Abstract: A pyrometric temperature measuring instrument including at least one optical wave guide (1a) with a core (5) and a cladding (6), a light detector (3) and at least one pyrometric sensor (2a). The at least one optical wave guide (1a) has a large numerical aperture. The pyrometric sensor (2a) is located at one end of the at least one optical wave guide (1a) and covers at least a cross-section of the core (5) of an optical wave guide (1a). In a preferred embodiment, the light detector (3) is an InGaAs photodiode. The optical wave guide (1a) has a numerical aperture of 0.3 or more, a diameter of the core (5) of approximately 100 .mu.m or more, and is surrounded by a light-tight cover (7).

Abstract: Several specific types of optical sensors capable of measuring temperature, pressure, force, acceleration, radiation and electrical fields, fluid level, vapor pressure, and the like, are disclosed, along with an electro-optical system for detecting the optical signal developed by the sensor. One such probe utilizes a convex shaped structure consisting of an elastomeric material attached to an end of an optical fiber, the elastomeric material being coated with a luminescent material, a combination that is capable of measuring both temperature and pressure. Such a probe is also specifically adapted for measuring surface temperature by making a good physical contact with the surface being measured. Another such probe utilizes a similar structure but of a non-elastomeric material for the purpose of detecting both temperature and either index of refraction or vapor pressure changes.

Abstract: A technique of measuring very high temperatures by positioning a blackbody sensor in thermal communication with an environment or object whose temperature is to be measured, communicating infrared emissions having an energy level proportional to such temperature from the sensor to an infrared absorber positioned a distance away from the sensor where the ambient temperature is significantly reduced, and then optically measuring the temperature of the absorber by a technique that uses visible or near visible optical radiation, such as one using a luminescent sensor. The measured temperature of the absorber is proportional to that of the blackbody sensor.

Abstract: Temperature measurement is effectively carried out by converting pulses derived from a pulse generator, in which the pulse gaps change as a result of a measured condition, for example temperature, by converting electrical pulses received from the pulse generator into light pulses, and then evaluating the light pulses with respect to a clock rate in a counter (22). The light pulses can readily be transmitted via a light pickup (9b) and fiber optic or the like (9a) to a remote evaluation unit. Preferably, the light is generated by a light emitting diode or a laser diode (8'), serially connected with a switching transistor (13') and energized upon receipt of a pulse from the pulse generator. The arrangement permits use of a piezoelectric element (2) such as a frequency determining quartz to control the frequency of an oscillator, the frequency of which is then converted into the pulses with the respective pulse gaps.

Abstract: A system for measuring temperature within a region to be tested includes a sensor means responsive to the temperature within the region for transmitting light energy along an optically-transmissive path and detector and amplifier means responsive to the light energy for producing an output signal which represents the intensity of the light energy. A signal processor electronically calculates a display signal from the output signal which represents the temperature within the test region. The signal processor performs this calcuation by solving Planck's equation, and a successive bisection technique is utilized to achieve extremely fine resolution of the temperature.

Abstract: The distributed temperature sensor employs an optical fiber as sensing element located in an ambient or near a body of which the temperature is to be monitored or measured. A source of light pulses sends into the fiber, pulses of predetermined duration. The backscattered radiation is collected for each pulse and the frequency spectrum variations in the backscattered radiation with respect to the incident radiation are analyzed. A computer obtains the temperature from said variations. The source and the spectrum variation analyzer are part of an optical time domain reflectometer which allows the temperature information to be associated with the information on the position of the backscattering point along the fiber.

Abstract: Method and apparatus for monitoring temperature along coil sections in a winding of an electromagnetic machine wherein each coil section comprises a plurality of electrical conductors. One or more hollow core conductors are placed in each coil section during manufacture of the coil sections. Before or after the stator core winding is installed, a distributed sensor probe is threaded through selected hollow core conductors for monitoring the temperature along the coil sections.

Abstract: An optical time-domain reflectometry method of sensing respective values of a physical parameter, such as temperature, at different locations along an optical fibre, in which back-scattered optical radiation is used to produce output signals indicative of the values being sensed, is improved by employing optical filtering means to ensure that the back-scattered radiation used is restricted to a preselected single spectral line resulting from inelastic scattering in the fibre, for example one of the Anti-Stokes Raman lines, or to two mutually adjacent such lines.

