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Патент USA US2122222

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June 28, 1938.
A. w. VINGERHOETS
2,122,222
DEVICE FOR AUTOMATIC INTERRUPTION OF RADIATION
Filed Oct. 12, 1934
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W/LHELMUS
2,122,222
Patented June 28, 1938
UNITED STATES
PATENT OFFICE
2,122,222
DEVICE FOR AUTOMATIC INTERRUPTIONA
0F RADIATION
‘
Antonius Wilhelmus Vingerhoets, Eindhoven,
Netherlands, assignor to N. V. Philips’ Gloei
lampenfabrieken, Elndhoven, Netherlands
Application October 12, 1934, Serial No. 748,151
In Germany November 6, 1933
7 Claims. (CL 250-34)
The present invention relates to devices for the
automatic interruption of the radiation caused
by X-rays, gamma rays etc., after such radia
tion has produced a desired effect, for instance,
6 a sufficient exposure (blackening) of a photo
graphic plate. My invention will be described
in its application to the taking of X-ray expo
sures.
'
It is known that X-rays cause the ionization of
'19 air, and that ionization chambers, placed be
hind the object and the photographic plate and
ionized by the X-rays penetrating through same,
can be used for measuring the eiiect of the rays.
It has already been proposed to use the loss of
voltage of a charged condenser in combination
with such an ionization chamber to automaticab
1y interrupt an X-ray exposure, when a sufficient
exposure of the photographic plate or film has
taken place. Such a device has been described
in the Netherlands Patent 29,448, in which an
ionization chamber is subjected to the effect of
X~rays during the exposure, and the ionization
in the chamber causes a pare-charged condenser
to lose its charge. rShe condenser biases the
2d grid of a triode, the plate circuit of which con
trols, by means of a switch, the operating cir
cuit of the X-ray tube; whereby upon loss of
charge of the condenser, the increased plate cur
rent of the triode causes the actuation of the
3d switch and the interruption of the operating cir
cult of the X-ray tube.
Such arrangement, however, behaved too er
ratically to be of practical use and too short or
too long exposures were obtained under appar
35 ently identical circumstances.
er to a terminal of the charging source.
This
eliminates an important source of leakage.
_
Furthermore, instead of providing a separate
condenser the ionization chamber itself is
formed as to constitute the condenser. For this
purpose the electrodes of the ionization chamber
are given a sufficiently large area as to give the
required capacity. This causes the elimination
oi further leakage sources. This increased in
sulating resistance makes it possible to use a 10
much smaller capacity, which increases the sen~
sitlveness of the adjustment. ‘The grid being
solely connected to one electrode of the ioniza==
tion chamber, the connecting lead between these
members can be made quite short and can be 16
hermetically sealed, which decreases the surface
leakage of this lead to a minimum.
Preferably the ionization chamber is rigidly
connected to the vacuum tube by a tube of in
sulating inateriai which encloses the connecting 20
lead between the grid and the ionization cham
her, which tube is preferably exhausted. The
ionization chamber and electron relay may
thereby constitute a single device.
To further reduce the leakage current the in
of the ionization chamber can be intercepted by
a conductive zone to which zone a negative po
tential may be applied, which potential may be
that 01' the grid or may be still lower.
This per
If desired, the same source can be used to
leakage outside of the ionization chamber, the
value of the leakage currents greatly depending,
tered, and across which is connected a potenti
The lack of reliability of the arrangement
40 as a rule, upon accidental and secondary influ
ences, such as the moisture content of the air,
surface conditions of the leads, etc., resulting in
great variations in the discharge time of the
condenser.
.
The present invention has for its objectto
avoid such deleterious and accidental in?uences
of leakage outside of the ionization chamber, and
to thereby provide a device of this kind which is
reliable and accurate.
50
According to the invention, instead of provid
ing a separate charging circuit for the condens
45
ometer, from which the various desired voltages 40
can be tapped off.
To improve the constancy of the voltage a gas
discharge path may be provided. As such a dis
charge path has a de?nite ignition voltage, the
voltage applied on the device does not vary when 45
the voltage of the supply mains shows an inci
dental increase.
