELATES TO AN ELECTRICAL HEATING DEVICE IN WHICH THE MAIN HEATING EFFECT IS OBTAINED BY DISSIPATION OF AN ELECTRIC CURRENT BY JULY EFFECT IN A LAYER 28 OF A MATERIAL WITH A POSITIVE COEFFICIENT OF VARIATION IN RESISTANCE WITH TEMPERATURE, PLACED BETWEEN CONDUCTORS 24, 26. ACCORDING TO THE INVENTION, THE TWO ENDS OF EACH CONDUCTOR ARE CONNECTED TO ONE ANOTHER SO THAT, IN THE EVENT OF A BREAKDOWN OF ONE OF THE CONDUCTORS, THE VOLTAGE DROP IS MINIMUM AND IS LOW RISK OF. CREATE DISRUPTIVE DISCHARGES. APPLICATION TO HEATED BLANKETS.

Description

The present invention relates generally to blankets

  heating mattresses and heating pads, and more specifically it concerns a

  an improved heating circuit for such

  vertures, mattresses and cushions. Electric blankets, heated mattresses

  and the heating pads are analogous in that they

  all carry a flexible and elongated heating element of one type or another, placed with a curvy configuration

  inside a fabric or a plastic material

  to surround and hide it. The material surrounding the heating element, in the form of a fabric or material

  plastic, is sometimes called an "envelope" and

  several passages in which the heating element is threaded

  so that the heat it releases is distributed evenly

  memento the entire surface of the blanket or cushion.

  There are normally a number of spaced sections of electrical elements placed transversely to the surface of the blanket, cushion or mattress, the parts

  of elements being sufficiently close so that, when the

  is powered, the user has the illusion of

  more or less uniform coverage over the entire surface of the

green, cushion or mattress.

  In the blankets, cushions and mattresses known,

  a device is for adjusting the application of energy

  cushion, blanket or mattress, and a device for detecting conditions of

  overheating at particular locations of the heating organ

  ghost. The local detection of the heating is necessary because the device of adjustment of the device can detect at the

  the need for energy transmission and

  overheating at any location on the

  mattress or cushion, called a "heating device"

  fant "generically in the remainder of this memoir.

  Such a local overheating condition may be due to self-bending of the heating element or overlap by the mattress or couvexture so that the temperature tends to increase in this area

  special. In the case of such folding or

  cover, the heat is not released by the élémnent to

  the same speed as in the other regions of the

  ture or mattress or cushion, and unsafe conditions

  overheating begin to appear.

  The temperature detection device, intended to be controlled by such overheating conditions,

  is usually made in the form of several

  bimetallic mostats placed throughout the entire heating device.

  ghost or continuous son of more or less parallel detection

  to the heating element and for detecting conditions

  overheating, along this element. A third solution implements a heating element which contains a material having a positive coefficient of variation

  resistance with temperature, as a heating element

  wise. This type of material provides automatic regulation - -

  because the increases in local temperature, over the length of the heating element, cause the transmission of a lower current to this part of the element and therefore

  a reduction of the energy transmitted to the superheated zone.

  There are a number of patents which describe heating element configurations for such heating blankets including a coefficient material.

  positive resistance variation with temperature.

  One of the problems with known circuits

  comprising heating elements comprising such a machine

  The material with a positive coefficient of variation of resistance with temperature is such that a rupture of one of the conductors of the heating element causes the occurrence of severe disruptive discharges at the location of the rupture, so that some Safety modules must be incorporated into the circuits of these covers. These security modules include devices for stopping the operation of the cover when an open circuit is detected in any one of the conductors. As

  the incorporation of such a module intended to stop the

  tioning. of coverage in case of open circuit is

  expensive, it is desirable that a circuit eliminates the need for

  the use of such a module or safety circuit.

  The invention relates to an electric heating device

  such as a blanket, mattress or cushion, having a heating cable having a positive coefficient of resistance variation with temperature, comprising two conductors separated by a layer of such material having a positive coefficient of variation of resistance with the temperature. The cable is placed along a sinuous path in the heating device, the ends of the

  cable being connected so that the ends of each

  one of the two conductors is connected to each other.

  A connector with a cord is for transmitting power to each of the two conductors. In the case of a break or the existence of an open circuit in any one of the two conductors of the heating cable, the voltage drop at the break is very small since the ends of the broken conductor are connected to each other. Thus, the only voltage difference at the break corresponds to the position of the break from the ends of the conductor. A break in the middle gives no voltage drop at the break while a break at one end of the conductor

  gives a voltage drop equal to the total fall of

  in the section of conductor, which may be of the order of less than 10 V. Thus, the invention relates to an improved circuit for an electric heating device, comprising a heating cable made of a material having a positive coefficient.

  of resistance variation with temperature, the extremes

  of the heating cable being connected to each other

  so that the voltage drop at the level of a break some-

  which can take place in any of the

the cable, which is minimal.

  It also relates to such an improved circuit comprising a positive coefficient heating element

  of resistance variation with temperature that does not require

  site no security module for the interruption of the func-

  circuit when an open circuit exists in

one of the drivers.

