US3579216A - Particle detector - Google Patents

Abstract

A smoke detector in which a light for illuminating smoke particles also illuminates a photocell providing a circuit path to maintain an alarm actuating device in a deenergized condition, and means is provided responsive to the detection of smoke to illuminate a second photocell to cause energization of the alarm.

Description

United States Patent lnventor Alfred W. Vasel 222 Linwood St., Abington, Mass. 02351 App]. No. 845,646 Filed July 8, 1969 Patented May 18, 1971 Continuation of application Ser. No. 533,140, Mar. 10, 1966, now abandoned.

PARTICLE DETECTOR 2 Claims, 3 Drawing Figs. 11.5. CI 340/237, 340/251 Int. Cl ..G08h 17/ 10,-

G08b 19/00 Field of Search 340/237, 251

References Cited UNITED STATES PATENTS 1,877,279 9/ 1 932 Dawson 250/209 2,032,746 3/1936 Grant, Jr. 340/237SUX 2,033,466 3/1936 Grant, .11. 340/237SUX 2,668,284 2/1954 Mapes 340/237 3,202,883 8/1965 Wells et al. 317/132 3,207,932 9/1965 Tongret 307/141 3,226,703 12/ 1965 Finkle 340/237 2,278,920 4/ 1942 Evans et al 340/237UX Primary Examiner-John W. Caldwell Assistant Examiner-Daniel Myer AttorneyR0bert E. Ross ABSTRACT: A smoke detector in. which a light for illuminating smoke particles also illuminates a photocell providing a circuit path to maintain an alarm actuating device in a deenergized condition, and means is provided responsive to the detection of smoke to illuminate a second photocell to cause energization of the alarm.

PATENTEU HAY] 8 |97| In men far A lfrea W Vase/ PARTICLE DETECTOR This application in a continuation of my application Ser. No. 533,l40,filed Mar. 10, I966, now abandoned.

This invention relates generally to a device for detecting particles in a fluid-suspending medium and to a circuit-controlling system adapted for use therewith, and has particular reference to a smoke detector of the diffusion type.

Particle detectors of this type utilize a dark chamber with means projecting a light beam across the chamber, and a photocell viewing the medial portion of the light beam and shielded from direct radiation from the light source. When a fluid medium carrying suspended particles enters the housing through suitable openings and passes through the light beam, the particles carried by the fluid medium cause radiation from the light source to be reflected or diffused onto the photocell. The resulting change in resistance of the cell is utilized to actuate an external alarm system.

Since such devices must operate for long periods of time with a minimum amount of attention and maintenance, it is desirable to incorporate into the alarm control circuit a socalled fail-safe provision, by which the alarm will be actuated by the failure of the light source or the power source, in addition to being actuated by the presence of smoke particles in the chamber.

The object of the invention is to provide a smoke detector of the diffusion type, which has control means energized by the energization of the light source to maintain a normally on" alarm switch in the of? position, and means responsive to the presence of smoke particles in the detector to deenergize said control means.

A further object of the invention is to provide a smoke detector of the diffusion type in which a direct current relays normally closed contacts are connected to an alarm-actuating circuit, said relay is energized to the open position by the energization of the light source, and means is provided responsive to the existence of smoke particles in the detector to deenergize the relay.

A further object of the invention is to provide a circuit'controlling system having switching means responsive to direct current to maintain a circuit in a first condition and responsive to alternating current to maintain the circuit in a second condition.

Other objects of the invention will be apparent to one skilled in the art from the following detailed description of a specific embodiment thereof.

In the drawing;

FIG. I is a top plan view of a particle detector labyrinth embodying the features of the invention, partly broken away to show the interior arrangement; I

FIG. 2 is a view in section taken on line 2-2 of FIG. ll;

FIG. 3 is a schematic diagram of the electrical circuit of a particle detector embodying the features of the invention.

Referring to the drawing, there is illustrated a particle detector 10, which comprises generally a housing 12, a light source 14 disposed outside the housing and a detector element 16 disposed in the housing in operative relation to appear hereinafter.

The detector 110, in the illustrated embodiment, is particularly adapted for use as the detector unit of a smoke alarm and for this purpose the housing 12 comprises a peripheral wall 18 having a pair of end caps 20 and 22 fomiing an internal dark chamber 2 The end caps extend beyond the periphery of the wall 18 and have inwardly turned flanges 26 and 28 which are spaced outwardly from the wall. Each end of the wall is provided with a series of outwardly inclined spacing lugs 30, which are adapted to engage frictionally the inner surface of the flanges to retain the caps in assembly. The flanges 26 and 28, in conjunction with the spacing lugs 30, form a peripheral passageway at each end of the wall to permit smoke to enter the chamber from the surrounding atmosphere.

To direct and control the beam from the light source 14, a focusing tube 32 extends through the housing wall on one side thereof, and a light trap tube 34 is disposed in the housing wall on the opposite side in alignment with the focusing tube 32. A

lens 36 of the converging type is disposed in the focusing tube 32, with a focal length such that light from the source 14 is focused in a converging beam onto the bottom of the light trap tube 34, so that the beam from the light has a minimum size at the bottom of said trap, and a minimum amount of the light from the source falls on any other portion of the interior surface of the housing.

A detector tube 38 extends through the housing wall between the light trap tube and the focusing tube, and is disposed generally perpendicular to the axes thereof. The detector element 16 is disposed in the detector tube, and to restrict the field of view of the detector, a lens 40 of the converging type is disposed in the detector tube between the detector element and the chamber. The lens 40 has a focal length such that the image of the detector element is focused onto a minimum area on the opposite surface of the housing wall and the cone of focus of the detector element is directed across the cone of focus of the light beam, so that the detector element views only the medial portion of the light beam and the field of view of the cell at the opposite wall portion is confined to the medial portion of the wall, so that the cell does not view the peripheral apertures at the top and bottom of the wall. Hence substantially no light reaches the detector element except light appearing in the focus cone of the lens 40. To further insure that a minimum amount of the internal stray light reaches the detector element, the end 42 of the detector tube on the side adjacent the light tube extends forwardly to the cone of focus of the light beam to provide a shield against stray light from the inside surface of the focus tube. The end of the detector tube from this foremost point is inclined rearwardly at an angle such that the inside surface of the detector tube cannot view the inside surface of the focus tube. To prevent stray reflected light from the inside of the light trap tube from reaching the detector lens 40, the side of the end of the detector tube adjacent the light trap tube is provided with an inclined shield 44!.

In the illustrated embodiment the housing 12 is adapted to be mounted onto a support panel 46, and the light source M is also mounted on the panel in alignment with the focusing tube 32, and connected to a suitable source of electric current. The external mounting of the light source provides a visual check on its condition and makes replacement convenient.

The detector element 16 may be any type of device which is responsive to a change in light intensity, such as a photoelectric or a photoresistive cell. One type of cell which has been found satisfactory is cadmium sulfide, which responds to an increase in light intensity by a decrease in resistance. Hence in the illustrated embodiment a detector circuit may be con nected to the detector element and adjusted to the cell resistance under normal conditions of no smoke so that a predetermined further decrease in cell resistance will actuate an external alarm connected to the detector circuit. When smoke enters the housing and appears in the light beam, light from the smoke particles in the portion of the light beam viewed by the detector is reflected or diffused onto the detector cell, thereby lowering the resistance of the cell and actuating the alarm circuit.

Referring to FIG. 3, there is illustrated an alarm and control circuit for use with the labyrinth of FIGS. 1 and 2. The circuit of FIG. 3, which may be energized from an alternating current source E is intended to actuate means for energizing an alarm A when the cell 16 views illuminated particles in the labyrinth, and also to actuate a control device D which may control the operation of a fire door or the like. For example, fire doors are ordinarily designed to be biased by weights or springs to the closed condition, and are held open by a retaining means which may include a control wire having a portion responsive to excessive heat to release the retaining wire and allow the door to close. The retaining means may also include an electrically operated latch, which is normally energized, and which on deenergization releases the control wire to allow the door to close. In the drawing the device D represents an electrically operated latch which, when energized, retains a fire door or analogous device (not shown) in the open condition, and when deenergized, releases the door to-allow it to close automatically.

In the illustrated embodiment the alarm A may be energized by a separate source of power such as a battery B, whereas the door control device may be energized by the source E.

To provide a fail-safe" type of operation, it is necessary that the alarm be sounded and fire doors be closed if any portion of the circuit for actuating the alarm and the door control devices becomes inoperative. For this purpose the alarm is connected to its power source B, through normally closed contacts X1 of a direct current relay R1 said contacts being held open when the relay coil is energized, and the door control device D is connected to the power source E through normally open contactsXZ of said relay, the contacts X2 being held closed when said relay is energized. During normal operation of the device, when no smoke is present in the housing, the coil of relayRl is energized from the AC source E through a series connected photocell PCZ and a diode rectifier D1. Also connectedfin series with the relay coil across the AC source is a third photocell PC3 and a diode D2 which is reversed in polarity in relation to the diode D1 for a purpose to appear hereinafter.

