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Патент USA US3030556

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April 17, 1962
R. c. OHLMANN ET AL
3,030,546
THERMAL IMAGE CONVERTER SYSTEM
Filed Deo. 23, 1957
6,485
A/r
`
United States Patent Üffice
1
3,030,546
3,030,546
Patented Apr, 17, 1962
2
vto modulate the ñying spot characteristics and thereby
control the photothermionic output
These and other objects, features and advantages of
`
THERMAL IMAGE CONVERTER SYSTEM
Robert C. Ühlmann, Albany, Calif., and Max Garbuny,
Pittsburgh, Pa., assignors, by mesne assignments, to
the invention will become more apparent from the follow
ing description taken in connection with the accompany
ing drawing illustrating a preferred embodiment of the in
the United States of America as represented by the
Secretary of the Air Force
y,
Filed Dec. 23, 1957, Ser. No. 704,843
vention wherein an infrared image 9 is focussed onto the
photoelectric screen 31 of photothermionic tube 10 by
reflector 16 forming a temperature image corresponding to
This invention refers to the conversion of thermal im 10 the temperature pattern of the observed scene. Auxil
ages to visible screen images and more particularly to
iary kinescope 12 produces a light beam which is focussed
such conversion with automatic compensation for vari
onto the photoelectric screen of tube 10 by directive lens
ations in the sensitivity of the photothermionic surfaces
system 15. The light beam or scanning spot is controlled
2 Claims. (Cl. 315-9)
by deiiection coil 14, electrically activated by scanning
or in other factors, such as the emission coeflicient of the
scanning phosphors.
15 circuit 28 which also activates dellection coil 13 of the
In image conversion systems of the type using a ther
mal image on a photoemitter and a light spot for scanning
the photoemitter surface, serious problems are encoun
receiving or viewing kinescope 11.
The master pulse generator 22 provides pulses` through
bias supply 21 to grid 19 of photothermionic tube 10,
tered in achieving faithful image reproduction. Some of
through line 30 and bias switch and level control 27 to
these problems are due to physical nonuniformities in the 20 grid 18 of auxiliary kinescope 12, and through switch cir
sensitivity of the photoemissive surface or the phosphors
cuit 24 to grid 17 of receiving kinescope 11.
producing the scanning spot or both. For example, the
scanning spot of light is generally obtained from a phos
Electrons are collected on collector electrode 20 of
photoelectric tube 10, fed to Wide Band Amplifier 23,
then through switch circuit 24, to amplitude comparison
phoresceut screen of a cathode ray tube and projected by
a lens system onto the photoemitter surfaceearrying the 25 circuit 25 and compared to standard level 26. The dif
thermal image. A variation of intensity of the scanning
ference between the fixed standard and the output of tube
light spot will result in a corresponding variation in elec
10 in ramplitude and polarity is fed to the grid 13 of
tron emission from the photoemitter. Since the thermal
scanning tube 12 through the bias switch and level con
image should be the sole electron emission controlling
trol 27.
factor, such Variations in scanning light spot intensity 30 The output of photoelectric tube 10 is amplified in
Wide Band Amplifier 23 and modulates viewing kinescope
produce undesired, erroneous, image reproducing electron
11 through switch circuit 24 and grid 17.
emission response. Similarly, variations in sensitivity of
Sensitive surface 31 is scanned with light of relatively
the photoemitter surface due to physical nonunlformities
cause corresponding erroneous electron emission responses
to the scanning light spot.
Heretofore it has been attempted to confine image re
producing, electron emission response to the thermally
induced variety by limiting the scanning phosphors to
those having the characteristic of emitting light rays of
relatively long wavelengths. The scanning light was con 40
ñned to long wavelengths in order to limit the liberation
of electrons of the photoemitter to those in the thermally
sensitive energy levels. Thus for a cesium antimony
short wavelength which causes photoemission of both ther
A grid 19 be
35 mally sensitive and insensitive electrons.
tween the sensitive -surface 31 `and the collector 20 has a
negative bias upon it suiiicient to prevent all but thermally
sensitive electrons from reaching the collector. How
ever, a positive pulse is applied to the grid at regular
intervals to remove the bias and allow thermally insensi
tive electrons to flow to the collector. The resulting im
age signal varies with the incremental sensitivity of the
infrared sensitive surface, and is used to derive a control
potential to compensate for such variations. Pulsing of
photoemitter surface, red phosphors have been used to
obtain a long Wavelength scanning spot. However, the 45 the retarding field allows discrimination between photo
electrons produced by infrared and the photoelectrons due
resulting long wavelength scanning light has an undesir
able slow response.