  It also relates to an improved heating circuit for an electric heating device, such as a

  blanket, a mattress or cushion, having an element

  heating wire with a positive coefficient of resistance variation with temperature, connected so that it receives energy at both ends so that all

  problems posed by discharges in the event of rup-

  ture of one of the drivers, be deleted.

  Other features and advantages of the invention

  will be better understood by reading the description

  which will follow, made with reference to the annexed drawing on the-

what:

  FIG. 1 is an electrical diagram of a cover

  electrical system according to the invention; Figure 2 is a greatly enlarged section of the heating cable of the type used in the cover of Figure 1; and

  Figure 3 is a wiring diagram of the cover

  FIG. 1, showing the material with a positive coefficient of variation of resistance with the temperature under

  form of a series of distributed parallel resistors.

  FIG. 1 represents a heating device

  such as an electric blanket, a heated mattress

  fant or a heating pad. The heating device 10 has an envelope 13 which is usually formed of several

  layers of fabric so that passages are

  for the threading of a heating element 12. This, as shown in Figure 1, has a sinuous configuration, comprising a plurality of parallel branches connected to each other so that the heating element 12 is disposed over the entire surface of the casing 13 and the heat is distributed in a relatively uniform manner over

  the surface. The heating element 12 results in extremes

  12a and 12b which enter a connection module 14

  ment or connector which is shown schematically in greatly enlarged form. This connector module 14 does not have more

  a few centimeters from the sides and is attached to the

  13. Conductors 16 and 18 which form part of a power cord terminating in a receptacle 22,

  also enter module 14.

  Referring now to FIG. 2, which is a greatly enlarged section of the heating element 12, for a

  better understanding of the nature of this heating element

  12. Element 12 has two distant conductors 24 and

  25 separated by a layer of material 28 exhibiting

  both a positive coefficient of resistance variation with temperature, which also surround conductors 24 and 26 and form a dumbbell-like configuration

  sectional. The material 28 is itself surrounded by a coating

  insulation material 30. The material 28 may consist of any

  a suitable conductive polymer having

  positive variation in its resistance with the temperature

  at a suitable temperature, as is known to those skilled in the art. Suitable compositions for making this material 28 are described in US Pat. No. 4,277,673. Conductors 24 and 26 must have a conductivity sufficiently high that the main heating effect created in the Cable 12 is from material 28 and not leads 24 and 26. US Patent No. 4,309,596 provides details of flexible conductors which may be

  used in such an application.

  In an example of electric heating cover, the length of the heating element 12 is of the order of 45 m and the voltage drop along the length of one of the conductors 24 or 26 is of the order of 10 V , during the

  connection to a conventional 110 V AC power supply

  tive. So far, one of the leads 24 has been connected at one end to one side of the feed line and the other end to the other conductor

  on the other side of the power line. The purpose of the connection

  of the opposite ends of the opposite sides of the feed line is to obtain a uniform potential between

  the two conductors 24 and 26 along the entire length of the

  12 heating. Thus, the heat dissipated at a location

  Any cement along the heating element 12 is always the same. Although this is less desirable, it is also possible to connect the

  first end of the cable 12, at each of the terminals of

  tion so that the element 12 is thus fed.

  One of the problems that is posed by electric blankets using this type of heating element is

  due to the consequences of a break-up of one of the drivers.

  In such a case, the voltage drop between the broken ends of the wire is significant, this fall being of the order of 100 V. This type of voltage drop causes

  the creation of a disruptive discharge or arc that has a certain

  There is a tendency to dissociate the polymeric material to form a flammable gas. It has therefore been necessary to incorporate a circuit module of any type enabling the circuit to be stopped or opened whenever a break in one of the conductors can

  disruptive discharge, as previously described, was

  festée. U.S. Patent No. 4,436,986

  describes an example of such a safety circuit module.

  However, such modules are expensive and their use is difficult to justify vis-à-vis the customer who does not know

  nothing to the need to use a security module.

  The invention relates to a method for connecting conductors

  which makes this security module superfluous.

  As shown in Figure 1, the end of the

  heating element 12a has ends 2a and 26a

  conductors and the end 12b of the cable has ends 24b and 26b of the conductors. The ends of the conductor 24, called 24a and 24b in the module 14, are connected to one another at 32. The ends of the conductor 26 which bear the references 26a and 26b are connected to each other in -34 . These common connections 32 and 34 are connected to the conductors 16 and 18 of the power cord. A fuse 36 is connected in series with the conductors 16 and the element

12 heating.

  FIG. 3 is a diagram of the circuit described above.

  Referring now to FIG. 1. In FIG. 3, the heating element 12 is shown with the conductors 24 and 26 and a plurality of parallel resistors 28a placed therebetween. The resistors 28a are used simply to show how the layer 28 of the material has a positive coefficient of variation of resistance

  with the temperature is used in the circuit. The heater

  The effect of the Joule effect, produced by the heating element 12, is essentially the result of the flow of current in the material 28, which can be considered as consisting of an infinite number of resistors connected in parallel between

drivers 24 and 26.

