Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS2877453 A
Publication typeGrant
Publication dateMar 10, 1959
Filing dateJan 17, 1956
Priority dateJan 17, 1956
Publication numberUS 2877453 A, US 2877453A, US-A-2877453, US2877453 A, US2877453A
InventorsMendenhall Jr Alfred L
Original AssigneeMendenhall Jr Alfred L
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Smoke detecting device
US 2877453 A
Abstract  available in
Images(3)
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

March 1959 A. L. MENDENHALL, JR

SMOKE DETECTING DEVICE 3Sheets-Sheet 1 Filed Jan. 17, 1956 Q INVENTOR. 41,9950 1 .Mf/VflE/YAWIL,

BY ,5QZ

March 10, 1959 Filed Jan. 17, 1956 3 Sheets-Sheet 2 x-IIIIMnIMuI March 10, 1959 A. L. MENDENHALL, JR 2,877,453

SMOYKE DETECTING DEVICE Filed Jan. 17, 1956 3 Sheets-Sheet 3 INVENTOR. 41/3950 1 Wi/VDi/VHALL @F WV United States Patent Ofiice 2,877,453 SMOKE DETECTING DEVICE Alfred L. MendenhalL JL, Chicago, Ill. Application January, 1956, Serial No. 559,656 I 20 Claims Cl. 340-237 My invention relates to detector devices and more particularly to -a system for continuously monitoring the operation of the components of a smoke detector device. This application is a con tinuation in part of copending application Serial No. 221,831, filed April 19, 1951, now Patent 2,783,390.

' Smoke detector devices as presently used operate on the principle of projecting a beam of light into an atmosphere such as the atmosphere which passes through a ventilating duct which is shielded from extraneous light Upon the presence of foreign particles such as smoke or dust in an amount exceeding a predetermined amount, the initial light beam is sufliciently altered to activate a light sensitive device which could be a photomultiplier. Since the smoke or dust can be rapidly circulated, it is clear that a single'detector will quickly cause the alarm even though the foreign particles are initiated at a point remote from the smoke detector.

In an obscuration type of smoke detector, a light beam can be continuously projected through an atmosphere and into a light sensing device. 3 The presence of smoke or dust in the atmosphere, however, will decrease the amount of light which reaches the light sensing device and thereby change'the'output of the light sensing device to subsequently activate an indicating device or alamL i Similarly, in a reflective type of smoke detecting device, a light sensing device is remotely situated to be impinged upon only by light which is reflected or scattered from foreign particles in the atmosphere.

It should be noted that the reflective type of smoke detector is much more sensitive than the obscuration type since the output -'of the' light sensing device, which could be a photomultiplier to achieve freedom from microphonics, goes 'from'anessentially zero value to a finite value, and this difference is easily sensed in commercially available amplifying devices for the subsequent operation of indicating devices.

Until thepresent time, a major disadvantage of the above type units has been the lack of a simple monitoring system'which' will monitor the operativeness of the smoke detector elements. That is, since the unit will probably be inoperative over long periods of time (since it may operate only upon the outbreak of a fire), it has been a major problem to assure that the light beam, light sensing device, amplifier and power supply are in an operative condition and that none of the components of the system are burned out or disabled. It is obvious that to assure operativeness, of the detecting system is of utmost importance since a failure of a smoke detector may result in an uncontrolled fire and all of its consequences. I

It is to be noted that monitoring. of smoke detector devices has been, attempted but has always been directed to systems for assuring operativeness of tube filaments and the bulb filament.

Clearly this type of monitoring is undesirable in that the other GOmPQnents. of the device; can fail although an improvement for smoke duced in a manner to make it distinguishable from the after altered to be distinguished from the first light first light beam, the first light beam being used for the actual smoke detection, and to continuously impinge the second or monitoring light beam upon the light sensing device of the smoke detector whereupon the output sig nal of the amplifier associated with the light sensing device will selectively operate (since the output signal due to the second light beam is distinguishable from that due to the first light beam) an indicating device to indicate normal operation. Hence, upon the presence of foreign particles in the" atmosphere being protected, the first light beam will be impinged upon the light sensing device which could be a photomultiplier, and the amplifier output signal which is distinguished from that due to the monitoring light beam can be used to activate an alarm or second-indicating device. I Since the second or monitoring light beam can be initiated from the source of the first light beam and therebeam, my novel monitoring system will therefore continuously monitor the operation of each of the light source, photocell, amplifier, amplifier output filter-(if used), and the power supply-Which normally en'ergizes' the above components. A -system or the components of the smoke detector will therefore be substantiallyinstantaneously indicated by theindicating device which can indicate normal or ab normal operation of the complete system;

More specifically, I can make the first or particle. de-

- tecting light beam distinguishable from the second or? monitoring light beam by dividing the light from a light source into two beams and thereafter interrupt the I'first light beam a first predetermined number of times'per second, and interrupt the second light beam a second predetermined and Obviously, this is only one of many acceptable ways of varying the first and second light beam in such a way as to produce electrical signals responsive theretofor selectively operating indicating devices. That is, it would polarization or first and second principle of my frequencies to distinguish between the light beams without departing from the invention.

The use of a chopped light beam for at least the first or smoke monitoring beam, however, provides certain advantages which allow a high level of sensitivity for the smoke detecting device. As was previously mentioned, the second or monitoring light beam is so diverted that it iscontinuously impinged upon a light sensing device such as .a photomultiplier whereas the first or smoke detecting beam is so directed that (in a reflective type smoke detector) it will impinge upon the photomultiplier only when refiected or scattered by foreign particles. Therefore, the intensity of reflected light in p the presence of a few foreign particles will be very low. -However, by providing a chopped light beam for the smoke detection beam the output of the photomultiplier due to the low intensity of reflected light willbe in the form of a pulse, the frequency of which is the a frequency at which the light beam is being'interrupted.

Hence the photocell output can be appliedto an A. C. amplifier or if desired can be directly applied to circuits which are resonant to this frequency. As a typical example the phototube output can be applied to an A. C.

, v amplifier and the output of the A. C. amplifier can be Patented Mar. 10, 1959 v failure of the monitoring.

different number of times per second.v

3. passed through narrow band circuits which in turn are connected to the resonant devices. Obviously this system will result in a very high signal-to-noise ratio.