In the case when, according to the invention,
the condenser is charged through the electron
relay, instead of a recti?ed current an alternat 50
ing voltage may be used.
-
er, the condenser is charged through the vac
uum tube to the grid of which it is connected,
Various further novel features and objects of
my invention will appear as the speci?cation
thereby avoiding the lead connecting the grid
progresses.
55 and the corresponding electrode of the condens
30
mits compensation of the leakage between the
grid and the cathode (which is positive with re
spect to the grid).
charge the ionization chamber (condenser) and
to supply the plate current for the electron re
lay. Such source may be, for instance, a recti
fled alternating current, which is preferably ?l
was primarily due to the various sources of
25
sulating member supporting the two electrodes
In order that the invention may be clearly un
2
2,129,!)22
derstood and readily carried into eil'ect, it will
In such an arrangement, at the lead 85 con
now be described more fully by way of example
with reference to the accompanying drawing, in
which:
necting the condenser with the negative side of
the charging source, and at the leads Bil-6| in
terconnecting the condenser with the ionization
Figure 1 is a circuit diagram of a device ar
ranged and connected according to the prior art.
Fig. 2 is a circuit diagram showing the ar
rangement and connection or a device according
to one embodiment of my invention.
10
Fig. 3 is a circuit arrangement showing a pre
chamber, a considerable and uncontrollably vary
ing leakage may occur.
This source of leakage can be eliminated by
an arrangement according to the invention as
ferred form of my invention, also showing die»
grammatically a device combining the ioniza
tion chamber and the electron relay in a single
unit.
15
Fig. 4 is a fractional and sectionized side view
of the combined ionization chamber and elec
tron relay.
~
Referring to Figure 1, there is provided an
ionization chamber I to which is connected in
20 parallel, through leads 60 and iii, a condenser 2.
The condenser 2 can be charged from a suitable
D. C. current source 3, a switch 4 being provided
in the negative branch 65 of the charging cir
cuit. A high vacuum triode 6, having an ln~
25 candescent cathode 5, a grid 8, and a plate I0,
is connected with its grid 8 to the negative elec
trode of the condenser 2 and to the negative
electrode 62 of ionization chamber i. The plate
circuit of tube 6 includes a suitable current
30 source 9, a device H to control the energlzation
of the X~ray tube, and a switch 1, to open or
close this circuit. The device H may for ex
ample consist of a magnetic relay, the coil of
which is connected in the plate circuit, and the
35 armature of which controls the primary circuit
of the high voltage transformer of the X-ray
tube. The circuits for such a control by device
ll, being obvious to one skilled in the art, have
been omitted for the sake of simplicity. The
same applies to the heating circuit of the oath
ode 5.
The negative electrode 62 of the ionization
chamber I, as stated, is connected with the grid
8 of the tube 6, whereas its positive electrode 63,
together with the positive side of source 3 and
of condenser 2, is connected at Bl to the plate
circuit or the tube 6.
Before taking the X-ray exposure the con
denser is charged to the proper voltage by clo
sure of the switch I. For taking the exposure
the cathode 5 is brought to its operating tem
perature and the switch 1 is closed, and after an
intermediate closure of switch 4 the latter is
opened simultaneously with the closure of the
55 main operating switch of the X-ray tube.
The grid 8, being initially negatively biased
with respect to the cathode 5, prevents altogether,
or at least to a great extent, a current flow
through the plate circuit of the tube, thus keep
ing the relay switch ll closed. As the X-ray
exposure progresses, ionization in the ionization
chamber, establishes a discharge circuit for con
denser 2 and the condenser gradually discharges
through this circuit.
05
This reduces the negative bias of grid 8 and in
creases the plate current, and after a given
time interval, which is predetermined by the
proper selection of the various factors involved,
and which corresponds to the desired blacken
70 ing of the photographic ?lm, the grid bias as~
sumes a value which allows a su?lciently high
plate current to pass through the coil of relay
Ii to cause the relay to open the operating cir
cuit of the X-ray tube, thereby terminating the
75 exposure.
shown in Fig. 2.
