RU2151382C1 - Process of pyrometric measurement - Google Patents

Abstract

FIELD: optical methods of contact-free measurement of actual temperature of object. SUBSTANCE: intensity of inherent radiation of object is measured at several, but not less than three, temperatures T₁ < T₂ <...< T_N in several spectral intervals. Total radiation described by Stefan- Bolzmann law can be measured instead of one of intensities. Number of measured intensities M and number of values N of temperature at which measurements were taken should be tied up by number of unknown parameters determining intensity of radiation. EFFECT: increased measurement accuracy without use of preliminary graduation and possibility of plotting of thermodynamic temperature scale by radiation. 1 dwg

Description

 The invention relates to measuring equipment, and more particularly to optical non-contact methods for measuring the true temperatures of various objects.

 In optical pyrometry methods, the measurement result depends not only on temperature, but also on the properties of the surface of the emitting body and the transmission of the intermediate medium. A priori information about these parameters when measuring true temperature is usually used in the form of emissivity and transmission coefficients of the intermediate medium, tabulated in the reference literature. The incompleteness of the data on these coefficients, the mismatch of their values in real conditions with the tabulated ones, the change in the properties of the emitting surface and the intermediate medium during the measurement process lead to the appearance of methodological errors that are ten times greater than the instrumental errors. On the other hand, without definite a priori information about the radiative characteristics of the test object, the very task of measuring its temperature using optical pyrometry methods is groundless. To solve the problem of measuring the true temperature of an object, it was proposed to use various additional a priori information on the radiative properties of the object, in particular, the temperature dependence of the spectral emissivity.

 From the prior art, the known method of pyrometric measurements / Light D.Ya. Optical methods for measuring true temperatures, Moscow, Nauka, 1982, pp. 250-253 /, including the measurement at two temperatures of an object of its own radiation intensity in the spectral range corresponding to the spectral region of the object’s own radiation, in which the Wien approximation is valid, and the radiation intensity object in the spectral range beyond the validity of the Wien approximation.

 The disadvantage of the known method of pyrometric measurements is that it does not provide a measurement of the true temperature, since the underlying position - the constancy of the emissivity when the temperature of the object - is incorrect. Indeed, the dependence of the emissivity on temperature follows not only from the theory / of the relationship between emissivity and electrical conductivity /, but from extensive experimental data for various substances, primarily for metals.

 A known method of pyrometric measurements, which uses a linear dependence of the spectral emissivity on temperature / Lincoln R. C., Petit R.B., High Temperatures High Pressures, 1973, v 5. p. 421 /. According to this method, the intensities of its own radiation in two spectral ranges are measured at two temperatures of the controlled object.

 The disadvantage of this method is that for one of the values of the temperature of the object, for example for room temperature, the values of the spectral emissivity must be known. However, this a priori information is not enough for a direct solution of the obtained system of equations since the temperature coefficients of emissivity in both spectral ranges are not known. In addition, since in practically important cases the temperature interval / the difference between the object’s temperatures at which its own radiation intensity is measured / can reach 1000 K, therefore, for some substances, a linear approximation of the temperature dependence of the spectral emissivity may be incorrect.

 There is also a known method of pyrometric measurements / copyright certificate N 1770779, class. G 01 J 5/50, 1992 /, taken as a prototype, including measuring at two given temperatures of the object the intensity of its own radiation, determining the emissivity of the object and its temperature coefficient, measuring the intensity of the radiation of the object in the same spectral range, determining its true temperature lying in the interval between two predetermined temperatures. In this method, by narrowing the temperature interval between two predetermined temperatures, a higher measurement accuracy is achieved by using a linear approximation of the temperature dependence of the emissivity.

 The disadvantage of this method is that the true temperature of the object at the borders of the temperature range of measurements is determined by the contact method, i.e. essentially a pyrometer calibration is needed.

 The basis of the invention is the task to develop a method of pyrometric measurements that provides, regardless of the degree of surface roughness, a non-contact measurement of the true temperature of an object with high accuracy without using a calibration operation and without determining the numerical value of the temperature coefficient of emissivity based on the use of the redundancy of the information contained in the thermal radiation spectrum.

The problem is solved in that in the proposed method, when heating or cooling, several spectral intensities of intrinsic radiation are measured with effective wavelengths λ ₁ , λ ₂ , ..., λ _i at several, but not less than three temperatures: T ₁ , T ₂ , ... T _j , T _{j + 1} .

 Intensities can be emitted in any areas of the Planck radiation / from Wien to Rayleigh-Jeans /.

 In addition, instead of one of the spectral intensities, the full spectrum of radiation described by the Stefan-Boltzmann Law can be used.

