EP1903524B1

EP1903524B1 - Smoke detector

Info

Publication number: EP1903524B1
Application number: EP07116913A
Authority: EP
Inventors: Domenico Arancio
Original assignee: Elkron SpA
Current assignee: Elkron SpA
Priority date: 2006-09-22
Filing date: 2007-09-21
Publication date: 2009-11-04
Anticipated expiration: 2027-09-21
Also published as: ES2335937T3; EP1903524A1; PL1903524T3; DE602007003063D1; ATE447750T1; ITTO20060676A1

Abstract

The invention relates to a smoke detector comprising a detection chamber in which are positioned an emitter device which emits electromagnetic radiation (typically infrared type) and a receiver device which receives it. The smoke detector also comprises a main printed circuit board electrically connected to both the emitter device and the receiver device. The receiver device and/or the emitter device are located on dedicated printed circuit boards which are electrically connected, possibly through connectors, to the main printed circuit board.

Description

The present invention relates to a smoke detector according to the preamble of claim 1.
In particular, the invention relates to optical smoke detectors of the optical type based on Tyndall's effect, and aims especially at reducing production costs and simplifying some maintenance tasks required by the devices.
Smoke detectors based on Tyndall's effect consist of a detection chamber, called smoke chamber, characterized in that, thanks to a labyrinth located on the edge of the chamber, light cannot enter the chamber from the outside while smoke can.
The detection chamber houses a receiver diode and an emitter diode, the respective reception and emission fields intersecting within the chamber.
Detectors of this type commonly use traditionally mounted emitter and receiver diodes (THT, Through Hole Technology), which are installed in such a way that emission and reception occur in directions substantially parallel to the bottom of the chamber and with an optical focus located at a height which is typically half the overall height of the chamber, as, for example, shown in patent application US2005/0242967 .
Thanks to their long rheophores and to the use of properly sized mounting spacers, traditionally mounted diodes can be positioned easily inside the detection chamber.
Generally, the emitter and receiver diodes are located on respective spacers having a suitable height (i.e. such as to determine the height of the optical focus), which are appropriately secured to a printed circuit board outside the detection chamber.
Diodes and spacers are then inserted into the chamber through holes obtained in the chamber bottom.
This solution however suffers from the drawback that ad hoc spacers must be used and that the diodes must be welded after the printed circuit board has been prepared.
According to an alternative and less costly solution, the spacers are plastic profiles moulded inside the chamber. In this case, the diodes are secured mechanically onto the spacers, and then their rheophores are routed through holes in the bottom of the detection chamber and welded to a printed circuit board located outside the chamber.
In both of the above-described solutions, the external printed circuit board is then made integral with the chamber by means of mechanical clamps of various kinds.
A metal shield adapted to prevent interference is then mounted onto the receiver diode; this shield must also be connected electrically (typically by soldering) to the electric ground of the printed circuit board.
These detector solutions suffer from several drawbacks.
First of all, they require many manual operations (diode positioning and welding), which increase the total cost of the detector.
Furthermore, the efficiency of these solutions depends on the operator's ability to position the diodes on the spacers perfectly. Any small offset of the diodes may considerably affect the sensitivity of the detector.
Finally, the maintenance tasks required by known detector solutions are rather time-consuming and expensive. For example, if a diode fails, it will be necessary to disassemble the detector completely in order to unsolder the failed diode and replace it with a new one. This problem particularly affects those above-described solutions in which the rheophores or the diode shields pass through the detection chamber. In such cases, the welded joints of the rheophores and/or shields prevent the detection chamber from separating from the printed circuit board unless the emitter and receiver diodes and the shield are unsoldered manually beforehand.
Some known solutions disclosed by patent US 5,451,931 and patent EP1272992 use SMD (Surface Mounted Device) components, which involve lower assembling costs than traditional devices.
However, this saving is not reflected on the total cost of the device, because special and expensive architectures must be employed.
For example, patent US 5,451,931 uses mirrors, while patent EP1272992 uses surface mount diodes (SMD) which are very expensive and which receive and transmit in a direction parallel to the printed circuit board on which they are mounted.
With both solutions, moreover, if either diode fails it can only be replaced after being unsoldered from the printed circuit board, so that maintenance is time-consuming and costly.
The main object of the present invention is to reduce the production times of known smoke detectors while still using simple architectures.
US 6,288,647 discloses a smoke detector wherein light emitting element and light receiving element are mounted on respective dedicated printed circuit boards mounted on a main board.
It is another object of the present invention to improve the efficiency of known detectors by making their efficiency less dependent on the assembler's skill.
It is a further object of the present invention to solve the problems related to maintenance times and costs of known smoke detectors.
These and other objects of the present invention are achieved through a smoke detector incorporating the features set out in the appended claims, which are intended as an integral part of the present description.
The basic principle of the invention consists in using SMD type emitter and receiver diodes mounted on dedicated printed circuit boards (PCB), which are then mounted crosswise to the main printed circuit board containing the rest of the detector circuitry.
This solution allows to eliminate the spacers traditionally used for positioning THT diodes and to use essentially only SMD components, thus reducing the cost of the detector.
Advantageously, the dedicated printed circuit boards carrying the receiver and emitter diodes are provided with connectors (SMD or traditional type) to be plugged into respective connectors available on the main printed circuit board, which houses the rest of the detector circuitry.
This solution allows to connect the receiver diode and the emitter diode to the printed circuit board in a removable manner, thus allowing them to be easily replaced if they should fail.
In another advantageous solution, differently shaped cavities are obtained on the underside of the printed circuit boards for providing a polarization function, i.e. for preventing the dedicated circuit boards from being plugged into the main printed circuit board if they are not positioned correctly.
Also advantageously, the dedicated printed circuit boards of the diodes are connected to one side of the main circuit board by stamping or through peduncles. According to this embodiment, during the assembly stage it is sufficient to disconnect the dedicated printed circuit boards from the main one and plug them into the contact connectors and into the polarization cavities provided on the main printed circuit board.
Also advantageously, on the dedicated printed circuit boards of the emitter and receiver diodes it is possible to obtain a ground plane (solid copper) which, once electrically connected to one or more contacts included in the connector for providing contact with the ground of the underlying printed circuit board, acts as a shield offering protection from external interference, thus eliminating the need of manufacturing and mounting a metal shield.
Further objects and advantages of the present invention will become apparent from the following description and from the annexed drawings, wherein:

Fig. 1 is a general view of a finished basic smoke detector according to the present invention.
Fig. 2 is an exploded view of the smoke detector of Fig. 1.
Fig. 3 is a bottom view of the smoke detection chamber bottom of the detector of Fig. 1.
Fig. 4 is a general view of the printed circuit board of the smoke detector according to the present invention.
Fig. 5 shows the dedicated printed circuit boards of the emitter and receiver diodes.
Fig. 6 shows a printed circuit board containing all printed circuits of the detector according to the present invention.

In the following description, identical or equivalent means/elements, i.e. providing the same technical function, will be referred to by using the same reference numbers.
Fig. 1 shows a general view of a smoke detector 1.
Detector 1, an exploded view of which is shown in Fig. 2, comprises a base (not shown in Fig. 2 for simplicity), a cover 20 of the smoke detection chamber bottom, a main printed circuit board 51 housing the printed circuit boards for receiver 53 and emitter 54, a smoke detection chamber bottom 40, a grid 30 and a cap 10.
As known, the base has slots required for inserting the screws used for securing the detector to a wall or a ceiling. The base also comprises means required for providing the power connections and any other connections to remote devices (e.g. sirens) needed for exchanging signals (e.g. power, control or alarm signals) with the main printed circuit board 51.
Main printed circuit board 51 is located between a special housing 48 obtained on the detection chamber bottom of the detection chamber and cover 20 of the smoke detection chamber bottom.
The smoke detection chamber comprises the printed circuit board 51 and is clamped inside the cap 10; the assembly is then secured to the base, thus making the finished detector 1.
The fluid in the environment (air and possibly smoke) enters the smoke detection chamber by flowing through the cap 10 and the grid 30.
Bottom 40 for the smoke detection chamber comprises a base 41 on which a labyrinth 42 extends perpendicularly, which labyrinth is made up of a plurality of V-shaped elements 43 preventing light from entering the smoke detection chamber from the outside.
Once positioned, grid 30 and smoke detection chamber bottom 40 delimit, at the top and at the bottom, respectively, a volume 44 within labyrinth 42, which volume is the smoke detection chamber.
In detection chamber 44 there are two housings 45 and 46 for a receiver device and an emitter device, respectively.
In the preferred embodiment described below, the emitter and receiver devices are diodes.
In chamber 44 there is also a divider element 47 which is used, in combination with the positioning of housings 45 and 46, for preventing the receiver diode from detecting the presence of the electromagnetic radiation (preferably infrared type) emitted by the emitter diode when there is no smoke.
Fig. 3 shows the rear side of body 40, which comprises a housing 48 for main printed circuit board 51, shown in Fig. 4, which carries out the functions of supplying power to diodes 55 and 56 and of receiving an output signal from the receiver diode.
Two apertures 52 on the main printed circuit board fit onto two pins 49 of housing 48, thus holding the board in the proper position.
Fig. 3 also shows two openings 50 for inserting dedicated printed circuit boards 53 and 54 supporting the receiver and emitter diodes, respectively.
As shown in Fig. 4, in a preferred embodiment receiver 55 and emitter 56 diodes are of the surface mount type (SMD) and are located on respective printed circuit boards (53 and 54) mounted perpendicularly to the plane of main printed circuit board 51.
The size, and in particular the length, of the dedicated printed circuit boards 53 and 54 depends, in a known way, on design constraints which set the height of the optical focus of the diodes, and thus the height at which diodes 55 and 56 must be positioned inside the detection chamber.
With particular reference to the non-limiting example of Fig. 4, emitter diode 56 employed is of the rear view type.
Fig. 5 shows detailed views of the dedicated printed circuit board 53 of the receiver diode and the dedicated printed circuit board 54 of the emitter diode.
The dedicated printed circuit board 53 comprises receiver diode 55 and a connector 57 which, in a preferred embodiment, is of the Pin-Strip type and comprises three pins 58.
The dedicated printed circuit board 54 comprises the emitter diode 56 and a Pin-Strip connector 57 having three pins 58.
Connector 57 is plugged into a matching connector 59 installed on the main printed circuit board.
In the embodiment of Fig. 5, two of the three pins 58 are used for supplying power to the diode being present on the dedicated printed circuit board. The third pin of connector 57 connects, through connector 59 on the main printed circuit board 51, a ground plane available on the dedicated printed circuit board to the detector ground located on the main printed circuit board.
As an alternative, the ground pin may be omitted and replaced with a traditional metal shield. In this case, Pin-Strip connector 57 only requires two pins.
In the example of Fig. 5, the male elements of the pin strips are located on printed circuit board 53, while the matching female elements are provided on the main printed circuit board. Of course, the male and female elements may be inverted.
In a preferred embodiment, the profile of the dedicated printed circuit board 53 has at least one notch 60.
Distal surface 61 of notch 60 acts as an abutment when assembling the detector. During this stage, printed circuit board 53 is inserted into suitable cavities obtained on printed circuit board 51. The depth of notch 60 determines the height of the diodes above the main printed circuit board, and thus the height at which the diodes will be positioned inside the detection chamber.
Since the heights of connectors 57 and 59 vary from manufacturer to manufacturer, in order to keep unchanged the possibility of using several equivalent suppliers for connectors 57 and 59 without changing the height of the optical focus of the diodes, stopping of the dedicated printed circuit boards 53 and 54 is advantageously obtained by abutment of surface 61 against the surface of main printed circuit board 51, in place of abutment between connectors 57 and 59.
The advantages of the present invention are apparent from the above description. The printed circuit boards of the diodes can be removed easily for maintenance purposes because the connections of the emitter and receiver diodes are provided by means of connectors.
Furthermore, the use of SMD components allows to cut down the production costs of the detector and to completely eliminate the need of carrying out manual tasks for defining the height of the optical focus of the diodes.
As shown in Fig. 6, both the main printed circuit board 51 and the dedicated ones 53 and 54 can be provided through a single base 62 wherein the dedicated printed circuit boards 53 and 54 are connected to the main printed circuit board by means of a stamping 63 or peduncles.
In the example of Fig. 6, printed circuit boards 53 and 54 have different profiles. In fact, notches 60 and 60' have different widths, thus preventing an incorrect installation of the dedicated printed circuit boards on the main printed circuit board.
It is also clear that many changes may be made by those skilled in the art without departing from the principle of the invention as described and claimed. For example, the connectors and devices employed may be either of the traditional type or of the surface mount type.
Furthermore, the connectors may be of different types as well: while the above-described embodiment uses Pin-Strip connectors, these may nonetheless be replaced with any other removable connection means capable of ensuring electric contact.

