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Патент USA US3100848

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Aug. 13, 1963
Filed NOV. 23, 1959
---- -
United States Patent 0
Patented Aug. 13, 1963.
George B. Foster, Worthington, Ghio, assignor to indus
pensive and readily adaptable to present day industrial
gauging systems.
Other objects and features of the present invention will
trial Nucleonies Corporation, a corporation of Ohio
become apparent from the following detailed description
Filed Nov. 23, 195?, Ser. No. 854,622
11 Qiaims. ((Il. 250-52)
when taken in conjunction with the drawings in which:
‘FIG. 1 is a typical application of a nuclear radiation
gauging system.
This invention relates generally to nuclear instrumenta~
FIG. 2 is a graph illustrating the rate of exposure of
tion for the control of continuous industrial processes and
a product subject to radiation vs. the speed of the process.
particularly to an automatic radiation dosage limiter for 10
FIG. 3 is a schematic diagram of a preferred embodi
~ the protection of materials in continuous gauging systems.
ment of the present invention.
The observation of certain properties of materials by
‘FIG. 4 shows the relationship of the time allowed for
subjecting them to ?elds of ‘radiation of various energies,
the continuation of irradiation for differing process rates.
characteristics, and dosages has been applied ‘to many
FIG. 5 is an illustration of an indicator panel suitable
industrial and domestic operations. vMore recently, radia
for use with the present invention.
tion instrumentation has been developed to the extent
FIG. 6 is a simpli?ed diagrammatic showing of a di
that emissions from radioisotopes, X~ray tubes, linear
?verter for the process.
accelerators and the like are being applied commercially
‘Referring now to FIG. 1, there is illustrated a radia
to the measurements of food and food intermediates.
tion type ?uid density gauge. The normally moving
These applications of radiation generally involve very
material 11 is subject to a radiation ?eld in the test sec
low dosages to the measured material and are not in
tion '13 which separates the radiation source 15 from the
tended to alter the physical, chemical, molecular or
detector 17. The radiation iield existing at any point in
atomic properties of the materials involved in the manu
the measured volume is a function of the strength of
facturing operations. This is in distinction from the ir
the source of the radiation, its ?ux distribution and the
radiation of materials such as in the sterilization of foods 25 absorption suffered by the radiation in passing through
and their long term preservation. In these applications
intervening (material. For the purposes of illustration,
the properties of the irradiated material are purposely
assume that the radiation ?eld on the lower surface
altered. These latter effects are based on phenomena
which occur at some energies of radiation and at some
of the measured volume is isotropic, and that the pipe
section is of square cross section. The radiation dosage
total dosages of irradiation, whereby certain changes can 30 received by the material lying closest to the emitting
surface .19 will receive the highest dosage by reason of
ference between the effects produced by radiation for
passing through the highest ?eld density. Material lying
material measurement purposes and the radiation ap
at greater distances will be subjected to a lesser intensity
plied for material alteration purposes lies at least partly
by reason of the energy absorption occurring in the inter
in the amount of radiation dose received by the mate 35 vening material. In the illustration let V==process ve
rial. It is important that radiation applied for the one
' purpose does not inadvertently produce a second, un
L=the path length of the irradiated section.
desired result due to excessive dosage.
iD=the integrated dosage in rads received by a unit
be induced in the material. It is apparent that the dif
Many food products are packaged in such a way that
of the process when subjected to continuous exposure
the degree of ?lling of the package is an important con 40 throughout the irradiated path length L.
trol parameter. Examples of this are the level of ?ll of
R=radiation ?eld in rad per unit time.
liquids in cans and bottles. In this instance, too, radia
T=time duration of radiation exposure to unit process.
tion has been utilized for the observation of the ?lling
Then the time ‘duration of exposure of unit process in
level of containers and the adjustment of the machinery
passing through the measured volume is
performing the ?lling operation. Such operations sub 45
ject the material to irradiation in the course .of making
the necessary measurements of degree of ?lling. The
measurement of some characteristic of materials which
The dosage received by unit process is then
are brought into close proximity to foods, such as pack
aging materials, might also. require attention to insure 50
that deleterious effects are not induced therein through
any reaction from radiation.