Здесь: C₁, C₂ - пирометрические постоянные
ζ_i - аппаратная функция измерительного канала
ε(λ_i,T_j) - спектральная излучательная способность, зависимость которой от температуры можно записать в виде полинома:
ε(λ_i,T_j) = ε(λ_i)_o+α_iT_j+β_iT $\genfrac{}{}{0ex}{}{\text{2}}{\text{j}}$ +...+γ_iT $\genfrac{}{}{0ex}{}{\text{n}}{\text{j}}$ ,
У большинства веществ, в частности металлов в ограниченных интервалах температур порядка 100-200 и более градусов зависимость излучательной способности от температуры линейна /см. например "Излучательные свойства материалов" под ред. А.Е. Шейндлина, Энергия 1974 г./.For narrow spectral ranges in which the values of effective wavelengths independent of temperature can be read with high accuracy / for example, when using “sharp” interference filters or monochromators / for the spectral intensities U (λ _i , T _j ) of the intrinsic thermal radiation of the substance in condensed phase at temperatures T _j-1 <T _j <T _{j + 1} you can write:

Here: C ₁ , C ₂ - pyrometric constants
ζ _i - hardware function of the measuring channel
ε (λ _i , T _j ) is the spectral emissivity, the dependence of which on temperature can be written in the form of a polynomial:
ε (λ _i , T _j ) = ε (λ _i ) _o + α _i T _j + β _i T $\genfrac{}{}{0ex}{}{\text{2}}{\text{j}}$ + ... + γ _i T $\genfrac{}{}{0ex}{}{\text{n}}{\text{j}}$ ,
For most substances, in particular metals, in limited temperature ranges of the order of 100-200 degrees or more, the temperature dependence of the emissivity is linear / cm. for example, “Radiative Properties of Materials,” ed. A.E. Sheindlin, Energy 1974 /.

При использовании спектральных составляющий, лежащих в области Релея-Джинса:

Соответственно при использовании вместо одной из интенсивностей интенсивности полного излучения, описываемого законом Стефана - Больцмана:

U_Σ(T_j) = ζ_Σσε_Σ(T_j)/T $\genfrac{}{}{0ex}{}{\text{4}}{\text{j}}$ ,

Здесь σ - постоянная Стефана-Больцмана.Thus, expressions for spectral intensities can be written as:

When using spectral components lying in the Rayleigh-Jeans area:

Accordingly, when using instead of one of the intensities the intensities of the total radiation described by the Stefan-Boltzmann law:

U _Σ (T _j ) = ζ _Σ σε _Σ (T _j ) / T $\genfrac{}{}{0ex}{}{\text{4}}{\text{j}}$ ,

Here σ is the Stefan-Boltzmann constant.

 If the spectral range for each of the spectral intensities needs to be expanded, for example, to increase sensitivity, increase the signal-to-noise ratio, the effective wavelength will change with temperature.

As predicted by Nating / Bull. Buro of Standarts, USA, 1916 /, shown in Coates / T. Coates, Metrologia - 1977, v. 13, p. 1 / and strictly, by the method of a small parameter, it was proved in the work of D.Ya. Sveta and O. Popova / Metrology 1987, N 2 / change in effective length with temperature, regardless of the type of spectral characteristic / triangular, U-shaped, Gaussian / is described by the expression:
λ _eff . _i = λ _oi (1 + μ _i / T _j ),
where λ _oi is the value of the central wavelength,
μ _{i /} is a constant depending on the type of spectral characteristic.

Здесь количество неизвестных параметров в каждой интенсивности будет:

и неизвестные температуры: T_j-1; T_j; T_j+1.Thus, in the case of wide spectral ranges, the spectral intensities should be written as:

Here, the number of unknown parameters in each intensity will be:

and unknown temperatures: T _j-1 ; T _j ; T _{j + 1} .

 By measuring the intensities during heating or cooling of an object for N-temperatures and M-intensities, one can obtain a sufficient number of equations to determine all unknowns.

где m_i - количество неизвестных параметров в i-ой интенсивности излучения.To solve this problem, it is necessary that

where m _i is the number of unknown parameters in the i-th radiation intensity.

 In the written expression, the left side is the number of equations, the right is the number of unknowns.

 So, if all intensities are measured in sufficiently wide spectral ranges in the Wien region and the temperature dependence of their emissivity is linear, to solve the problem, one should measure three spectral intensities at six temperatures.

In this case, the number of unknown parameters in each of their intensities: 4; N = 6 and M = 3
Therefore, 6x3 = 6 + (4 + 4 + 4) -18
and we get a system of 18 equations and 18 unknowns.

