A system that obtains true temperature and emissivity from brightness temperatures at two wavelengths.

Abstract

The true temperature and emissivity at two wavelengths of the object being measured are obtained. [Solution] The radiation emitted by the object being measured is captured at two wavelengths, and the brightness temperature at each of the two wavelengths is calculated. Separately, the relative radiation temperature at the two wavelengths is used as an approximate indicator to calculate the two-value provisional emissivity at the two wavelengths, and the provisional true temperature is calculated from the brightness temperature of the first wavelength and the provisional emissivity of the first wavelength calculated earlier. The provisional true temperature of the second wavelength is calculated in the same way. The emissivity of the first wavelength and the emissivity of the second wavelength are changed and input through trial and error so that the two provisional true temperatures match, and the temperature at which they match is taken as the true temperature, and the emissivity of both wavelengths used at that time is taken as the emissivity at each wavelength.

Description

Technical Field

[0001] In order to obtain the true temperature using a radiation thermometer or a thermograph, correction based on the emissivity is necessary. In a radiation ratio thermometer (two-color thermometer), the true temperature can be obtained without the need for emissivity correction, but it is an absolute condition that the emissivities at two wavelengths are equal. According to the present invention, even when the emissivity is unknown and the emissivities at two wavelengths are different, the true temperature and the emissivity can be known.

Background Art

[0002] A method of measuring temperature non-contact is achieved by measuring the amount of electromagnetic waves including light and infrared rays radiated from the measurement object. A device that measures the radiation amount from the entire wavelength or a wide wavelength range of electromagnetic waves to obtain the temperature is called a radiation thermometer, and a device that measures the radiation amount from a single wavelength or a narrow wavelength range to obtain the temperature is called a brightness thermometer. However, in either case, correction based on the emissivity that depends on the wavelength specific to the measurement object is required.

[0003] However, since it is difficult to obtain an accurate emissivity, the radiation ratio temperature method (two-color temperature method) that does not depend on the emissivity has been frequently used. The radiation ratio temperature method receives the radiation amount from the measurement object at two wavelengths and calculates the temperature from the ratio. When the emissivities at two wavelengths are the same, the emissivity can be excluded from the calculation. Depending on the measurement object, there may be cases where the emissivities cannot be made the same. Also, by narrowing the interval between the two wavelengths for the purpose of making the emissivities equal, while the difference in emissivities can be reduced, the signal / noise ratio deteriorates due to the reduction in the radiation amount difference.

[0004] The present invention measures the radiation amount from the measurement object at two wavelengths, calculates the radiation ratio temperature and two brightness temperatures at two wavelengths, and then obtains the true temperature and two emissivities by trial and error to change and assign the obtained provisional emissivity values.

[0005] The amount of radiation from a blackbody, an object that either radiates or absorbs all energy, can be determined by Planck's radiation law. However, within the normal measurement range of approximately 4000 Kelvin or less, Wien's radiation law can be applied, and the relationship between radiation and temperature is expressed by equation (1). TIFF2026097684000002.tif31105TIFF2026097684000003.tif2383

[0006] The objects typically measured are not black bodies, and they do not radiate or absorb 100% of their energy. The ratio of the amount of radiation to that of a black body is called emissivity and is expressed by ε. Applying this to equation (1) yields equation (2). TIFF2026097684000004.tif1384

[0007] If we take the combined efficiency of the sensors, amplifiers, AD converters, etc., and denote the system conversion rate as β, then the system output value is given by equation (3). TIFF2026097684000005.tif1484

[0008] Expanding equation 3, the true temperature is obtained using equation 4. TIFF2026097684000006.tif20100

[0009] If the luminance temperature, which is the temperature of a non-blackbody before emissivity correction, is denoted by Tb, then the luminance temperature measured by the measurement system is expressed by equation (5). TIFF2026097684000007.tif21110

