Nov. 9, 1954 J. F. ENGLISH, JR RADIATION DETECTION Filed June 7, 1951 _. < %\NN ommw _N 2,694,162 United States Patent 0 ” ICC 1 2,694,162 Patented Nov. 9, 1954 2 after the manner shown in at least the Rutherford et al. 2,694,162 RADIATION DETECTION James F. English, Jr., Lakewood, Ohio, assignor to Bailey Meter Company, a corporation of Delaware Application June 7, 1951, Serial No. 230,406 3 Claims. (Cl. 317-130) patent 2,524,478. The tungsten ñlament of the bolom eter will change resistance or is responsive, to all radia tion to which it is exposed including the visible and infra-red ranges. There is substantially no discrimina tion in the bolometer response, the resistance changing in accordance with the intensity, or quantity, of the radiation. The tungsten element is enclosed in an evacu ated housing whose one side is a transparent window which limits to some extent the length of the infra-red radiations passed to the filament. It can readily be understood that the thermal responsive device is essen tially a filament upon which is concentrated all of the radiation coming to it for generating heat to change My invention is generally directed to the detection of 15 the temperature of the filament and raise its electrical radiation. Although the particular embodiment with resistance. which l express my invention is responsive to radiations in the infra-red region, the principle is applicable to any radiation which varies, pulsates, iiuctuates or is other wise “chopped." lf direct the disclosed embodiment to the detection of radiation given oli' by what I recognize as commercial combustion processes. These combustion processes sus tain fiame areas under process or power furnaces and may use oil, gas or coal as a fuel. Under any condition On the other hand the classes of selective light re sponsive devices are expanding at present. For exam ple, there is the photoemissive cell which is essentially 20 composed of two electrodes enclosed in a gas, or vac uum, and whose operation consists of having7 electrons ejected from the electrode-cathode by radiation imping ing thereon and the released electrons fiowing to the other positively charged electrode-anode. Secondly, there is the photovoltaic or barrier-plane of combustion of this nature there is produced from the i cell which depends for its function upon a current flow iiarne area continuous, band or line emission, part or all between a thin layer of semi-conductor and a metal of which occurs within the infra-red wave length region. when light is allowed to penetrate the former to the It is the general purpose of my invention to make use junction between the two. of variations in the intensity of the combustion radia 30 A third type of the selective light responsive devices tions in the infrared region in order that a furnace op is the photoconductive cell operating on the principle erator will be informed when the flame of the combus of the inherent resistance change to radiation of a semi tion process is established, or having been established, conductor material between two electrodes. The most fails. common material in this usage has been selenium, al It is sufficient for the purposes of my present inven 35 though thallinm sulfide has been used and lead sulfide tion to observe that flame areas do flicker in radiation as and germanium have been brought under recent investi commercially propagated. in a general way we may gation. The operation is on the principle of emission surmise that the iiickering characteristic is possibly, in of electrons within the semi-conducting material due to part, due to the turbulent mixing prior to and during light impact thereon. ln their motion due to applied combustion and possibly, in part, due to the convection 40 potential, these electrons cause ionization, equilibrium currents created by the hot ñame contacting the rela being estab‘ished when the rate of formation is equal tively cooler ambient surrounding it. Of course there to disassociation. may well be very short periods of steady combustion Lead sulfide is now in commercially available quan when flickering does not actually occur, but unsteadi tities and form for use in photoconductive cells in a va ness of this nature is predominant unless laboratory con 45 riety of grid sizes and sensitivity resistance classifica ditions of supply and environment are maintained. tions. Specifically it is distributed as Cetron lead sul Proportions of fuel and air to combustion processes fide photoconductive cell which has a peak response may be varied in accordance with demand on the fur near l micron and 21/2 microns. The speed with which the lead sulfide cell changes resistance in response to ra incandescent carbon, denoting incomplete combustion, 50 diation makes it quite practical for use in mv invention. or maintained clean and blue or colorless, with perfectly Germanium is also in commercial availability in com balanced proportions, measurable quantities of infra-red plete cell form. Germanium photocells are referred to radiation are emitted with an unsteadiness which I now as point-contact rectiiiers having a useful photo response recognize as characteristic of commercial flame areas. when radiant energy in the red and near infra-red region Therefore, in connection with the device sensitive to the 55 falls upon