Smoke detector

Details Smoke detector Smoke detector

1999-12-14

2001-05-29

Hofsass, Jeffery (Department: 2632)

Communications: electrical

Condition responsive indicating system

Specific condition

C340S628000, C340S577000, C340S578000

Reexamination Certificate

active

06239710

ABSTRACT:

PRIOR ART
The invention is based on the generic type defined by the preamble to independent claim
1
.
For detecting fires early, smoke alarms are generally used. One method of detecting smoke particles is to measure radiation scattered at smoke particles. Such smoke alarms based on the scattered radiation principle typically employ the method of forward scattering, because with it larger signals can be attained at the radiation receiver. Such a smoke alarm comprises a radiation transmitter (normally pulsed), a lens for focusing the rays, and a radiation receiver, for instance a photo diode, optionally with a lens for capturing the scattered radiation. Radiation receivers and radiation transmitters have no direct visual communication but instead are optically separated from one another by suitable mechanical provisions. There is an obtuse angle between the direction of radiation transmission and the direction of reception, and the scattering angle at the smoke particles to be detected is also obtuse.
Along with these forward scattering smoke alarms, there are versions with back scattering. In them, radiation transmitters and radiation receivers are disposed side by side, and the scattering angle is acute (German Patent DE 38 31 654 C2). A disadvantage of each of the known methods is that only a small proportion of the scattered radiation strikes the radiation receiver, while the remaining scattered radiation is lost to measurement. Also, only one of the preferred measurement effects is used at a time, that is, either forward scattering or back scattering.
ADVANTAGES OF THE INVENTION
The subject of the invention as defined by the characteristics of claim
1
has the following advantage:
The invention makes it possible to deliver virtually all the radiation scattered at the smoke particles to a radiation receiver in the form of a measurement signal. This signal includes not only the forward scatter and the back scatter but also the scattered radiation from all the ranges in between. This makes the measurement more sensitive overall, since there is almost no loss from uncaptured radiation. The smoke alarm of the invention also takes into account the scattering properties that are due to different particle diameters.
Advantageous refinements are defined by the dependent claims, whose characteristics can also be combined with one another as appropriate.
A light-emitting diode, semi-conductor laser or flash lamp can be provided as the radiation transmitter.


REFERENCES:
patent: 4181439 (1980-01-01), Tresch et al.
patent: 4647786 (1987-03-01), Guttinger et al.
patent: 5127729 (1992-07-01), Oetliker et al.

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