Substituting from (1) (gives
Certain kinds of radiation are more likely to produce
undesired residual eli‘ects than others in a spec?c mate
ZD= 7
rial being examined. "However, for any kind of radia 55
For any given instrument con?guration and point in, time
tion there is some value of integrated dosage which
could be designated as being “safe,” or in any event,
not prohibited from use. The present invention teaches
the quantities R and L are physical‘ constants. Let the
product RL {be treated as arcoe?icient, l’, whose value
can be obtained by calculation or observation.
a method and means. for a manufacturer or other user
employing a radiation device to prevent subjecting the
material under observation to a total radiation dosage
greater than the “permissible” limit.
Accordingly the principal object of the present inven
* Thus the ‘dosage received by unit process or product
tion is to provide method and means for limiting ‘the
which is a part'of a continuously or intermittently mov
radiation dosage for the protection of materials in con 65 ing medium exposed in a measuring section or region is
tinuous gauging systems.
inversely proportional to the velocity of the process and
Another object of the present invention is to limit the
proportional to the radiation ?eld‘ intensity. This rela
radiation dosage in a continuous gauging‘ system to a " tionship is shown in FIGURE 2. From. this relation,
‘maximum level irrespective of the radiation source size
which has the form"
or speed or ?ow of the product.
‘It is a further object of the present invention to pro-'
as “ ‘
vide a radiation dosage limiter that is relatively inex
causes the radiation intensity of the surface 19 to be
it is apparent that lfor any ?nite value of I’ the dosage
approaches in?nity as the process speed approaches zero.
The effect of different values of the coef?cient P are
substantially reduced. This action alters the value of the
R term of the product RL=P. The effect here is seen
in the curve 46, corresponding to a new radiation coef
illustrated in the curves labelled P1, P2, P3 . . . etc.
?cient Q1. A much lower value of V, shown as Ve,
may now be tolerated prior to potentially exceeding the
permissible dosage z'Dz to unit process. However since
Q1 has a ?nite value the dosage limit iDz can still be
These would correspond to diiierent values of radiation
?eld ‘strength or irradiated path length.
The coefficient P is a constant it the radiation ?eld has
a constant intensity with time or it may be treated as
a constant with time for practical purposes such as in the
potentially exceeded as V approaches zero if this con
use of a radioactive substance of long half life. The other 10 dition continues .over a su?‘icient period of time. Thus
a further action may he required even after the shutter
term L of the product RL is a constant arisingirom a
29 'has been closed in order to assure that the integrated
physical dimension of the measured v‘olume,>i.e. the
dosage limit iDz is not to be exceeded when the process
path length over which the process is exposed to the
velocity goes below the value VB. The lowered level of i
In the event that the intensity of the radiation source 15 radiation iield and a low value of process velocity may
is not constant ‘for practical purposes and the rate at
which it is changing in intensity as a ‘function of time
thus still combine to produce a potentially excessive dose
is known, means may be employed for automatically
varying the value of the coe?icient P in accordance
with this known variation in radiation intensity. A.
method of accommodating this variation in the radia
close 1132.
of radiation pDz which can become an actual excessive
The nature of the corrective actions required is thus
\diiierent in the two cases of coefficients P1 and Q1.
After the ‘automatic closure of the shutter 29‘ an alarm
may be sounded for the convenience of the process op
erator to indicate that measurement has been discon
tion intensity when the radiation source is a radioactive
material is described ‘by copending application of Neil
Handel, Ser. 722,259, ?led March 18, 1958, now U.S.
