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: An infrared heat source is directed through a chopper or modulator and beam splitter to the surface of the water. A pair of radiometers are provided, one located behind the back surface of the wafer to measure transmittance, the other adjacent to the beam splitter to measure wafer reflectance. The wafer temperature may then be calculated using an experimentally determined relationship between wafer radiance W.sub.W and wafer temperature, with wafer radiance being provided by the relationship ##EQU1## where r.sub.BS is the reflectance of the beam splitter, W.sub.W is the blackbody radiance of the wafer, W.sub.a is the blackbody radiance equivalent to ambient temperature, and e.sub.W is the wafer emittance. Alternatively, rather than locate a radiometer behind the wafer to measure wafer transmittance, a mirror may be located behind the wafer to reflect the transmitted energy back through the wafer on a periodic basis for a short part of each duty cycle.

Abstract: An optical pyrometer makes a temperature measurement of a remote body that is insensitive to spurious radiation by modulating the temperature of the body of optical irradiation in a first optical wavelength range at a low modulation frequency and synchronous detection of emitted optical radiation in a second optical wavelength range, together with modulation in the second optical wavelength range and detection in the first wavelength range. The measurement so made are combined to form a parameter representative of the body temperature that is insensitive to the environment of the body.

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 improved optical system for a radiation thermometer is provided wherein a range finding system is coincident with the optical system of the infrared measurement. The finder optical system can utilize various forms of focusing members.

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: In a pyrometer system, a pyrometer provides output signals to a processor indicative of the temperature of rotating blades in a gas-turbine engine. The processor includes a synchronization unit and a gate controlled by the synchronization unit. After monitoring the output of the pyrometer to identify which parts of the output signal arise from radiation from the blades and which arise from the combustion chamber, the synchronization unit is set in synchronism with the blade signals and the gate is controlled to pass signals from the blade and to interrupt signals arising from the combustion chamber. The output of the processor is thereby indicative of blade temperature and is insensitive to combustion chamber radiation.

Abstract: A cryogenic thermometer using molecular luminescence determines temperature. A sensor material is used which is capable of emitting radiant energy from a spin multiplet when excited, the excited state being characterized by a large zero field splitting (ZFS), and in which two of the sublevels split by the ZFS are radiative in the visible or near infrared region and are optically resolvable from each other. Spin-lattice relaxation rates between the sublevels are much larger than the sublevel decay rates to other states in order that their populations remain close to thermal equilibrium during optical pumping. The relative intensity of the two bands of radiation is determined and the temperature calculated therefrom. Xanthione (XS) dissolved in n-hexane may be used as a sensor material in the optimum range of 3 to 10K, with estimated precision varying between 0.4 mK and 3.0 mK within this range.

Abstract: A radiation instrument has a purging air flow system for passing air over the lens to keep it clean and free from particulate contaminants and also for providing a positive flow of air away from the lens. The air supply used for such purging is controlled adequately so the flow changes direction and particles are removed from the main flow of purge air by inertial separation prior to the time the air contacts the lens. Such air entrained particles might otherwise deposit on the lens. A flow control orifice provides a secondary flow to carry the particles separated from the main flow out of the flow passageway.

Abstract: A high optical efficiency dual spectra pyrometer for measuring the temperature of a target includes an optical guide for collecting and guiding a target optical beam to a detection module which comprises an interference filter and photodetectors adjustably positioned to provide efficient coupling of the target optical beam thereto. The pyrometer additionally includes a signal processor which receives the signals from the photodetectors, as well as signals indicative of an estimated fireball equivalent black body temperature and the spectral width difference between the two detector signals, and provides a compensated temperature signal.

Abstract: The invention is a temperature sensor which uses the variation in the critical angle between two optically transparent media, at least one of which has an index of refraction variable as a function of temperature, to variably refract and reflect portions of a spectrum incident on the junction of the media at angles less than and greater than the critical angle to produce an optical signal variable as a function of temperature.

Abstract: The present invention relates to an optical system of a radiation thermometer in which the measuring optical system and the finder optical system can be focused. The central portion of the sub-mirror in Cassegrainian type optical system is used as a finder lens of the finder optical system. The third mirror is located between the main and sub-mirrors in order to reflect the light passed through the central portion of the sub-mirror. The light reflected on the third mirror is used for finder observation.

Abstract: In a method of determining the rate of heat transfer from a surface due to liquid convection, a coating of a material capable of dissolving in the convecting liquid and whose optical properties on irradiation are proportional to the thickness of the coating, is applied to the surface and is then exposed to radiation and to the convecting liquid, the change in the amount of radiation transmitted or reflected from the coating giving an indication of the rate of heat transfer.

Abstract: A radiant-energy temperature measuring apparatus of a scanning type having a linear array of light-sensitive elements which generate photoelectric signals corresponding to respective amounts of radiant energy produced at different points of an object and vicinities thereof on a straight line corresponding to the above linear array, and further having a device for determining a temperature of the object at desired one of its different points, based on the photoelectric signal generated by one of the light-sensitive elements which optically matches the desired one point of the object. The apparatus includes an edge detector for detecting an edge of the object, based on the photoelectric signals generated by the light-sensitive elements, and a selector for selecting the desired one point of the object, by designating a number of the light-sensitive elements as counted from the element corresponding to the detected edge of the object, to the element which corresponds to the above-indicated desired one point.

Abstract: A pyroelectric thermal sensor for measuring the surface temperature of an object on a non-contact basis using the signals produced by a pyroelectric element and a reference thermal sensor is operative to reduce the level of the output signal from the pyroelectric element proportionally by switching an interruptive time for interrupting a heat ray incident to the pyroelectric element when the output of an amplifier for amplifying the pyroelectric element signal approaches the state of saturation.

Abstract: An optical sensor (1) is connected to an electro-optical transducer unit (35) and a measuring circuit (36) via an optical delay line (14) and an optical path (15). Error-free measurement values which are independent of the attenuation characteristics of the optical delay line (14) are obtained if the optical sensor (1) comprises a polarization splitter (3) which receives light pulses from the optical path (15) and from the optical delay line (14) and which is followed by a sensor body (2) which is traversed by the light pulses. A mirror (4) arranged on the side of the sensor body (2) on which the light is not incident reflects the light pulses back into the polarization splitter (3), which couples the light pulses back into the optical path (15) and the optical delay line (14).

Abstract: Cleansing of a pyrometer lens is achieved by directing purge air spirally inward over the lens surface. The vortex formed by the spiral air flow is highly effective in removing contaminating matter from the lens surface. A light blocking or masking element is attached to the center of the lens where the purge air stagnates to prevent deposit of particles or other material on the center portion of the lens. This invention relates to a temperature sensing device and, more particularly, to an optical pyrometer and a method for effectively cleaning the same.

Abstract: Diacetylene segmented copolymers having first and second segments are disclosed. The preferred segmented copolymers of this invention are prepared from three basic monomers: a diisocyanate, a flexible elastomeric prepolymer and a chain extender containing a diacetylene unit. The resultant segmented copolymers exhibit the mechanical properties of elastomers and also many of the novel characteristics of the polydiacetylenes. Also for the first time, a polydiacetylene has been produced which exhibits mechanochromism.

Abstract: A reflection corrected radiosity optical pyrometer includes an optical guide for receiving a target optical beam from a turbine blade in a jet engine. The target optical beam is provided to a detector module that divides the target optical beam into two beams, one having a spectral width selected to be less than the target optical beam spectral width. A signal processor receives signals from the detector module indicative of the energy of the two beams, calculates a reflection corrected energy signal directly therefrom and provides a correct target temperature signal.

Abstract: A device for measuring properties of plasma projects linearly polarized light to an object plasma as incident light, and the light coming from the plasma in response to the incident light is separated into an S-polarized component and a P-polarized component, so that temperature and other properties of the plasma are determined from such S- and P-polarized components.

Abstract: Fiber optic probe apparatus usable for measuring temperatures with increased dynamic range and frequency domain response and desirable measurement accuracy. A black body signal source, fiber optic signal coupling, and extension of the transducer dynamic range with optical multiplexing are employed; the instrument operates in the range of 1.6 micrometers of optical energy wavelength and preferably employs recently improved indium gallium arsenide photodiode transducer devices and transducer frequency domain compensation. Use of the instrument in measuring combustion flame transient temperatures is disclosed.

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 dual spectra optical pyrometer having an air pressure sensitive shutter for measuring the temperature of a turbine blade includes a sight tube located in the jet engine receiving an optical beam from the turbine blade. Located within the sight tube is a shutter responsive to the jet engine air pressure and providing the turbine blade optical beam only above a selected threshold magnitude of said air pressure. A detection module receives and divides the turbine blade optical beam and provides signals to a signal processor. From these signals and signals indicative of an estimated fireball equivalent black body temperature and the spectral width difference between the two detector signals, the signal processor provides a signal indicative of a compensated turbine blade temperature.

Abstract: The present invention relates to an optical system of a radiation thermometer in which the measuring optical system and the finder optical system can be focused. The central portion of the sub-mirror in Cassegrainian type optical system is used as a finder lens of the finder optical system. The third mirror is located between the main and sub-mirrors in order to reflect the light passed through the central portion of the sub-mirror. The light reflected on the third mirror is used for finder observation.

Abstract: A pyrometer for viewing the blades of an engine has a forward lens which produces a first image of the blades in an image plane P.sub.1. Rearwardly of the image plane P.sub.1 is an assymetric faceted lens assembly having a central region with a long focal length, and an outer annular region of shorter focal length. The outer region of the rear lens assembly forms a second image of the first image in a second image plane P.sub.2. The inner region forms a third image of the forward surface of the first lens in the second image plane P.sub.2. A disc mask is fixed centrally to the forward surface of the first lens, and an annular mask is located in the first image plane P.sub.1. The forward end of a fibre-optic cable is located in the second image plane P.sub.2 and comprises a central bundle of fibres which receives the second image, and two outer bundles which receive different parts of the third image.

Abstract: A novel dual spectra optical pyrometer for use in in-flight control of jet engines includes an optical probe containing a shutter sensitive to the air pressure within the jet engine. The shutter provides an optical beam from rotating turbine blades to an optical fiber only above a threshold pressure. A serial array of photodetectors receives the optical beam and provides first and second signals therefrom. A signal processor receives the first and second signals as well as signals indicative of the energy ratio therebetween, and provides reflection corrected energy signals from the difference between the first signals and the product of the energy ratio signals and the second signals.

Abstract: A photoelectric device for use as a radiation thermometer capable of measuring the temperature of a target without being in contact therewith is provided. The photoelectric device can include a photovoltaic cell of germanium that is suitable for a radiation thermometer capable of measuring the temperature of a target between 200 degrees C. to 800 degrees C. The electrical output of the photovoltaic cell corresponding to the intensity of radiation is made independent of any change of the characteristic of the cell resulting from temperature.

Abstract: A radiation pyrometer has an inner tube with a lens mounted in a rear portion which is stepped to a forward portion of reduced diameter that is open at its forward end. An outer tube extends coaxially around the inner tube and is separated from it by an annular gas passage. The outer tube has an aperture at its forward end that is smaller that the external diameter of the forward end of the inner tube and larger than the internal diameter. The outer tube has gas inlets into the passage which are located rearwardly of the forward end of the inner tube, the area of the gas inlets being greater than the gap between the forward end of the inner tube and the outer tube. Gas flows through the inlets, along the passage, across the forward end of the inner tube and out the aperture, thereby setting up a substantially constant pressure in the rear portion of the inner tube and reducing the entry of contaminants.

Abstract: A slight tube assembly, in combination with a sensing instrument, such as an optical pyrometer, for use in continuously monitoring the temperature of the first row of rotating blades in large gas turbines, particularly the type used in industry. Temperature data received by the pyrometer unit is fed to a control circuit, which regulates fuel input to the tubine to control the firing temperature. The key to obtaining reliable blade temperature data in the practice of this invention is the position of the sight tube in the turbine, which enables the pyrometer to "view" the rotating blades along a direct line of sight that penetrates a hot gas duct, but not the turbine section of the engine.

Abstract: A hand held radiation detector may be used for scanning of a surface from a distance to obtain a gross indication of temperature variations in the surface. The radiation detector is provided with a nosepiece having a conical cup therein which can be placed directly against a surface. The radiation sensor views the surface through the cup to obtain an accurate indication of temperature substantially independent of the emissivity of the surface. The radiation sensor and a temperature sensor are potted with high conductivity material in an insulating sleeve within the nosepiece. The nosepiece is of high conductivity material and is thermally connected to a main housing which serves as a heat sink. Temperature indications are obtained from the sensed radiation indication by means of a piecewise linear gain analog circuit.

Abstract: Apparatus which measures temperature in the high voltage environment of an electrical generator includes a temperature sensing element which includes a polarizing filter rotatable as a function of temperature. Light from a source is passed through the filter and the polarized light is again polarized through the use of a constantly rotating second polarizing filter behind which is a detector operable to provide an AC signal as a function of the doubly polarized light intensity. A reference beam is passed through the second rotating filter as well as a manually rotatable polarizing filter and is detected so as to provide a second AC signal. After an initialization, the AC signals are compared in phase, with the phase difference between them being a function of the temperature being measured.