Abstract: The sensing head of a two-color band ratioing pyrometer of a known type using a fiber optic cable to couple radiation to dual detector photodiodes is improved to have high spatial resolution by focusing the radiation received through an objective lens (i.e., by focusing the image of a target area) onto an opaque sheet spaced in front of the input end of the fiber optic cable. A two-mil hole in that sheet then passes radiation to the input end of the cable. The detector has two channels, one for each color band, with an electronic-chopper stabilized current amplifier as the input stage followed by an electronic-chopper stabilized voltage amplifier.

Abstract: An optical pyrometer for a gas-trubine engine has a radiation receiving head located to view the blades of the engine and supply radiation from the blades to one end of a fibre-optic cable. At the other end of the cable there is mounted a detector comprising a cylindrical metal casing containing a photodiode and a signal conditioning circuit that amplifies the photodiode output. The output circuit is supplied to an electrical connector mounted on the casing. The detector can be mounted directly on the casing of a processing unit by mating its connector with an electrical connector fixed on the processing unit casing thereby avoiding the need for cables between the two casings. The connector on the detector has a flange that provides good thermal contact with the connector on the processing unit so as to help equalize the temperatures of the two casings. The processingunit casing is cooled by means of a thermal transfer unit supplied with liquid fuel.

Abstract: A temperature measuring device comprises an optical temperature probe (20) and a control module (21). Thermal emission from a recess (28a, 28b) in the tip end portion (23) of an optical fiber (22) is transmitted to the remote end (26) of the fiber for detection by the control module. The recess provides improved sensor capability with regard to maintaining constant emissivity and rapid response time. The recess is suitable for both single crystal optical fiber and optical fiber with a core-and-cladding construction.

Abstract: Apparatus and method for optically measuring temperature by spectroscopically determining the temperature-induced changes in the wavelength spectrum of light interacting with a semiconductor temperature sensor. The method includes providing illumination from a radiant energy source with a broad wavelength spectrum, guiding the radiant energy to a remote semiconductor sensor, returning the radiant energy after interaction with the semiconductor sensor, and analyzing the returned wavelength spectrum to determine the temperature-induced spectral changes due to the absorption edge of the semiconductor sensor. One embodiment of the invention comprises a quartz-halogen lamp, an optical multiplexer, optical fiber lightguides, a gallium arsenide semiconductor sensor, a fast scan spectrometer, an analog to digital converter and a microprocessor for processing the information of the returned wavelength spectrum for determining and displaying the sensor temperature.

Abstract: An optical temperature measurement technique that utilizes the decaying luminescent intensity characteristic of a sensor composed of a luminescent material that is excited to luminescence by a light pulse or other periodic or other intermittent source of radiation. The luminescent emissions of a preferred sensor exhibit an approximately exponential decay with time that is the average of a distribution of chemically reproducible crystallites and are repeatable with a high degree of accuracy regardless of excitation level or prior temperature history of the sensor.

Abstract: An optical fiber temperature sensing probe for implantation into a human body or other object that is being heated either by ultrasonic radiation alone or by a combination of ultrasonic and electromagnetic (radio frequency or microwave) energy. Several embodiments are described of probes adapted to measure temperature in an ultrasound field without errors being introduced by direct absorption of ultrasonic energy or by viscous heating, even when plastic fiber is utilized.

Abstract: An interferometric sensor (10) employs a sensing optical fiber (12) and a reference optical fiber (14). The sensing fiber (12) has a coating 16 thereon responsive to radiated thermal energy while the reference fiber is shielded therefrom. Both the sensing and reference fibers are subjected to the same ambient environment so that both fibers are subjected to heating by convection or conduction in essentially the same amounts. As a result, the sensor (10) is substantially nonresponsive to convected or conducted thermal energy while being highly responsive to radiated energy, particularly in the 6-30 micron wavelength region.

Abstract: A temperature sensing and measuring system in which a luminescent material is excited using a light source. The luminescence emitted decays with time, the decay time being dependent on temperature. Thus by monitoring the excitation and luminescence transmitted to and from the material via an optical fibre, the decay time constant and thus the temperature can be determined.

