IL34813A - Ionization smoke detector - Google Patents

Description

IONIZATION DETECTOR This invention relates to an ionization smoke detec including a closed ionization chamber an open ionization chamber which is opened so that smoke can come in for detecting growth of the from change of impedance of the open ionizatio chamber which occurs when the smok ionization smoke detector generally comprises a closed chamber having a radioactive an open ionization chamber having also a radioactive source therein and connected in series with the closed a field effect transistor ed as for deriving a change of impedance of the open ionization chamber occurs when smoke grows as a signal of current or voltage and a switching as SCR which is driven into conduction when the output signal from the FET reaches a prede ermined Sensitivities of ionization smoke detectors having such structure are unstable because of irregularity of intensity of the each radioactive source and electric characteristic mechanical construction of the other componenfr s and in the ior ionization smoke such means that a potentiometer is used as a load resistor of the PET and the movable contact thereof is as the output teminal and is adjusted its position has been adopted for adjusting the detection such means has had such disadvantages as very narrow range of sensitivity control requirement of expensive an object of this invention is to enable the characteristic of the ionization chamber itself to be controlled or thereby the disadvantages as exhibited by the prior ionization The Ionization smoke detector according to this 1s provided with an outer Ionization chamber enclosed a mesh or outer electrode as shown n the drawing so as to freely communicate with the an Inner Ionization chamber enclosed by a Intermediate electrode so as to hardly communicate with the external and radioactive sources for Ionizing said outer and Inner Ionization chambers characterized In that said Inner Ionization chamber 1s disposed In said outer zation chamber to enclose the Inner Ionization chamber with the outer Ionization chamber and a electrode for controlling the spacing between a part of said outer electrode and said Intermediate electrode 1s attached to said outer the Ionization smoke detector of this Invention be described in detail in conjunction with an embodiment shown in the drawings In the Figure 1 1s a diagram of an Ionization smoke detector according to this and Figure 2 Is a diagram representing construction of a main portion of the Ionization smoke detector of Figure 1 Throughout both Figures 1 and same or analogous ponents are Indicated by same reference Referring to Figure a closed Ionization chamber 10 and an open Ionization chamber 20 are connected 1n series between conductors 1 and The closed Ionization chamber 10 Includes a pair of electrodes 11 and 12 and a radloactlce source 13 and the open Ionization chamber 20 also Includes a of 21 and 22 and a source The junction of the two ionizatio chambers 10 20 is connected to the gate electrode of a FET30 whose drain electrode 32 is connected to one 1 of the conductors and source electrode 33 is connected through a Zener 5 the gate electrode 41 of a SCR The anode 42 of the SCR 40 is connected to said one conductor and the cathode 43 thereof is connected to the conductor The conductors 1 and 2 are connected to a circuit a power The practical constructions of the closed ionization chamber 10 and the open ionization chamber 20 are shown in Figure As clearly found from the one electrode 22 of the open ionization chamber 20 is partly or fully constructed as a mesh so as to enable smoke to be introduced lowermost portion of the electrode 22 is fixed to a base In the electrode 22 disposed in ionization chamber 10 whose one 11 is led out through a The electrode of the closed ionization chamber 10 is to the other electrode 11 of the open ionization chamber and these are shown in Figure 2 as a common electrode A radioactive source 13 for the closed ionization chamber is placed on one face of the common electrode 33 and a radioactive source 23 for the open ionization chamber is placed the The portion of the common is the junction 3 of the two ionization A boss 24 is fixed to the top of one electrode 22 of the ionization A sensitivity control electrode 7 is screwed i the boss 24 and projects downwards from the bottom face The sensitivity control electrode is of course a part of the electrode 22 and the length L of the portion projecting toward In the illustrated ionization smoke the source current of the FET 30 during the normal watching time is set to be zero or so that the voltage at the source electrode 33 of the FET is than the Zener voltage of the Zener diode When smoke comes the open ionization the ionization current This exhibits the effect as in the case that the internal impedance of the open ionization chamber 20 becomes and raises the voltage the junction that at the gate electrode 31 of the FET With increase of the voltage at the gate electrode 31 of the FET the current flowing through the of the above FET 30 thereby increasing the source voltage 33 of the FET 30 to which the load resistor 4 is When this increased voltage exceeds the Zener voltage of the Zener diode a gating signal is supplied to the gate electrode of the SCR the 40 conducts to transmit smoke growth to the power supply through the conductors 1 and As described ionization smoke detectors have of due to no of characteristics of various especially of the ionization In the present ionization smoke the characteristic of the open ionlzationjhamber 20 can be directly controlled by rotating the control electrode 7 to change the length L of the portion extending from the electrode 22 toward the radioactive source More when the control electrode 7 is rotated to reduce the distance between the top thereof and the radioactive source an electric field in the open ionization chamber is intensified to increase the ionization current when said distance is rily the electric field the open ionization of Figure 1 where a resistor 17 by a dotted as a phantom is inserted in parallel to the ionization chamber 20 the value of this resistor is the voltage at the junction that at the gate electrode the FET 30 can be controlled into a of op imum operational by rotating the control electrode 7 to vary the length L of the portion projecting from electrode the ivity of the ionization detector can be controlled into an optimum in rative the control electrode 7 is composed of a having a constant a control electrode having a conical or frustoconical top portion ma adopted so that it is rotated to change the average sectional area of its projecting top In the ionization smoke detector according to this sensitivity can be easily established in an arbitrary no its very simple cons insufficientOCRQuality

Claims (2)

Claims:

1. An Ionization smoke detector comprising an outer Ionization chamber enclosed with a mesh or grid-l ike outer electrode as shown 1n the drawing so as to Heely communicate with the external air, an inner ionization chamber enclosed by a box-shaped intermediate electrode so as to hardly communicate with the external air and radioactive sources for Ionizing said outer and Inner Ionization chambers , characterized 1n that said Inner Ionization chamber Is disposed 1n said outer Ionization chamber to enclose the inner Ionization chamber with the outer Ionization chamber and a rod-shaped electrode for controlling the spacing between a part of said outer electrode and said Intermediate electrode 1s attached to said outer electrode.

2. An Ionization, smoke detector substantial ly as described hereinbefore and with reference to the accompanying drawings. For the Applicants Wolff , Bregman and Gol ler By: