The present invention belongs to areas of modern optical technology, fiber optics sensor technology and photo-electronics technology. It illustrates a non-contact temperature measurement etalon, which can be used for high precision temperature sensing and calibrating or demarcating the traditional temperature sensors.
The present invention introduces a temperature measurement etalon, which is a gauge tool for the temperature measurement. The measurement tools for temperature measurement are generally called temperature sensors. As we know, precision of gauge tool is preferred to be at least 1-2 orders of magnitude higher than the measurement tools. Platinum resistors (minus 200 to 900° C.) and Pt—Rh (platinum-rhodium) thermocouples (300□1450° C.) are used as contact temperature measurement etalon, for the reasons of their point temperature measurement, irrelevant to the contact material, and higher measurement precision under the circumstance that the temperature change is limited or slow. There is still no non-contact temperature measurement etalon by now, because most non-contact temperature sensors such as infrared thermometer can not measure a point temperature, be relevant to the material of the surface to be measured, and also be relevant to the measurement distance. Other non-contact temperature sensors such as pyrophotometer, unlike infrared thermometer, measuring temperature with luminance, are with low precision and can not be used as temperature measurement etalon. The theory of infrared thermometer is based on Planck law, i.e. black body radiation law. The reason for Planck conducting his experiment was to revise Wien's displacement law, i.e. the wavelength of the peak of the emission of a black body and its temperature when expressed as a function of wavelength. But the significant contribution for the experiment was to offer an evidence for quantum optics. There were no photodiode and infrared detector at the time Planck doing his experiment. He used a hollow sphere as black body, putting a thermocouple with detecting end at the center for non-contact measuring black body's radiation wave. The radiation wave would heat the thermocouple to get an electromotive force because of thermoelectricity effect. That is the photoelectricity transform process described in Planck's law. But it is a thermoelectricity transduction not the photoelectricity transduction indeed. There are several problems when using Planck's law for temperature measuring. Firstly, only the thermocouple used in contact way can get higher temperature measurement precision. Non-contact way like Planck did can only get a relatively low precision. Secondly, the black body Planck used is a hollow sphere, integrating all the temperature energy come from each small area from the sphere surface to the center. That application situation can not be occurred for the actual application of the non-contact temperature sensors.
The present invention indicates that the temperature change in a material surface would induce the change of wave energy and heat energy, both of which can represent the temperature respectively. There are two energies, radiant energy and conductive energy, on each material surface and sum of the two energies is the same if temperature remains the same. Black body is also with the two energies, but with a much higher radiant energy than conductive energy. So when measuring different material in same temperature, thermocouple will get same temperature measurement results by contact measurement, but non-contact measurement may get different output, especially when the materials to be measured are among good conductors such as gold, silver, copper and aluminum etc. The radiation intensity described in Planck's law is verified related to the material, surface color and roughness. Generally, the radiant coefficient is during the range of 0.04-1.0 according to material, surface color and roughness, radiant coefficient of black body can be defined as 1.0. The uncertain radiant coefficient may induce confused temperature measurement results. The present invention use wave energy to measure the temperature. Because heat energy and wave energy are two different physical quantity, wave energy can be used for temperature measurement in high speed measurement, for the reason that transmitting speed of wave energy is 300 thousands kilometers per second. A high speed response photoelectricity detector can obtain wave energy by non-contact measurement. The process is same to contact heat energy measurement only with different sensor. The present invention also validates that for the influences of convection, conduction and radiation, temperature distribution in a material surface is asymmetry. Even for a vacuum flask, there is still temperature grade on its surface.
Only the point temperature can represent an accurate temperature measurement. The present invention shows a way for getting point temperature by non-contact measurement. By using the lens imaging and phase transformation function, emanative spherical wave radiated from each point on the object plane may be transformed to the focal spherical wave. Due to the Fourier transform function, wave energy from each point on the object plane can be transferred to the rear focal plane of the lens, i.e. the image plane. Wave energy from wave source is usually larger than the radiation wave's wave energy. Like a camera taking a photo, if the photo is focused with no distortion, that means wave energy of the object surface (wave source) will reach image plane; if it is with distortion, that means there are some radiation waves reach the image plane. Although the radiation wave is a part of the wave energy of wave source, its waveform is unlike the waveform of wave source. If there is no distortion, waveform of the image plane is the same as that of the wave source. Optical fiber can be used for coupling and transmitting the image. By precisely adjusting the distance, the input end of optical fiber can achieve good image coupling. The output of the optical fiber is the optical analog data, which can be converted to the optical digital data and transmitted for a long distance. It also can be converted to the electrical digital data. Such digital data represents corresponding wave number which is proportional to temperature. The digital data can be processed by a microprocessor system and the temperature value can be obtained and displayed. The temperature measurement etalon is realized as the non-contact optical point temperature measurement, irrelevant to the material, radiant wave, heater surface area and measurement distance. Such etalon can be regarded as a temperature gauge tool, which precision is at least 1-2 orders of magnitude higher than that of the temperature sensors to be calibrated.