Similarly,,when the second or monitoring light beam is of. the. chopped type, the resultant photomultiplier output will once again be an A. C. current which difiers in frequency from' that due to the. first or smoke detecting light beam and if plifier, the narrow band circuits and subsequently to devices which. are resonant to the frequency of the A. C. current, due to the second light, beam. Once again, the desired high signal-.to-noise ratio is provided.

It is 'now clear that the signal due to the second or monitoringv light beam continuously monitors the operation of the amplifier which. is also used toamplify the signal due. to the first or smoke detecting lightv beam upon the detection of foreign particles in the atmosphere being protected. The output of the amplifier will normally be of the frequency determined by ;the-monitoring. light beam. and it is. obvious, that this output can be used to activate an indicating device which is responsive to that particular frequency or, if desired, to its rectified output to. allow-the use of D. C. activated indicating devices.

Similarly upon: the occurrence of. foreign particles in the atmosphere being protected, the A. C. output of the amplifier will be at the characteristic frequency of the smoke detecting lightbeam and this frequency may then be; used to operateI an indicating device which is operable only' by: that. particular frequency.

Thisv indicating device could in itself be an alarm, if desired could trigger alarms which are placed at points remote from the area being protected. As an alternative, or in additionv to the indicating devices used in the immediate vicinity of the smoke detecting device, both the. monitoring output signal and the particle detecting signal could be fed. through the lines of an organization such as the American District Telegraph and to their control office alarm station where the monitoring signal will perform the additional function of monitoring the. A. D. T. lines; signal is. received at the. A. D. T. otfice, to. initiate their. function.

Accordingl a primary object of my invention is to provide a system for continuously monitoring the operation of each component of a smoke detecting device.

Still another object. of my invention is to provide a second. light beam which is. distinguishable from the light beam which is used for smoke detection and to impinge the. second light beam upon the lightv sensitive device of a smoke detecting system. whereupon continuous operation of the excited light. sensing device, its associated amplifier, power supply and indicating. device will be assured.

Still another object of my invention is. to. provide. a monitoring lightbeam for a smoke detector. device. which is distinguishable from the smoke. detecting light beam. and is initiated from the same source which initiates the smoke detecting light beam.

Still another object of my, invention is to provide. a first and second light beam for a, smokedetector device wherein these beams are interrupted a different number of times per second, one of the light beams beingused for smoke detection and the other light beam being used to assure continuous operation of the smoke detection device.

Still another object of my invention is to provide a smoke detector having a monitoring lightbeam which continuously energizes operation of a light sensitive device such as a photomultiplier and its associated amplifying and indicating devices.

A still further object of my invention is to provide a smoke detecting device wherein a photomultiplier will have a continuous A. output signal of one frequency and the occurrence of foreign particleswill initiate an A: 6. signal of a-secondfrequency;

desired can be passed through the am When, however, the alarm. it will serve A still further object of my invention is to use a first or smoke detecting light beam and a second or monitoring light beam, each. of which is interrupted at a different frequency to subsequently impart an A. C. output for their associated photomultiplier wherein the output frequencies are distinguishable from one another and circuits responsive to these frequencies are provided to actuate indicating devices.

My invention also contemplates'a system whereby a constant smoke or particle detection level is maintained. it has been found that with presently used devices that the system sensitivity or detection. level. changed due to amplifier drift and changes in intensity in the detecting light beam. Hence, due to the accumulation of dust on the various reflecting surfaces or a decrease in the light intensity of the light source or the like, a given particle density will reflect less light into the light sensitive device.

I have overcome this disadvantage by providing an amplifier which delivers a constant output for a wide.

range of input signals. One methodby. which this canbe done is by using an amplifier. having an automaticgain control circuit of well known design.

It is to be clearly noted that this type of. system can now be used to great advantage in view of the additional monitoring light beam of my invention. That is, the intensity level of the. monitoring beam can. be compared to the intensity of the detecting beam which is reflected from a predetermined density of foreign particles.

Clearly, therefore,- if the monitoring. light beam in.-. tensity is cut down or if the amplifier drifts, signals due to the monitoring light beam (as well as the signal due to the light which would be reflected byforeign particles) will be amplified by av greater amplification factor. Hence, upon the reflection of light by foreign particles, the amplification factor of theamplifier will. be preadjusted to give a predetermined output. for the decreased smoke detection signal.

It is therefore seen that the. sensitivityof my novel unit can be controlled by adjusting the intensity of monitoring light since it is. this value-that adjusts the amplification factor of the amplifier. If, for example, this intensity is small, then the amplification factor of. the amplifier will be high and a light will be detected. Conversely, if the monitoringlight is made more intense,1 the amplifier amplification factor will be decreased to decrease the level of sensitivity of. the unit reflected light.

Accordingly, an ancillary objectofi-my. invention is to provide a smoke detector of the type having a moni-' toring light beam wherein: theintensity; of.-'themonitoring light beam varies: theamplification-factor of? the ampli fier;

Still another object of my invention is tOwPlIOVldfi'). a smokedetector whereby the intensity: of; the monitoring light. beam. is. adjusted to. the intensity of. light. which: is reflected from a minimum; predetermined amount of. foreign particles.

Another object of my invention. is. to'providc a. smoke detector whereby the intensity of. a monitoring light: beam varies the amplification". factor-of the amplifier to thereby assure a signal due to the smoke detecting. beam being reflected from a predetermined? density of foreign particles even though the intensity of the. smoke detecting beam is'decreased.

These and otherobjectsfof my invention will become apparent from the following description taken in connection with the drawings in which:

Figure 1 shows aperspective-view of smoke detector which contains my novel monitor system.

Figure 2' shows atop view: of. Figure I and further locates many of the associated components of the-smoke detector. i

Figure 3 is a-block diagram which indicates howtlie small amount of reflected amass 1 the photocell to block diagram of Figure 3. v v

Figure 5 shows a detailed diagram of a photomultiplier which'is used in accordance with my inventiom: Figure 6 shows a detailed diagram of an annunciator panel which can be activated -byv the smoke. detector of .my' .device- :Figure 7'shows a typical :power supply .which gcansbe, used to energize the components of the, smoke detector.

device of my invention.

Referring now to Figures 1 and 2, an air duct 10 con-"- ducts an air flow which is generally shown'by the arrows. The duct entrance 11 can if. desired. contain a sail switch to indicate air flow and a device such a'sthe fan 12 causes this air flown Obviously this is only-to in-.

dicate-"that-my smoke detector device willbe applied-in an environment wherein a changing atmosphere is avail-- able and the constructionshown herein is for'illustrative purposes only.

