Smoke detector adapted to a smoke sensing apparatus

Abstract

A smoke detector is disclosed which comprises an inner electrode, an intermediate electrode with a hole for passing radioactive rays therethrough, an outer electrode having openings for allowing smoke to flow therethrough, and one radioactive source, the inner and intermediate electrodes forming an inner ionization chamber, the intermediate and outer electrodes forming an outer ionization chamber, the radioactive source being disposed in the inner ionization chamber. A proper quantity of radioactive rays from the radioactive source is applied into the outer ionization chamber through the hole provided in the intermediate electrode.

Description

RELATED CASE

This application is a continuation of Ser. No. 860,357 filed Sept. 23, 1969, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to improved smoke detectors adapted to a smoke sensing apparatus comprising a smoke detector and an electric indicating or alarm device including a relay such as, for example, a control electric valve the control electrode of which is connected to the output terminal of said smoke detector, and more particularly to smoke detectors in which a kind of radioactive substance is used in common in two ionization chambers.

Hitherto, as a method of detecting particles contained in any kind of smoke, it has been well known to utilize ionization of said particles. For this purpose, a smoke detector provided with two inner and outer ionization chambers each including a radioactive substance therein has been generally used, said outer chamber being denoted as an outer ionization chamber and being provided with a metal wire net for passing outer gas therethrough, and said inner chamber being denoted as an inner ionization chamber and being constructed so that penetration of said outer gas into said inner ionization chamber is very difficult.

In the conventional smoke detectors as mentioned above, there are disadvantages such that the detector becomes large in its structure, very complicated in its construction, and uneconomical because each of the inner and outer ionization chambers is provided with a radioactive substance therein, and, furthermore, the quantity of the radioactive rays is relatively large, thereby increasing harmful effects on human bodies.

Furthermore, in the conventional smoke detectors as mentioned above, precise detection at various temperature condition or precise detection unaffected by variation of the surrounding temperature is very difficult and simple temperature compensation or alarming of an emergency temperature itself cannot be attained. For the purpose of temperature compensation of the smoke detectors, various compensating circuits utilizing any kind of various thermistors have been conventionally utilized, but these circuits are relatively complex and cause expensive structure of the smoke detector provided with said circuit.

SUMMARY OF THE INVENTION

It is therefore an essential object of the present invention to provide improved smoke detectors adapted to a smoke sensing apparatus comprising a smoke detector and an electric indicating or alarm device the input of which is connected to the output terminal of said smoke detector, and having no disadvantages of the conventional smoke detectors mentioned already.

Said object and other objects of the invention have been attained, according to the invention, by a smoke detector which comprises outer, inner and intermediate electrodes, said intermediate electrode forming an inner ionization chamber therein and said outer and intermediate electrodes forming an outer ionization chamber therebetween, and comprises a radioactive substance provided in a position of said inner chamber to cause ionization in said chambers.

The objects, characteristic features and function of the invention will be described in detail in conjunction with the accompanying drawings, in which the same or equivalent members are designated by the same reference numerals and characters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view, in section, for showing the principle of an example according to the invention;

FIG. 2 is a sectional side view for showing another example of the invention, corresponding to FIG. 1;

FIG. 3 is a sectional view for showing a further example of the invention, corresponding to FIG. 1;

FIG. 4 is graph showing the relation between output voltage deviation ΔE of the device, as illustrated in FIGS. 1, 2 or 3, and the surrounding temperature;

FIGS. 5 and 6 are schematic side views, partly in section, of other examples of the invention, respectively; and

FIG. 7 is a plan view showing a part of a modification of the example illustrated in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

One example of the invention as illustrated in FIG. 1 comprises an insulating support member 4 made of a synthetic resin having a large electrical resistance, a metal wire net 1 functioning as an outer electrode, an a way away from the inner electrode 3 in either an abrupt or gradual manner, thereby to increase the voltage E_o up to a value sufficient to operate the smoke sensing apparatus, not shown.

FIG. 6 shows a modification of the example of FIG. 5. In the case of the example of FIG. 6, the inner electrode 3 is supported on its support member 5 by means of the thermally responsive element 9 so as to be moved up and down, said support member 5 being passed through the insulating member 8 held by the insulating support member 4. The element 9 is made of, for example, a bimetal and designed to compensate for the influence caused by variation of the surrounding temperature. In the example of FIG. 6, an adjusting screw, not shown, adapted to adjust the sensibility sensitivity of the element 9 can be provided, or the end face 5a of the support member 5 and a contact 10 confronting said end face 5a and supported by an arm 10a can be utilized for signalling by alarm a specific emergency temperature, for example, 70°C, by inserting said end face 5a and contact 10 in the circuit of an alarm device of the smoke sensing apparatus, not shown.