the crystal in the immediate vicinity of the intensity of infra-red radiations, I have invented a cir point-contact. At least some of the germanium cell cuit to detect the presence of the flame area in its pro characteristics roughly parallel those of the lead sulfide duction of an irregularly pulsating quantity of radiation. cell and to such extent there is available another de It is well established that combustion processes of the tectnr useful with mv invention. commercial variety involving oil, gas or coal produce 60 Whatever specific form of detector is utilized with my nace, but whether the flame is momentarily yellowed by radiations emitting substantially through the visible range invention, it is essential that it respond by establishing a lying roughly between .4 to .7 micron and well into the voltage variable in accordance with a variable and that infra-red range which lies roughly between .7 and 400 the speed with which it alters the established voltage fol microns. It can generally be expected that these flames low the change in magnitude of the variable very closely. will produce radiations throughout the infra-red band For detection of commercial flame area propagation, the but with the specific detector l employ, I am concerned detector may be one or another of those described supra. primarily with the region between .7 and 20 microns Their response is greatest in the near infra-red region of which is within the so-called near infra-red region. ln radiation and the high degree of selectivity is desirable for, cidental identifications include what is known as the as observed supra, the output in this region is generic to intermediate infra-red band from 20 to 40 microns and 70 all types of these flames. the far band which lies between 40 to 400 microns. Therefore, a general object of my invention is the de The specific detectors that I employ in my circuit are tection of the sustainment period of a source of some var selectively responsive to a narrow band, or bands of iable. infra-red radiation within the near infra-red region. I Another object of my invention is to sense the presence feel it advisable in specifying a specific detector to out 75 of a source of pulsating light radiations. line the differences between thermal detectors such as the v Another object of my invention is to indicate when a bolometer, thermopile and radiometer, and selective flame is established which produces infra-red radiations at radiation responsive devices such as the photoemissive, a variable rate. photovoltaic and photoconductive cells. It is another object of my invention to control the The thermal responsive device with which I am most 80 circuit. of a relay device that said relay will be actuated familiar is the bolometer employing a tungsten filament upon termination of a combustion process. 2,694,162 4. 3 The single figure of the drawing represents a practical embodiment of my invent-ion» employing a- gener-1c de tector sensitive to the varyingradiation source of a flame bod . Ig» the drawing I show a crossl section of aafurnace por. tion: into which'l propagate a, ñamebodyf 1, by'` any of a number of injectorsgof-4 various;> typesl of fuels. _I1 wish to large portion fluctuates in accordance with character istic4 ñarne~ propagation. With detector element S properly exposed to the vary ing, or fiickering, radiations of flame body 1, it can be logically explained how the resistance variation can be utilized to establish a voltage drop across resistance 9 for amplification to energize the circuit of relay 5. The two stage amplifying network I specifically em ploy, and designate- generally at 3,A is Well-known in operatemy system: to detect', at" station 2, radiations from this body 1 and establish an electrical' signal for 10 the electronic art. The patents to at least Hornfeck amplification The signalì amplified by the; at electric` 3i is applied networktoI the designate control.atgrid 2,437,603y and Ryder 2,333,393. disclose the network which is characteristically dominated by a dual triode of thyratron tube Ãtrarranged in circuit with a relay de such as I show here. vice I show- at 5. The circuit ofl relay'5 normally en The: grid of the triode in the first stage of amplifica ergized during.` periods: of fiame propagation so that the condition: of extinguishinent, or. disappearance, ofthe 15 tion has the detector. circuit signal applied directly to it. Considering that the` total Voltage drop across load fiaine:> will deenergize theN circuit and' release relay 5` for resistor 9 is composed of both A.-C. components, a capacitor 14 is used to isolate, or block, the D.-C. com ponent in the drop across load resistor 9. The voltage The iîectifying section dis; established to furnish the 20 drop across resistor 15 is therefore A.-C. and represents, giving signal of- thez condition orI exerting a control action to. affect thezcondition. _ necessary and thyratron D. C. 4'. supply The components to the detector of section at 2, 6amplifier are physi cally distributed: ink the` embodiment asreduced to practice and'niay take other specific> formsv than I' disclose. I em in its» irregular and cyclic‘variations, the flickering radia tions» ofy ñame body 1. Electronic amplification ofthe first stage» then has 16 as a load resistor across which the amplified signal is established, withl components ponents of section 6 for clarity ofexplainiiig its functional 25 of both- A.