0'
.
United States Patent 1191
[111
Loy
1451 Mar. 27, 1973
[54]
APPARATUS FOR REMOTELY
2,848,626
8/1958
DISPLAYING TEMPERATURE
2,963,910
12/ 1960
DIFFERENCES OF AN OBJECT
2,879,424
3/1959
7
_
[75] Inventor: Fernand Rene Loy, cholsyde-rol,
3,264,931
3,333,656
8/1966
8/1967
3,722,282
Brackmann ................... ..73/3s5 R x
Astheimer . . . . . . . . . .
Ackermann et
....73/355 R X
Astheimer ................... ..350/16»1X
France
‘
. . . . . . ..73/355 R
Garbuny et a1. .............. ..73/355 R X
I
[73] Assignee: U.S. Philips Corporation, New
York, N.Y_
Prima'y Exami'w"_L°ui5 R- Prince
Assistant Examiner-Frederick Shoon
[22] Filed:
A"°'"ey_Fra“k R‘ Tnfa“
061. 22, 1970
[21] Appl. No.: 83,104
[57]
[30]
ferences of an object in which a modulator device is
‘
'
[52]
[51]
[58]
An analyzing device for displaying temperature-dif
Foreign Application Priority Data
Sept 26 ‘969
’
France
ABSTRACT
6932987
""""""""""""""""" "
us. 01 .................. ..73/3s5 R, 350/161 356/45
’ 356/46’
Int. Cl ............................. ..G01j 5/62, G02f 1/34
Field of Search .... ..73/355 R, 355 EM; 350/161;
inclined at an angle to the principal axis of the analyz
ing device and alternately transmits the rays which
emanate from a P0int °f the Scene to be analyzed and
a reference beam which indicates the mean tempera
""6 of the Smd Scene
356/45, 46
[56]
References Cited
, UNITED STATES PATENTS
3,611,806
10/1971
l-lishikari .......................... ..73/355 R
2 Claims, 4 Drawing Figures
v3,722,282
‘ PATENTEUM/mmn
SHEET 10F 2
INVENTOR.
BY
FERNAND
RENE LOY
PATENTEDMARUIQB
3,722,282
SHEET 2 [IF 2
INVENTOR.
BY
FERNAND RENE LOY
AGENT
/
,
1
3,722,282
2
APPARATUS FOR REMOTELY DISPLAYING
TEMPERATURE DIFFERENCES OF AN OBJECT
FIG. 2 shows schematically a modi?cation of the
beam switching means.
In the Figures, elements which correspond to those
shown in FIG. 1 of the main application are designated
by like reference numerals.
In the device shown in FIG. 1 a parallel infrared
The present invention relates to an analyzing device
for an apparatus for remotely displaying temperature
differences of an object comprising a converging opti
cal system and a centrally apertured oscillating plane
radiation beam emitted from a point of the scene to be
analyzed enters through a port or window 8 to strike a
mirror which is arranged at an angle to the principal
axis of the optical system between this system and its
focus, which device further comprises a modulator
which modulates the radiation emanating from the ob
re?ecting mirror 1. A plane oscillating mirror 2
receives the rays re?ected by the mirror 1 and re?ects
them to a stationary concave spherical mirror 3. The
axis of the mirror 3 coincides with the optical axis XIXZ
of the analyzing device. After re?ection at the mirror 3,
French Pat. speci?cation No. 1,600,930.
the
beam passes through an aperture 20 provided cen
The apparatus for remotely displaying temperature
trally of the oscillating mirror 2 and then converges at
differences of an article, hereinafter for brevity to be
F, the focus of the mirror 3.
referred to as thermal viewing apparatus, according to
A modulator disc 4 is arranged at F at an angle of (in
the aforesaid French patent is provided with an analyz
the embodiment under consideration) 45° to the prin
ing device which by opticalmechanical means and with
the aid of detectors sensitive to infrared radiation scans 20 cipal axis XIXZ‘. This disc is rotated by a motor M. The
disc comprises radial areas which are alternately
the object, and with a display device containing elec
troluminescent diodes.
re?ecting and transmitting. When a transmitting area
In order to prevent the occurrence of very-low
of the modulator disc 4 transmits the beam emanating
frequency noise due to the cooling systems of the de
from the scene to be analyzed, a detector 7 measures
tectors in the known analyzing device, the received 25 the temperature of an elemental point of the scene
ject.
The present invention is an improvement over
beam of radiation is modulated so as to operate in the
viewed in the elemental ?eld (01. When a re?ecting area
frequency range between 20 kHz and 40 kHz (for an
of the modulator disc intercepts the beam emanating
InSb detector).
In the apparatus described in the French patent this
from the scene, a reference beam which enters through
modulation is obtained by means of a rotating disc 30
detector 7.
which is arranged at right angles to the optical axis of
the analyzing device and contains alternate re?ecting
and transmitting areas. When a re?ecting portion of the
disc screens the beam emanating from the scene to be
the port 8’ and passes through an objective 9 strikes the
i
The spherical mirror 3, having a surface ares S1 and
the detector 7 determine an elemental ?eld ml; the
geometrical dimensions 81ml are equal to the geometri
cal dimensions S20), of the objective 9, the area S2 being
displayed, the detector delivers a signal which is pro 35 smaller than S1 and the ?eld 002 being greater than 001.
portional to the temperature t of the detector. When a
The ?eld m2 is determined by the objective 9 and by the
transmitting portion of the modulator disc transmits the
detector 7.
beam emanating from the scene to be displayed, the de
Under these conditions, the flux received in the ?eld
tector delivers a signal which is proportional to the
w, and that received in the ?eld (02 are equal when the
temperature T of the scene. Thus, the signal delivered
temperature of the scene is equal in both ?elds.
by the detector is proportional (T- t), where (T- t) is
The ?eld m2 is ?xed: hence the ?ux received in this
large compared with the small temperature differences
?eld is constant and has the mean value of the scene,
A Tto be detected in the scene to be displayed.
corresponding
to the mean temperature t of the scene.