Referring to Fig. 2 the changes, compared to
Figure 1, include two steps: The first step com
prises the elirnination of the connection between
the grid and the charging source.
The con
denser 2, indicated in dotted lines, instead of be
ing charged directly, is charged through the 15
electron tube 6. A. two-position switch [2 is
provided instead of the two switches 4 and ‘l.
The condenser 2 is charged ‘through the following
circuit: Positive terminal of source 3, condenser
2, grid 8, cathode 5, switch l2, contact 40, back 20
to the negative terminal of source 3.
The heat
ing circuit of the cathode (not shown) being
closed and the grid being positive with regard
to the cathode, a current of sufiicient magnitude
flows through the plate circuit to keep the relay 25
H open.
When taking the exposure the switch i2 is
moved into its right-hand position to engage
contact 4|. This connects the cathode 5 to the
positive side of ‘the condenser 2, which renders
the grid negatively biased in respect to the oath
ode 5. This in turn cuts off the plate current
and deenergizes relay H, thus closing the op
erating circuit of the X~ray tube. During the
exposure, the ionization chamber becoming con
ductive, the condenser 2 is gradually discharged
and the potential of grid 8 becomes less nega
tive in respect to the cathode 5, until ?nally the
plate current becomes sufficiently large to actu
ate the relay and interrupt the exposure.
40
The second step to improve the arrangement
consists in the omission of the condenser by using
a properly designed ionization chamber as the
condenser. For this purpose the two electrodes
62 and 63 of the ionization chamber are given 45
su?icient area and they charge up and discharge
in the same manner as has been just described
for condenser 2.
'
By omitting the condenser and its correspond
ing leads, further sources of leakage are removed, 50
and at the same time the device is greatly sim
pli?ed. The greatly reduced leakage also makes
it possible to use much smaller capacities, there
by increasing the sensitiveness and accuracy of
the device.
55
In Fig. 3 the ionization chamber 13 and the
electron relay I4 are connected into a single
unit having, if desired, a common envelope. The
envelopes of these devices consist as a. rule of
vitreous material, and are interconnected by a
short tube [5 of insulating material, preferably
of vitreous material fused to the envelopes oi’
devices l3 and H.
The electrode I‘! of the ionization chamber and
the grid l8 of the vacuum tube are interconnect
ed by the connection I6 which is made as short
as possible and is perfectly air-tightly sealed in
the connecting tube l5. In this arrangement
a common current source is assumed for the
charging of the condenser and for the plate
current of the tube M.
70
This source supplies rec
tified and smoothed current from the ordinary
alternating current network 56. The primary
winding of a transformer 51 is connected to the
network and its secondary winding i9 is in se
75
2,122,222
ries with a rectifier 20. The recti?ed current so
obtained is smoothed by suitable ?ltering means,
for instance by a condenser 38 connected across
the series arrangement of the recti?er 20 and the
winding 19.
Connected across the condenser 38 at 45 and
46 is a resistor 23 acting as a potentiometer, from
which the various desired potentials are tapped
off. The electrode 2| of the ionization chamber
10 I3 is connected to the positive end 45 .of there
sistor 23, and the electrode I1 is connected to
the grid 18 of the'electron relay M by means
of lead I6. The end 46 of the resistor 23 is con
nected to the contact 66 of switch l2, whereas
15 the contact 61 of the switch is connected to a.
tap 24 of the resistance comparatively close to
the negative end 45 of the resistor 23.
In this arrangement, the device for the control
of the X-ray tube is not placed directly in the
20 plate circuit of the electron tube I4, but is in
directly controlled thereby. For this purpose,
the cathode 22 of the electron tube, I4 is con“
nected to the heel 39 of the switch I2, whereas
its plate 21 is connected to one end 48 of a va
25 riable resistor 26, a portion of which can be
short-circuited by means of sliding contact 58.
