US2981840A - Detecting device - Google Patents

Description

April 25, 1961 M. E. NAHMIAS DETECTING DEVICE Filed March 26, 1957 IN VENTOR MAUR/CE E. NAHM/AS A T TORNEY United States Patent 2 1 34 n TEcTlJG DEVICE Maurice Elie 13 Rue Colbert, Chatenay- I Filed Mar-.526, 1957, set. No. 648,662

" Claims. (cl. 250 -415 This invention relates to devices for detecting smoke and/ or radioactive gases, and which may in' certai-ncases also be used for "detectinglight or flame or: the-presence I of intruders.

smoke detecting'apparatus.

he ionizing properties of electromagnetic and corpuscular radiationsare well known and it is also known that smoke can cause recombination of the ions whereby the ionization currentproduced by a radio-active source-is diminished. This property has already been used in United 'Sta'tes Patent No. 2,702,898 describes the most developed form of this' type ofapparatus This detector,

the physicogchen'lical" evolution ofa plurality'of sources, *as'a function of tim; will be di'ft'erent and will influence "the penetrationofr dium salt'in each o the-source present invention to overcome. V "In"particularfone"disadvantage is the use however, has disadvantageswhich' itis the obj'ectfof the which has been proposed of. rndre thanone radioa'ctive source, since amasse-ss'wmoaiify heaipha emissions.

' 'iAsecond defect is due to the fact'that the radioactive source of known detectors in the test chamber' is" con- 'tinuouslyunder the "action of the"surroundingair and :dampness and dust which accumulate on the source jand influencetlie alphaemission of the sources AQthirdfrason for possibly; defective operation is due totlie poor insulation of theflzingewhich 'sep'aratesthe testl chambei from thecornparisbn'chamber.- In fact, like the "testlchamber this'flange is in direct and continuous contaetwi'th the surrounding'air which deposits conductcan "momm be attributed to the con M of ions in the test chamber.

isuntavofablfforsinoke detection." v Incontradistinctiontheretojthe presentinvention'proing matter on the flange.

thisdetectoris constructed so as to be sensitive to drafts "and the false alarms which: it commonly' 'gives equem movement lThe aforesaid "United States patent describes a device havingbnlya single s'clurceof alpha ray's confined "-between thin foils and "caus'inga symmetricaldonization fin'ieachof twdchamberslocatedo n each side of the source. Thic' symmetrical ionization in both chambers vides a pair of adjacent chambers, a single source of alphaa predetermined value, and means for the introduction of the gas to be monitored into one of said chambers.

A preferredform of smoke-detecting device will now be described'with refe'renceito :thet accompanying dia- -grammatic drawing in which:

=1- ;Figurelfillfistratesitliedevice in vertical section, and

V 1 Moreover,"-this="flange is not accessible without partly dismantling the device,'*so that cleaning can be done onlyhy 'a skille'd person familiar ring 21 (iii-conducting material which is groundedrinlthe 2,981,840 Patented Apr. 25, 1961 fl he device includes two ionization chambers I and II formed bya metal housing lhaving sidewalls. Zeand opposite parallel end walls 3 and 4'; the housing is divided approximately equally by a wall W comprising a window including a very thin foil M, or possibly twothinfoils, th'e'foil or foils having a thickness equivalent'to 1 cm. of air and being supported between a. pair of grids g and'-g mounted in central circular apertures in plates x and x whereby rupture of the foil is prevented as well asvibrations'which might cause a variation of capacity and give afalsealarm. a

single radio-active source S, preferably an alpha particle source of 10 ac. intensity, is carried bya stem 5 extending symmetrically through an insulating insert :i positioned centrally on the housing end wall 3,'the stem being: slidable axially in the insert. The. chamber Iris provided with two small holes 0 and 0 which. are such as to allow conditions within" chamber I to conform .to those of ambient air while the source is protected from dust and the'like. 1

Anelectrode E, which is maintained at a potential -|-V by the circuit indicated, extends into the chamber through an insert i of insulating material in a side wall 2 of the housing. The chamber II is provided with an 25 electrode maintained at a negative potential V which electrode-E extends through an-inserti -of'insulatin 'material, also in a side wall Zof the housing v The inserts are similar and are shown in detail in 'Figure 2:' each comprises an ap'ertured disc 20 through which the electrode E or E or thestem 5 passes, a guard operation-of the deviceandsurrounds the disc 20,..and an outer ring 22 of insulating'm'aterial. surroundingnthe "guard ring 21 and securedtothe housing wall; It willbe appreciatedthat the guard rings are readily accessible and visible so that, when cleaning is necessary, it cambeacwithout-needfor dismantling the device. -With the device illustrated (in that form which 'cbmplished in a minimum of time by an unskilledperson will be called the -dynamic form of the device), it isdesired to continuously monitor' gas from a remotepoint and two insulated tubes t and t are connected to the. chamber II opposite one another, one of the tubes extending tothe "remote point and the otheracting as an outlet. 1

' 4 A modification of the device illustrated (in that'form which will be called the static model) is designedto monitor the gas surrounding the device;- the. tubes :are

' dispensed with and the side walls of chamber IIiiare perforated. 1

' The housing 1 is electrically connected by means 0t conducting coil L with the electrode G of a cold cathode triode 6; the coil extends through a' central hole in; a

'' block'of transparent insulating material p such as Lucite,

at the base-of the chambers which'shields them' against outside deterioratinginfiuence. The ionization current of the chamber I is fixed at a value I higher than the current I of the chamber II,

by=adjusting the potentials +V and V and the position of the source S for a given thickness of the foil -:M.