Claims

Smoke detector (1) comprising a detection chamber (44) in which are positioned an emitter device (56) adapted to emit an electromagnetic radiation and a receiver device (55) adapted to receive said radiation, wherein said receiver device (55) and/or said emitter device (56) are located on respective dedicated printed circuit boards (53,54) which are electrically connected to a main printed circuit board (51), characterized in that said dedicated printed circuit boards (53,54) are removably mounted on said main printed circuit board (51), and in that said dedicated printed circuit boards have a profile comprising an abutment surface (61) for abutting the main circuit board (51) when assembling the detector, so as to determine the height of the corresponding device (54,55) relative to the main printed circuit board (51).
Smoke detector according to claim 1, characterized in that said emitter device (56) and/or said receiver device (55) are of the SMD type.
Smoke detector according to claim 1 or 2, characterized in that said emitter device (56) and/or said receiver device (55) are of the THT type.
Smoke detector according to any of the preceding claims, characterized in that said dedicated printed circuit boards (53,54) are electrically connected to said main printed circuit board (51) in a removable manner.
Smoke detector according to claim 4, characterized in that the dedicated printed circuit boards (53,54) comprise respective connectors (57) which are electrically connected to respective devices.
Smoke detector according to claim 4, characterized in that said connectors are of the SMD type.
Smoke detector according to claim 4, characterized in that said connectors are of the THT type.
Smoke detector according to claim 4, characterized in that said connectors are of the Pin-Strip type.
Smoke detector according to any of claims 4 to 8, characterized in that at least one contact of said connectors (57) is connected to a ground line available on said main printed circuit board.
Smoke detector according to any of the preceding claims, characterized in that the profiles of the dedicated printed circuit boards (53,54) match respective cavities obtained on said main printed circuit board.
Smoke detector according to claim 10, characterized in that the profile of the dedicated printed circuit board (54) of the emitter device (56) is different from that of the dedicated printed circuit board (53) of the receiver device (55).
Smoke detector according to claim 10 or 11, characterized in that the main printed circuit board (51) comprises cavities adapted to house the dedicated printed circuit boards in a univocal manner.
Smoke detector according to any of claims 1 to 12, characterized in that said dedicated printed circuit boards are modules consisting of a device and a connector electrically connected to said device.