Pursuant to the present invention the `above problems
have been overcome by adoption of image converting
to the scan of the light beam. This allows correction
of the infrared induced photoelectrons for fluctuations in
the total emission caused by nonuniformities of either the
phosphor light source or the photoemissive surface. The
magnitude of the current due to the thermally insensitive
is scanned by a flying spot created by light rays of rela
electrons will depend upon the sensitivity of the surface
tively short wave-length, and wherein the resulting elec
at the position of the scanning spot at the time of the
tron emission from the photothermionic surface is utilized
pulse. This current pulse will then be made to control
in two dilîerent ways, namely: (a) that portion of the
emission which is thermally induced is carried to the 55 the thermally sensitive electron current during the next
receiving kinescope of the system by Way of the collecting
part of the cycle when the bias is present. This control
electrode of the photothermionic device and an amplilier
can be accomplished by any of a number of methods,
some of which are described below. A switch circuit
circuit, while (b) that portion of the emission which is
24 in series with the intensity control 17 of the receiving
thermally insensitive is periodically--that is, during se
lected time cycles-_prevented from reaching the collector
kinescope 11 allows the intensity to be modulated only
electrode by electrical restraining means in the form of a
by the thermally sensitive electron current which is then
independent of the non-uniformities of the sensitive sur
biasing voltage `applied to such emission; on the other
face or of the scanning phosphore.
hand, this non-thermal emission is, in alternate time cycles,
While there is novelty in the combination and inter
allowed to ñow to the collector electrode by the electri
cal operation of positively pulsing the biased grid to re 65 relationship of the components illustrated in the drawing,
and in the mode of operation of the system incorporated
move its flow-inhibiting bias and thus permit the non
therein, and their functional effect, each upon the others,
thermally induced electron flow. This pulse-induced non
many of said components are not novel, per se. Thus, for
thermal emission, being thus added to the normal ther
example, pulse generator 22 may be of conventional con
mally induced emission, combines therewith in an ampli
tude comparison circuit to produce a correction voltage 70 struction comparable to that of the pulse generator “72”
illustrated in the drawings of U.S. Patent No. 2,611,820
that is thereupon applied to the control grid of the iiying
issued to Frank I. Somerson, Sept. 23, 1952; similarly,
spot-creating cathode ray kinescope, where it is elîective
methods and means wherein the photothermionic surface
'3,030,546
3
4
switch circuit 24 may be of conventional construction,
for the decrease sensitivity of the photoemitter or the
comparable to that of any conventional “on-ofT’” electronic
switch that may be operative normally to pass electric
current from element 23 to element 25, but will be cut off,
scanning phosphors.
What is claimed is:
1. In combination, an image tube having an element
'periodically and momentarily, each time generator 22
transmits a pulse thereto. By the same token, amplitude
comparison circuit 25 may be any well-known type of
sensitive to photo and thermal stimulus, said tube also
having 'a control grid and an electron collector electrode;
`means for applying a thermal image to said sensitive ele
difference ampliñer-see, for example, the difference am
plifier illustrated> in UÃ.S. Patent No. 2,780,682 issued to
photo-response current ñow to said electrode; means cou
ment; >light means for scanning said element to produce
Gerrit Klein on Feb. 5, 1957; and standard voltage level 10 pled to said control grid for producing a biasing voltage
26 may be any conventional battery or current generator
discriminating against the non-thermally stimulated por
capable »of maintaining its current output at constant volt
age, for Vstandardization purposes. Likewise, switch 27
may be of any conventional coincidence tube construction,
tion of said photo-response current ñow; means coupled
to the biasing means -for periodically removing said bias
voltage; and means in response relation to the last-mem
with dual input grids, as described, for example, by 15 tioned Vmeans »for controlling the intensity of said light
means in accordance with the density of electron flow to
Terman in “Electronic and Radio Engineering” (4th edi
tion), at page 659, said text having been published by
said electron collector electrode.
_
2. A system as defined in claim 1, including kinescopic
-McGraW-Hill in 1955. Ampliñer 23 may be any `D.C.
means for visually displaying an illuminated image repre
amplifier, of which there are countless well-known vari
eties.
20 sentative of said thermal image, and wherein said light
means is constituted by auxiliary kinescopic means having
a control grid energized by a voltage representative of the
the intensity control 18’of the auxiliary kinescope 12 to
difference lbetween a preselected voltage level and a volt
reduce the intensity of the light spot. This is necessary
age derived from the output of said image tube, as taken
since the thermally insensitive electron current would be 25 01T said collector electrode.
much greater than the thermally sensitive current if this
With the application of a pulse to the grid 19, as above
described, there is a simultaneous pulse transmission to
were not done, which might make control of each diñicult
in the lsame circuitry. The magnitude of this current con
trols the intensity of scanning spot during the next period
of thermally sensitive current ñow. Thus if the surface 30
becomes less sensitive in a particular region, the thermally
insensitive current pulse will be smaller, which would de
crease the control grid voltage, and increase the beam
current in the auxiliary kinescope 12 and increase the
brightness of the scanning spot suñìciently to compensate 35
References Cife'dvin ‘the are of this parent
UNITED sTATEs PATENTS
2,188,679
Dov'a'ston et al. -__~_ ____ __'__ Jan. 30, v1940
2,611,820
Vall Mierlo
Somers
_____'_.;_"_.:_"__"_'_'_:..
_a _____ _'_f_'_-_ Sept. 23,
16, 1952
2,804,498
Theile _____'__-_-_ _'_____ Aug. 27, 1957
2,938,141
2,979,622
Garbuny et al. --.7_- ____ __ May A24, 1960
Garbuny _a __________ __ Apr. 11, 1961
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