The other end 4'? of resistance 26 is connected to
a tap 25 of the potentiometer 23, which tap is
positive with respect to tap 24, and is also con
30 nected to the cathode 28 of a gas=?lled tube 29,
the control electrode 30 of which is connected to
the end M} of resistance 26. Tube 29 is of the
type acting with an arc discharge and is not ig
nited until the control electrode has exceeded
de?nite potential.
A current source 3%, supplying an alternating
or pulsating voltage, is provided in the plate cir»
cult of the gas-?lled tube 29, which circuit also
includes the coil 32 of an electromagnetic relay.
40 The armature 3d of this relay controls the ener
gization of the X-ray tube ‘ill, for instance by
closing the primary circuit of the high tension.
transformer which supplies the operating voltage
for the X-ray tube and is energized from the
45 means 12.
The end 49 of resistance 26 is negative com
pared to the end 41, the potential difference
between the two depending on the voltage drop
in resistance 26 and thus on the value of the
50 plate current of tube l4. When a large current
?ows through the plate circuit of tube l4, the
voltage drop in resistance 26 is large and renders
the control electrode 30 negative with respect to
the cathode 28. When the plate current of
55 tube I4 drops below a given value, the control
electrode 30 sharply cuts off the current flow
through the plate circuit of tube 29, which causes
the dropping of armature 34.
To oppositely charge the electrodes of the
iii) ionization chamber 23, the switch I2 is brought
into its right-hand position to engage contact 66.
The cathode 22 is thereby rendered negative with
respect to the grid l8, and the electrodes ii and
2! are charged up through the following charg~
65
ing circuit. From the positive end 45 of resistor
23 through electrode 2|, electrode ll, connecting
lead it, grid 58, cathode 22, switch i2, contact 68
and negative end 45 of resistor 23.
The cathode 22 being negative with respect to
the grid ill, a su?iciently large plate current flows
through tube M as to cause a voltage drop in re
sistance 26, which provides a su?icient negative
bias on control electrode 38 as to prevent cur
rent ?ow through the plate circuit of tube 29,
3
thereby keeping the coil :2 deenerglzed and the
armature 34 open.
To take the exposure—the ionization chamber
electrodes having been previously charged. as
just explained-the switch I2 is moved to its left
hand position contacting with contact 61. This
renders the cathode 22 positive with respect to
the grid l5, and whereby the current flow through
the plate circuit of the tube I4 is interrupted or
at least greatly reduced. This, in turn, reduces 10
the voltage drop in the resistor 26 and the bias
of control electrode 30 becomes less negative
(falling below its cut-off value) and thus a cur
rent passes through the plate circuit of tube 29,
which energizes coil 32 and causes, by means of 15
armature 34, the closure of the operating circuit
of the X-ray tube, which starts the exposure.
As the exposure proceeds, the X-rays passing
through the object and the photographic plate
strike the ionization chamber ll, causing it to be
ionized, which results in a gradual equalization
of the charges on the electrodes i1 and 2‘.
Thereby, the grid l8 loses its negative potential
and the plate current through tube l4 gradually
increases until it reaches a value which causes, 25
in resistance 26, a voltage drop which is suf
iiciently large to cause control electrode 30 to as
sume a sufliciently negative bias to cut oil’ the
current flow through the plate circuit of tube 29,
and by means of the relay, to interrupt the ex 30
vposure.
The various factors are so selected and ad~
justed as to cause this interruption to take place
at the instance when the exposure of the tube
has produced the desired blackening of the photo
graphic plate or ?lm.
Fig. 4 illustrates a construction in which the
ionization chamber l3 and the electron tube M
are rigidly interconnected to form a single unit,
the two being interconnected by means of a hol 40
low tube 35. The envelopes of chamber 13 and
tube M respectively, together with the tube 35,
may constitute a single vitreous body.
To lengthen the leakage path and to improve
the insulation, the ionization chamber is pro" 45
vided with a neck 68 of which tube 35 may form
an extension, and through which passes a re-en»
trant tubular portion 36 of considerable length.
