KR20130062658A - Apparatus and method for measuring oxide layer thickness of steel plate - Google Patents

Abstract

PURPOSE: An apparatus and a method for measuring the thickness of an oxide layer are provided to measure the thickness of the oxide layer with high accuracy by automatically correcting spectrum distortion due to the contamination of an observation door. CONSTITUTION: An apparatus for measuring the thickness of an oxide layer comprises a reflection plate(30), a light source part(10), a light collecting part(20), and a signal processing part(40). The reflection plate is positioned between an observation door(2) and a steel plate(1) according to control signals. The light source part penetrates through the observation door and irradiates measuring light to the steel plate or the reflection plate. The light collecting part collects first reflection light reflected from the reflection plate and second reflection light reflected from the steel plate. The signal processing part corrects distortion due to the observation door using the first reflection light and calculates the thickness of the oxide layer of the steel plate using the second reflection light.

Description

Apparatus and method for measuring oxide layer thickness of steel plate}

The present invention relates to an oxide layer thickness measuring apparatus and method, and more particularly, to an oxide layer thickness measuring apparatus and method capable of correcting distortion of reflected interference light due to contamination of an observation window.

In the continuous galvanizing line (CGL) process, the annealing is performed by heat treatment on a cold rolled steel sheet, followed by plating through a zinc bath (Zn-pot). In the heat treatment process for the annealing of the cold rolled steel sheet, because the steel sheet is heated to a high temperature (600 ~ 800 ° C), there is a possibility that a surface oxide layer is formed, such a surface oxide layer reduces the plating quality of the steel sheet. That is, when the oxide layer is formed on the surface of the steel sheet before plating, zinc wettability (Zn wetability) of the steel sheet is lowered and defects such as unplating and plating peeling may occur. Therefore, the heat treatment for the annealing is performed in a strong reducing atmosphere to prevent the formation of an oxide layer. However, since there is always a possibility that an oxide layer is formed due to oxidation / reduction characteristics according to steel grades or problems in the control of a heating furnace, it is essential to measure whether the oxide layer is produced online in a production line and to control the heat treatment conditions through it.

In addition, in the case of producing a high strength steel sheet for automobiles containing a large amount of oxidizing alloy element, the oxidation / reduction process is performed before plating to improve the plating property by preventing the surface concentration of the oxidizing alloy element. In order to improve plating properties through the oxidation / reduction process, an oxide layer having an optimal thickness is required. Therefore, in order to realize the plating property by applying the oxidation / reduction process, it is necessary to measure the thickness of the on-line oxide layer and control the thickness of the oxide layer through the same.

In order to measure the thickness of the on-line oxide layer, indirect measurement using a non-contact method is essential, and in particular, reflection coherence spectroscopy may be used.

The reflection coherence spectroscopy is a method of measuring the thickness of an oxide layer by irradiating light having a constant spectrum to a measurement point of the steel sheet, collecting light reflected from this point, and measuring the changed spectrum.

Since the steel sheet is made of a steel sheet passing through the inside or immediately after the heating furnace, it is necessary to irradiate the steel sheet for spectrum measurement light through the transparent observation window for the spectrum measurement.

However, the transparent observation window is very likely to be contaminated because it is placed in an environment of high temperature, high pressure, and high dust, and the spectrum for measuring the oxide layer thickness is distorted due to the contamination of the transparent observation window, so that the accuracy of the oxide layer thickness measurement is correct. There is a problem that can fall.

An object of the present invention is to provide an oxide layer thickness measuring apparatus and method capable of correcting distortion caused by contamination of an observation window.

Oxide layer thickness measuring apparatus according to an embodiment of the present invention, the light source unit for transmitting the measurement light to the steel sheet or reflecting plate through the observation window; A light collecting unit collecting the first reflected light reflected by the reflector or the second reflected light reflected by the steel plate; A reflection plate positioned between the observation window and the steel sheet according to a control signal, reflecting the measurement light from a surface to generate first reflection light, and reflecting the first reflection light to the light collecting part; And a signal processor configured to correct distortion caused by the observation window using the first reflected light, and calculate a thickness of an oxide layer of the steel sheet using the second reflected light.

Here, the oxide layer thickness measuring apparatus, the shielding plate guide provided between the observation window and the steel sheet; And a shielding plate which is movable up and down along the shielding plate guide, wherein the reflecting plate is further attached to the shielding plate.

The reflective plate may have a multi-faceted structure on a surface thereof, and the multi-faceted structure may provide an optical path through which the measurement light is reflected and collected by the light collecting unit.

Here, the signal processing unit calculates transmittance for each wavelength in the observation window using the first reflected light, corrects the spectrum of the second reflected light using the transmittance for each wavelength, and then forms an oxide layer formed on the surface of the steel sheet. The thickness of can be calculated.

Oxide layer thickness measurement method according to an embodiment of the present invention, the reflecting plate reflecting step of irradiating the measurement light to the reflecting plate through the observation window, and collecting the first reflected light reflected from the reflecting plate; A transmittance calculation step of calculating transmittance for each wavelength in the observation window by using the spectrum of the first reflected light; A steel sheet reflection step of irradiating the measurement light to the steel sheet through the observation window and collecting second reflected light reflected from the steel sheet; And an oxide layer thickness calculating step of calculating a thickness of the oxide layer formed on the surface of the steel sheet after correcting the spectrum of the second reflected light by using the transmittance for each wavelength.

According to the oxide layer thickness measuring apparatus and method of the steel sheet according to an embodiment of the present invention, the spectral distortion caused by the contamination of the observation window can be automatically corrected to measure the oxide layer thickness with high precision.

In particular, by installing a reflecting plate that can be opened and closed between the observation window and the steel sheet can measure the spectrum of the reflecting plate when necessary or periodically, it is possible to measure the amount of spectral change caused by contamination of the observation window, it is possible to correct the reflected light spectrum change of the steel sheet using this It is possible.

1 is a schematic view showing an oxide layer thickness measuring apparatus according to an embodiment of the present invention.
Figure 2 is a schematic diagram showing a reflector plate transfer unit according to an embodiment of the present invention.
3 is a schematic view showing a multi-sided structure of a reflecting plate according to an embodiment of the present invention.
4 is a graph showing distortion of the steel plate spectrum due to contamination of the observation window.
5 is a graph showing distortion of a reflector plate spectrum due to contamination of an observation window.
6 is a graph showing a steel plate spectrum which is corrected for distortion caused by contamination of the observation window.
7 is a flowchart illustrating a method of measuring an oxide layer thickness according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. In the following detailed description of the preferred embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. In the drawings, like reference numerals are used throughout the drawings.

In addition, in the entire specification, when a part is referred to as being 'connected' to another part, it may be referred to as 'indirectly connected' not only with 'directly connected' . Also, to "include" an element means that it may include other elements, rather than excluding other elements, unless specifically stated otherwise.

Figure 1 is a schematic diagram showing an oxide layer thickness measuring apparatus according to an embodiment of the present invention, Figure 1 (a) shows a case where the reflector is not located, Figure 1 (b) shows a case where the reflector is located. will be.

Referring to FIG. 1, an oxide layer thickness measuring apparatus according to an exemplary embodiment of the present invention includes a steel plate 1, an observation window 2, a light source unit 10, a light collecting unit 20, a reflecting plate 30, and a signal. It may include a processor 40.

Hereinafter, an oxide layer thickness measuring apparatus according to an embodiment of the present invention will be described with reference to FIG. 1.

The light source part 10 can transmit the measurement light to the steel plate 1 or the reflecting plate 30 through the observation window 2.

The steel sheet 1 may be heated to a high temperature in a heat treatment process for annealing, and the steel sheet 1 may be located in a furnace wall made of refractory material. Since the inside of the furnace wall is usually in a high temperature, high pressure, and high dust environment, it is difficult to directly install the light source unit 10 inside the furnace wall and directly irradiate the measurement light to the steel plate 1. Therefore, outside the furnace wall, the measurement light of the light source unit 10 may be irradiated to the transparent observation window 2 positioned on the furnace wall so that the measurement light is reflected from the surface of the steel plate 1.

Here, when the reflecting plate 30 is positioned between the steel plate 1 and the observation window 2, the light source unit 10 can irradiate the measurement light to the reflecting plate 30 through the observation window (2). have.

The measurement light irradiated by the light source unit 10 may have a predetermined spectrum, and the spectrum may vary according to a property of a reflective surface on which the measurement light is reflected. Therefore, when the spectrum of the reflected reflected light is analyzed, the thickness of the oxide layer formed on the surface of the steel sheet 1 may be measured.

The light collecting unit 20 may collect the first reflected light reflected from the reflector 30 or the second reflected light reflected from the steel sheet 1.

As shown in FIG. 1, the measurement light incident through the observation window 1 is reflected by the steel sheet 1 or the reflector 30 and is again reflected through the observation window 2 to the light collecting unit 20. Can be introduced into.

The light collecting unit 20 may be positioned according to an incident angle θ and a reflection angle θ of the measurement light emitted from the light source unit 10 to the steel sheet 1. That is, it may be positioned at an angle suitable for collecting the reflected light reflected from the surface of the steel sheet (1). The size of the incident angle and the reflection angle may be determined in consideration of field installation conditions and an optical system configuration.

The reflected light collected by the light collecting unit 20 may be transmitted to the signal processing unit 40, and the signal processing unit 40 may calculate the oxide layer thickness of the steel sheet 1 using the reflected light.

The reflector 30 is positioned between the observation window 2 and the steel sheet 1 according to a control signal, reflects the measurement light from the surface to generate a first reflected light, and collects the first reflected light into the light. It can reflect to the part 20.

As shown in FIG. 1B, the reflecting plate 30 reflects the measurement light incident through the observation window 2, and then returns to the light collecting unit 20 through the observation window 2. can send.

The reflective plate 30 may be transported up and down according to a control signal. When the reflective plate 30 is transferred upward, the measurement light of the light source unit 10 is irradiated onto the steel plate 1, and the reflective plate 30 is applied. When the light is transferred downward, the measurement light of the light source unit 10 may be irradiated to the reflector plate 30.

When the measurement light is irradiated, the reflector 30 may reflect the measurement light with a predetermined reflectance to generate first reflection light. In this case, the reflector 30 may maintain the same state of the surface at all times, thereby generating first reflected light having an abnormally constant spectrum in which the measured light is equally input.

However, the first reflected light may cause distortion in the spectrum due to surface contamination of the observation window 2. That is, the surface of the observation window 2 may be easily contaminated, and the surface contamination of the observation window 2 may affect the spectrum of the first reflected light so that the spectrum is distorted.

Specifically, referring to FIG. 5, FIG. 5 shows a spectrum of the first reflected light, where a is a spectrum when there is no surface contamination of the observation window 2, and b is a surface contamination of the observation window 2. If there is a spectrum. Therefore, as shown in FIG. 5, the distortion of the spectrum may appear large.

However, the degree of change of the spectrum due to the surface contamination of the observation window 2 can be known by comparing the spectrum before the surface contamination with the spectrum after the surface contamination, which can then be used for spectral distortion correction.

The reflector 30 may have a multi-sided structure on its surface, and the multi-sided structure may provide an optical path through which the measurement light is reflected and collected by the light collecting unit 20.

Referring to FIG. 3, the reflector 30 may have a multi-sided structure P. Referring to FIG. As shown in FIG. 3, the multi-faceted structure may allow the first reflected light reflected by the reflector 30 to be collected at the light collecting unit without changing the positions of the light source unit 10 and the light collecting unit 20. .

In addition to the structure shown in FIG. 3, the multi-faceted structure may be any type of material that allows the first reflected light reflected from the reflector 30 to be collected by the light collecting unit without changing the position of the light source unit 10 and the light collecting unit 20. Can also be utilized.

The reflection plate 30 may be located between the observation window 2 and the steel plate 1 according to a control signal, and the transfer of the reflection plate 30 according to the control signal may be performed by the reflection plate transfer unit 50. Can be.

As shown in FIG. 2, the reflector plate transfer unit 50 may include a shield plate guide 51 and a shield plate 52.

The shielding plate guide 51 is provided between the observation window 2 and the steel sheet 1, and may provide a frame for allowing the shielding plate 52 to move up and down.

The shield plate 52 is movable up and down along the shield plate guide, and the reflector plate 30 may be attached to the surface of the shield plate 52.

When the shielding plate is raised, the measurement light generated by the light source unit 10 passes through the observation window 2 and is irradiated onto the steel plate 1, and the second reflected light reflected from the steel plate 1 is collected by the light collecting unit ( 20).

On the contrary, when the shielding plate 52 is lowered, the optical path between the light source unit 10 and the steel plate 1 is blocked, and the measurement light irradiated by the light source unit 10 is applied to the surface of the shielding plate 52. The first reflected light may be transmitted to the light collecting unit 20 by reflecting by the attached reflector 30.

In relation to the vertical transfer of the shield plate 52, the driving unit 53 may be further included, and the driving unit 53 may transfer the shield plate 52 up and down using a motor or the like.

The signal processor 40 may correct the distortion caused by the observation window 2 using the first reflected light, and calculate the thickness of the oxide layer of the steel sheet 1 using the second reflected light.

The signal processor 40 may calculate the thickness of the oxide layer of the steel sheet 1 by using the second reflected light collected by the light collector 20. In detail, the signal processing unit 40 may spectrograph the second reflected light to measure the wavelength-specific spectrum, and then compare the relative intensities at the respective wavelengths to obtain the thickness of the oxide layer formed on the surface of the steel sheet.

As shown in Fig. 1, when the measurement light having a constant spectrum is incident on the steel sheet 1, some of the measurement light is reflected on the surface of the oxide layer formed on the steel sheet 1, and the other part is the steel sheet 1 Can be reflected from the surface of In this case, the light reflected from the surface of the oxide layer and the light reflected from the surface of the steel sheet may have a different phase according to a path difference, and each of the reflected lights may interfere with each other.

Accordingly, the second reflected light collected by the light collecting unit is reflected interference light interfering with the light reflected from the surface of the steel sheet and the surface of the oxide layer, and the spectrum of the second reflected light is a path difference according to the thickness of the oxide layer. It may vary. Therefore, the thickness of the oxide layer may be measured using a change in intensity of light according to the wavelength of the second reflected light.

Specifically, the second reflected light can be obtained by Equation 1 below.

Is the wavelength of light, S _R (λ) is the reflected interference light spectrum of the second reflected light, d is the oxide layer thickness, n _f is the refractive index of the oxide layer, and θ is the incident angle of light irradiated onto the steel sheet 1.

According to Equation (1), it is possible to know the wavelength of the cancellation / reinforcement interference in S _R (λ) by using the condition that the cos (δ) is maximum or minimum. (See Fig. 4)

Using the offset and constructive interference wavelengths, the oxide layer thickness d can be obtained by Equation 2 below.

Here, λ _M is the destructive / constructive interference wave. Therefore, after obtaining the reflected interference light spectrum of the second reflected light, the thickness of the oxide layer may be obtained using the constructive / destructive interference wavelength λ _M. N is the refractive index of air, k means any natural number.

Accordingly, the oxide layer thickness d may be calculated from Equation 2.

However, as described above, the steel sheet 1 is located in the furnace wall, and the inside of the furnace wall is an environment of high temperature, high pressure, and high dust. Therefore, the measurement light must be irradiated through the observation window 2 and the reflected light must be collected. do. Here, the observation window 2 may be made of a transparent material, but the surface may be easily contaminated under the environment of high temperature, high pressure, and high dust. Since the reflected light can only be collected through the observation window 2, the spectrum of the reflected light may be distorted due to contamination of the surface of the observation window 2.

Specifically, referring to FIG. 4, FIG. 4 (a) shows the reflected light spectrum before the observation window 2 is contaminated, and FIG. 4 (b) shows the reflected light spectrum when the observation window 2 is contaminated. It is shown. 4 is measured with respect to the same steel sheet having the same oxide layer thickness, and comparing the Figure 4 (a) and Figure 4 (b), the spectrum may be greatly distorted by the contamination of the observation window (2) It can be seen. Therefore, the position of the offset / reinforcement interference wavelength obtained from the reflected light spectrum is also greatly changed, so that an error occurs in the oxide layer thickness calculated by Equation (2).

Therefore, in order to accurately measure the thickness of the oxide layer, it is necessary to correct distortion of the reflected light spectrum due to contamination of the observation window 2, and the signal processor 40 may perform correction for the distortion.

The spectrum of the second reflected light collected by the light collecting unit 20 may be affected by the spectrum of the reflected interference light, the reflectance of the steel sheet, and the measured light spectrum of the light source unit, which may be expressed by Equation 3 below.

Here, S _A (λ) is a spectrum of the second reflected light collected by the light collecting unit 20, R (λ) is a reflectance at the steel sheet 1, and S _L (λ) is the light source unit 10. The spectrum of the measurement light, S _R (λ) may be the spectrum of the reflected interference light.

For ease of explanation, it is assumed that the second reflected light flowing into the light collecting unit 20 is the same as the reflected interference light, but in fact, in addition to the reflected interference light, the reflectance in the steel sheet 1 and the light source unit The measurement light of (10) may also be affected. In addition, although the spectrum due to the radiation of the steel sheet 1 heated to a high temperature may be considered, the radiation spectrum is very small compared to the spectrum due to the measurement light, the effect thereof is omitted.

Since the spectrum related to the thickness of the oxide layer among the second reflected light collected by the light collecting unit 20 is the spectrum S _R (λ) of the reflected interference light, the reflectance R (λ) of the remaining steel sheet 1 and The influence by the spectrum S _L (λ) of the measurement light needs to be eliminated or minimized. To this end, the steel sheet 1 and the light source unit 10 may be standardized.

That is, since the reflectance R (λ) of the steel sheet 1 may vary depending on the steel grade, the steel sheet 1 may be selected in advance after measuring and storing the reflectance R (λ) according to the steel grade of each steel sheet 1. Standardization may be performed by selecting and applying the reflectance R (λ).

In addition, the influence of the spectrum (S _L (λ)) of the measurement light may be determined by the light intensity of the light source unit 10, the use time of the light source, the surrounding environment. Therefore, the replacement cycle of the lamp for generating the light in the light source unit 10 may be regularly standardized to reduce the effect due to the spectrum S _L (λ) of the measurement light.

According to the standardization, such as the second reflected light is introduced to the reflectance (R (λ)) and the measurement light spectrum (S _L (λ)) is the light-collecting section 20 can be handled by a fixed constant is the reflection It can be seen that determined by the spectrum of the interference light.

However, as described above, since the entire spectrum collected by the light collecting unit 20 may be distorted by the contamination of the observation window 2, Equation 3 is based on the contamination of the observation window 2. By considering the change in the spectrum by the following equation (4) it can be modified.

Here, T (λ) is the transmittance of the observation window 2, the T (λ) may vary depending on the degree of contamination of the observation window (2).

As described above, the reflectance (R (λ)) and the spectrum of measurement light (S _L (λ)) may be represented by a constant through the standardization, and thus, the transmittance (T (λ)) of the observation window 2. In this equation, it is possible to correct the change in the entire spectrum S _A (λ) due to the contamination of the observation window 2.

In order to obtain the transmittance T (λ) of the observation window 2, the reflecting plate 30 is positioned between the observation window 2 and the steel sheet 1, and the measurement light is irradiated to obtain the first reflection light. Can be. At this time, if the surface state of the reflecting plate is always kept constant, R (λ) S _L (λ) S _R (λ) of Equation 4 can be seen as a constant A. (See Equation 5)

Accordingly, when the reflecting plate 30 is irradiated with the measurement light to collect the first reflected light by the light collecting unit 20, the transmittance T (λ) of the observation window 2 can be obtained.

Referring to Equation 5, since the spectrum S _A1 (λ) of the first reflected light is proportional to the transmittance T (λ), the first reflected light according to the contamination of the observation window 2 before and after The change in the spectrum may be expressed as Equation 6 below.

)이고, 상기 S_A1'(λ)는 오염된 이후에 측정한 전체 스펙트럼(

)이다. Here, T ₀ (λ) is the transmittance before the observation window 2 is polluted, T _C (λ) is the transmittance after the contamination, and S _A1 (λ) is the total measured before contamination spectrum(

) And S _A1 '(λ) is the full spectrum measured after contamination (

)to be.

