US 4,012,729 A · Multi-element ionization chamber

Abstract

A fire alarm system utilizes an ionization type aerosol detector having first and second intercommunicating and electrically in series ionization regions or chambers irradiated by a particle source. Electrodes are provided which operate in conjunction with a DC voltage source to establish a relatively large voltage gradient across the first region and a relatively small voltage gradient in the second region. Also, the location of the ion source and the effective volumes of the regions are arranged to establish a comparatively high ion density in the first region. In operation, the impedance or resistance of the first region to ion current flow is substantially uninfluenced by the presence of combustion or smoke aerosols due to the relatively high field gradient while the impedance or resistance of the second region is measurably changed thereby. The insensitivity of the first region to the presence of smoke is due to the high voltage gradient therein, as well as to the high ion density therein. The detector operates by the method of employing the second region as a signal or sensing ion chamber and the first region as a reference chamber, thereby to develop electrical signals on the electrodes representative of detected smoke aerosols for driving the associated fire alarm circuitry. The ion collecting electrode in the second region defines a sensing volume which communicates with the surrounding atmosphere to be monitored and which is located at the optimum distance from the particle source to maximize ion production and collection.

An aerosol detection device, comprising:

structure defining intercommunicating first and second substantially cylindrical ion chambers, each of said chambers having a longitudinal axis and first and second ends, the second end of said first ion chamber being in communication with the first end of said second ion chamber and the longitudinal axis of said ion chambers being substantially aligned to define a common axis, the effective volume of said first ion chamber being substantially smaller than the effective volume of said second ion chamber;
a first electrode having a center axis positioned at the first end of said first ion chamber, said first electrodes being in the shape of a disc and extending substantially perpendicularly to the common axis of said ion chambers with its center axis substantially aligned with said common axis;
a second electrode positioned within said ion chambers substantially at the intercommunication of the second end of said first ion chamber with the first end of said second ion chamber;
said second electrode being in the form of a ring to define an aperture in its center and having a center axis, the center axis of said ring being substantially aligned with the common axis of said ion chambers;
a third electrode positioned at the second end of said second ion chamber;
particle source means for substantially simultaneously emitting charged particles into said first and second ion chambers, said particle source means being a single source and having an axis of radiation along which emitted charged particles are radiated, said single particle source being in said first ion chamber adjacent said first electrode with its axis of radiation substantially aligned with the common axis of said ion chambers whereby to introduce charged particles into said first ion chamber and therethrough through the aperture defined by said second electrode into said second ion chamber;
means for establishing a single ion current flow of said charged particles third electrodes serially through said ion chambers, said means being operable to establish under clear air conditions a first voltage gradient in said first ion chamber between said first and second electrodes and a second voltage gradient in said second ion chamber between said second and third electrodes, said first voltage gradient being substantially higher than said second voltage gradient to render the electrical resistance characteristic of said first ion chamber to said ion current flow therethrough relative to said second ion chamber substantially insensitive to the presence or absence of smoke aerosols and the like;
and
means for connecting said second ion chamber in communication with atmosphere to be monitored so that smoke aerosols and the like therein enter said second ion chamber, the electrical resistance characteristic, of said second ion chamber to said ion current flow, increasing as the result of the entry of smoke aerosols and the like therein whereby to cause a change in the voltage on said second electrodes indicative of the presence of smoke aerosols and the like in the atmosphere being monitored.

6 more elements

Multi-element ionization chamber

Life of this patent

Multi-element ionization chamber

Life of this patent

Abstract

Claims16