The smoke detecting apparatus is shown as being generally housed'within the housings 13 and 14 and' the top of these housings 13 and 14 as well as a portion of the top of the duct 10 is shown in a cut awayuview to aiford observation of the essential smoke detector components. 7 r Y i Within the housing 13 there is shown a light source 15 which is illuminated by means of the electrical terminals 1'6=and 17. These'terminals are of course energized in a'ny desirable manner and the energizing meansis no'w 'shown herein. The light of thelig'ht source 15 of course radiates in all directions but interest is directed here only in the directions indicated by' the dot-dash line's. That is, a first'light beam" 18 is directed towards an outer series of holes such as a mirror 22 and then passed througha lens 23 which can'be used to adjust the light intensity] and'is thereafter directed upon a second series of"hols 24:

to allow the light beams 18 and 21 access't'o duct '10 in a, manner to exclude extraneous light; It is also to be noted that light beams due to source 15 which are in a random directionfare prevented from having access to the disk by means of theiwall 13a which has apertures 18" and 21' therein. Clearly, the apertures 18' and 21' are then positioned to allow only the'light beams 18 and 21 to be impinged upon thesdisk 20. "I

The disk 20 is then rotated at a predetermined speed. by means of a motor and associated gear'box which is shown schematically. as the motor 25. The output shaft 26 of motor and gear box is fastened in any; desired manner to the center of the disk 20 at the point 27. For illustrative purposes only, it is seenfin Figure, 1 that this fastening is accomplished by means of a plate 28 which isattached to shaft 26, this plate being maintained on the disk 20 by means of screws 29.

' It is clear, however, that is is only desirable to rotate the disk 20 in such a manner as to allow the outer holes 19 and the .inner holes 24,to interrupt the first light beam 18 and the second light beam 21 and this could be accomplished in any number of ways. Obviously, the interruption frequencies will be determined by the rotational velocity imparted to disk 20'by means-of the motor 25 and by the number of holes 19 which interrupt the light beam 18 and the number of 'holes 24 which interrupt the light beam 21. p

As an example, in a commercial embodiment it has been found practical to construct theseassociated elementsin such a manner as to provide an interrupted 19 of disk 20 and a second' light beam'21 is reflected by means of a reflecting devicefrequency of 210' cycles per second for the monitoring light beam cycles, per second for the smoke detectingbeam' 18. Clearly,

vention.

Theffirstlight beam, 18 as is further shown in Fig-- ures 1 and 2 is impinged upon a collimator 30 after the rotated apertures 19.; I Collimator 30is fastenedinsuch a manner as to direct the light being interrupted by beam 18 through the wall -of the housing 13and into the .air .duct 10; this light beam parallel bearnof light.

collimator 30. is further provided'with battles 30a;w l'1ich are so positioned -3S.'tO enhance. the confining of light; bafiles .300 are more, each preceding .battle beam 18 to a parallel beam. The particularly constructed; so. that shadows the'next to thereby decrea'se. the secondary source" reflection and assure a more-parallel light beam at the' outputof the collimator. Clearly,- however, the collimator 30 is but one example of many acceptable systems whichicould be used to parallel'the light beam the air duct'l0 which is so constructed as-to perform a blackbox like* function. "That is, by providing batfies- 31 in a suitable manner, the-parallel light beam 18, which can now'be recognized as the light beam'which will de-' tect the presence of foreign particles in theair flowing through the duct, will normally 'not be reflected from the w'allofithe air duct 10.-

The second-light beam 21, which can Y be shown as forming the monitoring light beam of my novel 'inven-- tion, is impinged upon a light conducting tube such as the tube 32'('which maybe constructed of Lucite) .after Passing through-apertures 24. I

Then the light beam 21 will be conducted-.throughthe Lucite tube' 32 which is constructed ito pass from the housing hand .into :the air duct 10" to' subsequently direct the beam 21 'at a substantial: rightangle to thes particle detecting beam 18 and. into' a mirror. -33Iwhi'ch projects "into. the air duct: 10 from'the housing 14.- J

A light'sensitive device 34--is positioned within the housing 14. Although device 34 'could beaxph'oto electric cell or phototube or any'bf suchlight sensitive devices, I will arbitrarily refer to the device 34.as 1a photomultiplier. Hence, it is seen-that'sthelight beam 21, which is the light beam to monitor the operation of the smoke detecting device, is continuously impinged upon thephotomultiplier 34. x t 1 Clearly, the? light beam 21 couldhave been brought to continuously impinge upon -the photomultiplier 34' or any other similar light sensing device in'manyacs ceptable ways such as by using. reflective. type devices" to guide the light beam and-the systemsho wn herein is merely an" example of one of thesemany ways.

It has been notedthat under normal operating conditions" the light beam 18- is conducted; into the air duct 1'0 where it is impinged upon a light baffle device 31 to prevent any reflection. Assuming now that aforeign particle such as the particle 35 enters: the 'air ductlt], it is clear that a portion of light beam 18jwhich impinges upon this particle can be reflected or scattered as is shown bydhe reflected beam 18aintofthe mirror 33, and subsequently into the photomultiplier 34. t There-'- t'ore, if the light beam 18a is interrupted at a frequency which is different fromthat oftbe frequency at whiclr'the light beam 21'isinterrupted,-the outputof the photomultiplier 34 will notonly hex-at thetinterrupted: he quency of the monitoring light beam21but "Will alsote' at the interruptedtrequency 0f 1 the light beam 18a which 21 and an interrupted frequency ,of [289i however, these are merely two illustrative val-, '1 nos and they need not be used to practice my novel in-v 18 ;now.being made a. -Asis shown, the two vvlenses. ofthe collimator are positioned toafiord a, minimumamount of aberration in theparalleledlight beam; The:

'After passing through the .wallof the -nduct '10,.th e light beam 18 is'then impinged upon the; other side of I enemas ofcourse -is" thesame' as the frequency of the lightb'eam 18. 4

"It has'now'been shown that the photomultiplier 34 of Figures -1 and 2 will, during'normal operation of each 05 the component's'mentioned heretofore (light source, motor, power supply, etc.) have an output of a frequency given by the interrupted frequency of the monitoring light beam 21'. However, uponthe/occurrence of a foreign particle such as 35 which could be smoke or dust, the interrupted frequency of the'light beam 18 will then be superimposed upon the output of the photomultiplier 34. Clearly, however, failure of any of the components which operate'on the light beam 18 will result in a loss ofthe: signal due to the monitoring light'beams 21 which will subsequently indicate 'inoperativeness of the device.

