JPH0510822A - Radiation temperature measuring instrument - Google Patents

Abstract

PURPOSE:To obtain a radiation temperature measuring instrument which can make measurement in a low-temperature area or a smaller target size area and, at the same time, can be also applied to an object having fluctuating emissivity in an environment where stray noise exists. CONSTITUTION:This radiation temperature measuring instrument is constituted of a stray noise shielding body 9, two sets of photon counters 3 and 4 for measuring two spectral radiation luminance signals defined by one or more different conditions of the wavelength and polarized light measuring angle, arithmetic unit 5, parameter input device 6, and computed result output device 7. Since the photon counters 3 and 4 are used, the number of photons can be discretely counted and the SN can be remarkably improved. In addition, since this radiation temperature measuring instrument finds temperatures by automatically calculating the emissivity by solving a relational expression between the two kinds of spectral emissivity, the measuring accuracy of this instrument can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation temperature measuring device for measuring the temperature of a heated object in a non-contact manner. INDUSTRIAL APPLICABILITY The radiation temperature measuring device according to the present invention can be used in many industrial fields such as a metal manufacturing process for steel and non-ferrous metals, as well as chemistry and machinery having a high temperature treatment process.

[0002]

2. Description of the Related Art Conventional radiation temperature measuring devices (for example, "medium temperature"
Of a radiation thermometer for electric use ", Electric Steelmaking, Vol.57, No.2, pp.10^Four
-111 radiation thermometer) uses Si, Ge, PbS as photoelectric conversion means.
Photoelectromotive force such as photon-type semiconductor detectors and thermopiles
Type photon detector is used, so photons are measured one by one
Is not possible, and is it a signal-to-noise ratio (SN ratio) constraint?
It was difficult to increase the measurable lower limit temperature. Well
Also, conventional single-color or two-color thermometers have
Since the measurement is performed assuming that the emissivity ratio is constant, the emissivity is
However, there is a problem in that it cannot be applied to a moving object.

[0003]

In order to accurately measure the temperature of an object in a non-contact manner by the radiation temperature measuring method, it is a principle to measure a spectral radiance signal having a wavelength as short as possible. As is known from the body radiation formula,
As the temperature decreases, the radiance signal from the object sharply decreases as the wavelength becomes shorter, so that the SN ratio cannot be secured, and there is a measurable lower limit temperature. The lower limit temperature is determined by various conditions such as the detection wavelength, the detection wavelength bandwidth, the detection element, the optical system, and the electric signal processing system. Among them, the most important are the detection wavelength and the detection element. The standard measurable lower limit temperature of the conventional radiation thermometer is a wavelength of about 1μ for Si devices.
Approximately 500 ° C with radiation thermometer of m, wavelength about 1.6 μ with Ge element
Approximately 350 ° C with a radiation thermometer of m, wavelength about 2.2 with PbS element
It is about 200 ° C. in μm.

The lower limit temperature that can be measured by the conventional radiation thermometer described above is a case where the measurement target surface area (target size) of the object to be measured is secured to a certain extent or more. To rise. That is, when a radiation thermometer with a wavelength of about 1 μm is used with a Si element, the temperature of an object with a diameter of about 10 mm 1 m ahead can be measured up to a lower limit of about 500 ° C. When trying to measure, the lower limit temperature must be 500 ° C. or higher for measurement.

The first problem to be solved by the present invention is
It is an object of the present invention to provide an accurate temperature measuring device that secures a high SN ratio in a temperature range where the conventional radiation thermometer cannot measure due to the limitation of the SN ratio or a target size range.

Further, the conventional monochromatic and dichroic thermometers have a problem that they cannot be applied to an object whose emissivity fluctuates because the measurement is performed assuming that the emissivity or the emissivity ratio is constant. A second problem to be solved by the present invention is to solve the first problem and to provide a temperature measuring device capable of accurately obtaining temperature and emissivity even for an object whose emissivity varies.