Abstract: A portable temperature data recorder for temporarily storing plural sets of temperature data representative of temperatures at a single location or at different locations, and automatically transferring the stored temperature data to a data processing unit. The portable recorder has a connector for connection thereof to the data processing unit. The portable recorder may further have a connector for connection thereof to a stationary temperature detector or thermometer installed at each measurement location. Alternatively, the temperature recorder incorporate a temperature detector for measuring the temperatures at the measurement locations. A clock circuit may be provided in the portable recorder, so that the temperature data may be stored together with measurement time data. The temperature detector may be a radiation thermometer provided at the measurement location, or built in the portable recorder.

Abstract: In one form of the present invention, an emissive substance radiates electromagnetic radiation as a function of temperature. The radiation is transmitted by a waveguide to a sensor which measures the intensity of the radiation and infers the temperature of the emissive substance therefrom.

Abstract: Temperature is measured by launching pulses of light into an elongate optical fibre and determining the temperature at positions along the fibre from the intensity of light scattered at those positions. The input pulses can have either the same or two different wavelengths, and the scattered light can be either Raman or Brillouin scattered and either forward scattered or backscattered. One position along the fibre can be maintained at a known temperature in order to provide a reference for other calculations. In particular embodiments the temperature is derived from the ratio between the intensities at two anti-Stokes wavenumber shifts or between an anti-Stokes scattered and a Rayleigh scattered intensity measurement. Otherwise the intensities of Stokes and anti-Stokes shifted Brillouin back scattered light can be used to derive the temperature.

Abstract: Several specific types of optical sensors capable of measuring temperature, pressure, force, acceleration, radiation and electrical fields, fluid level, vapor pressure, and the like, are disclosed, along with an electro-optical system for detecting the optical signal developed by the sensor. One such probe utilizes a convex shaped structure consisting of an elastomeric material attached to an end of an optical fiber, the elastomeric material being coated with a luminescent material, a combination that is capable of measuring both temperature and pressure. Such a probe is also specifically adapted for measuring surface temperature by making a good physical contact with the surface being measured. Another such probe utilizes a similar structure but of a non-elastomeric material for the purpose of detecting both temperature and either index of refraction of vapor pressure changes.

Abstract: A hollow dipstick is provided for immersion in molten material to determine the temperature of the molten material at any desired depth. The hollow dipstick is connected to an infrared detector by means of an optical fiber bundle for producing a signal indicative of the temperature of the molten material. An infrared focusing lens is provided within the hollow dipstick for transmitting the infrared radiation from the interior bottom surface of the dipstick to the fiber optic bundle. A container having a heating element therein is provided for receiving the dipstick when it is not in use so as to preheat the dipstick to a temperature close to the estimated temperature of the molten material to be measured to thereby prevent thermal shock to the dipstick upon immersion in the molten material. Alternatively the infrared detector is mounted directly on the dipstick.

Abstract: A luminous band display device is shown for the thermometer scale-like diay of the position of a control, e.g., of a turning knob or slide, having a series of luminous segments arranged in a circular or straight pattern. The luminous segments are formed by the ends of light guides which are led out from a generally cylindrical luminous center in a star-shaped or similar pattern. The luminous center consists of a cylindrical socket receiving a light source, and a cover which carries at least one color band and which can be rotated relative to the socket by means of the control is located between the light source and the beginning of the light guide. The light guides are arranged over approximately three fourths of the circumference of the luminous center. In order for all luminous segments of the entire display scale to light in only one color even in the stop positions of the control, an outlet opening and a guide for the color bands projecting from the socket are provided.

Abstract: A method and apparatus are provided for remotely monitoring temperature. Both method and apparatus employ a temperature probe material having an excitation-dependent emission line whose fluorescence intensity varies directly with temperature whenever excited by light having a first wavelength and whose fluorescence intensity varies inversely with temperature whenever excited by light having a second wavelength. Temperature is measured by alternatively illuminating the temperature probe material with light having the first wavelength and light having the second wavelength, monitoring the intensity of the successive emissions of the excitation-dependent emission line, and relating the intensity ratio of successive emissions to temperature.

Abstract: An optical measurement device in which changes in the output wavelength of the light source do not affect the measurement accuracy. Values representing the output wavelength of the light source are stored in a signal processing device and used to correct the measurement result for errors otherwise induced by the changes in the wavelength of the light source output.

