GB2373048A

GB2373048A - Testing gas detectors

Info

Publication number: GB2373048A
Application number: GB0105286A
Authority: GB
Inventors: Michael Jackson
Original assignee: Central Research Laboratories Ltd
Current assignee: Central Research Laboratories Ltd
Priority date: 2001-03-05
Filing date: 2001-03-05
Publication date: 2002-09-11
Also published as: GB0105286D0

Abstract

A device for testing a gas detector, typically a CO detector is characterised by having a cartridge 4 containing an electrical heater and a test gas generating means. The cartridge has electrical connectors 7 for releasable connection of the heater to a power supply and in use the heater heats the generating means to evolve a test gas. Typically the cartridge 4 is inserted into a housing 2 having corresponding electrical connectors 8 such that on insertion and operation of a switch 5 an electrical circuit is completed to operate the heater which preferably comprises a wire coated with PVA which generates CO on heating which then escapes from the cartridge via holes 12. The housing is placed over the detector undergoing testing or alternatively the test device may be an integral part of the CO detector.

Description

Device for testing the operation of gas detectors

This invention relates to the field of gas detectors, particularly Carbon Monoxide detectors.

In particular, this invention relates to a device for testing the operation of such detectors.

Carbon Monoxide (CO) is a poisonous gas, which is odourless, colourless and tasteless. In the UK alone, more than 50 deaths result every year from CO poisoning caused by faulty heating appliances. One reason why CO is so dangerous is that since it does not smell and has no taste, it is difficult to detect without a CO detector. Such detectors are becoming increasingly common, and for their correct implementation it is vital that they are tested periodically.

There are several known types of testing device for CO detectors. For example, it is known to provide a test-gas generator, either integral with the detector or separately, which on activation generates a test gas that may be used to test the operation of the detector.

Commonly, the gas used to test CO detectors is Hydrogen gas-see for example US5959188. However, the generation of H2, whilst relatively easy, does not provide the reliability of test that would be provided by the use of CO itself as a test gas-the detector response to H2 may well differ from its response to CO.

A device using smoke (of which CO is a major constituent) as a test gas is also known. This device includes a housing containing an inflammable pellet. The operator ignites the pellet and places the device near the CO detector, which should respond to the CO generated. However, since the operator must ignite the pellet, this device requires some dexterity, and is not without risk. It is therefore not suitable for all users, particularly the elderly or those with impaired dexterity.

Another device for testing a Carbon Monoxide detector is shown in US6098523. This shows a CO detector having a self-test facility. The self-test portion of the detector includes an array of electrical resistors coated with a metal oxalate, which emits CO in response to increases in temperature. Electrical power is supplied to a resistor so as to raise its

temperature, causing CO to be emitted. The detector response to the generated CO is then monitored.

This device, however, has disadvantages. The test-gas generator is built-in to the detector, and contains a number of CO-generating elements. Provision is made to switch between elements as each element is exhausted, but there is no suggested provision for replacement. Once all the test-gas-generating elements are exhausted, therefore, the testing mechanism will no longer work, and the whole detector must be replaced.

There is therefore a requirement for a gas-detector-testing device avoiding the above disadvantages. In particular, there is a requirement for a gas-detector-testing device that is simple and economical to construct and safe in operation, and which provides a reliable testing method.

It is an object of the present invention to fulfil the above requirements.

According to the above objects, the invention provides a device for testing the operation of a gas detector, said device having a test-gas generator in the form of a discrete cartridge containing an electrical heater and a gas-generating portion, electrical connection means being provided for connecting the heater to a compatible power supply means, the heater, in use, heating the gas-generating portion to generate the test gas, the said cartridge being constructed, adapted, and arranged, relative to the power supply means, so that it can be selectively releasably connected to, or disconnected from, the power supply means.

Preferably, the gas-generating portion comprises a coating applied to the said electrical heater. Advantageously the electrical heater comprises a wire.

According to one embodiment, the gas-detector-testing device is adapted to co-operate with a gas detector to be tested.

Alternatively, the gas-detector-testing device may be integral with the gas detector to be tested. Advantageously in this case, the said power supply means may also supply power to the gas detector.