The two ionization currents are in opposition and-the value (I 'I )'=I must be such that the voltage. at the '-=terminals of a resistance R in the associated-circuit, =V ='RI is normally smaller than the value I Y ofthe "voltage required to trigger the cold cathode tub'e'6:be-

'- tween G and K, which would then cause a dischzirgebe- *tween'Aand K. When smoke comes into the chamber which energizes the relay coil E and thereby operates ;the buzzeror' alarm B. I I

" Cold cathode-tubes have been heretofore used for the .for the detection of radio-active gases.

ionization curve of an alpha particle emitter, called Braggs curve, which shows three parts: the first shows a constant ionization along the path of the alpha particles until about 1 cm. from the end of their path. The second part shows a sudden ascentof the ionization current near the end of the path. Finally, the third part shows an almost vertical fall of the ionization in the last 3 mm. or so of the alpha particles path. The present invention takes advantage of the shape of this curve for producing the asymmetrical ionization conditions in the chambers I and II. The chamber I works on the constant part of the ionization curve whereas chamber II works on the variable part which is very sensitive both to ion recombination and density changes.

The device according to the invention can be used If the place to be monitored contains a radio-active gas, the ionization current in the chamber II, instead of decreasing, will increase and will be able in certain cases, where alpha emanations are present, to give a current I higher than 1 and to produce at the terminals of the resistance R a potential difierence higher than V whereupon an alarm will be given. Better sensitivity is obtained (withthe danger, however, of contamination of the source S) by 1 screwing the pipes t and in the holes 0 and O and by circulating the gas suspected of containing radio-acvalues of I and V and this will give the alarm with a better sensitivity than is obtained with the usual ionization chamber which is not coupled to a second ionization .tive gases through the chamber I. The current 1 Wlilf" increase due to the radio-active gases and will raise the chamber in opposition as is the case in accordance with v the invention.

- The cold cathode triode is normally surrounded by a metal cylinder H snugly received in a recess in the insulatingblock p within the cylinder are mounted two opaque disc-like masks H and H on either side of the cold cathode triode and at the end of the cylinder opparent insulating material. If the masks H and H, are taken off, and a cold cathode triode sensitive to light is used, such as the GKSO (Ferranti), the block p and disc p of transparent insulating material act to pipe.light to the cold cathode triode. lated and put in darkness, any flame or light triggers the cold triode, provided the potential on its grid G, in darkness, has been regulated (by moving the source S) to a value V suitably smaller than the triggering potential V e.g.: V -V 10 volts.

In normal use, for the detection of smokes, radioactive gases, and flames (or light), the whole deviceis surrounded by a screen in order to avoid alarms in case of inadvertent grounding of the chambers I or II.

Ifthe screen is removed the device will indicate as a resultof the grounding of either of the chambers the presence of an intruder, whether man or animal. Any outside contactwith the chambers I or- II is sufficient to trigger the triode and give the alarm. The effectiveness dow handles, contacts under carpets, and so forth which are conveniently insulated and will be grounded by contact with the visitor. The ground connection will cause the triggering of the cold. cathodetriode and will give the alarm.

.posite the block p there is secured a disc p of trans- What I claim is:

1. A detector device comprising a housing defining two adjacent chambers and including an intermediate wall separating the chambers, a window means supported in the intermediate wall, a single source of radiation energy supported in one of the chambers and radiating through said window means into the other of the chambers, electrodes positioned respectively in said chambers, one of the chambers being coupled to ambient air and the other chamber being coupled to a medium to be monitored, the asymmetrical arrangement of said source with respect to said chambers causing an unequal distribution of ionization current at said electrodes, a utilization means, and an electric circuit coupling said electrodes to said utilization means so that the normal unequal distribution of the current renders the utilization means ineffective, the presence of the medium in said other chamber redistributing the current at the electrodes to render the utilization means effective.

2. A device as claimed in claim 1, wherein said source of radiation energy is a source of alpha particles, said window means comprising a foil for the passage of said particles and a grid means encompassing said foil for the support thereof against shock and vibration.

' 3. A detector device comprising means defining a pair of adjacent chambers, a single source of alpha particles positioned asymmetrically with respect to said chambers to cause asymmetrical ionization in gases contained 1m both said chambers, means operatively disposed with re-- spect to the first said means to pass current through the ionized gases,' means sensitive to the difierence between the currents in each chamber to provide a signal with said-difierence exceeding a predetermined value, means coupled to the first said means for the introduction of the medium to be monitored into one of said chambers, and an intermediate member transparent to alpha radiation separating the chambers, the source of alpha particles being located in one chamber to direct radiation into the other chamber through said member, the secthe gas to be monitored in one of said chambers also passes through the other of said chambers.

5. A device as claimed in claim 3 wherein the chamber containing the source communicates with ambient air so as to permit slow diffusion only, the chamber remote from the source being adapted for introduction of said gas to be monitored.

6; A device as claimed in claim 3, wherein the first said means is a housing of metal and having side walls and opposite parallel end walls, said intermediate member dividing the housing approximately equally and including a thin metal foil rigidly supported in parallel to the end walls, said device further comprising a stem, and a plurality of insulating inserts in said housing, the source of alpha particles being supported by said stem which extends through one of said insulating inserts in one end wall, said pair of electrodes extending through the other insulating inserts, one electrode being positioned in each chamber, each said insert comprising two rings of insulating material and a conducting ring between the first said rings. 7 q

References Cited in the file of this patent UNITED STATES PATENTS (Other references on following page) UNITED STATES PATENTS Obcrmaier Apr. 14, 1953 Pompeo et a1. June 9, 1953 Meili Feb. 22, 1955 Greer Feb. 21, 1956 5 Dewan May 15, 1956 Jacobs et a1. July 31, 1956 Shamos Dec. 24, 1957 Marx Oct. 13, 1959 6 FOREIGN PATENTS Great Britain Sept. 21, 1933 OTHER REFERENCES

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