Nov. 9, 1954
J. F. ENGLISH, JR
RADIATION DETECTION
Filed June 7, 1951
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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
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