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Патент USA US2861233

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Nov. 18, 1958
Filed March 28, 1957
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Patented Nov. 18, 1958
When light is received by the cathode the amount of
current generated by the incidence of light on it is sensed
by a resistor 17. The resistor is temperature stable and
the voltage across it is compared to a secondary standard,
the difference ampli?ed by an ampli?er arrangement 18,
Edwin’ El. Smura, Apalaehin, N. Y., assignor to Inter
national Business Machines Corporation, New York,
which will be described, and fed to a suitable control
N. Y., a corporation of N ew York
Application March 28, 1957, Serial N 0. 649,219
winding of the lamp supply to control the light. Con
trolling the light controls the cathode current and thus
controls the intensity on the cathode ray tube screen by
10 controlling the electron density. This system is self com
pensating for aging of the light source, dust on the optics
and aging of the photocathode.
5 Claims. (Cl. 315-11)
As was previously stated an important feature of the
present invention is the provision of means for indicating
This invention relates to cathode ray tubes in general 15 that the light source has deteriorated to the point where
and in particular to an arrangement for controlling the
controlling of the beam intensity is no longer practical.
intensity of the electron beam in accordance with the
For this purpose, the output of ampli?er 18 is fed to a
amount of light received by the photoemissive cathode.
signal latch circuit 19 which will be described in detail
As is well known, the ?eld of high speed printing now
embraces the use of an electron-image tube for selecting
Referring to Fig. 2, there may be seen the detail cir
and displaying characters in‘ a luminous form, which may
cuitry for the ampli?er 18, signal latch 19 ‘and the lamp
then be photographically recorded. Such a tube usually
supply 11. When a drop in light occurs at the photo,
employs a font consisting of a chart of characters which
cathode due to any of the aforementioned reasons a fall
is projected onto a photoemissive cathode. Selections
off in current will take place at the cathode and a reduc
are made from the resulting electron-image stream and 25 tion of voltage will occur across the sensing resistor 17.
directed to the desired position on a phosphor screen.
The voltage drop across the resistor will cause a reduction
It can be readily understood that in such a printing opera
of cathode current in section “A” of a twin triode T
- tion it is important to maintain an electron stream of
resulting in a rise in potential at plate 20 and a drop in
constant intensity in order to obtain consistent images on
potential across the cathode resistor 21 of tube T. With
the screen and to accomplish this it becomes necessary 30 the grid of section “B” of the tube tied to a battery C
to compensate for such things as aging of the light source,
of constant potential the grid to cathode potential at point
dust on optical components and aging of the photoemis
sive cathode itself. Any of these factors will vary the
density of the beam current resulting in a change in the
initial velocity of the beam electrons which causes the 35
image characters to rotate.
22 will rise causing an increase of cathode ‘current in tube.
section “B” and consequently a drop in potential at the
plate 23.
The ?rst stage or tube T, then, acts as a differential
ampli?er since it compares the voltage drop across the
resistor 17 with the ?xed grid bias C and ampli?es the
Accordingly, an object of the present invention is to
provide an arrangement for controlling the intensity of
difference. In addition it also functions as a phase splitter
an electron beam is accordance with the amount of light
since a push-pull output from a single input signal is
40 obtained.
received by the beam generating means.
A further object of the present invention is to provide
The potential rise at plate 20 is fed to the control grid
a cathode ray tube having a photoemissive cathode for
24 of a pentode T1 and the potential drop at plate 23 is
generating an electron beam with ampli?er circuit means
fed to the control grid 25 of a second pentode T2. Pen~
todes T1 and T2 have their cathodes tied together to a
of the beam in accordance with the amount of light 45 resistor 26 and form a common D. C. differential ampli?er
under control of said cathode for controlling the intensity
received by the cathode.
which is noted for its stability under supply voltage
A still further object of the present invention is to
provide a cathode ray tube as in the preceding object and
The increase in potential on the control grid 24 causes
including signal means conditioned by said ampli?er cir
the potential at plate 27 to fall because of the increased
cuit means for indicating that controlling the intensity of 50 current in tube T1. The cathode potential of tube T1
the beam is no longer practical due to deterioration of the
tends to increase with the grid potential but is nulli?ed
light source.
