SE541450C2

SE541450C2 - Overheating alarm device for cell phone charger or similar device

Info

Publication number: SE541450C2
Application number: SE1850182A
Authority: SE
Inventors: Niklas Kvist
Original assignee: Jondetech Sensors Ab Publ
Priority date: 2018-02-19
Filing date: 2018-02-19
Publication date: 2019-10-08
Also published as: WO2019158769A1; SE1850182A1

Abstract

There is provided an alarm device (1) for monitoring the temperature of a second device (2) the second device having an outer surface (9), said alarm device (1) comprising a housing (3), said housing (3) forming an inner space (4) containing a heat sensor (13), the device (1) further comprising a sound alarm device (6), a battery (7), and an adhesive (8) for attaching the alarm device (1) to the outer surface (9) of the second device (2), where the heat sensor (13) is connected to the sound alarm device (6) to provide a signal to cause the sound alarm device (6) to cause a sound alarm if a temperature above a predetermined temperature is detected, where the housing (3) of the alarm device (1) has a an outer surface (12) exposing the adhesive (8), characterized in that the heat sensor (13) comprises a thermopile (5), in that the housing (3) has an aperture (10) for allowing IR radiation (11) from the surface (9) of the second device (2) to reach the heat sensor (13) in the space (4) of the housing (3), and where the heat sensor (13) is arranged in the space (4) of the housing (3) to receive IR radiation (11) through the aperture (10), and in that the alarm device (1) can be attached by the adhesive (8) to the outer surface (9) of the second device (2) so that the outer surface (9) of the second device (2) covers the aperture (10).

Description

Overheating alarm device for cell phone charger or similar device Field of the invention This invention relates to an overheating alarm device, which can be conveniently attached to a mobile phone charger.

Background Electricity transformers are used for charging laptops, tablet computers and in particular mobile phones. For examples, in a family home, several mobile phones can be charged during night time.

Transformers may be overheated, in particular transformers of poorly manufactured, lowcost mobile chargers. Dangerous fires have been caused by such chargers.

There is thus a need for a convenient, low cost device for monitoring transformers.

Prior art heat sensors are provided in a closed housing or encasement in order to protect the heat sensor, in particular where the heat sensor comprises a thermopile.

Summary of the invention In a first aspect of the invention, there is provided an alarm device for monitoring the temperature of a second device, the second device having an outer surface, said alarm device comprising a housing, said housing forming an inner space containing a heat sensor, the device further comprising a sound alarm device, a battery, and an adhesive for attaching the alarm device to the outer surface of the second device, where the heat sensor is connected to the sound alarm device to provide a signal to cause the sound alarm device to cause a sound alarm if a temperature above a predetermined temperature is detected, where the housing of the alarm device has a an outer surface exposing the adhesive, characterized in that the heat sensor comprises a thermopile, in that the housing has an aperture with no window or filter such that the aperture allows IR radiation from the surface of the second device to reach the heat sensor in the space of the housing without passing through any solid material, and where the heat sensor is arranged in the space of the housing to receive IR radiation through the aperture, and in that the alarm device can be attached by the adhesive to the outer surface of the second device so that the outer surface of the second device covers the aperture.

Short response times are important for this type of monitoring device, since dangerous overheating may occur rapidly. The arrangement with a thermopile provided naked in a housing and an aperture in the main housing minimises response times, while the fact that the second device covers the aperture minimises risk of damage to the heat sensor. Thermopiles have shorter response times than many other types of heat sensors but are sensitive to mechanical damage. Furthermore, in the room where the second device is used there may be convention of air, caused by for example ventilation or heating of the room. Convection of air may interfere with the temperature measurement of the device. The arrangement prevents convection of air to reach the inner space trough the aperture, and temperature measurement is carried out in a closed space. Convection of air may also cause dust or other particles to damage the heat sensor. The housing also prevents the heat sensor from being disturbed by direct light or sunshine in the room. The invention provides a device where disturbance by convection or radiation is minimized and where the sensor is sufficiently protected.

Also, the fact that the heat sensor does not have a separate housing but is provided naked in the main housing of the device, makes it thinner and possible to decrease production cost.