[0007]

A radiation temperature measuring apparatus of the present invention is a shield installed to face a measurement point on the surface of an object to be measured in order to remove stray light noise incident on the surface of the object to be measured, or A shield installed facing the measurement point on the surface of the object to be measured in order to remove stray light noise incident on the surface of the object to be measured and to increase the effective spectral emissivity of the surface of the object; Two sets of photon counters for counting the number of photons proportional to the spectral radiance on the surface of the measurement object under different spectral conditions such as wavelength, measurement angle, and polarization, and two sets of photon counters corresponding to each spectral radiance. A parameter input device for inputting a parameter for expressing a relational expression between spectral emissivities, a photon count value by two sets of photon counters, and two spectroscopic values preset by the parameter input device. An arithmetic unit for calculating the temperature of the object to be measured and the two emissivities from the relational expression between the emissivities, and an arithmetic result output unit for outputting the arithmetic result of the temperature and the two sets of spectral emissivity values obtained by the arithmetic unit. It is characterized by being composed of.

[0008]

The object to be measured at the temperature T has the spectral radiance represented by the following equation.

Lλ = ελ · Lb (λ, T) (W · m ⁻² · sr ⁻¹ · μm ⁻¹ ) (1) where ελ: Spectral emissivity (−) Lb (λ, T): Temperature T , Blackbody spectral radiance at wavelength λ (Wm ^-2 sr ^-1 μm ^-1 )

In the conventional radiation thermometer, the optical power proportional to the spectral radiance represented by the equation (1) Eλ = ελ · Eb (λ, T) = ελ · K · Lb (λ, T) (W) ( 2) However, K: constant determined by optical system (m
²・ sr ・ μm) Eb (λ, T): Since a continuous current signal proportional to the blackbody spectral radiance signal (W) is detected, shot noise and dark current noise generated with the continuous current signal are detected. Etc. were mixed in the detection signal.

If a photon counter composed of a photomultiplier tube and a counter is used, each photon can be discretely counted, so that shot noise and noise due to dark current can be reduced. That is, the photon counter counts the number of photons represented by the following equation. Nλ = Eλ / (h · ν) = ελ · Eb (λ, T) / (h · ν) (s ⁻¹ ) (3) where Nλ: photon count value from the object (s
^-1 ) h: Planck's constant (= 6.63 × 10 ⁻³⁴ ) (J · s) ν: Light frequency (= c / λ) (s ⁻¹ ) c: Light velocity (= 3 × 10 ⁸ ) (m / S) The photo counter was calibrated in a blackbody furnace, and Nb (λ, T) = Eb (λ, T) / (h · ν) (s ⁻¹ ) (4) where Nb (λ, T) : If the blackbody furnace photon count value at temperature T and wavelength λ is related to temperature T, the object temperature T can be immediately obtained from Nb (λ, T) if the measured value Nλ of the object to be measured is corrected by ελ. You can

Actually, since the quantum efficiency η on the photocathode surface of the photomultiplier tube is 1 or less, Nb (λ, T) = η · Eb (λ, T) / (h · ν) (s ^-1 (5) Nλ = ελ · Nb (λ, T) (s ⁻¹ ) (6)

As described above, since the photon counter can discretely count photons one by one, it is possible to significantly improve the SN ratio as compared with the conventional case where the light intensity is measured as a continuous current. Therefore, it can be measured at a lower temperature or with a smaller target size than the conventional method.

The radiation temperature measuring device according to the present invention can measure in a shorter wavelength band and lower temperature range than the conventional radiation thermometer. Therefore, in addition to the above-mentioned merits, There are such advantages. That is, a temperature measurement error ΔT = (λ · T ² / C ₂ ) · (Δελ / ελ) (° C. or K) (based on the emissivity setting error, which generally holds for all radiation thermometers) 7) However, C _2: second constant radiation (= 14,388) (mu
m · K) can be made significantly smaller. For example, in order to compare the case of measuring an object at a temperature of 300 ° C. with an emissivity setting error of 10%, a conventional radiation thermometer has a wavelength of λ = 2.2 μm, and a radiation temperature measuring device according to the present invention has a wavelength of λ = 0.5 μm. The temperature measurement error given by the equation (7) is ΔT = 5.0 ° C .: Conventional ΔT = 1.1 ° C .: The present invention, and a marked improvement in accuracy can be expected.