Abstract: Production-worthy method and system comprising two computer-based subsystems for determining temperature of an irradiant mass movable through process means in a hostile environment exemplified as coke guide and coke oven in a battery of ovens. System is usable in other industries such as at cement kilns and the like. First subsystem which is carried by a movable coke guide/door machine, includes one or more coke guide pyrometers arranged vertically, each with a sighting window monitor to detect optical errors, an onboard computerized and cooled electronics package for acquiring and processing temperature data and automatically detecting same for pyrometer drift and optical errors, and automatically correcting for these errors, and further including a plug-in portable terminal with a printer.

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: A pyroelectric detector comprising a functional portion in which opposed electrodes 111 to 118 are formed on both surfaces of a pyroelectric type substrate 101 and four light receiving electrode portions a, b, c and d are structured by the opposed electrodes 111 to 118. Among the light receiving electrode portions a, b, c and d, the light receiving electrode portions a and c in odd-numbered positions constitute one light receiving electrode group A and the light receiving electrode portions b and d in even-numbered positions constitute the other light receiving electrode group B. The light receiving electrode portions a and c and the light receiving electrode portions b and d are electrically connected alternately and in series, and the light receiving electrode group A and the other light receiving electrode group B are connected to have opposite polarities.

Abstract: To be of most use as an input signal for the control system of a gas turbine aeroengine, a pyrometer-derived turbine blade temperature signal should represent the average temperature of the hottest parts of the blades with fast and accurate response when the average temperature of the hottest parts changes with engine conditions. The invention achieves this by providing the pyrometer with an optical system adapted to give the pyrometer's photo-diode a large field of view which is rectangular at the face of the turbine rotor and which extends an integer number of inter-blade passage widths in the circumferential direction and a portion of the length of the blade aerofoils in the radial direction.

Abstract: A method and apparatus for determining a temperature profile along a single optical fiber. The temperature profile is determined by measuring the output power spectral distribution. By measuring n points along the spectral power distribution curve, n "resolution elements" of temperature can be determined.

Abstract: In a radiation pyrometer in a gas turbine engine, non-uniformly distributed changes in transparency of an optical element in the system, e.g. contamination of pyrometer objective lens L.sub.1 by combustion products from the turbine can be automatically detected. Lens L.sub.1 focusses radiation from target T onto an additional lens L.sub.2, which in turn focusses it onto the end E of the fibre-optic bundle F. Considered reciprocally, lens L.sub.2 images the end E of fibre-optic F into L.sub.1, so that although each optical fibre in end E receives radiation from all parts of target T, each fibre is imaged into a corresponding discrete area of L.sub.1. Fibre-optic bundle F comprises two (or more) sub-bundles F.sub.1 and F.sub.2 forming complementary sub-areas of end E and each sub-bundle is provided with its own photodetector P.sub.1, P.sub.2 and associated pre-amplifier A.sub.1,A.sub.2 adjusted so that their outputs A.sub.1 S.sub.1 and A.sub.2,S.sub.2 are matched at the non-contamination condition.

Abstract: A pyrometer system for a gas-turbine engine, or the like, has a high-resolution radiation pyrometer that supplies signals to a detector unit. The detector unit includes an inverter that inverts the pyrometer output and supplies these signals via a diode to one electrode of a capacitor. The other electrode of the capacitor is grounded, a resistor being connected across the capacitor so that it is slowly discharged. The charge on the capacitor approximately follows the high-value/low-temperature signals, which are reinverted by a processing unit to give an averaged temperature indication. The diode is short-circuited for periods, approximately equal to the blade rotational frequency. During these periods the charge on the capacitor drops to the instantaneous value of the pyrometer output, producing a low-voltage/high-temperature spike. The detector unit includes a store to which these spikes are supplied after reinversion.

Abstract: A two-wire transducer-transmitter for non-contact temperature measurement provides, in a unitary housing, a radiation sensing device producing a signal in response to sensed infrared or visible radiation, and electronic circuitry for processing the signal to provide at a two-wire output a current linerarly proportional to the sensed target temperature, on the same two wires as input power preferably in the range of from 4 to 20 milliamperes D.C. full scale.

