Ionization-type smoke detector

Details Ionization-type smoke detector Ionization-type smoke detector

1985-04-19

1988-04-26

Howell, Janice A.

Radiant energy

Invisible radiant energy responsive electric signalling

Including a radiant energy responsive gas discharge device

250381, G01T 118

Patent

active

047407034

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to an ionization-type smoke detector and, more particularly, to a constitution for increasing the insulation resistance between respective electrodes which is especially effective for a small size ionization-type smoke detector.


BACKGROUND ART

An ionization-type smoke detector is constituted so that both the inner and outer ionization chambers have a high resistance so that the insulation resistance between the respective electrodes must also be very high. For this reason an attempt has so far been made to increase the insulation resistance between the electrodes by corrugating the surface of the base on which each of the electrodes is mounted, thus lengthening the creepage distances between the electrodes.
Now an example of a conventional ionization-type smoke detector of this kind will be explained in reference to FIG. 1 of the attached drawings. In this drawing reference numeral 1 designates an insulating base the under surface of which is formed into concentric circles of corrugations. Below the surface of the insulating base 1 there are respectively supported an inner electrode 4 that is mounted together with a radioactive source 2 by a screw 3, an intermediate electrode 6 with a central opening 5, and a net- or grid-like air permeable outer electrode 7, whereby an inner ionization chamber 8 and an outer ionization chamber 9 are constituted by the inner and intermediate electrodes 4, 6, and intermediate and outer electrodes 6, 7, respectively. Further, in FIG. 1 the reference numeral 10 designates a circuit board of an insulating material which constitutes a circuit for detecting the electrical change in the outer ionization chamber 9, the outer periphery of the circuit board 10 being mounted on the upper part of the insulating base board 1 in contact therewith, and the respective electrodes 4, 6 and 7 are electrically connected to the circuit board 10. A rear cover 11 is mounted on the insulating base 1 at its upper rear side.
With such a constitution the creepage distances between the respective electrodes 4, 6, 7 become longer and the insulation resistances between the respective electrodes 4, 6 and 7 are respectively increased. However, like other detectors these ionization-type smoke detector are also now required to be of smaller size as the times demand. However, in this case there arises a defect that even if corrugations are formed on the under surface of the base 1 as shown in FIG. 1, the desired creepage distances cannot be obtained.


DISCLOSURE OF THE INVENTION

It is an object of the present invention to improve conventional ionization-type smoke detectors such as that shown in FIG. 1 so as to have smaller overall dimensions and yet to assure desired creepage distances between the inner, intermediate and outer electrodes, respectively.
The present invention is characterized in that in order to achieve the above object the support portions of the inner and outer electrodes are moved to other positions relative to the intermediate electrode so that the creepage distances between the respective electrodes can be easily lengthened, whereby sufficient insulation resistances can be assured between the respective electrodes.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a conventional ionization-type smoke detector, FIG. 2 is a vertical sectional view of one embodiment of the present invention; and FIGS. 3 and 4 are vertical sectional views of the essential parts of the other embodiments of the outer electrode support portions relative to the insulating base respectively.
In FIGS. 2 to 4 the elements corresponding to those shown in FIG. 1 bear the same reference numerals as those in FIG. 1.


BEST MODE FOR CARRYING OUT THE INVENTION

First, the present invention will be explained in reference to FIG. 2 wherein an embodiment thereof is shown. Just as in FIG. 1 an intermediate electrode 6 having a central opening 5 is supported on the under surface of an insulating base 1 which is provided with many corrugations in the form

REFERENCES:
patent: 4234877 (1980-11-01), Moruyama et al.
patent: 4328424 (1982-05-01), O'Connor

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