Figure 3 indicates how the outp'ut of the photo-multiplier 34 canbe taken from the photo-multiplier and to the subsequent indicating devices. As is'shown in the block. diagram of Figure. 3,v the'photo multiplier 34 feeds its. signal totheinput of an A. C. amplifier 37. The output of. the amplifier is then taken 'to a filter 38 and from. the filter the signalsbranch otf to a device which could be a relay which is operable only by the inter rupted frequencyof the smoke detecting. light beam 18 and to a rectifying device 40. The filter 38 contains narrow band circuits which, as was previously mentioned, operate to improve the signalto noise ratio of the system.

Hence, the rectifyingdevice 40 which is always operative in view of the continuous impingement of the monitoring light beam 21 upon the photo-multiplier 34 can be used to activate a D. C. relay 41 which in turn can be used to operatean indicating device 42 which will indicate normal operation of the system.

Similarly, the relay 39 which is operable only in response to the detection of foreign particles within the duct is then operable to energize a device 43 which can be an alarm device.

Therefore, during. normal operation, a light beam 21 initiated by the light source ofv Figures 1 and 2, is interrupted at a predetermined frequency by means of holes 24 of disk and is subsequently lead by means of a Lucite tube 32 to impinge upon a mirror 33 and to thereafter activate the photomultiplier 34. This char acteristic frequency is then asis shown in-Figure 3 applied by the photomultiplier 34 to the amplifier 37, filter or narrow band pass circuits 38,. rectifier 40, relay 41 and the indicating device 42 which indicates normal operation. Since the relay 39 is responsive only to the char-- acteristic interrupted frequency of the smoke detecting beam 18, this relay will not be operated and the alarm device-.43 similarly will not be operated.

However, upon failure in either the light source 15, motor which rotates the disk 20, photomultiplier 34, amplifier 37,filter. and narrow band circuits 38, rectifier 40, relay 41 or the power supply energizing the above devices, then. the indicating device 42-will lose its signal to thereby indicate to operating personnel that the smoke detecting device is inoperative.

Upon the presence of foreign particles in the duct 10, the light beam 18 which uses all of the above mentioned components which are continuously monitored by the monitoringbeam 21 will immediately cause the operation of the relay device 39 of Figure 3 which is responsive only to the characteristic interrupted frequency of the light beam 18 to thereby cause an alarm or indicating device 43' to be energized.

Therefore, it i's'seen that in using my novel monitoring system, all of the components of the" smoke detector must be operable to avoid the operation of a monitoring indicating" device. It is to be. noted, however, that the smoke alarm indicators are not (due to their inherent nature) mointored. However, it is feasible to assure operativenessof even these componentstby purposely actuatingthem tit-predetermined intervals.

It is to lie-emphasized at. this point that the preceding heavy dot dash lines.-

which the various voltages created by the power supply bodirnents. which my novel principle' can assume.

detectinga-change' in color of a medium and the other for monitoring the operation of the system. Similarly,

the density of a gas beyond predetermined limits may be detectedby areflected or refracted light beam and a second light' beam could monitor the operationv 'of the system.

Clearly, there are applications which would'not necessitate the use of a housing such as the housing 10 for.-

an air duct wherein the particle detector could'be'pre'set to give alarm when the density mined amount;

The components referred to in the block diagramofv Figure 3 are more specifically shown inv conjunction with the Figures 4, 5, v6 and 7 where Figure 4 containsthe amplifier',-:narrow band circuits and indicating. devices, Figure" 5 shows the motor, lamp and photomultiplier, Figure 6 shows the 'annunicator panel and Figure 7 is the powersupply. figures are mutually interwired and that the figures are clearly set apart fromone another by. means of. the Hence, the terminal block- 50 to of Figure- 7 are applied are similarly applied to terminal block 51 of Figure 5. In a like manner, the voltages appearing on the terminal block 52 of Figure 5 also appear on terminal block 53 of Figure 4'.

The output of photomultiplier 54 of Figure 5' is shown as being applied to the amplifier proper which in Figure-4 may be generally seen as comprising the tubes 57, 58'and S9. Theoutputof:the-amplifier shown in Figure 4 is then applied to the narrow band pass circuits or filter shown generally at 60, the output'of filter 60 being rectified in the rectifier 61- andbeing supplied to the relay 62 which is responsive only tothefrequency of the signal obtained under smoke detection conditions. Other relays shown as relays 63, 64, 65' and 66 as will be shown hereafter contribute to the selective-function of the system proper for indicating normal, operation of the signal due to foreign particles.

It is to be noted that the amplifier of Figure 4'is provided with automatic grid control circuits. This has been found desirable in practical applications since the intensity of light impinging upon photomultiplier 54 of Figure 5 is variable in view of dust accumulation on reflector surfaces etc. Therefore, the provision of the automatic grid control circuits in the amplifier allows an output signal, (with respect to the monitoring light beam) of constant magnitude.

This feature also allows the adjustment and maintenance of a constant sensitivity line. That is, by adjusting the intensity ofrnonitoring light, the amplification factor of the amplifier is determined and the signal due to reflection of scattering of the detecting beam required to operate its indicating device is similarly determined If it is desired to increase this intensity it is only required that the intensity of the monitoring light beam be decreased to thereby increase the amplification factor of the amplifier. Similarly, the sensitivity can be decreased by increasing the intensity of the monitoring light beam.

Inorder to maintain a desired sensitivity level, even though the intensity of the beams will be changed due to dust accumulation etc., it is only necessary that the monitoring light beam be adjusted to the intensity of light which would be reflected from a predetermined density of foreign particles, this level being constantly maintained by automatic grid control circuits even though the intensity of the light beam is varied.