If, in the previous example, total radiation is used as one of the intensities, at which the number of parameters will be two: [ζ _Σ • ε _Σ (T _j )] and α _Σ / ε _Σ (T _j ). The number of temperatures at which measurements are necessary can be reduced to five, i.e. 5x3 = 5 + 4+ 4+ 2, i.e. it turns out 15 equations with 15 unknowns.

 The solution of these systems of equations is carried out naturally with the help of a computer or a microprocessor built into the measuring system.

 The advantages of the proposed method over the known ones is that when measuring the temperature of an object with an unknown emissivity, both in the direction of increasing and decreasing it and measuring for each of its values the specified number of spectral intensities of the object’s own radiation, all unknown values of the true temperatures are determined without using which - or operations of preliminary calibration / calibration / optoelectronic path.

 The invention is further illustrated by the drawing and an example implementation of the proposed method.

 The drawing schematically shows a structural diagram of a device that implements the proposed method.

In this diagram:
1 - The object whose temperature is measured
2 - Heating or cooling device
3 - Concentrating optics
4 - Monochromatization device
5 - Radiation receivers
6 - Amplifiers
7 - Analog-to-Digital Converters
8 - RAM block
9 - Permanent memory unit
10 - Processor / microprocessor /
11 - Display
The solution of the resulting system of equations with many unknowns is conveniently carried out according to a special program or available in Matkath.

 At the same time, the necessary values of the constants and the data table are stored in the read-only memory block, and the necessary mathematical operations are performed with the main memory, as usual.

 As an example, due to some cumbersomeness of the obtained mathematical expressions, we give the simplest one for which a simple analytical solution is obtained.

Example: it is necessary to measure the true temperature of an object at temperature values providing a high signal to noise ratio at very "narrow" spectral ranges, i.e. consider effective wavelengths constant when the temperature changes. We further assume that all the measured intensities lie in the Wien region, i.e. λT ≤ 3000 μm / degree. In addition, we assume that the wavelength of one of the spectral intensities will be λ _i = λ _x , that is, it will lie at the point “X”, where, as is known, α _x = 0, i.e. spectral emissivity is independent of temperature. For tungsten, as is known, this wavelength is λ _x = 1.28 μm.

T₁; T₂; T₃; ζ_x•ε(λ_x); ζ₂•(λ₂,T₂); α₂/ε(λ₂,T₂);
и количество уравнений: MN = 3х2=6
Уравнения:

где
ε(λ_x,T₁) = ε(λ_x,T₂) = ε(λ_x,T₃),

Указаные шесть уравнений логарифмируем, вычитаем одно из другого и, вводя обозначения:

Путем несложных преобразований получаем:

где

Таким образом, неизвестные температуры определены.In this case, measurements at three temperatures must be carried out for only two spectral intensities, since the number of unknowns will be

T ₁ ; T ₂ ; T ₃ ; ζ _x • ε (λ _x ); ζ ₂ • (λ ₂ , T ₂ ); α ₂ / ε (λ ₂ , T ₂ );
and the number of equations: MN = 3x2 = 6
Equations

Where
ε (λ _x , T ₁ ) = ε (λ _x , T ₂ ) = ε (λ _x , T ₃ ),

The indicated six equations are logarithmized, subtract one from the other and, introducing the notation:

Using simple transformations we get:

Where

Thus, unknown temperatures are determined.

When the signal-to-noise ratio in the measuring channels is ~ 3000 and the intervals between the temperatures T ₂ - T ₁ and T ₃ - T _{2 are of the} order of 40 - 50 K, the unknown temperature values of the tungsten lamp strip are measured with an error of not more than ± 0.5%, t .e. corresponds to its graduation according to a model lamp of the 1st category.

 Thus, the proposed method allows, in the process of heating or cooling, without any calibration, to measure the true temperature values at unknown values of emissivity and to construct a thermodynamic temperature scale without using a black body, using, in principle, any substance in the condensed phase, in this case tungsten.

Claims (1)

A pyrometric measurement method, including measuring radiation intensities when heating or cooling the surface of a substance in the condensed phase, at several, but not less than three temperature values satisfying the inequality T ₁ <T ₂ <T ₃ ... <T _N , and determining the true values of these temperature, characterized in that for each unknown temperature in several spectral ranges determined by the corresponding values of the effective wavelengths, radiation intensities are measured, and instead of one From the spectral intensities, the total radiation described by the Stefan-Boltzmann law can be measured, while the number of measured temperature values N and the number of spectral intensities M must be related by the relation

where m ₁ , m ₂ , ... m _m - the number of unknown parameters that determine, along with temperature, the magnitude of each of the intensities (1st, 2nd, ..., Mth).