However, as is well known in the art, the action of Q
Patent No. 2,942,113, issued June 21, 1960.
the radiation shutter does not reduce the radiation from
The present invention teaches a unique and novel
the radiation ?eld to zero, but it merely approaches this
manner and means of limiting the maximum radiation
level as shielding is increased. If the process material
dosage to unit process or product below a pre-selected
were completely stopped tor example, the dosage accu
level. Such dosage levels are illustrated in the values
mulated by unit process would be:
iDX, iDy, iDz in FIGURE 2. These represent values of
radiation dosage which have been ?xed as the maximum
upper limits towhich the process material should be
' (2)
In this instance a time limit of continued exposure
would he solely governing the amount of radiation dos
‘In the apparatus of FIGURE 1 let the coe?‘icient of
radiation exposure P be of value P1, resulting from a
age received iby every unit irradiated area a in the total
irradiated area A.’ However, under the usual conditions
the process material is moving. Therefore, consider
L in the test section 13 of the ‘density measuring ap
specifically the material in the projected differential area a
paratus shown when the source shutter29 is open. A
which is at the furthest upstream end oi the sensing re
tachometer generator 33 provides a signal on line 37
responsive to the process velocity as detected ‘by the 40 glon corresponding to the commencement oi the region _,
13 de?ned by the limits of the irradiating surface 19.
rotating-device 31. The radiation source assembly and
differential projected area a require a time T2
its accompanying mechanical mounting and shielding
to pass over the entire length of the projected area of
28 is ?tted with a shutter 29, shown in its “open” posi
the irnadiator 19. The differential area a will thus re~
' tion.' When “closed” by the action of the spring 39 the
ceive a maximum permissible dose z'Dz if the condition
shutter serves to reduce the radiation intensity R at the
or process velocity V2 is permitted to persist over the
surface 19 to a low value compared to its intensity when
given level of radiation intensity R over the path length
the shutter is in the “open” position.
entire period of time Tz required for the differential
area to pass through the entire length of the irradiation
A cylinder 25
actuates the shutter by means of the rod 27 moving in
response to the. application of an air supply to the piston
of the cylinder 25 when the solenoid 21 actuates the
valve, 23.
In normal operation of ‘the gauging ‘device through '
which the material 11 is ?owing, the shutter 29 is with
In the preferred embodiment of theteaching- of this
invention-the alarm signal and corrective action is taken
immediately when the process velocity reaches the lower
limit Vz which thereby pnoduced a condition or‘ potern '
tial-ly excessive radiation dosage pDZ to unit, process. This
drawn, i.e. is in thef‘open” position. Let this condition
produce the radiation coefficient P1. The radiation 55 corrective action of reducing the incident radiation flux
dosage to the material being measured as a iunction of,
is thus taken in anticipation of ‘and to» prevent the occur
process velocity is then as shown in the curve 41 of
FIGURE 2. Let z'Dz be a maximum permissible level
of radiation dosage Vior unit process, ?xed in accordance
. rence of an excessive. radiation dosage which wouldroc
with a technical standard or regulatory ruling.v ‘Further,
60 tinue process irradiation atter the process rate has dropped
let the processvelocity have a normal average value
of Va, resulting in a normal average radiation dosage of,
iDa, and with normal variations’ of velocity occurring
between Vb at the lower limit of velocity and V0 at
the upper limit.
Under" the conditions of such variations of velocity it
is apparent from the relationships shown in \FIGURE 2
that the maximum permissible limit of radiation‘ dosage
our if the irradiation were continued over a su?icient
period of time. In the ‘event that it is desired to con
below the velocity VZ, this can be ‘accomplished by pro
viding timing apparatus which will delay the signaling ,
1 ‘ and/or corrective action until unit process has actually
received limiting dose iDz. Then if this level of dosage
65 should actually occur the corrective action can be ini
tiaited. FIGURE 4 shows the relationship of the time
allowed for the continuation 0t irradiation for process
rates ‘between the values V=0 to V=Vz and for the con
dition of radiation coe?icients I?1 and Q1; It can be
iDz' will not be reached nor exceeded. However, if'the
process velocity were‘ to be lowered to the value Vz, 70 seen that for velocities greater than Vz the allowable time
then unit process could ‘be exposed to the ‘dosage iDz
of irradiation‘ is in?nite, i.e. the process can be contin
and the allowable limit ofndosage'may be ‘reached. ' In
uously-irradiated and measured. ‘If the process is stopped
_'an elementary form of radiation dosage limiting ap
the time allowable for continued irradiation would he:
paratus when this condition of low process‘rate occurs,
a limit sensing circuit is immediately actuated which 75
where the radiation intensity R can have values of R1
for shutter open, or R2 for shutter closed conditions.