Abstract: The invention relates to an optoelectromechanical apparatus for measuring physical parameters, as pressure or force, comprising an emitting optical fibre coupled via its input with a light source, receiving optical fibre connected over its output to signal processing means and a carrier including a resilient member for bearing the emitting and the receiving optical fibres, wherein the input of the receiving optical fibre is in optical coupling with the output of the emitting optical fibre, advantageously through a spacing and the processing means comprise a first and a second photodiodes for detecting light of the light source and the light output of the receiving optical fibre.

Abstract: A temperature measuring arrangement including a relatively long optical fibre temperature sensor doped along its length with material that absorbs light in dependence upon temperature, launcher for launching into one end of the temperature sensor fibre contemporaneous light pulses of two different wavelengths and comparator for comparing variations with time in back-scattered light of the two different wavelengths returned along the sensor fibre in order to provide an indication of the temperature distribution along the fibre, the two wavelengths of the light pulses launched into the fibre sensor being chosen so that they correspond with different absorption bands of the doped material.

Abstract: A tire temperature measurement apparatus comprising a microwave receiver (9 or 11) sensitive to electromagnetic radiation in a waveband in the frequency spectrum 10 to 100 GHz and a directional antenna (5 or 7) coupled to the receiver input and responsive to radiation from a predetermined surface area only of the tire (1 or 3).

Abstract: An optical type temperature measuring device which provides an accurate output in spite of temperature variations of the sensor or degradation of the characteristics of the sensor over time. The device includes a light source, a spectroscope, and a temperature sensor made of a material having one end coupled through a first optical guide to the light source and the other end coupled through another optical guide to the spectroscope. The output of the spectroscope is converted to an electrical signal, which is subsequently detected with plural different comparison levels to obtain higher end values of the absorption wavelength ranges of the sensor at the respective reference levels. These higher end values are then processed to obtain a rising point of a temperature dependent light absorption characteristic curve of the temperature sensor.

Abstract: A radiation pyrometer for a gas-turbine engine has a fibre-optic cable with three discrete bundles. At one end of the cable, the bundles, are arranged in a jig with one bundle being positioned centrally, being the other bundles which are of C-shape and located on opposite sides of the central bundle. A converging lens focusses radiation from the turbine blades onto the end of the cable, the ends of the bundle being oriented such that each bundle receives radiation from a different region spaced along the length of the blades. At the other end of the cable, each bundle is connected to a respective detector.

Abstract: A method of measuring the temperature in a high pressure furnace of a hot isostatic pressing apparatus, wherein a closed-end pipe having its inside communicated with the inside of the high pressure furnace and enabling a pressure medium to pass therethrough is disposed in the furnace, an incident top end of an optical fiber, a bundle of optical fibers or like other equivalent optical rod-like memeber is disposed to the open end of the closed-end pipe so as to be capable of receiving thermally radiated light from the inside of the closed-ended pipe and an exit rear end thereof is led out through a cover and to the outside of said high pressure vessel and a measuring system is connected to said exit rear end to detect heat radiation power from the top end of the closed-end pipe to thereby measure the temperature inside of the furnace.

Abstract: An optical temperature measurement technique that utilizes the decaying luminescent intensity characteristic of a sensor composed of a luminescent material that is excited to luminescence by a light pulse or other periodic or other intermittent source of radiation. The luminescent emissions of a preferred sensor exhibit an approximately exponential decay with time that is the average of a distribution of chemically reproducible crystallites and are repeatable with a high degree of accuracy regardless of excitation level or prior temperature history of the sensor.

Abstract: A temperature measuring device for a metal caster comprises a radiation pyrometer including an IR diode for measuring the head radiation of the metal melt in the crucible of the metal caster. For this purpose, a graphite body dips into the metal melt. The graphite body is seated coaxially around one end of a hollow tube to whose other end is coupled a glass fiber cable which is connected with the IR evaluation diode. The graphite body which dips into the metal melt and simultaneously serves in a known manner as a closing plug for the crucible, now emits thermal radiation into the interior of the tube, such radiation substantially corresponding to the composition of the thermal radiation of a blackbody having the temperature of the metal melt. This thermal radiation is coupled into the glass fiber cable at the other end of the tube and fed to the IR diode for evaluation.

Abstract: An optical fiber temperature sensing probe is implanted into a human body or other object that is being heated, either by ultrasonic radiation alone or by a combination of ultrasonic and electromagnetic (radio frequency or microwave) energy. In order to measure temperature in an ultrasound field without the probe introducing errors, the probe is made to be substantially thermally non-conducting, made of materials that do not absorb compressional energy, and has a small diameter relative to the length of the ultrasonic heating waves.