As a further feature of' the'complete smoke detector, Figure 5 alsoshowshow electrical connections may be madeto'a detector service connector whereinsthe vital parts of the amplifier andtherelaysystem may be moniof foreign particles in the surrounding medium is dilferent. from some predeter- It is seen that. the components of the tored-from'outside means at any. time.

a In FigureS a detector terminal strip 67 is connected to the various out-.

diagram of Figure 3 and many variations could result in substantially the same operation. A detailed description is not deemed necessary here since all of the components are old and well known. I

The sequence of operation, however, entailedin the use of components such as those in Figure4 through 7 is as follows: To initiate operation, the main switch shown as switch 69 of Figure 6 is closed to thereby light the power on lamp 70, the trouble signal lamp 71, trouble buzzer 72 and relay 73 of Figure 7. Upon operation of relay 73 the motor shown generally at 74 (which rotates disk 20 of Figure 1) begins to operate and the transformer 75 of Figure 7 is energized. Transformer 75 then supplies power to the amplifier shown generally in Figure 4, the photomultiplier 54 of Figure 5, and the light source 76 of Figure (which will subsequently send out the first and second light beams or the monitoring and smoke detector light beams). Photomultiplier 54 therefore will be impinged upon by the monitoring light beam. as was shown in Figures 1 and 2 to thereby supply a predetermined signal to the amplifier of Figure 4.

Upon amplifier operation, it is clear that the relay 66 will be energized but since the frequency of the amplifier output is that due to the monitoring light beam and relay 64 will not operate. Operation of relay 66 subsequently causes the relay 65 to operate and also causes the relay 77 of Figure 7 to operate which thereby parallels contact 78a and 78b of relay 78 to subsequently operate relay 79 of Figure Upon operation of relay 79 of Figure 6 it is apparent that the normal operation lamp 80 will operate and the trouble lamp 71 and trouble buzzer 72 will be de-energized. After a predetermined time'which-begins with the operation of the manual switch 69, the relay '78 (which has a time delay) will operate to thereby ground the cathode of the photomultiplier tube 54 and take the parallel circuit off the contacts 78a and 78b of the relay 78. Hence, the system is now operating accordingly in a normal manner.

Assume now that the beam of light which is the smoke detecting beamof light (light beam 18 of Figure l) detects a particle in the duct through which the atmosv phere being protected is flowing. Clearly then the photomultiplier 34 will be energizedvto have an outputfrequency difierent from that from which it normally delivers due to the impingement thereon of the monitoring light beam. Hence, the second detecting signal will be amplified in the amplifier of Figure 4 to thereafteroperate the relay 62 which is so constructed as to be energized for operation responsive only to the particular frequency which is characteristic of light'beam. By providing the narrow band pass circuits 6 in the annunciator panel. I

the smoke detecting 60, this selective efl ect is enhanced since the signal to noise ratio is considerably increased. Operation of the relay 62 causes the subsequent operation of relay 63 which in turn operates the relay 64. after causes the smoke alarm light and bell 81 and 82, respectively, in Figure 6 to operate and also causes the relays 83 and 84 to allow energization of their external circuits which can be attached to other alarm or indicating devices at terminal block 85.

Relay 64 .there- If desired, the relays 83 and 84 may be latching re- I lays. If this is the case, a push button 86 can be provided to allow clearing of the relays 83 and 84, and a switch 87 can be similarly provided to. allow manual U obvious. Accordingly,

"'structed to be operative recycling. to achieve the alarm a secondtimeto-thereby testthe operation of the circuit.

currence of an alarm. As a further addition to my novel system, it is apparent that the annunciator. devices/can be of the normally on type, and the. currents of the: monitoring signal maintaining these normally on de- Therefore, upon failure of.

vices in their off position. the annunciator device, it will go to its on position which may be energizedby battery means to thereby be in, dependent of a power sourcefor indication of inoperative uess in the indicating devices or system. i H In the foregoing, I have described my invention only in connection with preferred .embodiments thereof. Many variations and modifications of the principles of my in:

scope of the description herein are I prefer to be bound not by the vention Within the specific disclosure herein but only byathe appending claims. 1 v

I claim: i I i l. A smoke detecting device for detecting the presence of foreign particles in a volume of air which is to be duct wherein the smoke detecting device has access to the air passing through said vent in a manner to exclude extraneous light from the duct, said.

circulated through a smoke detecting device comprising a light source for projecting a first and second light beam, an interrupting, means to interrupt said first light beam a first predetermined number of times per second and to interrupt said second light beam a second times per second, a photomultiplier, an amplifier, a narrow band pass circuit, a first and second indicating device and energizing means being connected to energize photomultiplier and 3111-; plifier; said first light beam being directed with-respectv operation of said light source,

to the position of said photomultiplier to be impinged upon said photomultiplier only upon reflection and scattering from foreign particles put contains at least the tains at least the interrupted frequency of said second light beam, said second light beam being a monitoring light beam for assuring continuous operation of at least said light source, photomultiplier, amplifier and energiz ing means.

2. A smoke detecting device for detecting the presence particles in a volume of air which passes.

of I oreign through a'duct; the said smoke access to the air passing through to exclude extraneous light; said smoke detecting device comprising a light source for projecting a first and .sec- 0nd light beam, an interrupting means to interrupt said first light beam a-first predetermined number of times per detecting device having second and to interrupt said second light beam a second predetermined number of times per second, a photo-multb plier, an amplifier, and means for energizing said light source, photo-multi plier and amplifier; said first light beam being directedi with respect to the position of said tion' from foreign particles second light beam being directed to continuously impinge multiplier being connected to predetermined number of in said atmosphere, said second light beam being directed to continuously im pinge upon said photomultiplier; the output ofsaid photomultiplier, being connected to the'input of said amplifier, the output of said amplifier being passed through "said narrow band circuits and thereafter to said first and second indicating devices; said first indicating device be ing constructed to be operative when said amplifier outinterrupted frequency of said;- first light beam, said second indicating device being conwhen said amplifier output con- 1 said ductin a manner a first and second indicating device.

photo-multiplier tobe impinged upon said photo-multiplier only upon reflecin .said atmosphere, said the output" of'sa'id amplifier being connected to said first and second indicating devices; said first indicating device being constructed to be operative when said amplifier output contains at least the interrupted frequency of said first light beam, said second indicating device being constructed to' be operative when said amplifier output contains at least the interrupted frequency of said second light beam, said second light beam being a monitoring light" beam for assuring continuous operation of at least saidlight source, photo-multiplier, amplifier and energizing means.