By using the above proportional expression, distortion of the second reflected light spectrum due to contamination of the observation window 2 can be corrected. In more detail, the correction may be performed by Equation 7.

)이다. Here, the S _A '' (λ) _strip is the corrected spectrum of the second reflected light, S _A '(λ) are the uncorrected spectrum of the _strip and the second reflected light (

)to be.

Therefore, in order to correct distortion caused by contamination of the observation window 2, a proportional expression of Equation 6 may be used.

The corrected second reflected light is illustrated in FIG. 6 and can be obtained in a form very similar to the spectrum of the second reflected light before pollution in FIG.

The signal processing unit 40, receives the reflected light that is first reflected light reflected by the reflecting plate 30 in the demand or periodically, and to calculate the transmittance (T _C (λ)), the transmittance (T _C (λ The reflected light reflected from the steel sheet 1, that is, the second reflected light, can be corrected using the)).

7 is a flowchart illustrating a method of measuring an oxide layer thickness according to an embodiment of the present invention.

7, the oxide layer thickness measurement method according to an embodiment of the present invention, pollution degree determination step (S10), reflector reflection step (S20), transmittance calculation step (S30), steel sheet reflection step (S40) and oxide layer thickness It may include a calculation step (S50).

Hereinafter, an oxide layer thickness measuring method according to an exemplary embodiment of the present invention will be described with reference to FIG. 7.

The contamination level determining step (S10) is a step of determining whether to measure the contamination level of the observation window in order to correct distortion of reflected light due to contamination of the observation window.

The oxide layer thickness measuring method is to measure the thickness of the oxide layer formed on the surface of the steel sheet after the heat treatment process for annealing, the steel sheet may be located in the furnace wall made of refractory. Since the inside of the furnace wall is typically an environment of high temperature, high pressure, and high dust, measurement light may be irradiated onto the steel sheet through an observation window outside the furnace wall.

However, the high temperature, high pressure, and high dust environment may easily pollute the observation window, and the spectra of the reflected light may be distorted by the contamination of the observation window. In order to correct the spectral distortion of the reflected light, the oxide layer thickness measuring method may consider the degree of contamination of the observation window.

Here, the pollution degree determining step (S10) may determine whether to consider the degree of contamination of the observation window. Specifically, the contamination level determining step (S10) may measure the contamination level of the observation window when a predetermined cycle arrives, or may measure the contamination level of the observation window when a user's observation window contamination level measurement signal is input. The period of the observation window contamination degree measurement may be set to an optimized period in consideration of the measurement time and accuracy.

If it is determined that the contamination level of the observation window is measured in the contamination determination step (S10), the process proceeds to the reflection plate reflection step (S20), and if it is determined that the contamination degree of the observation window is not determined, the steel sheet reflection step (S40). You can proceed to.

Reflecting plate The reflecting step (S20) may transmit the measurement light to the reflecting plate through the observation window, and collect the first reflected light reflected from the reflecting plate. In the reflecting plate reflecting step (S20), the reflecting plate may be positioned between the viewing window and the steel plate, and the measured light incident through the viewing window may be reflected by the reflecting plate.

In the reflecting plate reflecting step (S20), the measurement light irradiated from the light source unit is reflected from the reflecting plate through the observation window, and then enters the light collecting unit through the observation window. Since the reflected light spectrum when the observation window is free of contamination is already known, the spectral distortion caused by the observation window contamination can be extracted from the first reflected light.

Here, the reflector may be positioned between the steel plate and the observation window by a reflector plate transfer part, and the reflector plate transfer part may selectively position the reflector between the steel plate and the observation window according to a control signal. That is, in the reflective plate reflection step S20, a control signal may be transmitted to the reflective plate transfer unit so that the reflective plate is positioned between the steel plate and the observation window.

In the transmittance calculation step S30, the transmittance of each wavelength in the observation window may be calculated using the spectrum of the first reflected light.