The above is a brief description of the advantages of a radiation temperature measuring device using a photon counter, which is expected when a certain wavelength λ is focused.

A spectral radiance signal can be physically distinguished and handled if any one or more of wavelength, measurement angle (angle formed by radiation line of object to be measured and radiation signal light) is different. If the photon count values proportional to two spectral radiances that are different in this sense are Nx and Ny, respectively, they are expressed by the following equation.

Nx = εx · Nbx (T) (s ⁻¹ ) (8) Ny = εy · Nby (T) (s ⁻¹ ) (9) where x, y: wavelength, measurement angle, or polarization Subscript Nx, Ny: Radiance signal count value from the surface of the object to be measured (s ^-1 ) Nbx, Nby: Blackbody radiance signal count value at temperature T (s ^-1 )

One of the inventors of the present invention is Japanese Patent Application No. 63-2710. To 47
By the method of solving the relational expression between the two spectral emissivities
It shows that the temperature of an object and two emissivities can be calculated simultaneously.
It was If this method is applied,     εy = f (εx) (10) However, f: emissivity characteristic relation showing the relationship between emissivity
number (8) and (9) are solved simultaneously by solving
It is possible to obtain T and two emissivities εx and εy at the same time.
Wear.

The emissivity characteristic function f may be experimentally obtained in advance or may be theoretically determined.

Since the radiant temperature measuring device according to the present invention can simultaneously measure temperature and emissivity by using two different spectral radiance signals, it can be used in an atmosphere accompanied by a phenomenon of surface change such as oxidation or alloying. It has a feature that accurate measurement can be performed even in a situation where the emissivity can change drastically like the steel plate temperature measurement described in (1).

By the way, when the temperature of an object is measured by the radiation thermometry, if a higher temperature object or a flame exists around the object, a heat radiation signal from the object is incident on the object surface and a part of the object is detected. The reflected signal (stray light noise) enters the radiometer and causes measurement errors. Further, when detecting radiation signals in the near-infrared region and visible region, radiation signals from sunlight or fluorescent lamps may also become stray light noise, resulting in temperature measurement error. Hereinafter, the effect of stray light noise will be described by taking the case of a monochromatic thermometer as an example.

In the presence of stray light noise, the number of photons counted under a certain spectroscopic condition (wavelength, measurement angle, polarization condition) is approximately Nλ = ελ · Nb (λ, T) + (1-ελ ) .Nb (λ, Ts) (11) where Ts is represented by the apparent temperature of the surroundings. The second term on the right side of the equation (11) is the stray light noise term.

The above problem can be easily solved by using a shield which is installed so as to face a measurement point on the surface of the object to be measured. That is, if a shield made of, for example, an opaque body such as metal is installed facing the measurement point, stray light from the surroundings is blocked by the shield and does not enter the measurement point. The stray light noise signal of item 2 does not enter the radiometer.

On the other hand, when measuring the temperature of a metal such as a cold-rolled steel sheet, in general, the spectral emissivity is often low in the near-infrared and visible wavelength bands, so that the signal becomes smaller and the emissivity setting error occurs. The temperature measurement error based on may increase.

This problem can be easily solved by using a shield whose surface facing the measurement point on the surface of the object to be measured is processed to have high reflectance. That is, stray light from the surroundings is blocked by the outer surface of the shield so that it does not enter the measurement point, and the light emitted from the measurement point is multiply reflected by the inner surface of the shield and the surface of the measured object, as shown in the following equation. This is effectively detected by the radiometer as a larger spectral radiation signal. Nλ = ελ ′ · Nb (λ · T) (12) where ελ ′: Effective spectral emissivity

Since the temperature measurement error based on the emissivity setting error is expressed by the equation (7), the temperature measurement error can be reduced by effectively increasing the spectral emissivity. In order to make the inner surface of the shield have a high reflectance, for example, gold plating may be performed.