These produce the allowable times T1 and T2. A means
for accomplishing this more sophisticated protective meth
od is later described.
The irradiation monitoring and calculation operations
can be performed by the circuits. of FIGURE 3. An an
alog computer is employed to perform the computations.
radiation shutter position control solenoid 21 through
the opening of the contacts 66 and 7d.
lif desired the
contacts as and 72 can be used to actuate an indicator
or alarm to call attention to the fact that the shutter
closing action has occurred.
When this ?rst action has occurred, the exposure co
efficient has been changed from the value P1 in this illus
tration, to the value Q1, curve as of FIGURE 2. Under
this condition a lower value of process rate will corre
spond to the condition ‘of potential overexposure pDz.
In the computer of FIGURE 3 this lower value of ex
posure coe?icient is obtained from the position of the
arm 91 of the potentiometer 9e, and its value is indi
cated as E52. ‘The voltage level sensor 76 is then sensi
tive to the value of IES2 dropping below the voltage Be.
where [D is the potential dosage (to unit process in 15 This
condition could occur at some low value of process
rads at a process velocity V. P is a coefficient applicable
velocity such as that shown in V6 in FIGURE 2.
during normal operation of the process, with the radia
The delay device 78 acts in a manner similar to the
tion shutter open and Q is the coefficient with shutter
delay device 71. The, output of the voltage level sensor
closed. A voltage representative of the computed value
76 indicates that the process rate has reached a value
of the potential dosage [D is compared with a preselected
value and a signal is obtained when this ‘computed value
exceeds the preselected value. Two circuits are used
in the illustrative example
FIGURE 3 to provide the
needed comparisons tor the two coef?cients P and Q.
Additional apparatus may be employed to delay the com
mencement of corrective actions until the actual inte- -
grated dose exceeding the preset limit is reached, if this
should the desired. Thus, corrective action may be de
layed until pDZ has been convented‘to iDz.
In FIGURE 3 let a DC. voltage proportional to proc
ess velocity appear on line 37. This voltage is applied
to potentiometer 51 whose arm 53‘ is calibrated for po
such that unit process could receive an integrated dose
of radiation in excess of a preselected upper limit if this
condition were to persist over the period of time re
quired for unit process to pass over the path length L
within which it is being irradiated.
The delay 71 and78 is provided in the elements pro
vided by a timing device such as a timing circuit whose
delay period is inversely proportional to the voltage ap
peering on the signal line 37 over a region of process
velocities less than V2. An output signal from the volt
age level sensor' 76 initiates a timing period in the de
vice 78 and likewise the sensor as can initiate a timing
cycle in the delay device '71. The duration of this tim
sition in terms of the quantity l/L where L is the length
of the path of the irradiation section 13. Thus longer 35 lag period is long if the signal on line 37 is large, rep
resenting high process velocity. The timing period is
path lengths correspond to the output or a smaller fraction
shorter as the process velocity becomes slower. The
of the voltage applied to this potentiometer. The .output
lower limit of process velocity which commences such
voltage thus obtained is next applied to a second multi
timing sequence is lower when the coe?icient Q1 exists
plying potentiometer 54 the position of whose arm 55
than when coe?’icient P1 applies. This is re?ected in
is proportional to 1/12, the inverse of the radiation ?eld
the position of the arm 91 on the potentiometer 9t} be
ing set to pick on a higher proportion of the available
7 Thus a smaller propontion of the voltage applied to
potentiometer 54 will appear at its output as the radiation ' signal output from the arm 53 than does the arm 55' pick
field is increased and vice versa. The output voltage from
this potentiometer is next applied to the input of a
voltage level sensing device 68 which can/be any of a
oil ‘from the potentiometer 54.