Preferably, means are provided to control the temperature of the electrical heater. According to one aspect, said temperature-control means includes a switch manually actuable by a user. Alternatively or in addition, the said temperature-control means may include timer circuitry adapted to supply current for a predetermined time. The said temperature-control means may include a thermostat adapted so as to monitor the temperature of the gasgenerating portion and stop the supply of current when a predetermined temperature is reached. According to another aspect, the electrical heater may be constructed so as to fuse at a particular temperature, the said temperature having been previously determined to be high enough so that sufficient gas has been generated.

Preferably, the test gas is Carbon Monoxide. In this case, the gas-generating portion may contain Poly Vinyl Alcohol (PVA). Alternatively or in addition, the gas-generating portion may contain powdered incense and/or Sodium Formate.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings which show schematically various embodiments of the present invention. The figures are not to scale.

Figure 1 shows a gas-detector-testing device according to one embodiment of the present invention; Figure 2 is a schematic diagram of the device of Figure 1; and Figure 3 shows another embodiment of the invention.

Figure 1 shows a gas-detector-testing device (1) in particular a device for testing a Carbon Monoxide detector. The device includes a device housing (2), which is adapted to cooperate with (in this case fit over) a CO detector to be tested (not shown). The housing has a

front face in which is formed an aperture (3) shaped so as to receive a replaceable gasgenerating cartridge (4). A test switch (5) and an indicator light (6) may also be provided. The cartridge (4) is provided with electrical connectors (7), the connectors in use cooperating with corresponding connectors (8) located on the housing, so that on insertion an electrical circuit is completed. The cartridge (4) is preferably disposable, being replaced each time the testing device is used or after a certain maximum number of uses. The cartridge may incorporate means (not shown) for indicating the number of times it has been used, or it may incorporate means (also not shown) for preventing re-use-these means can be realised in many ways apparent to the skilled person. The cartridge (4) also has an insertion tab (9), which aids in its insertion and removal.

Looking now at Figure 2, the gas-generating cartridge (4) contains an electrical heater comprising a heating element in the form of a wire (10) which has a coating (11) of a substance that generates CO on heating such as Poly Vinyl Alcohol (PVA). The PVA may be mixed with or replaced by e. g. powdered incense or Sodium Formate. When current is supplied to the wire (10) its temperature rises, causing CO to be generated. The CO escapes from the cartridge through holes (12) in its casing, which also serve to allow air into the cartridge. The detector to be tested will, if functioning correctly, detect the CO and respond accordingly.

The proper functioning of the detector to be tested may be monitored in different ways.

Detection of the test gas may set off an audible alarm. Alternatively, if the detector has a display showing the amount of CO detected it may be possible to construct the housing of the test device so that the display may be visually monitored while testing takes place. In this case the correct functioning of the detector may be monitored without actually setting off an alarm. An extendible arm may be provided for testing detectors at ceiling height-in this case, an alternative to the test switch (5) is provided so that the device may be actuated by the operator.

The test device also contains a power source (12) such as a battery. Also provided is electronic circuitry (shown in block form as 13) for controlling the temperature of the heating element by controlling the current provided to the heater (10). This circuitry may be realised in many different ways. For example, the circuit may be a timer circuit which provides current to the heater for a pre-set time, which has been determined to be enough time for the generation of a sufficient amount of CO but not enough time for combustion to take place. Alternatively, a thermostat (not shown) may be provided which detects the temperature in the region of the electrical heater and switches off the current when the required temperature is reached. In another realisation, the current to the heater may be simply be controlled manually by the operator using the test switch (5).

In operation, the user selects a cartridge (4), inserts it into the aperture (3) in the device housing (2), places the device over the detector to be tested and presses the test switch (5).

The indicator lamp (6) will light up to show that the device is in operation. Current will flow through the wire (10) in the cartridge, heating the coating (11) so that CO gas is generated.

The gas will pass through holes (12) in the cartridge (4) and enter the detector, and if the detector is operational it will detect the CO. The circuitry (13) will then switch off the testing device, and the lamp (6) will go out. Should no CO have been detected, the user may, if desired, replace the cartridge (4) and perform the test again. Should the detector fail to detect the test gas, it should be replaced.