3. A smoke detecting device for detecting the presence of foreign particles in a volume of air, means being provided to circulate the said volume of air through a vent; the said smoke detecting device having access to the air passing through said vent, said smoke detecting device comprising a light source for projecting a first and second light beam, an interrupting means to interrupt said first light beam a first predetermined number of times per second and to interrupt said second light beam a second predetermined number of times per second, a light sensing device, an amplifier, and a first and second indicating device; said first light beam being directed with respect to the position of said light sensing device to be impinged upon said light sensing device only upon the presence of foreign particles in said air, said second light beam being directed to continuously impinge upon said light sensing device; the output of said light sensing device being connected to the input of said amplifier, the output of saidamplifier being connected to said first and second indicating devices; said first indicating device being constructed to be operative when said amplifier output contains at least the interrupted frequency of said first light beam, said second indicating device being constructed to be operative when said amplifier output contains at least the interrupted frequency of said second light beam, said second light beam being a monitoring light beam for assuring continuous operation of at least said light source, light sensing device and amplifier.

4. A'smoke detecting device for detecting the presence of foreign particles in a volume of air which is circulated through a duct; the said smoke detecting device having access to the air passing through said duct, said smoke detecting device comprising a light source for projecting a first and second light beam, means to vary said first and second light beam according to a first and a second mode, a light sensing device, an amplifier, and a first and second indicating device; directed with respect to the position of said light sensing device to be impinged upon said light sensing device only upon its reflection from foreign particles in said air, said second light beam being directed to continuously impinge upon said light sensing device; the output of said light sensing device being connected to said first and second indicating devices; said first indicating device being constructed to be operative when said amplifier output contains at least the mode of variation of said first light beamg'said second indicating device being constructed to be operative when said amplifier output contains at least the mode of variation of said second light beam, said second light beam being a monitoring light beam for assuring continuous operation of at least said light source, light sensing device and amplifier.

5. A smoke detecting device for detecting foreign particles in air; said smoke detecting device comprising a light source for projecting a first and second light'bcam, means to vary said first and second light beam according to a first and a second mode, a light sensing device, an amplifier, and a first and second indicating device; said first light beam being directed with respect to theposition of said light sensing light sensing device only upon the presence of foreign particles insaidair; said second light beam being directed to continuously impinge upon saidlight sensing device;

the'outputof said light sensing" device being connected to said first light beam being device to be impinged uponsaid 12 the input of said amplifier, the output of said amplifier being connected'to said first and second indicating devices; said first indicating device being constructed to be operative when said amplifier output contains at least the mode of variation of said first light beam, said second indicating device being constructed to be operative when said amplifier output contains at least the mode of variation of said second light beam, said second light beam being a monitoring light beam for assuring continuous operation of at least said light source, light sensing device and amplifier.

6. A smoke detecting device for detecting the presence of smoke in air which is drawn through a duct comprising a synchronous motor, a disk having apertures therein being driven said synchronous motor, a light source, a photomultiplier, means to amplify the output of said photomultiplier and a first and second indicating device connected to said amplifier, said light source being con structed to provide a first and a second beam of light, said motor driven disk apertures being positioned relative to said first and second beam of light to synchronously interrupt said first beam of light in a first predetermined manner and to synchronously interrupt said second beam of light in a second predetermined manner upon rotation of said disk; said first interrupted beam of light being introduced into said duct in such a direction as to be reflected into said photomultiplier when smoke is drawn through said duct, said second interrupted beam of light being constantly impinged upon said photomultiplier; said first indicating device constructed to be operatedwhen the amplified output of said photomultiplier is due to said first interrupted beam of light, said second indicating device constructed to be' operated when the amplified output of said photomultiplier is due to said second interrupted beam of light.

7. A smoke detecting device for detecting the presence of smoke in air comprising a motor, a disk having apertures therein being driven by said motor, a light source, a photo-multiplier, means to amplify the output of said photo-multiplier and a first and second indicating device connected to said amplifier; said light source being constructed to provide a first and a second beam of light, said motor driven disk apertures being positioned relative to said first and second beam of light to synchronously interrupt said first beam of light in a first predetermined manner and to synchronously interrupt said second beam of light in a second predeterm'ined manner upon rotation of said disk; said first interrupted beam of light being directed to be reflected into said photo-multiplier when smoke is present in the air, said second interrupted beam of light being constantly impinged upon said photo-multiplier; said first indicating device being constructed to be operated when'the amplified output of said photo-multiplier is' 'due to said first interrupted beam of light, said second indicating device being constructed to be operated when the amplified output of said photo-multiplier is due to said second interrupted beam of light.

8. A smoke detecting device for detecting the presence of smoke in air comprising. a motor, a disc being driven by said motor, a light source, a light sensing device, means to amplify the output of said light sensing device and a first and second indicating device connected to said amplifier; said light source being constructed to provide a first and a second beam. of light, said motor driven disc being connected to synchronously interrupt said first beam of light in a first predetermined manner and to synchronously interrupt said second beam of lightin a second predetermined manner; said first interrupted beam of light being dire'ctedto impinge upon said light sensing device responsive to the presence of smoke in the air, said second interrupted beam of light being constantly impinged upon said light sensing device; said first indicating device being constructed to be operated when the amplified output of said light sensingdevice is due to said first interrupted beam of light, said second indicating device being constructed to be operated when the amplified output of said light sensing device is due to said second interrupted beam of light.

9. A smoke detecting devicefor detecting the presence of smoke in air comprising a motor, a disk being driven by said motor, a light source, a light sensing device, means to amplify the output of said light sensing device and a first and second indicating device connected to said amplifier; said light source being constructed to provide a first and second beam of light, said disk being constructed to synchronously interrupt said first beam of light according to a firstfrequency and to synchronously interrupt said second beam of light according to a second frequency upon rotation of said motor; said first interrupted beam of light being directed to be reflected into said light sensing device when smoke is present in the air, said second inter'rupted beam of light being constantly impinged upon said light sensing device; said first indicating device constructed to be operated when the amplified output of said light sensing device is due to said first interrupted beam of light, said second indicating device constructed to be operated'when the amplified output of said light sensing device is due to said second interrupted beam of light.

10. In a device for detecting particles in an atmosphere comprising a lightv source, means to vary the light of said light sourceaccording to a first and second mode, a light sensing device and alarm means, the light of said light source being varied according to said first mode being directed to continuously impinge upon said light sensing device and the light of said light source being varied according to said second mode being directed to be impinged upon said light sensing device by reflection from said particles to be detected, said alarm means being constructed to be actuated upon the loss of the signal due to said light being varied according to said first mode, said alarm means being further constructed to be actuated when the output of said light sensing device is partially due to said light means being varied according to said second mode.