FIGURE 4 shows the relationship of the timing cycles
of the delay devices 71 ‘and 78 and the process velocity.
At velocities greater than VZ, the allowable duration of
radiation exposure is in?nite since unit process cannot be
large number of such devices Well known in the art.
The voltage level sensing device is responsive to the
overexposed. 'At values of process velocity below V2
ditierence between the output voltage Es1 of one polarity
and the value cl’ a bias voltage E0 of the opposite polar‘ 50 and for a radiation coe?icient P1 a continually decreas
ing duration of allowable ‘exposure must be ?ollowed.
ity provided by the potential source 61 modi?ed by the
In the limit when V=0, the allowable limit is
position of the arm 63 of the potentiometer 67. The
voltage level sensor es operates ‘a relay 65 when the value
of B51 becomes less than the valueof EC. The polarity
designations shown for E51 and EC are illustrative.
Both . ‘
polarities could be reversed if desired.
The value of EC is' chosen to be the voltageanalog
of the value of radiation dosage which it is desired not
Where T is the allowable ‘duration of the exposure, z'D '
‘is the integrated dose and R is the dosage rate of irradi
It can be seen that the allowable exposure period is
to exceed; the voltage ES1 is likewise proportional to the
longer {or the curve corresponding to the coefficient Q1
dosage rate received by unit process. Thus the compari 60 than it is for the cole?‘icient P1. This is because the co
son [between E51 and Ec provides the analog or compar
e?icient Q1 corresponds to a lower intensity radiation
ing the existing level or potential radiation. dosage to,
‘?eld, existing when the radiation shielding shutter is
omit process with the maximum level desired.
The signal from the voltage level sensor 68 which ac
tuates the relay 65 may be affected by the action of the
.delay device 71 if it is desired to delay the operation
of the relay '65 until the integrated radiation dose re
ceived by unit process. has actually reached the maximum
allowable limit of permissible exposure ‘instead of al
lowing the sensor ‘68' to actuate relay 65 when the con
dition of process rate has been reached which potentially
could result in unit process receiving excessive radiation
‘ closed over the radiation source.
When the timing‘ cycle has‘ expired corrective action
is necessary. If the process velocity rises- above the
value which initiated a timing cycle, then the timing
cycle is discontinued and the cycle is reset to zero in
preparation for a further timing zcycle. Alternatively
corrective action may be undertaken without the use of
the timing cycle, by actuating the relays ~65 and 77 di
rectly from the output of the voltage level ‘sensors 68
“ and 76 directly fromconsiderations previously treated.
dosage if said condition were to be continued for a suf
In the event that action ‘of-relay 65 occurs, this causes
?cient period of time.
the radiation ?eld to belowered and appropriate indica
‘ When the relay 65 operates it removes power from the
“tors or alarms of this condition to be operated. The -
one of many possible embodiments of the, same. The
invention, therefore, is not to be restricted to the exem
process can in the meanwhile continue to pass through
the measuring section since it is not receiving an actual
plary structure shown and described.
or potential excessive dosage of radiation. However
measurement action has ceased since the radiation source
has been shuttered or otherwise greatly attenuated such
‘as by removing the accelerative voltage from vacuum tube
1. The method of illmiting the radiation dosage re
ceived by material moving through ‘a ?eld of radiation of
known intensity comprising the steps of establishing an
excessive value for said radiation dosage, measuring the
rate of said material movement through said ?eld, com
‘radiation generators.
However, when relay 77 is operated, this indicates
that a condition exists which requires the removal of the
material exposed from further irradiation in order to 10 puting the integrated dosage received by said material in
accordance with said rate measurement relative to said
prevent the potential accumulation of excessive dosage.
?eld intensity, comparing said‘ computed dosage with said
In the event that the timing device '78 has been used in
excessive value, and substantially reducing the intensity
connection with the level sensing device 76 to delay the
of said radiation ?eld whenever said computed dosage
action of relay 77 until the maximum permissible limit
of integrated radiation dosage has been reached, then 15 exceeds said. excessive value.