Abstract: The invention relates to a temperature measuring method and device. The device comprises a diffraction grating raised to the temperature to be measured, a monochromatic light beam source in which the beam is directed on to the grating and means for measuring the angular position of the diffracted beam.It is used in measuring the temperature of materials immersed in an ionized medium.

Abstract: A method and apparatus for thin film thickness measurements with thermal waves in which heating and detection laser beams are focused onto the film, normal to the surface of the film, with the two beams parallel and non-coaxial.

Abstract: A method for measuring thermal waves in a sample is disclosed. More particularly, thermal waves, which may be used for imaging, are generated in a sample through local periodic heating as, for example, by impinging an intensity modulated beam of energy on the surface of the sample. A laser probe is focused on a portion of the heated area on the surface of the sample in a manner such that the beam is reflected from the surface. The angular displacement of the reflected beam, resulting from the local angular change in surface conditions of the sample due to the thermal waves are monitored. By this arrangement, the displacement of the reflected beam can be used to detect the thermal waves.

Abstract: A process for the remote measurement of the emissivity .epsilon. of a body (1) with relatively smooth surface, consisting: in making, with a detector (6) and a converter (9), a first measurement A of the luminance at a point M on the surface at an emission angle .theta., the thermal radiation (2) on which the measurement is made being polarized (at 4) in a first direction with respect to the emission plane, in making a second measurement B of the luminance at the same point and at the same emission angle .theta., the thermal radiation being polarized in a second direction, different from the first one, finally, in determining the emissivity ##EQU1## .theta..sub.1 being the angle of the axis of the polarizer for A and .theta..sub.2 being the angle of the axis of the polarizer for B, measured with respect to a polarization perpendicular to the emission plane.

Abstract: A pyroelectric detector with an optimized quality factor, having a dielectric material inserted between two parallel electrodes, the material being a monodomain ferroelectric monocrystal. The faces of the monocrystal in contact with the electrodes form an angle differing from 90.degree. with the polar axis of the monocrystal. The detector is useful in infrared imaging and detection.

Abstract: In a method of and apparatus for making remote measurements of temperature and pressure in a gas, laser beams are transmitted through the gas to a reflecting target, which may be either a solid surface or particulate matter in gas or the gas molecules and the return beams are measured to determine the amount of energy absorbed by the gas. For temperature measurements, the laser beam has a wavelength whereat the gas exhibits a relatively temperature sensitive and pressure insensitive absorption characteristic, whereas for pressure measurements, the laser beam has a wavelength whereat the gas has a relatively pressure sensitive and temperature insensitive absorption characteristic. To reduce the effects of scattering on the absorption measurements, a reference laser beam having a weak absorption characteristic is transmitted colinearly with the data beam having a strong absorption characteristic. The two signals are processed as a ratio to eliminate back scattering that is common to the two beams.

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 ladle preheat station includes a wall, a ladle base for holding a ladle juxtapositioned to the wall on one side thereof, and burner extending through the wall for firing into the ladle interior. The wall includes a sight tube extending therethrough. An infrared pyrometer is mounted and spaced from the side of the wall opposite the ladle and is positioned to transmit a signal through the sight tube to measure the radiation of the ladle bottom and convert it into an electrical signal for control purposes.

Abstract: A radiation pyrometer, or other optical sensor, has a mirror assembly capable of withstanding high temperatures. The mirror assembly is a block of a steel containing between 15 and 20% chromium, 4.0 and 5.2% aluminium, 0.05 and 0.4% yttrium, 0.2 and 0.4% silicon, and 0.00 and 0.03% carbon. A reflective surface on the assembly is provided by an aluminium oxide layer. The assembly is formed by heating a body of the steel such as to produce the aluminium oxide layer which is then polished to a reflective finish. After heating, the body is machined to the desired shape of the mirror assembly.

Abstract: Apparatus for measuring the temperature distribution along the inside walls of narrow, shaft-shaped spaces such as heating flues of coking and similar ovens using a radiation pyrometer with an evaluating arrangement, whereby a radiation optical system is disposed at one of the ends of the space and contains a mirror tiltable about an axis, for optical coverage of the entire length of the space and forwarding of the detected radiation into the path of rays to be evaluated, as well as a positioning arrangement for tilting the mirror over the area to be optically covered. Therewith a fixed mirror is arranged after the tilting mirror and the path of rays to be evaluated is focused to the end of a photoconductor, which, in a transportable and coolable measuring lance, is directed to an evaluating arrangement. The measuring lance can be coarsely and finely positioned by means of a carriage arrangement.