by the drop of potential at the grid 25 of tube T2 which
Other objects of the invention will be pointed out in
tends 'to lower the cathode potential. I The increase of
the following description and claims and illustrated in
current in tube T1 is fed through a control windin'gi‘28 ’
the accompanying drawings, which disclose, by way of 55 to increase the voltage to theilamp and restore the illu
examples, the principle of the invention and the best
mination to its original value. The illumination will not
mode, which has been contemplated, of applying that
reach its original value unless the loop gain of the system
is in?nity, but for all practical purposes the loop gain is
In the drawing:
high enough to cause the illumination to return to its
Fig. l is a block diagram showing the general arrange 60 original value minus a small almost immeasurable amount.
ment of the system embodying the invention.
The resistor 29 across the control winding acts as a‘
Fig. 2 is a circuit diagram of the ampli?er, signal latch
damping element to suppress system oscillations. A po
and lamp supply.
tentiometer P is also provided in the circuit to allow for:
adjustment of the lamp intensity.
Referring to Fig. l, the system comprises a lamp 1i}
and a suitable lamp supply 11 therefor, along with a con 65
As shown within the dotted section identi?ed as 11
densing lens 12 and projection lens 13 for directing light
on Fig. 2; the lamp supply includes a reactor which com?
from the lamp through a letter chart matrix 14 and onto
prises the control winding 28 for the ampli?er output,
the photoemissive cathode 15 of a cathode ray tube 16.
a laminated iron core 30 and a winding 31 one end of
The letter chart is projected steadily on the photocathode
which is connected to one of the alternating current
to produce the compound electron stream from which 70 input lines 32 through a switch S. A full wave bridge
selections are made for projection on the screen of the
recti?er R is shown with its input terminals connected
to the alternating current input line 33 and to the
other end of the winding 31. The direct current termi
erated by said latch circuit for indicating near end of
nals of' the recti?er are taken to the lamp 34 and hence
life of said light source.
it can be understood that an increase in current through
the control winding 28 will result in an'increase in di
' ‘
2. In a system for controlling light intensity, a light,
source, a light source supply, a photosensitive element‘,
recticurrent. Voltage supplied’ to the lamp to increase-its 01 for receiving light from said light source, said element‘ -.
intensity. Conversely, of course, a decrease in current
generating a current proportional to the amount of light’, E
through vthe control winding will result in a decrease in
the voltage supplied-to the lamp' to decrease ‘its intensity.
The detailstof the signal latch circuit for indicating a
near‘ end of life condition of theilamp are shown within
the dotted section identi?ed as 19 on Fig. 2. It will be
remembered'that as the photocathode current drops due
to adecrease-in-light from the lamp, tube T1 increases
in: conduction. and simultaneously the voltage at grid 25
is decreased resulting in decreasing conduction of'tube'
T2. Accordingly, _-the voltage at plate 35 of tube T2
increases and t-hisvuincrease 'in voltage is fed through a
received, means for sensing ‘said current and obtaining,"
two push-pull ‘signal voltages, means for amplifying said
to, included
one of said
in said
source sup-5'
controlling said supply to maintain the intensity of the 1' :
light source constant, a latch circuit operated by a pre-
determined ‘value of said other signal voltage, and sig
nal means operated by said latch circuit for indicatingfl "
near end of life of'saidlight'sdurce.
3. In a system for controlling light intensity, a light'f»;
source, a light source supply, a photosensitive elementt
diode. 36 'to the grid of va triode T3 in the latch circuit.
for receiving light from said light source, said element,v ;
The voltage at ‘the plate 37 goes down and this is re
generatinga aphase
circuit responsive
to the amount
to' theofoutpuf‘;
?ected on the grid of a‘ triode ‘tube T4 decreasing ‘the 20 received,
conduction’ of the tube. vThe resultant rise in voltage at
the plate 38 of tube T4 is fed to the grid of triode tube
of saidvoltages,
an ampli?er
in said
source sup-f1
of _ :5
T5 raising the cathode potential of tube T5 and this
risein cathode potential is fed back through wire 39
ply and responsive to the negative going signal voltage?
anddiode. 40 to the grid'of tube T3 to latch the circuit 25 from said ampli?er for controlling said supply to main '
in ‘its present state. >
tainv the intensity of the light source constant, a latch.