2. The method of claim 1 further including the step of
the irradiated material must be removed from further
delaying said ?eld intensity reduction for a time propor
exposure immediately by means of process ?ow diverters
tional to said measured rate of material movement.
or conveyors as actuated by the contacts 80‘ and 84 of
3. The method of limiting the radiation dosage received
relay77. The contacts ‘81 and ‘82 of the relay 77 can
(be used to apply or inject suitable marking or labeling 20 by material moving through a ?eld of radiation of known
intensity comprising the steps of establishing a standard
materials into the i roduct if excessively irradiated to
value for‘said radiation dosage, measuring the rate of said
assure that it'Will not be inadvertently processed vfurther
material movement through said ?eld, computing the in
into goods sold or otherwise fall into the hands of un
tegrated dosage received by said material in accordance
suspecting persons.
In the construction of devices to perform the com 25 with said rate measurement relative to said ?eld -intensity,'
comparing said computed dosage with said standard value,
putations and timing cycles described above many tech
' substantially reducing the intensity of said radiation ?eld '
niques may .'be employed. Pneumatic mechanisms, hy
draulics, magnetics, Hall Eifect devices and operational
‘whenever said computed dosage exceeds said standard
value, computing the integrated dosage at said reduced
ampli?ers for example may he more desirable in some
?eld intensity, comparing said newly computed dosage
with said standard value, and interrupting said material
FIGURE 5 shows a possible arrangement of control
movement in said radiation ?eld when said newly com
settings which would be appropriate to the use of this
puted dosage exceeds said standard value.
4. The method of claim’ 3 [further including the step
dial is preset to the value of radiation ?eld intensity
delaying the interruption of said material movement
which exists when the radiation ‘?eld intensity reduc
for a time proportional to said measured rate of material
tion means are operative, i.e. closing a shutter over the
radiation dosage limiting method.
The ?rst or “A”
source of radiation if obtained ‘from the emissions from
radioactive material, lowering the voltage on an accel
erator or vacuum tube generator etc.
The second or
intensity comprising means ‘for establishing an excessive
value for said radiation dosage, means tfor measuring the
“B”wdial is preset to the normal value of radiation ?eld
intensity existing during the measuring mode and the
rate of said material movement through said ?eld, means
third or “C” dial is preset to the maximum allowable
integrated dose to unit process which it is vdesired or re
quired not to exceed.
5. Apparatus for limiting the radiation dosage received
by material moving through a ?eld of radiation of known
for computing the integrated dosage received by said ma
terial in accordance with said rate measurements rela
tive to said ?eld intensity, means for comparing said com
. .The voltage level on signal line 37 can the generated 45
puted dosage vwith said excessive value, landgmeans for .
in such a manner as to represent the exposure duration
substantially reducing the intensity of said radiation ?eld
of unit process occurring with materials which are not
whenever said computed dosage exceeds said excessive
in continuous movement but are. indexed sequentially
into the exposure region. Such might occur in processes
6. Apparatus substantially as set forth in claim 5 which .
such as container ?lling. In this instance an integrator
'tfurther'inc'ludes means for delaying the interruption of
‘circuit applied to a signal consisting of pulses of volt
said material movement for ‘a time proportional to the a
age whose duration corresponds to the time of exposure
measured rate of said material movement.
can \be applied so that the resultingsignal appearing on
7. Apparatus for limiting the radiation dosage received
line 37 can be used for computation in the same manner
by material moving through a ?eld of radiation of known
as was the tachometer generated signal.