11. In a device for detecting changes in the reflectivity of a gaseous medium comprising a light source, means to vary the light of said light source according to a first and second mode, a light sensing device and alarm means, the light of said light source being varied according to said first mode being directed to continuously impinge upon said light sensing device and the light of said light source being varied according to said second mode being directed to be impinged upon said light sensing device by reflection from said gaseous medium, said alarm means being constructed to be actuated upon the loss of the signal due to said light being varied according to said first mode, said alarm means being further constructed to. be actuated when said light sensing device is impinged upon by said light varying according to said second mode of an amount greater than a predetermined amount.

12. A means to monitor the operation of a smoke detecting device which has a light source for projecting light into an area which is shielded from outside light; a light sensing device and amplifier therefor, said light sensing device being positioned to receive light of said light source which is reflected by foreign particles in said shielded area and a first indicating device connected to said amplifier and constructed to operate responsive to the reception of light reflected from said shielded area; said monitoring means comprising a first means for producing a monitoring light beam and a second indicating device; said monitoring light beam being continuously,

impinged upon said light sensing device, the amplified output of said light indicating device due to said monitoring light beam being incapable of operating said first indicating device, said second indicating device being constructed to be operated responsive to the amplified output of said light indicating device due to said monitoring light beam.

13. A smoke detecting device for detecting the presence :14 of foreign particles in a circulated through a duct wherein the smoke detecting device has access to the airpassing through said-vent in a manner to exclude extraneous light from the duct, said smoke detecting device comprising a light source for projecting a first and second light beam, an interrupting means to interrupt said first light beam a first predetermined number of times per second and toy interrupt said second light beam a second predetermined number of times per second, a'photomultiplier, an A. C. amplifier, a narrow band pass circuit, a first and second indicating device and energizing means being connected to energize operation of said light source, photomultiplier and am plifier; said first light beam being directed with respect to the position of said photomultiplier to be impinged upon said photomultiplier only upon reflection and scattering from foreign particles in said air, said second light beam being directed to continuously impinge upon said photomultiplier; the output of said photomultiplier, being connected to the input of said A. C. amplifier, the output of said A. C. amplifier being passed through said narrow band pass circuit and thereafter to said first and second indicating devices; said firstindicating device being constructed to be operative when said amplifier output contains at least theinterrupted frequency of said first light beam, said second indicating device being constructed to be operative when said amplifier output contains at least the interrupted frequency of said second light beam, said second light beam being a monitoring light beam for assuring continuous operation of at least said light source, photomultiplier, amplifier and energizing means, said amplifier containing automatic gain control means for varying the amplification factor of said amplifier to maintain a substantially constant output of said amplifier.

14. A means to monitor'the operation of a smoke detecting device which has a light source for projecting light into an area which is shielded from outside light; a light sensing device and amplifier therefor, said light sensing device being positioned to receive light of said light source which is reflected by foreign particles in said shielded area and a first indicating device connected to said amplifier and constructed to operate responsive to the reception of light reflected from said shielded area; said monitoring means comprising a first means for producing a monitoring light beam and a second indicating device; said monitoring light beam being continuously impinged upon said light sensing device, the amplified output of said light indicating device due to said monitoring light beam being incapable of operating said first indicating device, said second indicating device being constructed to be operated responsive to the amplified output of said light indicating device due to said monitoring light beam, said amplifier being constructed to maintain a substantially constant output signal responsive to the input signal due to said monitoring light beam.

15. A smoke detecting device for detecting the presence of smoke in air comprising a motor, a disk having apertures therein being driven by said motor, a light source, a photomultiplier, means to amplify the output of said photomultiplier and a first and second indicating device connected to said amplifier; said light source being constructed to provide a first and a second beam of light, said motor driven disk apertures being positioned relative to said first and second beam of light to synchronously interrupt said first beam of light in a first predetermined manner and to synchronously interrupt said second beam of light in a second predetermined manner upon rotation of said disk; said first interrupted beam of light being directed to be reflected into said photomultiplier when smoke is present in the air, said second interrupted beam of light being constantly impinged upon said photomultiplier; said first indicating device constructed to be operated when the amplified output of said photomultiplier is due to said first interrupted beam of light, said second volume of air which is to be indicating device constructed to be operated when the amplified output of said photomultiplier is due to said second interrupted beam of light, said amplifying means being constructed to maintain a substantially constant output signal responsive to' the input signal due to said monitoring light beam.

16. A means to monitor the operation of a smoke detecting device which has a light source for projecting light into an area which is shielded from outside light; a light sensing device and amplifier therefor, said light sensing device being positioned to receive light of said light source which is reflected by foreign particles in said shielded area and a first indicating device connected to said amplifier and constructed to operate responsive to the reception of light reflected from said shielded area; said monitoring means comprising a first means for producing a monitoring light beam and a second indicating device; said monitoring" light beam being continuously impinged upon said light sensing device, the amplified output of said light indicating device due to said monitoring light beam being incapable of operating said first indicating device, said second indicating device being constructed to be operated responsive to the amplified output of said light indicating device due to said monitoring light beam, said amplifier being constructed to maintain a substantially constant output signal responsive to the input signal due to said monitoring light beam; the sensitivity of said smoke detector being varied by varying the intensity of said monitoring light beam.

17. in a smoke detecting device having a light source for projecting a first and second beam of light into an area which is shielded from extraneous light; said first and second beams of light' being varied according to a first and second mode; said first beam of light being directed to impinge directly upon a light sensitive device, said second beam of light being impinged upon said light sensitive device upon reflection from foreign particles in said shielded area; an amplifier being connected to amplify the output of said light sensitive device, the amplified output of said amplifier being connected to indicating devices operable in response to reception of signals being varied according to said first and second modes; and means for maintaining the output signal of said amplifier at a constant value when the input of said amplifier is varied.

18. In a smoke detecting device having a light source for projecting a first and second beam of light into an area which is shielded from extraneous light; said first and second beams of light being varied according to a first and second mode; said first beam of light being directed to impinge directly upon a light sensitive device, said second beam of light being impinged upon said light sensitive device upon reflection from foreign particles in said shielded area; an amplifier being connected to amplify the output of said light sensitive device, the amplified output of said amplifier being connected to indicating devices operable in response to reception of signals being varied according to said first and second modes; and means for maintaining the output signal of said amplifier at a constant value when the input of said amplifier is varied, adjusting means being provided to vary the intensity of said monitoring light beam to thereby vary the amplification factor of said amplifier to a predetermined sensitivity.