로 나타낼 수 있다. 여기서 상기 제1반사광은 S_A1(λ), 상기 관찰창의 투과율은 T(λ)이고, 상기 A는 임의의 상수이다. 즉, 상기 제1반사광은 상기 관찰창의 투과율과 비례한다.Specifically, the first reflected light reflected by the reflector

. Wherein the first reflected light is S _A1 (λ), the transmittance of the observation window is T (λ), and A is any constant. That is, the first reflected light is proportional to the transmittance of the observation window.

와 같이 나타낼 수 있다. 여기서, 상기 T₀(λ)는 상기 관찰창이 오염되기 전의 투과율, 상기 T_C(λ)은 오염된 이후의 투과율을 나타내는 것이고, 상기 S_A1(λ)는 오염되기 전에 측정한 제1반사광의 스펙트럼, 상기 S_A1'(λ)는 오염된 이후에 측정한 제1반사광이다. Therefore, the change in the spectrum of the first reflected light before and after the contamination of the observation window

As shown in Fig. Here, T ₀ (λ) is the transmittance before the observation window is contaminated, T _C (λ) is the transmittance after the contamination, and S _A1 (λ) is the spectrum of the first reflected light measured before being contaminated S _A1 '(λ) is the first reflected light measured after being contaminated.

In other words, if the spectrum of the first reflected light is measured before and after the observation window contamination and the ratio thereof is obtained, the transmittance after the contamination can be obtained.

Steel plate reflection step (S40), through the observation window to irradiate the measurement light to the steel sheet, it may collect the second reflected light reflected from the steel sheet. In this case, since the measurement light should be irradiated to the steel sheet, the reflecting plate may be transferred so that the measuring light is not irradiated to the reflecting plate.

The second reflected light may be affected by the spectrum of the reflected interference light caused by the light reflected from the surface of the steel sheet and the surface of the oxide layer, the reflectance of the steel sheet and the measured light spectrum of the light source, and the transmittance of the observation window. Can be.

로 표현될 수 있으며, 여기서, S_A'(λ)는 제2반사광의 스펙트럼이고, R(λ)은 강판의 반사율, S_L(λ)은 상기 광원부의 측정광 스펙트럼, S_R(λ)는 반사간섭광의 스펙트럼이며, T_C(λ)는 상기 관찰창의 투과율이다. 여기서, 강판의 반사율(R(λ)) 및 상기 광원부의 측정광 스펙트럼(S_L(λ))은 규격화를 통하여 일정한 크기의 상수로 취급할 수 있다. this is

Where S _A '(λ) is the spectrum of the second reflected light, R (λ) is the reflectance of the steel sheet, S _L (λ) is the measured light spectrum of the light source unit, and S _R (λ) is It is the spectrum of reflected coherence light, and T _C (λ) is the transmittance of the observation window. Here, the reflectance R (λ) of the steel sheet and the measurement light spectrum S _L (λ) of the light source unit may be treated as constants of a constant size through standardization.

Specifically, the reflectance of the steel sheet may be normalized by measuring the reflectance according to steel grade in advance, and applying the reflectance according to the selected emphasis, and the spectrum of the measured light may be set by constantly setting a lamp replacement cycle of the light source unit. Can be standardized.

Therefore, the spectrum of the second reflected light may be determined by the transmittance of the observation window and the spectrum of the reflected interference light.

In the oxide layer thickness calculating step S50, after correcting the spectrum of the second reflected light by using the transmittance for each wavelength, the thickness of the oxide layer formed on the surface of the steel sheet may be calculated.

로 표현될 수 있고, 상기 관찰창의 투과율은,

와 같이 나타낼 수 있다.
Like Salpin Bar earlier, the spectrum of the second reflected light

It may be expressed as, the transmittance of the observation window,

As shown in Fig.

If the spectrum of the second reflected light due to contamination of the observation window is corrected using the above formula,

으로 나타낼 수 있다. 여기서, 상기 S_A''(λ)_strip은 보정된 제2반사광의 스펙트럼이고, S_A'(λ)_strip은 보정전 제2반사광의 스펙트럼이다.

It can be represented as Here, the S _A '' (λ) _strip is the corrected spectrum of the second reflected light, S _A '(λ) is a _strip pre-compensation spectrum of the second reflected light.