Another method of realising the device is to eliminate the need for a switch, the circuit automatically being made on insertion of a cartridge into the housing. The circuit may be broken either by a thermostat or timer as discussed above or by physical removal of the cartridge. Alternatively, it may be possible to dimension the wire so that it can withstand sufficient current to generate a detectable amount of CO but will fuse before a temperature is reached which might ignite any component or give rise to any danger-in this embodiment, careful dimensioning of the wire is critical. According to this embodiment, the user simply inserts the cartridge and waits for a specified time. During this time, sufficient CO should have been generated to set off the CO detector. If the detector has not been activated, the user removes and discards the used cartridge. The user may then insert

another cartridge in order to check the detector again or may choose to replace the detector without further testing. If a one-shot cartridge such as the above is used, it is preferable to provide means (such as a tab which is broken off on insertion of the cartridge) to indicate that the cartridge has been used, to prevent the user from selecting a used (and therefore zn non-functioning) cartridge.

The device according to the invention is economical, since the device and associated circuitry can be re-used many times, whereas the test-gas cartridge (a simple housing containing a coated wire) is disposable. The test-gas cartridge is simple to use and does not expose the operator to any risk of burning or require a high level of manual dexterity.

Different shaped housings may be provided, each being suitable for a different model of CO detector and each using the same standard cartridge.

Figure 3 shows another useful embodiment of the invention, wherein the testing device is provided integrally with the CO detector itself, providing a self-test facility. The CO detector (14) comprises a detector housing (15) having an opening (16), which allows ambient air into the housing. The CO detector may be constructed in any known manner. A CO sensor (not shown) inside the housing monitors the CO content of the air. The detector housing (15) has an aperture (3) into which a test-gas cartridge (4) is inserted. According to one mode of operation, the user inserts a test-gas cartridge (4) into the aperture (3) and depresses the test switch (5). The indicator light (6) illuminates, showing that the test-gas generator is activated. CO will escape from holes (12) in the test-gas cartridge (4) and travel to the CO sensor, which should detect the CO and activate the detector as discussed above. Alternatively, means (not shown) may be provided so that the supply of current to the heating element (and the response thereto of the gas detector) may be remotely monitored.

In this case it is preferable to use a multi-use test-gas cartridge which will remain inserted in the gas detector until unless replacement is required e. g. in case of suspected malfunction. In the embodiment of Figure 3, the same power supply may power both the testing device and the detector.

Claims

1. A device for testing the operation of a gas detector, said device having a test-gas generator in the form of a discrete cartridge containing an electrical heater and a gas generating portion, electrical connection means being provided for connecting the heater to a compatible power supply means, the heater, in use, heating the gas generating portion to generate the test gas, the said cartridge being constructed, adapted, and arranged, relative to the power supply means, so that it can be selectively releasably connected to, or disconnected from, the power supply means.

2. A device according to claim 1 wherein the gas-generating portion comprises a coating applied to the said electrical heater.

3. A device according to claim 2 or claim 3 wherein the electrical heater comprises a wire.

4. A device according to any previous claim wherein the gas-detector-testing device is adapted to co-operate with a gas detector to be tested.

5. A device according to any of claims 1-3 wherein the gas-detector-testing device is integral with the gas detector to be tested.

6. A device according to claim 5 wherein the said power supply means also supplies power to the gas detector.

7. A device according to any previous claim wherein means are provided to control the temperature of the electrical heater.

8. A device according to claim 7 wherein said temperature-control means includes a switch manually actuable by a user.

9. A device according to claim 7 or claim 8 wherein the said temperature-control means includes timer circuitry adapted to supply current for a predetermined time.

10. A device according to any of claims 7-9 wherein the said temperature-control means includes a thermostat adapted so as to monitor the temperature of the gas generating portion and stop the supply of current when a predetermined temperature is reached.

11. A device according to any of claims 7-10 wherein the electrical heater is constructed so as to fuse at a particular temperature, the said temperature having been previously determined to be high enough so that sufficient gas has been generated.

12. A device according to any previous claim wherein the test gas is Carbon Monoxide.

13. A device according to claim 12 wherein the gas-generating portion contains Poly Vinyl Alcohol (PVA).

14. A device according to claim 12 or 13 wherein the gas-generating portion contains powdered incense.

15. A device according to any of claims 12-14 wherein the gas-generating portion contains Sodium Formate.

16. A cartridge for use in a gas-detector-testing device according to any previous claim.

17. A gas-detector-testing device substantially as herein described and illustrated in the accompanying drawings.