The tube 36 supports and is partly surrounded
by a hood-shaped inner electrode l1 formed of 50
foil, whereas the electrode 2i which is arranged
substantially parallel to the chamber envelope
is made of thin sheet metal, although it may be
formed of a foil coating of the wall or a metal
deposit thereon. The electrode 2| is supported 55
from the envelope of chamber l3 by a wire 63
which also serves as a lead thereto.
A portion
of the envelope and the tube 36 form a very long
leakage path between electrodes I‘! and 2!,
which path is also interrupted by a metal ring 37.
Great care must be taken that the lead between
the electrode i‘! of the ionization chamber and
the grid E8 of the electron tube has a very high
insulation so as to minimize all loss of elec
tric charge. Therefore, the lead 55-55' is sup 65
ported only at its two ends at 53 and 54. The
lead 55—55' may form a single lead or may be
separate leads interconnected at ‘l6. As a rule, I
prefer to manufacture the ionization chamber
and the electron tube separately and thereafter 70
interconnect them by fusing the tube 35 to the
respective envelopes of the ionization chamber l3
and the discharge tube H4.
The tube 35 is preferably sealed from both the
ionization chamber I3 and the relay tube I4, 75
2,122,922
and is exhausted. However, the space within
tube Il may also be interconnected with either
the ionization chamber II or with the relay tube
ll. In the latter case, of course, the tube can
not be exhausted before the two are iused to
gether.
When the device is in operation, the metal ring
ll may be connected to a negative potential, for
_ instance, to the end 46 of resistance 23 (Fig. 3).
10 whereby the leakage set up between the grid i8
and the ring 31 compensates for the loss of nega~
tive charge towards the cathode. The charge
?rst lost by the leakage flow between the grid
and the cathode is afterwards, when the grid
15 potential increases, regained by the leakage ilow
between the ring 31 and the grid. The ring 31
also prevents the condenser from being dis
charged along the wall of the ionization chamber.
While I have described my invention with re
20 spect to a specific application and have illus
trated specific embodiments thereof, I do not
wish to be limited thereto, but desire the append
ed claims to be construed as broadly as permissi~
ble in view of the prior art.
What I claim is:— '
1. A device for automatically determining the
duration of irradiation, comprising a vacuum
discharge tube having a cathode, a plate and a
grid, said grid being adapted to control the plate
current 01’ the tube, switching means controlled
by the plate current of said tube to initiate and
terminate said irradiation, an ionization chamber
having a wall adapted to be subjected to said
irradiation and comprising at least two electrodes,
one of said electrodes being connected to said,
duration of irradiation comprising a vacuum dis
charge tube having a cathode, an incandesclble
plate and a grid, said grid being adapted to con
trol the plate current or the tube, switching means
controlled “by the plate current of said tube to
initiate and terminate said irradiation, a source
of direct current having a positive connection
point and at least two negative connection points
of di?erent potential, an ionization chamber hav
ing a wall adapted to be subjected to said
irradiation and comprising two electrodes, one
chamber-electrode being connected to said grid
and the other chamber-electrode being connected
to the positive connection point, and a change
over device to connect at will the cathode to 15
either one of said two negative connection points.
4. A device for automatically determining the
duration of irradiation comprising a vacuum dis
charge tube having a cathode, a plate and a
grid, switching means controlled by the plate 20
current of said tube to initiate and to terminate
said irradiation, an ionization chamber having a
wall adapted to be subjected to said irradiation
and comprising two electrodes, a lead connecting
one of said chamber-electrodes to said grid. a 25
member connecting said ionization chamber with
said discharge tube and air~tightly surrounding
Said lead, and means including a source oi direct
current to establish a potential difference be
tween the cathode and the other chamber elec 30
trode whereby the cathode is negative with re—
spect to said latter electrode and to establish a
predetermined reduction of said potential dii
ierence.