The adhesive may be provided around the aperture so that the inner space is closed off from the surrounding when the alarm device is attached to the outer surface of the second device. This prevents convection and risk of damage to the sensor even more and prevents the measurement to be disturbed by air convection or heat radiation in the room where the sensing device is being used.

The adhesive may be provided on an elastomer. The elastomer makes it easier to attach the device on an uneven outer surface of the second device and provides a sealing effect. It also makes it easier to attach the device to a small device, such as a mobile phone charger.

The leads of the thermopile may be arranged approximately parallel to the incoming radiation and embedded in a matrix. A design (axial design) of the thermopile is sturdy and not so sensitive for mechanical damage and is therefore particularly advantageous where there is an aperture. Moreover, it makes the heat sensor scalable. Also, the matrix shadows the cold side of the thermopile.

The heat sensor may comprise a heat sink in contact with the thermopile arranged between the thermopile and the aperture.

The adhesive may have a removable release liner that extends over the aperture such that the aperture is covered.

In a second aspect of the invention there is provided a cell phone charger with a device according to any one of claims 1 to 6 attached to it.

Brief description of drawings The accompanying drawings form a part of the specification and schematically illustrate preferred embodiments of the invention and serve to illustrate the principles of the invention.

Fig. 1 is a schematic front view of an alarm device.

Fig. 2 is a schematic cut through view of the alarm device of Fig. 1.

Fig. 3 shows the alarm device of Fig. 1-2 attached to a second device.

Fig. 4 shows a schematic front view of an alarm device.

Fig. 5 shows a schematic cut trough of the alarm device of Fig. 4.

Fig. 6 shows a schematic cut trough of an alarm device attached to a second device.

Fig. 7 is a side view of a heat sensor.

Fig. 8 is a front view of a cut through along line A-A in Fig. 7.

Detailed description With reference to Figs. 1-3 the alarm device 1 for monitoring the temperature of a second device 2 comprises a housing 3 forming an inner space 4 in which a heat sensor 13 comprising a thermopile 5 is arranged. The alarm device 1 further comprises a sound alarm device 6 that able to make a sound alarm, such as a siren, powered by a battery 7. Preferably the sound alarm device 6 is loud enough to wake up a person in the same home. The second device 2 has an outer surface 9 for example the outer surface of a housing. The device comprises an adhesive 8 for attaching the device 1 to the outer surface 9 of the second device 2. The second device 2 may be or comprise a transformer, for example a transformer for charging a third device. The second device may be a charger for a mobile phone.

The thermopile 5 is able to provide a signal to the sound alarm device 6 in case a temperature above a predetermined threshold temperature is detected. The threshold temperature may be for example 55°C, but a suitable temperature threshold can be selected by a person skilled in the art.

The thermopile 5 and the sound alarm device 6 may be connected with suitable electric circuitry that may comprise an amplifier, an analog to digital converter, and a processor that may comprise a memory with firmware. The thermopile 5 may be electrically connected to an amplifier that amplifies the signal from the thermopile 5. The signal from the amplifier may be digitalized by the analog digital converter that provides the digitalized signal to the processor. The processor may have firmware that comprises the temperature threshold such that the processor provides a signal to the sound alarm device 6 if the detected temperature is above the threshold. The processor may also provide functionality for, for example, battery status check. Processor and other electronic devices are preferably powered by battery 7.

Housing 3 has an aperture 10 that connects the inner space 4 of the housing 3 with the surroundings. The aperture 10 allows IR radiation 11 from the surface of the second device 2 to reach the heat sensor 13 with thermopile 5 inside the space 4 of the housing 3. The heat sensor 13 is arranged inside the space 4 so that it can detect IR radiation 11 that enters the space 4 through the aperture 10. The aperture 10 does not have a window or filter of a solid material such that IR radiation 11 can pass from the outer surface 9 of the second device 2 into the inner space 4 to surface 30 of the heat sensor 13 without passing through any solid material and by passing through the air only. Thus, the IR radiation 11 can reach the surface of the thermopile 5, (or when a heat sink 14 is used, the surface of the heat sink 14), directly from the outer surface 9 of the second device 2 by travelling through air only.