Optical spectrum information of the goal surface transmits to the objective lens 1, and be separated into two routes by the demultiplexer 2. One of the two routes is focused to the index plate 3 and can be read by the ocular lens 4. Another route will focus wave energy from each point of object plane to the focal plane of the objective lens. The GRIN lens 6, optical spectrometer □ and the large core optical fiber 8 will realize the characteristics of the point temperature measurement and irrelevance to the radiant coefficient. The functions of photodetector 10, logarithm amplifier 11, operation amplifier 12 and optical switch 13 are to convert the optical analog data to the optical digital data. The functions of infrared 100 MBPS LED 14, photodiode 15, pulse shaping amplifier 16, optical fiber 22 and photodiode comparing circuit 24 can avoid interference between analog data and digital data. Microprocessor 17 will take count of digital signals and connect to computer 18 for displaying temperature value. All the components are fixed in a mechanical fixture. To conveniently aim at the goal to be measured, there are one LCD screen and 4 pushbuttons on the fixture. The function extension chip 19 is used to extend and update the functions. Control signal can be either the analog data from the function extension chip 19 or the digital data from the computer 18.
The present invention is a non-contact temperature measurement etalon used for calibrating temperature sensor. As a gauge tool for temperature measurement, there are two characteristics must have. (1) It can obtain a small zone (point) temperature; (2) The measurement results must be irrelative to the radiance of surface material to be measured. The etalon has a higher precision and it is at least 1-2 orders of magnitude higher than that of the temperature sensors to be calibrated. If precision of the temperature sensor to be calibrated is 1° C., then the precision for the temperature measurement etalon must be at least 0.1° C.
To reach the above claim, the present invention uses a lens with visual angle less than 20 degree, which adds a GRIN lens (a micro plane lens) can be a point image telescope. The wave energy on object plane will pass through the point image telescope before it separating to radiation wave and conductive wave. The wave energy of heat source surface will image to the rear end of the GRIN lens with no distortion. The optical spectrometer then chose only the max-value wave energy of each point on the object plane entering into optical spectrometer and other wave energy can not enter. Sensor optical fiber will couple the max-value wave energy on the image plane to reduce the measured area, that can be regarded as point temperature measurement. The waveforms of the output of sensor optical fiber are similar to the wave energy waveform of the heat source surface. The wavelength variety will be measured by the optical spectrometer. Because the wavelength is a reciprocal of the wave number, the output analog data can be converted to the optical digital data by the differential means, such process fit the rule that peak wavelength became shorter and wave number became larger with the temperatures increase. The wave number can be converted to the fringe number by a crystal oscillator. Microprocessor will take count of bits to obtain corresponding temperature value. The types of crystal oscillator will determine the precision of the etalon. For example, a temperature change of 0.1° C. may correspond to 10 bits or 100 bits and even more. Higher fringe number means higher precision. To keep image plane in focus, some methods such as manual focusing, auto focusing and even non-focusing are adopted. Non-focusing means that a two dimensional diffraction screen is put on the former focus of objective lens so that the image plane remains focused. To solve the issue that resolution of the image plane may decrease with the increase of the measurement distance, another optical fiber with large core can be used for coupling other relative max-value wave energy from the optical spectrometer as a reference. By comparing the reference signal and the max-value wave energy, the measurement results could be irrelevant to the measurement distance.
The present invention shows a non-contact temperature measurement etalon. A novel signal processing method, with no linear calibration is used to make the measurement with high precision and adjustable precision. As we know, an analog data can be divided into several micro units by differential process. If these micro units enter a ‘gate’ one by one, they can form a line of output which is same to convert the analog data level to the digital data level the in a signal processing circuit. The key is how to find the rule for forming the line. It can be seen from
Black body furnace is not necessary to be used as the calibration furnace of present invention, some light source such as incandescent lamp can be used, as