Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1994-10-11
1996-06-04
Swarthout, Brent A.
Communications: electrical
Condition responsive indicating system
Specific condition
340628, 250574, G08B 1710
Patent
active
055237444
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a device for testing the operation of smoke detectors of a type used in fire alarm systems for the early detection of fires. Such detectors serve to detect smoke particles or aerosols appearing during a fire, and if necessary to send a signal to a central process unit where the signals are evaluated.
BACKGROUND
Examples of smoke detectors for the early detection of fires are ionization smoke detectors in which the change in conductivity of ionized air is utilized to indicate fire aerosols, and optical smoke detectors in which the absorption or scattering of light by smoke particles is used. Since in ionization smoke detectors radio activity - albeit low-level is present, optical smoke detectors are increasingly used, especially scattered-light detectors, since the latter can be of a construction having a small space requirement.
Optical smoke detectors operating on the scattered-light principle contain a radiation source and a radiation detector. The detector is arranged outside the direct radiation area of the radiation source, but, in the presence of smoke or fire aerosol in the radiation area (measuring chamber), the detector is exposed to scattered radiation and generates electrical output signals depending on the strength of the scattered radiation. These signals are evaluated in an electronic circuit present in the smoke detector for alarm generation, or they are passed to the central process unit. In order to avoid interference by outside light, the light sources frequently operate in a pulsed manner, for example see the smoke detector system described in EP-B1-0'079'010.
Fire alarm systems must be ready for operation over long time periods. The smoke detectors are exposed to the harmful effects of the surrounding atmosphere, e.g. dust or corrosive vapors. Furthermore the quality of the electronic components, especially the radiation source and the radiation detector, can be reduced by aging. It is therefore necessary to check the operational capability of the smoke detectors at regular intervals.
In practice, this checking is usually effected by igniting a small test fire underneath the smoke detector, to produce smoke which can enter the detector and make it respond. Testing also has been carried out by placing a burning wick, e.g. on a rod, directly under the detector (for example see U.S. Pat. No. 4,271,693). Apart from the fact that these methods are rather cumbersome, they frequently result in contamination of the detector, which could render it incapable of operation.
An attempt has therefore been made to replace the smoke by droplets of fluid, e.g. artificially-produced mist, since such aerosols affect the smoke detectors in the same way as smoke from fires. For example, a mist of water droplets has been produced and used for the test. The layer of water deposited on the inner surfaces makes the detector inoperative over long periods.
Test agents which have proved most successful are mixtures of halogenated hydrocarbons (propellants) which have a suitable boiling point and which are blown directly into the smoke detectors from suitable storage containers arranged in so-called detector testers (for example see DE-B2-20'54'027). Due to the pressure-loss during discharge a suitable quantity of aerosol is produced for testing the smoke detector. Due to the high vapor pressure of the halogenated hydrocarbons, the propellant evaporates within a short time and the operational capability of the detector is not impaired.
A suitable detector tester for the testing of smoke detectors with halogenated hydrocarbons consists of a housing open at one end, which can be placed over the smoke detector, whose volume is at least twice the volume of the smoke detector, and a container connected to the housing that contains the propellant liquified under pressure and which, with the housing in place, has a spray valve operated manually or automatically, whose nozzle leads into the inside of the housing.
Because of the environmentally-harmful properties of halogenated hydrocarbons, these
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JP-A-53-99899: Abstract in English.
Cerberus AG
Lee Benjamin C.
Swarthout Brent A.
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