The housing 3 may have any suitable shape. In Figs. 1 to 5 a rectangular housing 3 is shown but housing 3 may have any suitable shape such as oval, triangular, puck-shaped, spherical, etc, such as for example the shape seen in Fig 6. The IR radiation 11 does not have to be focused with mirrors or a lens and non-imaging optics can be used for arranging the heat sensor 13 inside housing 3.

The housing 3 may be a common housing for the heat sensor 13, the sound alarm device 6, the battery 7, and optional circuitry of the alarm device 1.

The alarm device 1 can be attached by the adhesive 8 to the outer surface 9 of the second device 2 so that the outer surface 9 of the second device 2 covers the aperture 10. This does not mean that the inner space 4 is sealed from the surroundings as there may still be passages between clumps of adhesive 8, as shown in Figs. 1-3.

The adhesive 8 is arranged on the outer surface 12 of the housing 3. The adhesive 8 may be any type of useful adhesive. The adhesive 8 is exposed on the outside of the housing 3 so that device 1 can be attached to the outer surface 9 of the second device 2. The adhesive 8 may be covered by a release liner that can removed by the user prior to attachment of the alarm device 1 to the second device 2. The release liner may cover the aperture 10 such that space 4 is closed off before use. The adhesive 8 is arranged on the outer surface 12 of housing 3 so that the aperture 10 faces the second device 2 when device 1 is attached to the second device 2 with the adhesive 8.

A limited part of surface 12 may be covered with adhesive. The adhesive 8 may be arranged on dots, clumps or strips on the surface 12 of the housing 3. For example, the adhesive 8 may be arranged next to aperture 10 on the surface 12 as seen in Fig. 1, where the adhesive is provided as four dots on surface 12. Alternatively, a large part of an outer wall of the housing 3 may be covered with adhesive 8.

The adhesive 8 may be provided as an elastomer, or on an elastomer on the surface 12, for example as a strip of an elastomer. The elastomer may be an elastomeric foam, for example a thin foam strip. The adhesive 8 and the optional elastomer is preferably rather thin such that a close contact between the housing 3 of the device 1 and the outer surface 9 of second device 2 is obtained. In particular it is useful if the design of the housing 3 and the adhesive is such that the gap 15 between the aperture 10 and the outer surface of the second device 2 is small, preferably less than 5 mm, more preferably less than 3 mm more preferably less than 1 mm.

In one embodiment, schematically shown in Fig. 4-5, the adhesive 8 is provided around the aperture 10 so that the inner space 4 is can be closed off from the surroundings when the alarm device 1 is attached to the second device 2. Off course, the inner space 4 is only closed off if the alarm device 1 is attached to the second device 2 in a correct manner and not in an oblique or off set manner. The adhesive 8 or the elastomer that the elastomer 8 is provided on closes off the gap 15 between the outer surface 12 of the housing 3 and outer surface 9 of the second device 2. The adhesive 8 may for example be provided on a strip of elastomeric material around the edge of the aperture 10. The arrangement of this embodiment prevents convection of air to reach the inner space 4 trough aperture 10. However, the adhesive 8 does not have to create a gas tight seal. Thus, there may still be pores or small openings in the adhesive 8.

With reference to Figs. 7 and 8, the heat sensor 13 comprises a thermopile 5. A thermopile 5 comprises at least two thermocouples. Each thermocouple consists of a first lead 21 of a first metal and a second lead 22 of a second metal, where the first lead 21 and the second lead 22 have different Seebeck coefficients. Thus, there is at least a first lead 21 that has a first Seebeck coefficient and a second lead 22 that has a second Seebeck coefficient. Examples of suitable pairs of metals include chromel-constantan (type E thermnocouple), iron-constantan (type J), chromel-alumel (type K). The leads 21, 22 of the thermopile 5 is preferably embedded in matrix 27. When there is a temperature difference between the hot side 23 and the cold side 24 a voltage potential will be generated. Matrix 27 is made from a non-conductive material such as, for example, an epoxy polymer. The material of matrix 27 is preferably a poor conductor of heat and electricity. The material of the matrix 27 can be selected by a person skilled in the art. The leads 21 and 22 may be connected with connectors 29 on the hot side 23 and the cold side 24 of the thermopile 8. The individual thermocouples pairs 21,22 and 21', 22' of the thermopile 5 are coupled to provide a voltage potential that is sufficient to be detected. The cold side 24 side of the heat sensor 13 may comprise a cold sink 20. A useful thermopile with this design is described in W02004098256.