Therefore, the spectrum of the second reflected light may be corrected by using the transmittance for each wavelength.

The corrected spectrum of the second reflected light is shown in FIG. 6, and can be obtained in a form very similar to that of the pre-contaminated second reflected light of FIG. 4 (a).

The thickness of the oxide layer formed on the surface of the steel sheet may be calculated using the corrected spectrum of the second reflected light.

As described above, since the reflectance R (λ) of the steel sheet and the measurement light spectrum S _L (λ) of the light source unit may be treated as constants, the second reflected light may be determined by the reflected interference light. It may be.

The reflection coherence light, the light reflected from the surface of the steel sheet and the light reflected from the surface of the oxide layer interfere with each other by the path difference, the intensity of light according to each wavelength may vary according to the thickness of the oxide layer. . Therefore, the thickness of the oxide layer may be measured using a change in intensity of light according to the wavelength of the second reflected light.

의 관계식이 성립하므로, 상기 cos(δ)가 최대 또는 최소가 되는 조건을 이용하여, 상기 S_R(λ)에서의 상쇄/보강간섭되는 파장을 알 수 있다. Specifically,

Since the relational expression holds, the wavelength at which the cancellation / reinforcement interference in S _R (λ) can be known using the condition that the cos (δ) becomes the maximum or the minimum.

의 관계식에 의하여 구할 수 있다.When the offset and constructive interference wavelengths are used, the oxide layer thickness d is

It can be obtained by the relational expression of.

Here, λ _M is the destructive / constructive interference wave. Therefore, after obtaining the reflected interference light spectrum of the second reflected light, the thickness of the oxide layer may be obtained using the constructive / destructive interference wavelength λ _M. N is the refractive index of air, k means any natural number.

Accordingly, in the oxide layer thickness calculating step S50, the oxide layer thickness d may be calculated.

The present invention is not limited by the above-described embodiment and the accompanying drawings. It is intended that the scope of the invention be defined by the appended claims, and that various forms of substitution, modification, and alteration are possible without departing from the spirit of the invention as set forth in the claims. Will be self-explanatory.

1: steel plate 2: observation window
10: light source unit 20: light collecting unit
30: reflector 40: signal processing unit
50: reflector plate transfer portion 51: shield plate guide
52: shield plate 53: drive unit
S10: pollution degree determination step S20: reflection plate reflection step
S30: transmittance calculation step S40: steel plate reflection step
S50: oxide layer thickness calculation step

Claims (5)

A reflection plate positioned between the observation window and the steel sheet according to the control signal;
A light source unit transmitting the measurement light to the steel sheet or the reflecting plate through the observation window;
A light collecting unit collecting the first reflection light reflected by the measurement light from the reflection plate or the second reflection light reflected by the measurement steel plate; And
And a signal processing unit for correcting distortion caused by the observation window using the first reflected light and calculating a thickness of an oxide layer of the steel sheet using the second reflected light. The method of claim 1,
A shielding plate guide provided between the observation window and the steel sheet; And
An oxide layer thickness measuring apparatus including a shielding plate which is movable up and down along the shielding plate guide, wherein the reflecting plate is attached to the shielding plate. The method of claim 1, wherein the reflector is
As having a multi-faceted structure on the surface,
And the multi-sided structure provides an optical path through which the measurement light is reflected and collected by the light collecting unit. The method of claim 1, wherein the signal processing unit
The oxide layer calculates the transmittance for each wavelength in the observation window using the first reflected light, corrects the spectrum of the second reflected light using the transmittance for each wavelength, and then calculates the thickness of the oxide layer formed on the surface of the steel sheet. Thickness measuring device. A reflection plate reflection step of irradiating measurement light to the reflection plate through the observation window and collecting the first reflection light reflected by the reflection plate;
A transmittance calculation step of calculating transmittance for each wavelength in the observation window by using the spectrum of the first reflected light;
A steel sheet reflection step of irradiating the measurement light to the steel sheet through the observation window and collecting second reflected light reflected from the steel sheet; And
And an oxide layer thickness calculation step of calculating a thickness of an oxide layer formed on a surface of the steel sheet after correcting a spectrum of the second reflected light by using the wavelength-specific transmittance.

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