19. In a device for detecting particles in an" atmosphere comprising a light source, a light responsive means,

an amplifier having two output devices, one of said output devices being a particle alarm device, the second being a supervising device, a light circuit from saidlight source for impinging light on said light responsive means, means whereby said light circuit generates a predetermined signal in said amplifier circuit, means whereby said supervisory device is controlled by said predetermined signal, a second light circuit fromsaid'source to said light responsive means, means whereby said second light circuit generates a second predetermined signal in said amplifier and means is controlled by said second predetermined signal.

20. In a device for detecting particles in an atmosphere comprising a light source, means for synchronously interrupting said light source, a photo-multiplier tube, an A.-C. amplifier, a narrow band filter and an indicating device; said photomultiplier being positioned to receive the light pulses of said interrupted lightbeam by reflection of said light pulses from particle's appearing in said atmosphere to thereby impart a pulse output to said photomultiplier; said A.-C. amplifier being connected to amplify the pulse output of said photomultiplier; said narrow band circuit being connected to the output of said amplifier and constructed to pass the pulse frequency imparted thereto by the frequency of interruption of said light source; output of said narrow band filter.

References Cited in the file'of patent UNITED STATES PATENTS 1,672,671 Young June 5, 1925 1,828,894 Freygang Oct. 27, 1931 1,996,233 Darrah Apr. 2, 1935 2,301,367 Cahusac et al. Nov. 10, 1942 2,486,622 White Nov. 1, 1949 whereby said particle alarm device said indicating device being operated by the

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1672671 *Jan 20, 1927Jun 5, 1928Gen ElectricPhoto-electric photometer
US1828894 *Oct 30, 1928Oct 27, 1931Kidde & Co WalterSupervisory system for detecting suspended matter in fluids
US1996233 *May 26, 1930Apr 2, 1935Darrah William AAutomatic measuring apparatus
US2301367 *Mar 19, 1940Nov 10, 1942C O Two Fire Equipment CoSmoke detector and signal
US2486622 *Oct 30, 1947Nov 1, 1949Southern Res InstPhotoelectric apparatus for determining the physical properties of substances by alteating exposure to light
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3078756 *Jun 4, 1956Feb 26, 1963Phillips Petroleum CoNephelometer and control system
US3127464 *Nov 1, 1960Mar 31, 1964Royco Instr IncLight source standardizing device
US3151248 *Dec 19, 1960Sep 29, 1964Burroughs CorpPhotosensitive light gun
US3240109 *Jul 24, 1962Mar 15, 1966Specialties Dev CorpSupervised apparatus for detecting suspended matter in fluids
US3312826 *Dec 28, 1965Apr 4, 1967Finkle Sam MPhotoelectric smoke detector with ventilation induced by light source
US3396387 *Sep 23, 1965Aug 6, 1968Kidde & Co WalterSupervised apparatus for detecting suspended matter in fluids
US3407692 *Apr 24, 1964Oct 29, 1968Du PontLong ends detector
US3409885 *Mar 26, 1964Nov 5, 1968Guardian IndustriesSmoke detection apparatus
US3436152 *Mar 31, 1965Apr 1, 1969Gulf General Atomic IncMethod and apparatus for measuring the power in a light beam
US3524707 *Aug 14, 1967Aug 18, 1970Hansen Julian E JrPulsating light source smoke detector
US3528743 *Jun 29, 1964Sep 15, 1970Litton Systems IncLaser densitometer
US3617756 *Mar 24, 1969Nov 2, 1971Sick ErwinOptical measuring apparatus using measuring and comparison light beams
US3634839 *Mar 11, 1968Jan 11, 1972American District Telegraph CoMethod and apparatus for suppressing spurious alarms in an electrical protection system
US3656157 *May 18, 1970Apr 11, 1972Romney Russell HApparatus and method for producing and transmitting signals
US3668674 *Jan 30, 1970Jun 6, 1972Impulsphysik GmbhMethod and arrangement for testing of visibility measuring arrangements
US3733596 *May 16, 1972May 15, 1973Tokyo Hachiki KkAlarm circuit
US3746452 *Sep 3, 1969Jul 17, 1973Compteurs Comp DDevice for determining the transparency of the atmosphere
US3805066 *Aug 14, 1972Apr 16, 1974Chijuma TSmoke detecting device utilizing optical fibers
US3850529 *Oct 26, 1972Nov 26, 1974Brugger RDevice for calibrating a transmissometer
US3885162 *Jul 1, 1974May 20, 1975Contraves Goerz CorpOptical measuring apparatus
US3936192 *Apr 19, 1973Feb 3, 1976Environment/One CorporationOptical fluid contamination and change monitor
US4021713 *Mar 29, 1976May 3, 1977Shigeru SugaApparatus for sequential measurement of light transmitted through smoke
US4131888 *Aug 18, 1976Dec 26, 1978American District Telegraph CompanyDual projected-beam smoke detector
US4166698 *Jun 10, 1977Sep 4, 1979American District Telegraph CompanySecondary light testing in optical smoke detectors
US4199755 *Aug 21, 1978Apr 22, 1980Nittan Company, Ltd.Optical smoke detector
US4237452 *Jan 4, 1979Dec 2, 1980Malinowski William JSmoke detection system and method
US4258360 *Jul 31, 1978Mar 24, 1981Nittan Company, LimitedOptical smoke detector
US4266219 *Sep 18, 1978May 5, 1981Baker Industries, Inc.Supervisory control system for a smoke detector
US4306230 *Dec 10, 1979Dec 15, 1981Honeywell Inc.Self-checking photoelectric smoke detector
US4396286 *May 2, 1980Aug 2, 1983Ppm, IncorporatedElectro-optical system and method and apparatus for providing automatically-compensating, traceable calibration and zeroing for light scattering devices
US4904988 *Mar 6, 1989Feb 27, 1990Nesbit Charles EToy with a smoke detector
US7106187 *Jan 8, 2002Sep 12, 2006Thorn Security LimitedFire detector
US20040112114 *Jan 8, 2002Jun 17, 2004Penney Steve JFire detector
EP0122489A1 *Mar 19, 1984Oct 24, 1984Nohmi Bosai Kogyo Co., Ltd.Function test means of photoelectric smoke detector
Classifications
U.S. Classification340/630, 356/338, 340/815.42, 250/233
International ClassificationG01N21/47, G01N21/53
Cooperative ClassificationG01N21/53
European ClassificationG01N21/53