GB2409319A

GB2409319A - Synthetic smoke generator and smoke detector tester

Info

Publication number: GB2409319A
Application number: GB0329128A
Authority: GB
Inventors: Stewart Pepper; David Sharp
Original assignee: Sata Ltd
Current assignee: Sata Ltd
Priority date: 2003-12-16
Filing date: 2003-12-16
Publication date: 2005-06-22
Anticipated expiration: 2023-12-16
Also published as: GB2409319B; GB0329128D0

Abstract

Apparatus for testing a hazard detector comprising an open-topped housing (15) for receiving a detector (16) under test, the housing containing a smoke generator device (30), a chamber for receiving smoke generated by the generator device and means for directing (12,13) the smoke in the receiving means towards the detector under test, characterised in that the smoke generator device (30) comprises a source of vaporisable liquid (9), a capillary arrangement (3), one end of which is provided with an electrical heater (1) for vaporising the liquid in the capillary (3) in order to generate smoke.

Description

240931 9

SYNTHETIC SMOKE GENERATOR AND SMOKE DETECTOR TESTER

USING SUCH A GENERATOR

The present invention relates to a device for generating synthetic smoke and also to a hazard detector tester utilising such a device.

In the past, hazard detectors such as smoke detectors, have been tested by utilising an aerosol of fine particles dispensed from a pressurised can. One such tester is the one sold under the trade name "Trutest" where an aerosol container is discharged into an intermediate chamber to accumulate the aerosol particles prior to delivering them through to the detector. However, the use of pressurized containers is not particularly convenient as they are classified as "hazardous" and hence costly to transport. Also, the propellants used cause cliff culty either because they are flammable, are greenhouse gases or attack the ozone layer.

While it is possible to utilise suitable propellants and so overcome any environmental issues, there is a market for an alternative to the use of pressurized containers in certain circumstances.

It has previously been proposed in GB 2299005 to provide a device for vaporising liquids in order to produce synthetic smoke utilising an electrically heated heat exchanger. In this prior proposal, smokeproducing fluid which is to be vaporised is forced into a thin-walled metal tube by means of a pump, compressed air or gravity and the tube is connected to a source of current in order to directly heat the liquid in the tube. While this arrangement has some advantages over the use of a pressurised aerosol can, the need to force liquid under pressure through the tube is inconvenient.

A further proposal for generating synthetic smoke electrically is disclosed in US 3,891,826 and utilises a capillary tube one end of which sits in a reservoir of liquid. Within the capillary tube is located a further tube and the gap between the outer wall of the further tube and the inner wall of the capillary tube creates an annular space which has capillary dimensions and which draws the liquid up into the annular space where it is heated by an electrically operated heated element housed within the further tube. This particular arrangement of a series of tubes within tubes is costly to manufacture and maintain which thus renders it inappropriate for use in a commercial situation and in particular for use with a tester which must reliably produce synthetic smoke.

It is an object of the present invention to provide an electrically operated synthetic smoke generator which utilises capillary action but avoids the disadvantages of the prior arrangements.

From a further aspect, the present invention provides an apparatus for testing a hazard detector comprising an open-topped housing for receiving a detector under test, the housing containing a smoke generator device, a chamber for receiving smoke generated by the generator device and means for directing the smoke in the receiving means towards the detector under test, characterized in that the smoke generator device comprises a source of vaporizable liquid, a capillary arrangement, one end of which is provided with an electrical heater for vaporising the liquid in the capillary in order to generate smoke.

In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawings in which: Fig I shows a schematic sectional side view of a smoke detector tester according to the present invention; and Fig 2 shows a schematic side view of a part of the smoke generator device utilised in the detector shown in Fig 1.

The preferred embodiment of the present invention is a smoke detector tester of a type which is portable and is capable of being mounted on the end of a pole so as to be lifted into the test condition by an operator standing on the ground while the detector under test is located on, for example, a ceiling. The tester is designed to cause a sample of test synthetic smoke to be emitted in the vicinity of a detector under test to cause the detector to be activated.

For ease of description, the tester is based on our earlier tester design which is disclosed in WO01/84520. This is merely by way of example and different overall constructions can be utilised.

Turning now to Fig 1, a detector under test is indicated by the reference numeral 16. A smoke detector tester includes a cup shaped housing 15 which has a flexible membrane 1 Sa with an opening of a size and shape capable of receiving the detector 16. The membrane has sufficient flexibility to allow for a range of different detector samples.

Within the housing 15 there is provided a synthetic smoke generator generally indicated by the reference numeral 30. As shown, the generator is housed in a lower portion of the cup shaped housing IS and communicates with the upper portion of the housing 1 S by means of a duct 13 which has a horizontally directed outlet 14 for directing the synthetic smoke directly towards the detector 16 under test. If desired, a spacer (not shown) may be provided in order to accurately locate the outlet 14 with respect to the detector.

The synthetic smoke generator comprises a reservoir 8 arranged to contain a vaporisable fluid in a collapsible bag 9. The fluid used is preferably a mixture of propylene glycol, all-propylene glycol and water. The top of the reservoir 8 is sealed by a diaphragm 11 and an air vent hole 10 in the reservoir 8 allows the bag to collapse as the fluid in the bag 9 is consumed. A smoke collection chamber 6 is located adjacent the diaphragm 11 of the reservoir 8 and contains a capillary tube 3 provided with an electrically actuated heater element 1. The end of the capillary tube 3 projects out of the chamber 6 and is preformed into a point so that it may be pushed into -the collapsible bag 9 through the diaphragm l l which is preferably made of rubber, or silicone or a similar compound.