The examples of FIGS. 1 to 3 can be modified so that the detector may be operated at a specific temperature. For this purpose, for example, such a mechanism as shown in FIG. 7 is additionally provided in the detector, said mechanism comprising a bimetal 11 attached at its one end to the intermediate electrode 3 by means of a support pin 11a and provided at its other end with a shield plate 13. If the bimetal 11 is designed so that when the temperature becomes a predetermined specific value, said bimetal 11 is turned in the direction of the arrow so as to shut the hole A of the intermediate electrode 3, whereby penetration of radioactive rays into the outer ionization chamber is stopped and the ion current flowing through said chamber disappears, the voltage E_o shown in FIG. 1 is abruptly increased at said specific temperature, thereby to operate a control electric valve, not shown.

Claims

1. An ionization-type smoke detector having only a single radioactive source, comprising: an inner electrode provided with a said single radioactive source; an intermediate electrode having at least one throughhole; and an outer electrode having openings through which smoke can enter; an insulating support member supporting said inner electrode, said intermediate electrode and said outer electrode; and an annular wall means projecting from said support member at a position inwardly of the outer circumference of said support member; said inner electrode and said intermediate electrode forming an inner ionization chamber in which said radiation source is arranged, said intermediate electrode and said outer electrode forming an outer ionization chamber, said inner ionization chamber being arranged inside located in a topmost portion of said outer ionization chamber which surrounds the inner ionization chamber, said intermediate electrode being secured to said annular wall means such that the surfaces thereof define said inner ionization chamber, and wherein a necessary quantity of radioactive rays emitted from said radioactive source is introduced directly into said outer ionization chamber through said holes.

2. A smoke detector as defined in claim 1, in which said inner electrode is movable upwardly and downwardly.

3. A smoke detector as defined in claim 1, in which said inner electrode is movable upwardly and downwardly.

4. A smoke detector as defined in claim 1, in which said inner electrode is supported on a supporting member having an annular projecting wall, and wherein said intermediate electrode is secured to

said annular projecting wall. 5. An ionization-type smoke detector having only a single radioactive source, which comprises: an inner ionization chamber; an outer ionization chamber within which said inner chamber is positioned located at a topmost portion thereof; an intermediate electrode common to both of said chambers and forming a boundary therebetween; an inner electrode positioned within said inner chamber; an outer electrode defining the outer boundary of said outer chamber and having openings therein through which smoke can freely pass; an insulating support member supporting said inner electrode, said intermediate electrode and said outer electrode; and an annular wall means projecting from said support member at a position inwardly of the outer circumference of said support member; said inner electrode being provided with a single radioactive source positioned within said inner chamber; said intermediate electrode being secured to said annular wall means such that the surfaces thereof define said inner ionization chamber, said intermediate electrode including aperture means formed therein for substantially preventing smoke from entering said inner chamber from said outer chamber and for substantially preventing smoke from entering said inner chamber from said outer chamber and for facilitating the passage of radiation from said inner chamber into said outer chamber in order to improve the ionization efficiency therein, said aperture means comprising an unobstructed hole formed through said intermediate electrode.

6. The smoke detector as set forth in claim 5, further comprising: an insulating support member having an annular wall projecting therefrom at a position inwardly of the outer circumference thereof; said intermediate electrode being secured to said annular wall such that the inner surfaces thereof define said inner ionization chamber; the portion of said support member outside said annular wall forming a boundary for said outer ionization chamber; said outer electrode being secured to the outer circumference of said

member. 7. A smoke detector as defined in claim 1, in which said annular wall means consists of a projecting annular wall of said support member, the portion of said support member inside said annular wall forming a boundary for the top of said inner ionization chamber; the portion of said support member outside said annular wall forming a boundary for the top of said outer ionization chamber; said outer electrode being secured to the outer circumference of said support member. 8. A smoke detector as defined in claim 1, in which said annular wall means consists of a side wall of said intermediate electrode; the portion of said support member inside said side wall forming a boundary for the top of said inner ionization chamber; the portion of said support member outside said side wall forming a boundary for the top of said outer ionization chamber; said outer electrode being secured to the

outer circumference of said support member. 9. A smoke detector as defined in claim 5 in which said annular wall means consists of a projecting annular wall of said support member, the portion of said support member inside said annular wall forming a boundary for the top of said inner ionization chamber; the portion of said support member outside said annular wall forming a boundary for the top of said outer ionization chamber; said outer electrode being secured to the outer circumference of said support member.