By using the shield as described above, stray light noise can be removed, or at the same time, the spectral emissivity can be effectively increased for measurement. As a result, the conventional radiation thermometer has an SN ratio. It is possible to provide a high-accuracy temperature measuring device that secures a high SN ratio in a temperature region where measurement is impossible due to the above limitation or a target size region.

What has been described above by taking the case of the monochromatic thermometer as an example also applies to the case of measuring two different spectral radiances as in the apparatus of the present invention. That is, the stray light noise can be easily removed by using the shield, so that measurement without error becomes possible. Furthermore, when a shield whose surface facing the measurement point on the surface of the object to be measured has a high reflectance is used, the spectral emissivity can be effectively increased and two spectral radiances can be measured, resulting in high accuracy. Enables temperature measurement. In this case, the emissivity characteristic function f is expressed as εy ′ = f (εx ′) (13) by experimentally or theoretically as a function of the effective spectral emissivity εx ′ and εy ′. You just have to decide.

<Embodiment> FIG. 1 shows an embodiment of a radiation temperature measuring apparatus according to the present invention. 8 is an object to be measured, 9 is a shield, 1 is radiation signal light of x component from the object to be measured, 2 is radiation signal light of y component, radiation signal light 1,
2 enters a light receiving portion of two sets of photon counters indicated by 3 and 4 through a transmission window (not shown) provided in the shield. These photon counters 3 and 4 have a photon number Nx,
Each Ny is counted and transmitted to the arithmetic unit 5. The arithmetic unit 5 obtains the black body count values Nbx, Nby, the temperature T, and the emissivities εx, εy from the emissivity characteristic function f and Nx, Ny which are input and set from the parameter input unit 6 in advance. The calculation result output device 7 determines the N calculated by the calculation.
bx, Nby, T, εx, εy are output to the outside in an appropriate format such as current, voltage or digital.

The two photon counters 3 and 4 may be housed in one light-receiving device, or may be separately installed, especially when detecting signals having different measurement angles. It goes without saying that the light receiving portions of the photon counters 3 and 4 may be provided with an interference filter for limiting the wavelength, or of course, a polarizing plate may be provided for detecting the signal light of different polarization components. Yes.

The relationship between the temperature T and Nbx (T), Nby (T) may be known in the form of a table or a formula by performing calibration in a black body furnace as in the conventional radiation thermometer.

It goes without saying that the input means of the parameter input device 6 may be, for example, a keyboard, or a reading device such as a memory card, or an input means such as a line from an external computer.

Table 1 shows a count value Nbx (T) when one example of the radiation temperature measuring device according to the present invention is calibrated in a black body furnace,
It is a table of Nby (T). In this example the wavelength λ
Bandwidth of 0.1 μ at x = 0.7 μm and λy = 0.6 μm
m, measuring object diameter 10 mm, lens diameter 25 mm, distance 1 m
Detected in. The quantum efficiency η of the detector was about 0.1.

In the two sets of photon counters thus constructed, Nbx (T) and Nby (T) could be accurately expressed by the following equation: Nbx (λ, T) = 7.67 × 10 ¹⁷ · exp (-C ₂ / (λx · T) (s ⁻¹ ) Nby (λ, T) = 1.42 × 10 ¹⁸ · exp (−C ₂ / (λy · T) (s ⁻¹ ) where λx = 0.7 μm, λy = 0.6 μm and T are absolute temperatures (unit: K).

As is clear from Table 1, the radiation temperature measuring apparatus of this embodiment can measure a temperature range as low as 400 ° C. even though the wavelength range is as short as 0.7 μm and 0.6 μm. In the conventional radiation thermometer, considering that 500 ° C. is the detection limit on the low temperature side even in the long wavelength region of about 1 μm, the present invention enables the temperature region to be expanded to the low temperature region. Is clear.