intensity comprising means vfor establishing a standard‘
‘It can be ‘seen that the particular settings of these con
value for said radiation dosage, means for measuring the
trols can be altered at will in response to desired new
rate of said material movement through said ?eld, means
‘ values of radiation dosage limits arising from legal, medi
for computing the integrated dosage received by said
cal, physical or any other consideration. it could be
material in accordance with said rate measurement rela
readily arranged that va locked cover affixed with an ap 60
tive to said ?eld intensity, means for comparing said com
propriate seal of a regulatory authority be ?tted over the
control settings and that access to these controls be re- -
.stricted to persons speci?cally authorized to make such
adjustments. _In this way regulatory authorities would
puted dosage with said standard value, means for‘ sub
stantially reducing the intensity of said radiation ?eld
rwhenever said computed dosage exceeds said standard
value, means for computing the integrated dosage ‘at said
be afforded a means ‘for assuring the safety of materials 65 reduced ?eld intensity, means for comparing said newly
exposed to potentially deleterious amounts of radiation.
computed dosage with said standard value, and means for,
Referring to FIG. 6, material flow 11 through the sec
interrupting said material movement in said radiation
tion 13 may be Iby-passed therearound by means‘ of a
?eld when said newly computed dosage exceeds said stand- "
gate 92 pivotally mounted at 914 and adapted to swing
to the dotted line position 92a. A solenoid 96 is mechan 70 yard value. '
8. Apparatus substantially as set forth in claim 7 which
ically connected to theigate 92 and actuated by ‘a power
further includes means for delaying the interruption of
supply 98 through normally open contacts 80 of relay 7 7.
said material movement for a time proportional to said-V
The invention described hereinabove may ‘be varied in
measured rate of material movement.
construction within the scope of the claims, [for the [par
9; Apparatus for limiting the radiation dosage received
ticular device selected to illustrate the invention. is but
by material moving through a ?eld of radiation of known
intensity comprising a tachometer generator for provid
ing a ?rst electrical voltage of a magnitude proportional
to the rate of said material movement, voltage divider
circuit means providing a second electrical voltage of a
10. Apparatus substantially as set forth in claim 9
which further includes means for ‘delaying each of said
output signals for a time proportional to the measured
rate of said material movement.
polarity identical to that of said ?rst electrical voltage and
a magnitude proportional to a standard value of said
radiation dosage, a pair of parallel connected resistive ele
11. Apparatus substantially ‘as set forth in claim 9‘ in
which said radiation ?eld intensity reducing means com
prises 1a shutter adapted for rectilinear movement from a
?rst position away from said ‘radiation ?eld to a second
ments for algebraically summing the magnitudes of said
position in said ?eld, air cylinder and piston driving means
?rst and said second electrical voltages, at variable tap 10 connected to said shutter, and actuator means oormeoted to
on each of said resistive elements each providing a dif
said driving means for moving said shutter from said
ferent magnitude 'of said summed voltage, a ?rst voltage
?rst to said second position.
level sensor connected to the resistive tap providing the
lesser of said summed voltage magnitudes, said ?rst volt- .
References Cited in the ?le of this patent
age level sensor having input circuit means responsive 15
to the di?erence in said lesser summed voltage magnitude
Cliapp _______________ _.. Apr. 19, 1949
and said second electrical voltage magnitude to generate
Ratcliff _______________ __ ‘Feb. 19, 1952
an output signal whenever said difference is substantially
Herzog ______________ __ Oct. 7, 1952
zero, means responsive to said output signal for reducing
Wuppermann _________ __ Aug. 2, 1955
the intensity of said radiation ?eld, a second voltage level 20 2,714,669
Howard ______________ __ July 1, 1958
sensor connected to the other of said resistive taps provid
ing the greater of said summed voltage magnitudes, said
second voltage level sensor having input circuit means
responsive to the difference in said greater summed volt
age magnitude and said second electrical voltage mag 25
nitude to generate an ‘output signal Whenever said dif
ference is substantially zero, and means responsive to said
last named output signal for diverting said material move
ment from said radiation ?eld.
London ______________ __ Apr. 21,
MacDonald ___________ __ July 21,
Goodman ____________ __ Sept. 29,
Dijkstra ______________ __ Nov. 24,
Fearnside _____________ __ Jan. 26,
Clark et al ____________ __ Feb. 23,
Arrison ______________ __ Mar. 15,
Zimmer ______________ __ May 10,
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