[0010] Expand equations (4) and (5) to obtain the true temperature in equation (6). TIFF2026097684000008.tif2096

[0011] Brightness temperature = Tb1, measured at wavelength λ1, emissivity = ε1 Brightness temperature = Tb2, measured at wavelength λ2, emissivity = ε2 Applying this to equation (6), TIFF2026097684000009.tif2099TIFF2026097684000010.tif19100

[0012] Since the true temperatures T obtained from both equations are equal, we obtain equation (7). Substituting ε1 and ε2 into (6) when equation (7) holds true will give the true temperature, but since there are two unknowns, ε1 and ε2, multiple convergent values ​​will appear and cannot be determined through trial and error (cut and try).

[0013] To obtain the correct convergence value, the radiative specific temperature Tr is calculated as a near-value index, and provisional emissivity values ​​ε'1 and ε'2 are calculated based on this and substituted into equation (7). Using these as an index, ε1 and ε2 are input through trial and error to satisfy equation (7), thereby determining the true temperature and emissivity values ​​ε1 and ε2. The calculation of the radiative specific temperature Tr is as described in Japanese Patent No. 4378003, by deriving equation (8) from equation (3) and then expanding it to obtain equation (9). TIFF2026097684000012.tif2084λ1; First wavelength λ2; First wavelength M1; radiation dose at wavelength 1 M2; radiation dose at wavelength 2 ε1; emissivity at the first wavelength ε²; emissivity at the second wavelength

[0014] Assuming that the emissivity at both wavelengths is equal, ε1 = ε2, equation (9) is obtained as the emissivity ratio temperature. TIFF2026097684000013.tif25103

[0015] The provisional emissivity ε' is obtained by expanding equation (3) and using equation (10). TIFF2026097684000014.tif1689

[0016] When ε’1 and ε’2 obtained by equation (10) are applied to equation (7), a value close to “0” is obtained. Therefore, ε1 and ε’2 are substituted by trial and error (Cut and Try) to obtain the true temperature T, emissivity ε1, and ε2. In trial and error, the bisection method or Newton's method is used for efficient calculation.

Prior Art Documents

Patent Documents

[0017]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0018] Obtaining the true temperature and emissivities at two wavelengths.

Means for Solving the Problems

[0019] The radiation amount emitted by the measurement target is received at two wavelengths, and from this, two brightness temperatures at the two wavelengths and the radiation ratio temperature as a calculation index are calculated. Then, by inputting the emissivities at the two wavelengths by trial and error (Cut and Try), the true temperature and the emissivities at the two wavelengths are obtained.

Effects of the Invention

[0020] First, the true temperature can be obtained. Second, it is possible to evaluate the validity of determining the radiation ratio temperature (two-color temperature) as the true temperature. Third, for a radiation thermometer with a simple structure and low cost, it is possible to present the accurate emissivity of the measurement target and obtain the accurate true temperature.

Modes for Carrying Out the Invention

[0021] It is composed of a light receiving / camera unit consisting of an optical mechanism and an electronic circuit, and a computer and software based on a window base or a Linux base, etc.

[0022] In the two-sensor system, the image from the objective lens is split into two by a beam splitter. By using wavelength-selective materials such as dichroic mirrors in the beam splitter, light loss can be prevented.

[0023] The received light that travels straight through the beam splitter passes through the first wavelength filter, is input to the first photodetector, is amplified as an electrical signal, is digitally converted by an AD converter, and is output to the computer. The received light reflected by the beam splitter passes through the second wavelength (λ2) filter, is input to the second photodetector, is amplified as an electrical signal, is digitally converted by an AD converter, and is output to the computer.

[0024] The process is almost identical whether it's real-time processing or analysis from recorded images. This will be explained based on the system flow shown in Figure 5. ▲1▼ At the start of the analysis, ▲2▼ you select whether to perform the analysis on all pixels of the image, add a few surrounding pixels (e.g., 2x2 pixels), or perform temperature analysis on a specified area of ​​the image.