5. A device for automatically determining the 35
grid, 0. source of direct current, a circuit includ
duration of irradiation comprising a vacuum dis
ing said source, said chamber, grid and cathode,
ative charge to that chamber-electrode which is
chargetube having a cathode, a plate and a grid,
switching means controlled by the plate current
of said tube to initiate and to terminate said
connected to the grid, means including a con
irradiation, an ionization chamber having a wall
. said source supplying through the cathode a neg
denser connected in parallel with said ionization
chamber to provide for a greater negative charge
adapted to be subjected to said irradiation and
comprising two electrodes, a lead interconnect
on said electrode, and means co-operating with ' ing one oi said chamber electrodes and said grid,
said circuit to establish a predetermined decrease an insulating tube connecting said discharge tube
of the potential di?erence between the cathode and said chamber, said insulating tube being ex
and the other chamber-electrode, said negatively hau'sted and air-tightly enclosing said lead, and
charged electrode discharging through the ioni
means including a source of direct current to
zation chamber during a time interval which de
termines the duration of said irradiation.
establish a potential difference between the cath
ode and the other electrode whereby the cathode
is negative with respect to said latter electrode
and to‘establish a predetermined reduction oi’
said potential difference.
6. An X-ray responsive ionization device com
prising a sealed envelope having an insulating
portion forming an electrode chamber, an insu
lating neck portion having a considerably smaller
cross-sectional area than that of said chamber,
and an insulating re-entrant portion connected
to said neck‘portion and extending into said
electrode chamber, a gaseous ?lling within said
envelope and ionizable by X-rays, an electrode
within said chamber and supported from said
re-entrant portion, a second electrode within said
chamber and surrounding said first electrode in
spaced relationship and supported from a point 65
on one 01’ the other of said insulating portions,
and a member of conductive material forming
part of said neck portion and intercepting the
leakage path over the envelope between said point
and said re-entrant portion.
70
7. A device for automatically determining the
duration of irradiation, comprising a vacuum dis
charge tube having an incandesclble cathode, a
plate, and a grid to control the plate current of
the tube, switching means controlled by the
2. A device for automatically determining the‘
duration of irradiation, comprising a vacuum dis
charge tube having an incandesclble cathode, a
plate and a grid, said grid being adapted to con-‘
trol the plate current of the tube, switching
means controlled by the plate current of said
tube to initiate and terminate said irradiation,
an ionization chamber having a wall adapted to
be subjected to said irradiation and comprising
at least, two electrodes, one of said electrodes be
ing connected to said grid, a source of direct cur
rent, a circuit including said source, said ioniza
tion chamber, grid and cathode, said source sup
plying through the cathode a negative charge to
the grid-connected chamber-electrode, a plate
circuit including said discharge tube, said switch
ing means and at least a portion of said source,
and means associated with said ?rst circuit to
establish a predetermined decrease oi’ the poten
tial difference between the cathode and the
70 chamber-electrode which is not connected to the
grid, the negative charge of said grid-connected
electrode discharging through the ionization
chamber during a time interval which determines
the duration of the irradiation.
3. A device for automatically determining the
2,122,222
plate current of said tube to‘ initiate and to ter
minate the irradiation, an ionization chamber
adapted to be subjected to the irradiation and
comprising an electrode connected to said grid,
and a second electrode, a circuit connecting said
electrodes and including a direct current source,
said grid, and said cathode, said source being
connected between said cathode and said sec
ond electrode to supply through said tube a nega
5
tive charge to said grid-connected electrode, and
means associated with said source to establish a
predetermined decrease in the potential differ
ence between said cathode and said second elec
trode, the negative charge of said grid-connected 5
electrode discharging through said chamber dur
ing a time interval which determines the dura
tion of the irradiation.
ANTONIUS WILHELMUS VINGERHOETS.
CERTIFICATE OF CORRECTION.
June 28, 1958.
Patent‘ No. 2,122,222.
ANTONIUS WILHELMUS VINGERHOETS.
It is hereby certified that error appears in the printed specification
of the above numbered patent requiring correction as follows: Page 14., second
column, line 2, claim}, for the‘ words "a cathode, an incandescible" read
an incandescible cathode, a; ‘and that the said Letters Patent should be
read with this correction thereinvthat the same may conform to the record
of the case in the Patent “Office.
Signed and sealed this lrth day' of October, A. D. 1958.
Henry Van Arsdale
(Seal)
Acting, Gonnnissioner of Patents.
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