Heat sensor 13 may comprise a heat sink 14 arranged in contact with thermopile 5 such that IR radiation 11 from the second device 2 can be absorbed by the heat sink 14 and transferred to leads 21, 22 of thermopile 5. The heat sink 14 may be a heat absorbing layer. The heat absorbing layer is preferably arranged perpendicular to the direction of the leads 21, 22 of the thermopile 5. The heat sink 14 should be able to absorb heat and conduct heat to thermopile 5. Suitable materials for the heat sink 14 includes materials that efficiently absorb IR radiation, for example a heat absorbing polymer or copper. The heat sink 14 preferably covers the hot side 23 of the thermopile 5, thus being arranged between the aperture 10 and the thermopile 5.

The detection surface 30 of the sensing element 13 may have any suitable shape. Fig. 8 shows a square configuration of the thermopile 5, but a circular detection area may be preferred.

As seen in the figures, the thermopile 5 is preferably of an axial design, i.e. where the direction of the leads 21, 22 are arranged so that they are approximately parallel to main direction of the incoming radiation 11. "approximately parallel" as used in this context comprises an angle of up to 10°, more preferably 5°, between the incoming radiation and the leads 21, 22 of the thermopile 5. This arrangement makes it possible to provide a large and scalable detection surface 30. It also makes it possible to embed leads 21, 22 in matrix 27, so that leads are protected from physical damage. Matrix 27 also shades the cold side 24 from radiation 11.

While the invention has been described with reference to specific exemplary embodiments, the description is in general only intended to illustrate the inventive concept and should not be taken as limiting the scope of the invention. The invention is generally defined by the claims.

Claims

1. An alarm device (1) for monitoring the temperature of a second device (2), the second device having an outer surface (9), said alarm device (1) comprising a housing (3), said housing (3) forming an inner space (4) containing a heat sensor (13), the device (1) further comprising a sound alarm device (6), a battery (7), and an adhesive (8) for attaching the alarm device (1) to the outer surface (9) of the second device (2), where the heat sensor (13) is connected to the sound alarm device (6) to provide a signal to cause the sound alarm device (6) to cause a sound alarm if a temperature above a predetermined temperature is detected, where the housing (3) of the alarm device (1) has a an outer surface (12) exposing the adhesive (8), characterized in that the heat sensor (13) comprises a thermopile (5), in that the housing (3) has an aperture (10) with no window or filter such that the aperture allows IR radiation (11) from the surface (9) of the second device (2) to reach the heat sensor (13) in the space (4) of the housing (3), without passing through any solid material, and where the heat sensor (13) is arranged in the space (4) of the housing (3) to receive IR radiation (11) through the aperture (10), and in that the alarm device (1) can be attached by the adhesive (8) to the outer surface (9) of the second device (2) so that the outer surface (9) of the second device (2) covers the aperture (10).

2. The alarm device (1) according to claim 1 where the adhesive (8) is provided around the aperture (10) so that the inner space (4) is closed off from the surrounding when the alarm device (1) is attached to the outer surface (9) of the second device (2).

3. The alarm device (1) according to claim 1 or 2 wherein the adhesive (8) is provided on an elastomer.

4. The device (1) according to any one of claims 1 to 3 where the leads (21, 21', 22, 22') of the thermopile (5) are approximately parallel to the incoming radiation (11), and where the leads (21, 21', 22, 22') of the thermopile (5) are embedded in a matrix (27).

5. The device (1) according to any one of claims 1 to 4 comprising a heat sink (14) in contact with the thermopile (5) arranged between the thermopile (5) and the aperture (10).

6. The device (1) according to any one of claims 1 to 5 where the adhesive (8) has a removable release liner that covers the aperture (10).

7. A cell phone charger (2) with a device (1) according to any one of claims 1 to 6 attached to it.