-C.v and Dr-C. making up the total signal. ploy diagrammatic licenseto enable meto group the com relation to; thek remainder.' of‘ thecircuit; Electronic lcom’ ponents of section 6 as specifically disclosed include one half of a dual diode I designate (’A)'.. A dual diode ~24 The. second stage of amplification is carried on in the samemanner. as- iii the first stage. Capacitor 17 blocks D.-C. components from the second stage triode grid and there is established across load resistor 1S the finally amplified signall made. up of components of both A.-C. reference and description hereinafter. The‘dual diode 30 and` D.-C. Capacitor 19 blocks the D.-C. in the same (A) is of initial’ importance because it supplies the con. manner as 14 and 17 and there is established across re starit' D.' C. for the detector circuit. Adiustable potenti sistor 20- the signal finally representative of the radia ometer 7 has a voltage drop across it supplied by‘the (A) mayk also be discerned' and` will.' be given. more specific tion. sourcey at 1> which Varies with the resistance of de section. This adjustable voltage is arranged in_ series with the detector elementv I house atV 8 and a resistor 9. 35 tector 8.. Adjustable contact" 21 enables a portion of the ampli The housing is specifically designated 10 and ‘is‘ ar`fied` flame-radiation signal to be selected for rectifica ranged to expose the detector element’ to the radiations tion by the (B) section of the dual diode, disclosed in the of flame body 1 for alteration off the electrical resistance divided- manner employed heretofore in rectifier section by the impinging radiations. The exposure of detector 8 to the radiations is regulated by structure designated 40 6. The A.-C. flame signal is` rectified by section (B) and. applied across- a parallel resistance-capacitor circuit at 11, 12 and> 13 which may be alternate in a particular installation. _ Device 11 represents a concentrating lens, 12 repre sentsA aV filter unit and 13 represents the .aperture into in the cathode circuit of the tube. Capacitance 22 and resistance 23` specifically form this parallel circuit, with 23f adjustableftogive means of varying- the rate at which the housing 10 >which mayl be'sized for particular require 45 a voltage difference on 22'will bleed off, or reduce; to ward zero.> ments. This structure is necessary when-the limitations The output' of. the rectifying and reducingV circuits 22, of'variousV detectors 81arev individually considered. Some 23' is used~ to activate a relay circuit which is thyratron detectors whose resistance is changed’ with the varying controlled. Ihave reduced the principle of- operation- to degrees of radiation in a satisfactorily rapid manner can . be saturated, that is, the change in resistance for a 50 practice by4 biasing»` the control grid 4’ of thyratron 4 with a potentialA of. negative polarity and opposing said changev in radiation magnitude may- approach .Azero With potential' by a- signal of positive polarity and normally in a particular range of’ magnitude of radiation. _If greater magnitudek from the rectifying and reducing cir flame body» 1', plus refractory background.` present, emits cuit 22, 23. The resistance-capacitor arrangement in a saturating quantity of’ radiation, aperture 13 offers a means for limiting the total" radiation magnitude. 55 thev cathode circuiti» of the dual diode (B) gives the positive signal. output for> opposition to the bias on the Should' the distance between the radiation source and thyratrongridA’. Therefore, with the ñame body 1 near detector 8', of itself, limit the total‘radiation through the normal. thyratron 4- will fire continuously with the buck largest practical size of' aperture 13', lens_11 may _be ing signals> on its` grid at> predetermined magnitudes with used to concentrate all radiation gathered into housing 10 on the relatively small' target area of detector 8. Be 60 the positive signal predominating. Should. theV flame body' 1 disappear and the ampli fied-radiation signal across resistance 2f) drop to zero, tector-target 8 and the source of'ra‘diation, it Will'be nec the potential.l across capacitor 22 will drop toward zero essary to size aperture 13 until~ the contribution by the as` it. discharges' through resistor 23. The- negativev bias ñ'ame body 1 will be- an amount whose variation will measurably alter the resistance of' detector 8.'~ If ' the 65 applied to` the? control grid‘ of thyratron 4 now preL dominates` andthe tube ceases> to pass current so the total radiation then falls below the desiredy range of the control circuitA is` deenergized and relay 5 falls to its detector, lens llíl may be employed to concentrate' the alternate position under the force of gravity or a spring. radiation ori target 8 until its resistancev reaches the d'e Rectifier section 6 has-been considered in its dualv diode sired- range of magnitude. Filter 121 is also used. in connection withv the detector 70 (A) which» supplies> the energy for the detector circuit'. The. completev dualdiode I employ at 24 bears a signifi` and' has- the function of predominating they bands or cant relation to the complete function of the entire radia lines of radiationÍ to which the. detector 8V has the greatest tion detection circuit.' It is obvious to those familiar response. These filters are well-known in the art- as y with the» amplifierI circuit of Hornfeck and Ryder, men band-pass filters. The devolpment- is largely empirical and IV have: selected a filter which narrowsy the frequency 75 tioned-supra, how the right hand'halfT of the tube sup bandV allowed toz pass,v to include substantially only' that pliessthe' D.