  The diagram in Figure 3 clearly shows the con-

  loop-shaped nexion of each of the conductors 24 and 26, the ends of each conductor being connected to each other. In this arrangement, the conductor 16 of the power cord transmits power to both ends of the conductor 24 of the element 12 and the conductor 18 transmits

  energy at both ends of the conductor.

  sequence, when one or the other conductor 24 and 26 breaks and opens the circuit at a particular location along its length, the voltage drop at the break is minimal because the two segments of the broken conductor are still connected to food. When the break is in the middle of the conductor, the voltage drop is even zero whereas, when it is at an e> trémité, there is a certain voltage drop on the longest driver's loncueur, this fall of tension not reaching

than 10 V approximately.

  In contrast, when only one end of each conductor is connected to the power supply, a break in one of the conductors can cause a voltage drop at the break of about 100 V when the unpowered end of the driver, the farthest from the break, tends to take the voltage across the line, causing all line

terminals of the break.

  As Figure 1 clearly shows, the extremes

  each driver 24 and 26 are sufficiently

  so that it is easy to make the connection in loop. The resulting circuit constitutes a simple and effective device for solving the very serious problem posed by disruptive discharges in heating devices

  known material comprising a material having a coefficient of positive variation of

  resistance with temperature.

  According to the invention, the voltage drop at the

  a break is preferably less than 30 V. The dissidence

  The energy consumption of the cable is of the order of 3 to 13 W / m in length, during a supply by the network. The length of the cable is preferably greater than 3G m, the conductors having a total resistance of less than 200 ohms. The cable

  may also have, in a particular device, a length

  about 6 m, its power being about 10 W / m.

  In addition, it is advantageous for the resistance of each of the conductors to be less than one sixth of the resistance of the layer of the material with a positive coefficient of variation.

  of resistance with temperature, so that the fall -

  of tension at the level of a break is sufficiently weak

  so that it does not cause disruptive discharges.

Claims (10)

  An electric heating device, characterized in that it comprises an elongate heating cable (12) having two spaced conductors (24, 26) separated by a layer (28) of a material having a positive coefficient of resistance variation with the temperature, the cable providing heating essentially Joule effect given the circulation of a current flowing in the material with positive coefficient of resistance variation with the temperature when the conductors receive an electric current, the ends of the cable (12) being connected in the form of a loop, the two ends (24a, 24b, 26a,   26b) of each conductor being connected to a separate terminal feeding.   2. Device according to claim 1, characterized in that the resistances of the conductors (24, 26) and the layer (28) of the material with a positive coefficient of variation of resistance with the temperature have a relation such that a rupture in the one or the other of the conductors, when the power supply is the conventional power supply network, forms a voltage lower than 30 V, so that the risks   to create a disruptive discharge at the level of are minimal.   3. Device according to claim 2, characterized in that the cable (12) dissipates the order of 3 to 13 W / m in length, when it is fed by the usual electrical network. 4. Device according to revendica ion 1, characterized in that it constitutes a heating blanket whose cable (12) has a sinuous configuration and is placed in a casing (13) of heating blanket, the cable having a length greater than 30 m, the total resistance of   each conductor being less than 200 ohms.   5. Device according to claim 1, characterized in that it constitutes a heating pad in which the cable is arranged with a sinuous configuration, in a flexible envelope (13), the cable having a length of 2574'612   the order of 6 m and a power of the order of 10 W] m.   6. Device according to claim 1, characterized in that the heating cable (12) is supported by a flexible envelope, the cable having a sinuous configuration, the envelope (13) being intended to have a flat configuration, the cable being intended to evenly distribute to   the heat on the entire surface of the envelope.   7. Device. according to claim 6, characterized in that the heating cable (12) is placed so that said ends are adjacent to each other, so that the ends of the conductors can be   directly connected to each other.   8. Device according to claim 7, characterized in that the envelope (13) has a configuration of generally rectangular shape, its ends are placed at   middle of an edge of the rectangle, the cable (12) forming   interconnected parallel branches that are sensi-   perpendicularly to said edge, the cable having portions thereof along that edge and starting from the middle   towards the outer part of the parallel branches.   A heating device of the type which comprises an electrically heated flexible cushion, having an elongate heating element (12) distributed with a sinuous configuration over the entire cushion so that the temperature is substantially uniform at all points of the tank, characterized in that the heating element comprises two spaced apart conductors (24, 26) and a layer (28) of a material having a positive coefficient of variation of resistance with temperature, placed between the conductors and enveloping them, a device t32, 34 ) connecting the two ends   each driver to each other so that each driver   creates a loop, a power supply connecting each   to one side of an alternative power supply,   the resistance of each of the conductors (U4, 26) being less than   less than one-sixth of the resistance of the: (28) of the material with a coefficient of positive coefficient of variation of resistance with the temperature, placed between the conductors, so that, in the event of a break in one of the conductors, the voltage drop at the break is less than that required for the creation of a disruptive discharge   at the level of the break in the conductor.   10. Device according to claim 9, characterized   rised in that the different parts of the heating element   (12) are spaced from one another except at the ends   with which the conductors are connected.