Further, with the radiation temperature measuring apparatus of this embodiment, the diameter of the object to be measured is reduced, and Nby at 500.degree.
^{Find the} diameter (d) at which (T) becomes a count value of about 200 (s ⁻¹ ). Considering that the square value of the measurement target diameter and the photon count value are almost proportional, (d / 10) ² = 200 / 4.81 × 10 ⁴ ∴d = 0.64 mm when calculated using the values in Table 1. That is, even objects with a diameter of 0 and 64 mm have a temperature of 500 ° C.
Can be sufficiently measured in. In the conventional radiation thermometer, the distance count (ratio between the distance and the diameter to be measured) has a value of about 100, whereas in the radiation temperature measuring device according to the present invention, the distance count can be a large value such as about 1500. , It becomes possible to measure the temperature even with a smaller measuring object.

In the radiation temperature measuring apparatus of this embodiment, the temperature of the alloy steel sheet was measured by using εy = f (εx) = 0.95 · εx + 0.014 as a relational expression representing the relation between two spectral emissivities. However, even if the emissivity was changed, the relative error ΔT / T could be accurately measured within about 1%.

In the radiation temperature measuring device according to the present invention,
Physically meaningful measurement can be performed by measuring the spectral radiance that differs by at least one of wavelength, measurement angle, and polarization. Table 2 shows the results obtained by conducting an experiment under different conditions when the relative error ΔT / T was measured within 1% and the condition was judged to be acceptable. In the table, λx and λy are detection wavelengths (unit: μm),
θx and θy are measurement angles (unit: °), p is p-polarized light, and s is s-polarized light. In addition, those without the subscripts x and y indicate the same conditions.

As is clear from Table 2, by using the radiation temperature measuring device according to the present invention, it is possible to measure a lower temperature range or a smaller object to be measured than the conventional radiation thermometer. Moreover, it is possible to perform accurate measurement even on an object whose emissivity varies.

Among the specific examples shown in FIG. 1, a measurement example is shown in which the temperature of the oxide steel sheet in the heating furnace is measured without treating the inner surface of the shield to a high reflectance. The inner surface of the shield used in this example had a cylindrical shape with a radius of 300 mm and a height of 150 mm, and the gap with the steel plate was 50 mm. In this case, the spectral reflectance at wavelength λx = 0.7 μm is 0.6 and the wavelength λx is 0.7 μm.
It was previously known by experiments that the spectral reflectance at y = 0.6 μm was 0.7. Although the steel plate temperature was 500 ° C. and the furnace inner wall temperature was 600 ° C., the photon count value by photon quantum was Nx = 1.31 × 10 ⁶ (s ⁻¹ ) Ny = 3.37 × due to the shielding effect of the shield. It was obtained as 10 ⁴ (s ^-1 ). The emissivity characteristic function f has been previously obtained by an experiment, and since (εx, εy) = (0.6, 0.7) is satisfied, the above Nx, Ny are used to obtain (8), (9), ( 1
By solving the equations (0) simultaneously, εx = 0.6 εy = 0.7 Nbx = 2.18 × 10 ⁶ Nby = 4.18 × 10 ⁴ T = 500 ° C. was accurately obtained.

On the other hand, when measured by the conventional method without using a shield, stray light noise from the inner wall of the furnace is mixed in, and the photon count value is Nx = 0.6 × Nbx (500 ° C.) + (1- 0.6) × Nbx (600 ° C.) = 0.6 × 2.18 × 10 ⁶ + 0.4 × 4.58 × 10 ⁷ = 1.96 × 10 ⁷ (s ⁻¹ ) Ny = 0.7 × Nby (500 ° C.) + (1-0.7) × Nby (600 ° C) = 0.7 x 4.81 x 10 ⁴ +0.3 x 1.68 x 10 ⁶ = 5.38 x 10 ⁵ (s ^-1 ) and the value without stray light noise Nx = 1.31 x 10 ⁶ , Ny = 3 The value is significantly different from 0.37 × 10 ⁴ (s ⁻¹ ), which naturally causes a large measurement error.

