Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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INFRARED LIGHT TRANSMISSION PATH
FIELD OF THE INVENTION
This invention relates to an infrared light trans-
mission path,
BACKGROUND OF THE INVENTION
Objects radiate infrared rays whose energy varies
with their temperature. The relation between the wavelength
for the peak of the magnitude of the radiation and the temper-
ature of the object is reprèsented by~formula ~1) that is
derived from Planck's law of radiation:
~m.T -~ K ................ (1
wherein ~m is the wavelength (~m)at which a maximum in~ensity '~ '
of light is radiated, T is the absolute temperature ~K) of
the object, and K is the constant (K = 2897 ~m.deg).
This formula indicates that the temperature of an object can
be known by detecting lts lnfrared spectrum.
A wide range of temperatures can be determined by
lnfrared light transmitting flbers made of a silver halide or
thallium halide crystal that transmlts light in the far "
infrared sp,ectrum of from 0.5 to 15 microns~ and which is easy
to produce polycrystalline fiber by~hot working. An,optical
temperature measurement generally involves the guiding of
light from a remote or inaccessible source to an infrared
spectrum detecting optical system by means of a lens, prism
or reflective mirror. This method
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requires much time in adjusting the optical axis precisely,
and to maintain the optical accuracy, the equipment must be
installed in a place where dust does not build up on the lens
or reflective mirror or where minimum vibrations occur.
A system is known that transmits light from the
source to the light detector over a desired path of quartz
glass fibers that are used as optical fibers for communicationO
The formula (1) indicates that the light radiated from an
object having a temperature of 773K ~500C) has a peak wave-
10 length at about 3.8 microns, and it shifts to a longer wavelength
if the temperature of the object is decreased. Therefore,
the system of using quartz glass is unsuitable for measuring
the temperature of cold objects; quartz glass has a great -- -
absorption loss at about ~.75 microns due to the vibration of
the lattice of Si-O bond and this affects the transmission of
infrared light.
SUMMARY OF THE INVENTION
Therefore, one object of this invention is to
eliminate these defects of the conventional technique and
provide an infrared light transmission path that transmits a
wide spectrum of light and hence can measure a wide range of
temperatures.
BRIEF DESCRIPTION OF THE DRAWINGS
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FIGS. 1 and 2 are illustrations of two ~ypes of
fibers that make up the infrared light transmission path of
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this invention;
FIGS. 3 and 4 are perspective views of the infrared
light transmission path of this invention according to two
different embodiments; and
FIG. 5 is a block diagram of a temperature measure-
ment system using the infrared light transmission path of
FIGS. 3 and ~.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 depicts a fiber having a circular cross
section produced by hot extrusion, and FIG. 2 depicts a fiber
having a rectangular cross section produced by hot rolling.
Either fiber is of step index type wherein the core ~1) has
a higher refractive index t.han the cladding ~2) to confine
light rays in the core. The fiber may be of graded index
type wherein the refractive index decreases from the center
outward. FIG. 3 illustrates an infrared light transmission
path comprising a bundle of fibers encased in a large-diameter
cylindrical plastic tube. In the figure, ~3) l5 an individual
fiber, ~4) is a primary coating, and ~5) is a secondary coat-
ing. FIG. 4 illustrates an infrared light transmission path
comprising a row of fibers encased in a flat plastic tube.
Each fiber is made of flexible silver halide or thallium halide
and is encased in an easily deformable plastic or rubber tube,
so the resulting infrared light transmission path is also
flexible. Each of the primary and secondary coatings serving
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as the flexible encasing may consist of t~o or more layers.
The infrared light transmission paths of FIGS. 3
and 4 are used in an optical temperature measuring system
as shown in the bloc~ diagram of FIG. 5, wherein (6) is an
object whose temperature is to be measured, (7) is an image
forming optical system (lens), ~8) is an infrared light
transmission path, and (9) is a temperature measuring unit
comprising a light detector and a signal processing section.
By using more fibers and collecting more light, a temperature
measuring system more sensitive than a single fiber can be
produced. By connecting the individual fibers to respective
light detectors, an image of temperaute distributlon, hence
an image of heat rays, can be measured. By connecting a
light detec~or to each of the fibers arranged in a row as in
FIG. 4, a system capable of detecting the position of an
object or detecting its movement according to a change in
time can be produced.
The halide of the silver halide crystal, a mixed
of the silver halide crystal, a mixed crystal of silver
halided, a thallium halide crystal or a mixed crystal of
thallium halide can be fluoride~, bromlde, chloride or iodide.
The fiber according to this invention is preferably composed
of the crystals having the same halide portion, but a mixed
crystal can be those having different halides. A preferred
silver halide is silver bromide or silver chloride.
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The proportion of these crystals is not critical
and can be any proportion in the fiber o-f this invention.
This invention is now described in greater detail
by reference to the follo~ing example which is given here for
illustrative purposes only and is by no means intended to
limit the scope of the invention.
Example
- A cylinder of ground silver bromide crystal was
. fitted into a hollow tube of ground silver chloride crystal
; 10 - to form an extrudable billet. The billet was hot extruded at
- - a temperature between 180C and 350C to form a fiber 0.5 to
1.0 mm in diameter made of a sllver bromide core and a silver
- chloride cladding. A hundred of these fibers were bundled into
a cylinder and covered with a primary coating of heat-shrinkable
, 15 tetrafluoride resin and a secondary coating of high-density
` polyethylene to thereby form an infrared light transmission
path about 1.5 cm in diameter. A length of about 40 cm of
the flexible infrared light transmission path was connected
- between the light source of a single-beam infrared spectroscope
and a light detector. A spectroscopic analysis with this
~ system gave a transmittance between about 60% and 70% in a
wavelength range of 1 to 15 microns, with the reflection loss
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at both ends of the transmission path measured. The system
could detect the light radiated from an object whose temperature
varied from about 3000K to about 2000K, so it was found to
be applicable to the measurement of temperatures.
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As described in the foregoing, the infrared light
transmission path of this invention uses fibers that is made
of silver halide or thallium halide that transmits infrared
rays, so it transmits a wide spectrum of light and can measure
a wide range of temperatures. The fibers are flexible, and
therefore a high degree of freedom is allowed for connecting
the transmission path between an object the temperature of
which is to be measured (a light source) and a detector (a
light detector~. A higher sensitivity can be obtained by
increasing the number of fibers to be encased so as to collect
more light. Another advantage is that an image of heat rays
can be produced by connecting detectors to the respective
fibers. The infrared light transmission path of this invention
is used with advantage in an o~tical temperature measuring
system, position detector, image forming device for temperature
distribution, etc.
While the invention has been described in detail
and with reference to specific embodiments thereof, it will be
apparent to one skilled in the art that various changes and
modifications can be made therein without departing from the
spirit and scope thereof.
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