-C. energization necessary for the function portion of the near infra-red radiation which causes the of the amplifier; The components associated with the greatest resistance change; in4 theV cell.v The band-pass diode; such as- the'choke 25, are familiar and used in filter will cut down on the total' radiationrcomingthrou'gh ways: well' known in the art to produce satisfactorily the sighting tubefand lens. but it is effective to pass 80 rectified: D.-C.`V Specifically, choke 25, as- a` reluctance; a. proportionately greater amount of the` infra-red band filters the pulsating löl-C.' produced by'rectifyinggA.-C. in which is found the greatest response in the:-d'etector-. to. reduce-1 harmonics which appear in the process. The ginning with the consideration ofthe distance between de-` rEhus;- with». sighting tube: 13:,vv lens 11,. and; filter: 12:: I pro negative bias signa'lfor~ tliyratronA 4' isi established', from vide; astructure- byawhich. there isfpasse‘d; to theJ detector this rectification, across. resistance 26'I and' is.’ made: ad 8, in housing 10, a:totali.amountíoff radiatiomofiwhichga 85 justable fori‘calibrationfpnrposes; 2,694,162 The left side of dual diode 24 is placed in the thyratron control relay circuit to insure that tube failure at this point will deenergize the relay circuit in a fail-safe manner. By far the larger percentage of tube failures occur in the filaments; should either filament of the dual diode 24 fail, both will fail, and as the energization of the circuit of relay 5 depends upon completion through the left hand side of dual diode 24, the relay will indi cate a malfunction upon this circuit being opened by filament burn-out. While I have chosen to illustrate and describe one preferred embodiment of my invention, it will be under~ stood that this is by way of example only and is not to be considered as limiting. What I claim as new, and desire to secure by Letters Patent of the United States, is: l. In a system for the detection of the ampli tude of the rapid fluctuations of a source of radiation, 6 2. In a system for detection of a rapidly and non-uni formly fluctuating variable having means responsive di rectly to the fluctuations of the variable establishing a fluctuating voltage directly representative thereof and means amplifying only said established voltage, the com bination which includes; a rectiñer; a load for said recti fier comprising shunt connected capacitance and resist ance units; means connecting the output of the volt age amplifying means, the rectifier and said load di rectly in series whereby the capacitance unit is charged solely in accordance with the amplitude, duration and frequency from said voltage amplifier; means providing a fixed potential of polarity opposite that from one pole of the capacitance unit; and means to compare said ca pacitance pole voltage with said potential to determine the amplitude of the variable including, a signal circuit including a thyratron whose grid is connected to both voltages, a rectifier for supply of the anode-cathode cir cuit of the thyratron, and a signal relay. ductivity varies rapidly in accordance with the in 20 3. The system as deIined in claim 2 in which the tensity of radiation striking it included in a circuit pro values of the capacitance and resistance units are se ducing a fluctuating voltage whose magnitude varies sole lected to provide a delay in voltage decline from the ly in accordance with the radiation and which is then capacitance unit commensurate with known variations amplified, the combination including, a reducing circuit of inconsequential duration and range. for the amplified iiuctuating radiation voltage producing 25 a potential of positive polarity which reduces in magni References Cited in the file of this patent tude at a determinable rate, a thyratron, a rectifier con nected to energize the anode-cathode circuit of said UNITED STATES PATENTS thyratron, a relay in said last mentioned circuit, a sec ond rectifier having its negative output biasing the con- - Number Name Date trol grid of said thyratron, and means connecting said 2,194,559 Koch ______________ -_ Mar. 26, 1940 of the type having a resistance device whose con reducing circuit positive potential to said control grid, said bias voltage being adjusted to cause relay energiza tion at predetermined radiation magnitude, said recti fiers being of the diode type with series connected fila ments whereby failure of one terminates operation of the other and the relay will indicate lack of radiation. 2,295,366 2,435,896 2,448,503 2,517,554 2,540,063 2,541,051 Stout _______________ __ Sept. 8, McIlvaine __________ __ Feb. 10, Wilson ____________ ..._ Aug. 31, Frommer ____________ __ Aug. 8, Victoreen __________ __ Jan. 30, Hanert _____________ __ Feb. 13, 1942 1948 1948 1950 1951 1951
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