Abstract: To measure the heat transfer coefficient of a sample, an element with temperature sensitive optical properties is placed in contact or implanted in the sample. The element is heated or cooled. The temperature difference between the element and the unheated sample and the rate of heating or cooling indicate the heat transfer coefficient of the sample. In one embodiment, the element is heated or cooled at a constant rate. The heat transfer coefficient of the sample is then inversely related to the difference in temperature between the element and the unheated sample. Alternatively, the element may be heated or cooled at such a rate that the temperature difference between the element and the unheated sample remains substantially constant. The heat transfer coefficient of the sample then varies directly with the rate of heating or cooling. The heat transfer coefficient of a sample is a measure of its composition and other physical properties.

Abstract: An apparatus for measuring bath temperature of metallurgical furnaces through a tuyere is disclosed. The apparatus comprises a periscope adapted to be inserted into a tuyere, a fiber optic cable having one end connected to the periscope for receiving radiation entering the tuyere from the bath of a furnace, and a two wavelength pyrometer connected to the other end of the fiber optic cable for analysing the radiations transmitted through the fiber optic cable to provide an indication of the temperature of the bath.

Abstract: A device for measuring the two-dimensional temperature profile of a surface comprises imaging optics for generating an image of the light radiating from the surface; an infrared detector array having a plurality of detectors; and a light pipe array positioned between the imaging optics and the detector array for sampling, transmitting, and distributing the image over the detector surfaces. The light pipe array includes one light pipe for each detector in the detector array.

Abstract: In an optical fiber type temperature detector using temperature change of refraction index in birefringent crystal, by using LiTaO.sub.3 or Sr.sub.x Ba.sub.l-x Nb.sub.2 O.sub.6 single crystal (0.5<x<1.0) as material (13) for sensor and quartz as material for setting temperature range, a high sensitive and highly stable temperature detector using light emitting diode as light source is realized. Furthermore, as configuration of sensor part, miniaturization and light weight is devised by disposing rutile (11) or calcite between optical fibers (8, 9) and rod lens (12) to make polarization separation.

Abstract: The temperature-measuring transducer of a temperature-measuring system that includes a device for emitting energizing radiation, a temperature-measuring transducer which, upon excitation by the energizing radiation, will emit luminescent light, a detector for detecting the luminescent light emitted by the temperature-measuring transducer, and at least one optical fiber interconnecting the various elements is made of a crystalline sensor material which contains luminescent ions, at least some of these luminescent ions being so located in the crystal lattice of the sensor material that for each of said at least some luminescent ions each immediately adjacent anion substantially shows inversion symmetry in relation to that luminescent ion.

Abstract: A temperature measuring device suitable for high temperature measurements in the range of 500.degree.-2400.degree. C. utilizing a blackbody cavity to emit radiation in the wavelength band of 0.3 .mu.m-1.0 .mu.m. The emitted light is transmitted to a photodetector via a high temperature ceramic fiber which is transparent to the wavelength band radiated. The radiance of the cavity is utilized as a measure of its temperature.

Abstract: An optical fiber temperature thermometer uses a thermochromic substance having optical absorption peaks which vary with temperature within a first waveband, and having substantially constant absorption with temperature in a second waveband. The radiation employed is in a wide band to include the first and second wavebands, and the radiation, reflected and attenuated as a result of the passage through the thermochromic substance, is split into two selected beams and filtered in narrow band pass filters for the first and second wavebands, to supply optical signals to respective detectors whose outputs are divided to produce a ratio signal representative of the temperature. The sensor is sufficiently compact for biomedical use, and, being unaffected by electromagnetic fields, is useful in regions of high tension or in microwave heating.

Abstract: The brazing wand comprises a hollow helically wound electrically conductive tubular member for conducting an electrical current and for conducting a coolant therethrough. The electrical current is used to heat a member to be brazed while the coolant is used to control the temperature of the brazing wand. The brazing wand also comprises an optical sensing device for determining and controlling the brazing temperature.

Abstract: In a brake assembly (10) having an infrared fiber optic element (54) for transmitting an operational signal to a sensor (66) through which an indicator (68) is provided with a substantially instantaneous indication of the temperature of the brake stack (26).