The present invention provides a device which does
not suffer from this disadvantage and in which the 45 The elemental ?eld m1 is variable, it analyses the scene
mean temperature of the scene itself and not the tem
dot by dot: hence the ?ux received in this ?eld is varia
perature of the detector is used as the reference tem
ble and corresponds to temperatures t + A t of the
perature t. As a result, (T — t) is of the same order of
scene.
The Figure also illustrates a modi?cation of the
In the device according to the invention the central 50 analyzing device which has been made possible by the
arrangement of the modulation disc at an angle to the
axis of the modulator is inclined at an angle to the prin
magnitude as is A T.
cipal axis of the optical system, the disposition of the
modulator relative to the object being such that the
modulator alternately transmits the radiation which
axis XlXZ.
If a second detector 7 ’ is disposed above the modula
tor disc 4 in the axis of the reference beam, this detec
emanates from the object and a reference radiation 55 tor 7' will receive the analyzing beam when the detec
tor 7 receives the reference beam and vice versa.
which indicates the mean temperature of the object.
By choosing suitable detectors 7 and 7 ’, forexample
This arrangement permits obtaining an interesting
modi?cation of the analyzing device so that it includes
by using a InSb - detector 7 operating at a wavelength
two detectors each of which operate in a different
of 4 uum and a I-IgCdTe detector 7’ operating at a
wavelength range and which alternately receive the 60 wave length of 10 gum, and by inserting in the path of‘
analyzing beam and the reference beam.
the beam which strikes the detector 7 a ?lter f which
Embodiments of the invention will now be described,
transmits radiation having a wavelength between 3
by way of example, with reference to the accompany
“um and 5 gum and by inserting in the path of the
ing diagrammatic drawings, in which:
beam which strikes the detector 7 ' a ?lter j’ which
FIG. 1 shows schematically the analyzing device of a 65 transmits radiation having a wavelength between 8
thermal remote viewing apparatus according to the in
gum and 14 #um a thermal remote viewing apparatus
vention, and
is obtainable which provides a two-color display.
3
3,722,282
4
In FIG. 1, the optical axis of the reference beam is
parallel to that of the analyzing beam. This arrange
ment enables the system to be automatically adjusted
between the two prisms is small (zit/l0) the beam FS
will be transmitted by both prisms without being
deviatedv and emerges from the assembly in the
to the mean temperature of the scene. However, the
direction B, whereas the beam FR emerges in the
device‘ according to the invention need not necessarily
have this arrangement. Alternatively, the reference
direction A after being re?ected in both prisms.
What isclaimed is:
1. Analyzing device for an apparatus for remotely
beam may emanate from a body of known temperature,
in which case the system allows an absolute measure
ment of the temperatures of the scene relative to the
displaying temperature optical di?erences of an object
comprising a converging optical system and a centrally
reference temperature.
apertured oscillating plane mirror which is arranged at
In another modi?cation, the beam may be switched
by other means than those described with reference to
an angle to the principal axis of the optical system
between said optical system and the focus thereof, said
FIG. 1, for example a total-re?ection prism (FIG. 2).
device further comprising a modulator which modu
It is known that if the gap e between the hypotenuse
lates the thermal radiation emanating from small ele
faces of the two total-re?ection prisms P and P’ is 15 ments of the object through said optical system, means
greater than the wavelength of the radiation, rays 1‘ and
responsive to a larger ?eld than said optical system to
i’ will experience total re?ection (FIG. 2a).
obtain reference radiation representative of the mean
If on the other hand the gap e is of the order of )t/ 10,
temperature, and ?rst and second detectors each
the rays i and i’ will be almost completely transmitted
responsive to radiation of different wave-lengths, said
by the two prisms which then behave as plates having
modulator having a central axis which is inclined at an
parallel faces (FIG. 2b).
angle to the principal axis of the optical system, said
modulator being disposed relative to the object to
Relative displacement of the prisms in order to
transmit the radiation emanating from the object to the
change e may be obtained, for example, by means of
piezoelectric elements.
first detector and said reference radiation to the second
FIG. 20 is a sectional view of two total re?ection 25 detector to indicate the mean temperature.
2. A device as claimed in Claim 1 characterized in
prisms made of germanium, which material transmits
that the modulator includes means for directing the
radiation emanating from the object and the reference
When the gap e between the two prisms P1 and P’1 is
radiation to the respective detectors comprising an as
large, the beam emanating from a scene FS will ex
perience two total re?ections in the prism P1 and will 30 sembly of two adjacent total-re?ection prisms, and
means to periodically ‘vary the spacing between the op
emerge from the assembly in a direction A; a reference
posed faces of the prisms.
beam FR experiences two total re?ections in the prism
*
*
*
*
ii‘
P’1 and emerges in a direction B. When the gap e
infrared radiation (re?ective index n#).
35
40
45
50
55
65