[0025] ▲3▼ Set the number of pixels to add or the measurement area.

[0026] ▲4▼Send a start-up command to the light-receiving / camera unit, or read image data from its own recording unit.

[0027] ▲5▼The captured image is separated into a first wavelength (λ1) and a second wavelength (λ2), and after processing such as amplification as determined, it is stored in a predetermined memory.

[0028] ▲6▼The luminance temperature (Tb1) at the first wavelength (λ1) is obtained from the radiance at the first wavelength (λ1) using equation (5). ▲7▼The luminance temperature (Tb2) at the second wavelength (λ2) is obtained from the radiance at the second wavelength (λ2) using equation (5). ▲8▼The specific radiation temperature (Tr) at the first wavelength (λ1) and the radiance at the second wavelength (λ2) is obtained from equation (9).

[0029] ▲9▼The provisional emissivity ε1' is obtained from the radiation amount and radiation ratio temperature at the first wavelength (λ1) using equation (10). ▲10▼The provisional emissivity ε2' is obtained from the radiation amount and radiation ratio temperature at the second wavelength (λ2) using equation (10).

[0030] ▲11▼The provisional true temperature for the first wavelength is obtained from the luminance temperature at the first wavelength λ1 and the emissivity temperature using equation (6a), and ▲12▼The provisional true temperature for the second wavelength is obtained from the luminance temperature at the second wavelength λ2 and the emissivity temperature using equation (6b).

[0031] ▲13▼The provisional true temperature obtained from the first wavelength and the provisional true temperature obtained from the third wavelength are calculated by checking if equation (7) is "0". If they are equal, that value is the true temperature, and the provisional emissivity ε1' and ε2' are the true emissivity. In this case, the radiative ratio temperature is the true temperature.

[0032] ▲13▼If the true temperature at both wavelengths does not equal "0" in equation (7), sequentially input values ​​near ε'1 and ε'2 for ε1 and ε2 using a cut-and-try method to find the value that equals "0". The value at which equation (7) shows "0" is the true temperature and the emissivity ε1 and ε2 at each wavelength. The search time can be shortened by using the bisection method or Newton's method during the trial-and-error input. The radiation levels at two wavelengths are processed by a computer. [Industrial applicability]

[0033] Its practical applications in research and development, as well as in thermal processing manufacturing sites, are foreseeable. [Brief explanation of the drawing]

[0034] [Figure 1] Figure 1 shows an example of the basic structure of a two-sensor light-receiving / camera unit. [Figure 2] This system has a dual-wavelength mosaic filter attached to the front of the sensor. [Figure 3] This system records two wavelengths separately using a single sensor. [Figure 4]This system features a dual-wavelength rotating filter mounted in front of the sensor. [Figure 5] This shows the flow of system processing.

Claims

1. A temperature measurement system that obtains the temperature of an object by measuring the radiation emitted by the object, and has the function of receiving the radiation amount divided into two wavelengths with a photoelectric element, calculating the brightness temperature of the first wavelength and the brightness temperature of the second wavelength from the output signals of each wavelength element, calculating the radiation ratio temperature from the radiation amount signals of the two wavelengths, and calculating the provisional emissivity of the first and second wavelengths obtained from the radiation ratio temperature, and calculating the true temperature and the emissivity of each of the two wavelengths by trial and error changing and substituting two provisional emissivity values ​​so that the provisional true temperature obtained from the brightness temperature of the first wavelength and the provisional emissivity of the first wavelength, and the provisional true temperature obtained from the brightness temperature of the second wavelength and the provisional emissivity of the second wavelength match.

2. A system according to claim 1, which uses an image sensor composed of multiple photoelectric elements.

3. A system according to claim scope 2, which increases the output amount and speed of output by setting a region and summing the pixels, and also obtains the true temperature quickly by applying the emissivity of that region to all pixels or other regions.

Images