Abstract: Apparatus for measuring the temperature and/or electrical intensity based on the Faraday effect. It comprises a probe constituted by an optical fibre, wound in a generally solenoid form and two optical fibre strands connecting the probe to an inlet coupled to a polarized light source and to an outlet coupled to means for measuring the rotation angle of the light polarization plane, the optical fibre portion constituting the probe being twisted about its longitudinal axis in a random single direction. The two optical fibre strands connecting the probe respectively to the inlet and outlet of the system are twisted in opposite directions, the number of twisting turns to the right of one of the strands being equal to the number of twisting turns to the left of the other.

Abstract: A technique of temperature measurement wherein an object or environment to be measured is provided with a phosphor material layer that emits at least two optically isolatable wavelength ranges whose intensity ratio depends upon the object or environment temperature, the emitted radiation being brought to a detector by an optical system that may include an optical fiber. Several specific applications of this technique are disclosed, such as temperature monitoring of electrical equipment and industrial processing, medical temperature instrumentation including the use of disposable elements that contain a small quantity of the temperature dependent phosphor, special and multiple probes, the use of liquid phosphors, and a phosphor paint for monitoring surface temperatures.

Abstract: Method and apparatus are provided for measuring temperature and for generating optical signals related to temperature. Light from a fiber optic is directed to a material whose fluorescent response varies with ambient temperature. The same fiber optic delivering the excitation beam also collects a portion of the fluorescent emission for analysis. Signal collection efficiency of the fiber optic is enhanced by requiring that the fluorescent probe material be in the shape of an oblong parabolically tapered solid. Reproducibility is enhanced by using Raman backscatter to monitor excitation beam fluctuations, and by using measurements of fluorescence lifetime.

Abstract: A dielectric heat sensor system for monitoring and measuring the effects of electromagnetic radiation on the performance or physical integrity of an electrical or electronic component includes a dielectric receiver in the form of a rectilinear array of fiber optic ends positioned to receive infrared heat waves from a bridgewire of an electro-explosive device and transmitting the infrared heat waves by way of a waveguide of electro optic fibers to an infrared detecting unit which is effective to activate an indicator.

Abstract: Remote measurement of temperature variations within polymer process melts is performed by irradiating the melt with a collimated radiation source such as laser light and relating the transmitted radiation to the temperature distribution within the melt. A method and apparatus for temperature profile determination is based upon the variation of light transmittance through the melt as a function of temperature and wavelength of the incident light.

Abstract: A light-guide unit comprises a light-forming rod and a light-transmitting rod, both rods being made from a light-permeable corrosion-resistant refractory material, for instance synthetic corundum, and coaxially arranged relative each other. According to the invention the length of the light-forming rod is equal to the thickness of the metallized layer of a lining, and the length of the light-transmitting rod is not less than the thickness of the remaining portion of the lining. The rods are connected by a protection sleeve made from a material featuring plasticity at the operating temperature of the lining, and disposed in the tube. The tube at the portion wherein the light-forming rod is disposed is filled with a first refractory material having a sintering temperature not higher than the sintering temperature of the lining, and whose resistance to the action of the products of melting is similar to that of the lining.

Abstract: A transducer for the measurement of temperature incorporates a fiber optic coupler having a coupling efficiency which varies in relation to the index of refraction of a thin layer of index matching liquid, such as index matching oil, placed between the optical fibers of the coupler. Since the index of refraction of the liquid varies predictably with temperature, the coupling efficiency of the transducer may be used to directly measure the temperature of the coupler and its surroundings.

Abstract: A temperature probe measures temperature changes within biological material while the tissue is being irradiated with microwaves. In order to measure tissue temperatures accurately a probe must be designed to function in a microwave field while causing minimum perturbation to the microwave field. This generally requires a probe being constructed of dielectric (non-metallic) material which utilizes physical phenomena which are thermally dependent yet unaffected by electromagnetic fields at the field strength and frequencies of interest. In one embodiment the structure of the probe basically includes an optical fiber bundle for conducting light both toward and away from a temperature sensitive luminescent element located at one end of the optical fiber bundle, the source for exciting the temperature sensitive element and a light responsive detection element located at the output end of the optical fiber bundle for detecting light emitted from the temperature sensitive element which is temperature dependent.