Ionization type smoke detector

Details Ionization type smoke detector Ionization type smoke detector

1984-01-10

1986-06-10

Howell, Janice A.

Radiant energy

Invisible radiant energy responsive electric signalling

Including a radiant energy responsive gas discharge device

250385, G01T 118

Patent

active

045945128

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a new and improved construction of an ionization type smoke detector having a single radioactive source.
The hitherto known ionization type smoke detectors may be classified into two categories. One such category encompasses two-radioactive source type smoke detector composed of an outer ionization chamber for measurement into which smoke can freely flow and an inner ionization chamber for comparison or reference into which no smoke can flow. Each of the ionization chambers is provided with a radioactive source. The other category encompasses single-radioactive-source type ionization smoke detectors in which an intermediate electrode partitioning the two ionization chambers has a small hole formed therein through which the outer ionization chamber is irradiated by a radioactive source disposed in the inner ionization chamber. The single-radioactive-source type smoke detector has advantages over the two-radioactive-source type smoke detector in that its structure is simplified and that a reduced amount of radioactive-energy is sufficient for operation of the smoke detector. However, operational tests of actual smoke detectors of the single-radioactive-source type have shown that there are disadvantages due to the structure which makes it difficult for smoke to flow into the inner ionization chamber through the small hole. Smoke which has once entered the outer ionization chamber is also difficult to be withdrawn therefrom and prevents the smoke detector from being rapidly restored to the initial or normal state. As an attempt to overcome the difficulty mentioned above, there has been made a proposal according to which the hole or opening formed in the intermediate electrode is enlarged in size while the ionization current flowing through the inner ionization chamber is maintained in a saturated state so that the resistance value of the inner ionization chamber remains invariable independent of smoke flowing therein. In this structure of the single-radioactive-source smoke detector, however, the radioactive source disposed within the inner ionization chamber is constantly exposed to the atmosphere, resulting in the radioactive source being subjected to contamination which, in turn, gives rise to changes in the ionization current and hence erroneous operation as well as generation of false alarms.


SUMMARY OF THE INVENTION

With the foregoing in mind, it is an object of the present invention to provide an ionization type smoke detector having a single radioactive source which is configured such that the radioactive source is difficult to be contaminated and that smoke supplied to the detector during operational tests thereof is promptly dispelled upon completion of the test, whereby the detector is rapidly restored to the initial or normal state.


BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein throughout the various figures of the drawings there have been generally used the same reference characters to denote the same of analogous components and wherein:
FIG. 1 is a partially sectional view of an exemplary embodiment of the ionization type smoke detector; and
FIG. 2 is an electric circuit diagram of the ionization type smoke detector shown if FIG. 1.


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Describing now the drawings, it is to be understood that to simplify the showing thereof only enough of the structure of the apparatus of the invention has been illustrated therein as is needed to enable one skilled in the art to readily understand the underlying principles and concepts of this invention. Turning attention now to FIG. 1 of the drawings, there has been illustrated in sectional view an exemplary embodiment of the inventive ionization type smoke detector and in FIG. 1 reference numeral 1 denotes a substra

REFERENCES:
patent: 4336455 (1982-06-01), Bryant
patent: 4361763 (1982-11-01), Bryant et al.

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