,It will be noted that the plate 38 of tube T4 is also
circuit responsive to a predetermined value of the pos‘
tied to a neon tube 41 which will be turned on upon
tive going signal voltage from said ampli?er, and signal
the occurrence of a predetermined rise in voltage at plate
means operated by said latch circuit for indicating near '
38 to-signal that the lamp is near end of life and that
end of life of said light source.
further. intensity regulation of the cathode ray ‘beam
4. In‘ a system for controlling light intensity, a ligh ’
is no longer practical. The neon signal will remain‘ on
source, a light source supply, a photosensitive elementfor i
until the circuit is reset by feeding a suitable reset pulse
receiving light from said light source, said element gen
through a diode 42 to the grid of tube T4 raising the
erating a current proportional to the amount of light rear
potential of the grid and decreasing the voltage on the
ceived,.m'eans for establishing a, voltage drop when said‘
plate 38» suf?ciently tov extinguish the neon tube. The
current output decreases due to a drop in light, mean
decrease in voltage at plate 38 is also reflected’ as'a
responsive ‘to said voltage drop for producing two signal
decrease in voltage at the grid and cathode of tube T5
and back to the grid of tube T3 thus, raising the voltage
of opposite
and responsive
polarity, means
anto ampli?er
in going
for light,E
am‘sig- 7,‘;
at the plate '37 and ‘resetting the latch circuit. Of course, 40
in asimilar manner, should the light increase the voltage
nal voltage from said ampli?er for controlling said sup-7
across resistor 11 will increase and the circuit will func
ply to increase the intensity of the light source, a latch ,
tion to send less current through the control winding
circuit responsive to a predetermined value of the posi :?
28- causing the lamp supply to decrease. In this case,
tive going signal voltage from said ampli?er, and signal? 1‘
the latch circuit will not be operated since the potential
at plate 35 of T2 drops.
It. will. be understood that the above system is not
means operated by said latch-circuit for ‘indicating near
limited to use with cathode ray tubes but can also be
cathodeiray tube, a light‘ source, a light source supply, a _l_
producing --aforcathode
ray ‘beam
light from
which said
is proportional
light source
the amount ‘of lightii‘e'ceived, said photocathode also gen
erating acurre‘nt which is proportional to the amount 0
light received, means for sensing the current output of
applied to, other ?elds usingphotocells as pick up devices‘
and monitoring face current. Uses of the present system‘
may: also extend into the ?elds of photography and
While therehave been shown and described and point
e'd out the fundamental novel features of the invention
as applied to a single modi?cation, it will be' under: '
stoodjthat various omissions and substitutions and changes
in‘the' form and ‘details of the device illustrated and in
its operation ‘may bemade by those skilled in the art. '
end of life of said light source.
5. In a-system‘fo'r ‘controlling the beam intensity of a_ ‘
said photocathode, means responsive to said sensing "
means for producing two signal voltages of opposite-polar’
ity, means for amplifying said signal voltages, mean
included in said lightsource supply and responsive to, one,
of said signal voltages for controlling the intensity"T011:I
without departing from the spirit of the invention. It is
60 the light source, a latch circuit responsive to a prede
the intention, therefore, to be limited only as indicated
termined value of the other signal'voltage, and’ signa
by theéiscope I of‘ the following. claims.
means operated by said latch circuit for indicating near
,Wh'atr' is claimed is:
> end of life of said light source.
. 1;v In a- system. for controlling light intensity, ‘a light:
source, alight source supply, a photosensitive element for
receivinglight from said light source, an ampli?er circuit
References Cited in the ?le of this patent
responsive to the intensity of light received by said‘ele
ment, means under control of said ampli?er circuit for
controllingi'said supply to maintain the intensity of the
light'source constant, a latch‘circuit operated by aipre
determinedl'output of said ampli?er, and signal means op 70
Ellis _____________ __i_§__ Ian. 29, 1957']
Great Britain _____.___.__ Dee-s, i9s4~~
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