The cellPCZ is physically positioned in relation to the light source bulb 14 so that when the bulb 14 is lit the cell PC2 receives radiation therefrom and its resistance is therefore maintained at a value low enough to permit sufficient half wave DC current to flow through the diode D5 and the coil of relay to hold contacts X1 open. Hence in case of bulb failure or power failure, the relay is deenergized, whereby the contacts X1 close to energize the alarm and contacts X2 open to deenergize the door control device D.

To cause the presence of smoke particles in the housing to actuate the alarm, the photocell i6 is connected to the AC source E in series with a calibrating resistor Kl, with a neon bulb 50 being connected in parallel with the resistor Kl, and in series with the photocell 16. In the absence of smoke in the housing the resistance of the cell 16 is so high that the voltage appearing across the resistor K1 and the neon bulb St) is not sufficient to ignite the bulb. However, when smoke particles diffuse into the housing 22 and enter the light beam, they are seen" by the cell 16 so that its resistance decreases. When its resistance has dropped to a predetermined value, the voltage across the neon bulb 59 and the resistor Kl becomes sufficient to ignite said neon bulb. The cell PCS, which is positioned to receive radiation from the bulb Stl is thereby illuminated and becomes conductive. Current can thereby flow through the diode D2 and the cell PC3, however only on the opposite halfcycle from that on which current flows through'the cell PCI and the diode Dll. Full wave AC voltage therefore appears across the coil of the relay R1 and the capacitor F. The capacitor acts as a low-impedance shunt to the AC voltage, thereby reducing the current through the coil of relay Rl to a value such that the relay is deenergized and the contacts Xl close to energize the alarm.

In the illustrated embodiment the alarm is automatically shut off when the smoke conditions are eliminated, since the resulting rise in resistance of cell 16 extinguishes the neon bulb 50, raising the resistance of cell PC3, so that only DC power is now impressed across the relay coil and the capacitor F. The relay coil is thereby energized again to open contacts X1 and close contacts X2, so that the door latch device is again energized. In some embodiments it may be desirable to have the alarm contacts lock closed when smoke is detected, which may be accomplished by a holding circuit to the relay coil as is well known in the art.

Although in the illustrated embodiment the circuit providing the direct current to the relay coil is completed through a photocell, in some cases in place thereof a relay can be provided having a coil in series with the light 14, said relay having normally open contacts in the D1 circuit to the relay R1, which contacts are maintained closed when the light is enerized. g The relay R1, condenser F'and the two circuit paths thereto including the diodes D1 and D2 form a circuit-controlling system which provides a method by which direct current is provided to maintain a controlled circuit in a first condition and alternating current is provided to maintain the circuit in a second condition. The specific embodiment illustrated also provides a system in which the illumination of one photocell maintains the circuit in the first condition, and the illumination of both photocells maintains the circuit in the second condition.

Although the circuit is illustrated herein as being applied to a smoke detector, its use as shown in this application is exemplary only, since it is adapted for use in many other types of electrical devices.

Since certain other obvious changes may be made in the device without departing from the scope of the invention, it is intended that all matter contained herein by interpreted in an illustrative and not a limiting sense.

lclaim:

l. A particle detector, comprising a light source for illuminating particles to be detected, photoresistive detector means positioned to view said illuminated particles, alarm-actuating means including a switch operated by a relay havingan operating coil energizable by direct current to maintain said switch in an open circuit condition, a capacitor in parallel with said operating coil, and a pair of circuit paths to said operating coil and capacitor, a first circuit path having a diode poled in one direction and normally open circuit-completing means in series therewith, the other circuit path having a diode poled in the opposite direction and said photoresistive detector means in series therewith, said circuit-completing means being responsive to the energization of the light source for maintaining said circuit-completing means in a circuit-completing condition, whereby when alternating current is applied to the relay and said circuit paths, direct current is applied through said first circuit path to the operating coil of the relay to energize said coil, and when the photoresistive detector means views illuminated particles a circuit is completed through said other circuit path so that alternating current is applied to said relay and capacitor whereby said relay is deenergized to actuate the alarm.

2. A particle detector as set forth in claim 1 in which said circuit completing means is a second photoresistive device positioned to be illuminated by said light source when said light source is energized.

Claims (1)

1. 2. A particle detector as set forth in claim 1 in which said circuit completing means is a second photoresistive device positioned to be illuminated by said light source when said light source is energized.

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