In use, when the capillary tube is f tted into the collapsible bag 9, vaporisable fluid moves into the region of the heating element l under capillary action. When the heating element is connected to a source of current, the heating element vaporises the fluid in the region of the heating element which causes a synthetic smoke, actually a fog or mist to be emitted from the top of the capillary tube into the chamber 6. The chamber 6 is provided with a fan or blower 12 which is arranged to blow the synthetic smoke into the duct 13 and thence to the outlet 14 at sufficient speed to ensure that the detector 16 is activated.

The flow of smoke from the chamber 6 into the duct 13 may be regulated by a flap valve 17 which can be opened and closed in a controlled fashion. In the present embodiment, control of the flap valve is achieved by utilising an actuating wire 18 made from a shape memory alloy, trade name Flexinol, which contracts in length by an appreciable amount (typically 5%) when heated by passing an electric current through it. This contraction causes the flap valve to open. The valve is normally held closed by a spring (not shown). The electrical connections to the actuating wire 18 are made via connection points 19 and 20. The tester is preferably battery powered and the batteries are most conveniently located at a position adjacent the tester body to reduce voltage drop between the batteries and the tester.

Control of the currents to the heating element 1, the fan 12 and the valve actuating wire 18 is accomplished using control circuitry on an electronic circuit board 21 which is arranged to control the heating element 1 in such a fashion that fluid in the capillary gap is continually boiled with the resulting vapour passing into the chamber 6 where it condenses to form a fog. This results in further fluid creeping up the capillary gap to maintain the process. Any large droplets of fluid or splashes which emerge from the top of the tube 3 will run down the interior walls of the chamber 6 where they collect for re-use in the vicinity of the capillary tube 3 due to the base (6a) of the chamber being conically shaped and the capillary tube 3 projecting through the apex of the cone. The capillary tube 3 is provided with a small hole 7 in its wall in the region of the base of the chamber so as to permit fluid to drain back into the capillary tube and hence be recycled.

Turning now to Fig 2, this shows in detail the preferred arrangement for the capillary tube 3 and heating element 1. In this embodiment, the capillary tube is a tube of electrically conductive material such as copper and the electrical heating element is fitted inside an electrically insulating tube or rod 2 which is preferably made of glass or a ceramic material. Electrical connections to the heating element are made by means of lead wires sealed into each end. The upper end of the tube or rod 2 extends beyond the end of the capillary tube 3 and the lead wire sealed into this end is then taken to a connection point 4 on the exterior of the chamber 6.

The lead wire sealed to the other end of the tube or rod 2 is connected to the capillary tube 3 which in turn is connected to a further connection point 5 on the exterior of the chamber 6. The lead wires are preferably relatively rigid and consequently locate the tube or rod 2 within the capillary tube 3 so as to create the capillary space between the tube or rod 2 and the inner diameter of the tube 3.

Additionally, they permit the heating element to be axially located so that it is adjacent the top of the tube 3 in order to maximise the heating effect of the heating element I and the capillary action of the tube 3.

Although not shown, the tester housing 15 can be fitted with a removable portion so as to enable the reservoir 8 to be replaced when the supply of fluid in the reservoir 8 is exhausted.

The above arrangement has the advantage that the synthetic smoke can be produced continually and the amount of synthetic smoke actually dispensed is controlled by operation of the valve 17 and the fan 12. This is in contrast to previous arrangements where the amount of smoke produced was totally dependent on the amount of smoke instantaneously generated by the generator.

Claims

CLAIMS: 1. Apparatus for testing a hazard detector comprising an

open-topped housing (15) for receiving a detector (16) under test, the housing containing a smoke generator device (30), a chamber for receiving smoke generated by the generator device and means for directing (12,13) the smoke in the receiving means towards the detector under test, characterized in that the smoke generator device (30) comprises a source of vaporizable liquid (9), a capillary arrangement (3), one end of which is provided with an electrical heater (1) for vaporising the liquid in the lO capillary (3) in order to generate smoke.
2. Apparatus according to claim 1, wherein the capillary projects in to the smoke receiving chamber (6) through a floor (6a) of the chamber (6) which is shaped to direct any condensed vapour towards the capillary which is provided with an opening (7) adjacent the floor of the chamber to permit the condensed vapour to be recycled.
3. Apparatus according to claim 1 or 2, wherein the chamber has an exit aperture for smoke generated by the generator device, which aperture is closed by an electrically actuable valve (17,18).
4. Apparatus according to claim 3, wherein the aperture in the chamber communicates with a duct (13) which has an outlet (14) arranged to be located within the housing in the region of the detector ( 16) under test.
5. Apparatus according to claim 3 or 4, wherein the chamber is provided with a fan (12) for blowing the smoke in the chamber (6) out of the aperture.
6. Apparatus according to any one of the preceding claims wherein the capillary (3) of the smoke generator is an electrically conductive tube and the electrical heater (1) is located in the bore of the tube (3) within an electrically insulating material.
7. Apparatus according to claim 6, wherein the electrical heater (1) has two lead wires for connecting the heater to an electrical current source, one of the lead wires being connected to the metal tube forming the capillary (3).
8. Apparatus according to claim 6 or 7 wherein the electrical heater is located in a tube or rod of glass or ceramic material.