Similarly, among the specific examples shown in FIG. 1, the shield
The inner surface of the cold-rolled steel sheet in the heating furnace is treated to a high reflectance.
An example of measurement when the temperature is measured is shown. The shield used in this example
The shape of the inner surface of the cover was the same as that of the above-mentioned example.
It was In the case of this example, cold rolling at the wavelength λx = 0.7 μm
The spectral emissivity of the steel sheet is 0.3, and the wavelength λy is 0.6 μm.
The spectral reflectance at was 0.4. High inside
Effective emissivity when facing a shield treated to reflectivity
According to the experiment,
I knew. Steel plate temperature is 500 ° C, furnace inner wall temperature is 6
The temperature was 00 ° C, but the photon
The photon count value by Unta is Nx = 1.53 × 10⁶   (S^-1) Ny = 3.85 × 10^Four    (S^-1) Was obtained. In this case as well, the practically increased spectral emissivity
The emissivity characteristic function f representing the relationship between
It has been determined that (εx, εy) = (0.7, 0.8)
Therefore, using the above Nx and Ny, (8), (9),
When equations (10) are solved simultaneously, εx = 0.7 εy = 0.8 Nbx (T) = 2.18 × 10⁶ Nby (T) = 4.18 × 10^Four T = 500 ° C Was obtained accurately.

On the other hand, the conventional method without a shield was used.
In this case, stray light noise from the inner wall of the furnace mixes in the photon meter.
The numerical value is from equation (11)     Nx = 0.3 x Nbx (500 ° C) + (1-0.3) x Nbx (600 ° C)         = 0.3 x 2.18 x 10⁶ +0.7 x 4.58 x 10⁷         = 3.27 x 10⁷                                  (S^-1)     Ny = 0.4 x Nby (500 ° C) + (1-0.4) x Nby (600 ° C)         = 0.4 x 4.81 x 10^Four  +0.6 x 1.68 x 10⁶          = 1.03 x 10⁶                                   (S^-1) And the value when there is no stray light noise     Nx = 1.53 × 10⁶ , Ny = 3.85 × 10^Four    (S^-1) Results in a value that is significantly different from
Cheat.

If a shield is used as in the present invention, stray light noise can be removed, or at the same time, the spectral emissivity can be effectively increased for measurement. As a result, the conventional radiation thermometer has an SN ratio. It is possible to provide a high-accuracy temperature measuring device that secures a high SN ratio in a temperature region where measurement is impossible due to the above limitation or a target size region.

[00044]

By using the radiation temperature measuring device according to the present invention, the lower limit of temperature measurement can be expanded as compared with the conventional radiation thermometer.
In addition to reducing the target size, accurate temperature measurement is possible even for objects with varying emissivity, and it can be used in various industrial processes where temperature measurement accuracy greatly affects product quality and productivity. The economic effects are immeasurable.

[Table 1]

[Table 2]

[Brief description of drawings]

FIG. 1 is an embodiment of a radiation temperature measuring device according to the present invention.

[Explanation of symbols]

1 Radiation signal light (x component) 2 Radiation signal light (y component) 3 Photon counter (for x component detection) 4 Photon counter (for y component detection) 5 arithmetic unit 6 Parameter input device 7 Calculation result output device 8 Object to be measured 9 Shield

Claims (2)

[Claims] 1. A shield installed facing a measurement point on the surface of the object to be measured, and a number of photons proportional to the spectral radiance of the surface of the object to be measured, which is one of wavelength, measurement angle, and polarization. Two sets of photon counters for counting under different spectral conditions, a parameter input device for inputting a parameter expressing a relational expression between spectral emissivity corresponding to two sets of spectral radiance, and two sets of photons An arithmetic unit for calculating the temperature of the object to be measured and the two sets of spectral emissivity from the relational expression between the count value and the spectral emissivity, and the temperature obtained by the calculation and the two sets of spectral emissivity values are output. And a calculation result output device for the radiation temperature measuring device. 2. The radiation temperature measurement according to claim 1, wherein the shield is a shield having a surface which is installed facing the measurement point on the surface of the object to be measured and which has been treated to have high reflectance. apparatus.