JP2004301793A - X-ray thickness measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for setting and controlling a leakage dosage in an X-ray thickness measuring instrument. <P>SOLUTION: This instrument is provided with an X-ray source 3 and an X-ray detector 6 for detecting a transmission X-ray arranged with a space to be opposed with a measured object 2 therebetween, a tube voltage control means 13b and a tube current control means 13a for the X-ray source 3, a reference plate setting means 5 and a reference plate driving means12 for setting a plate thickness reference in calibration, a thickness computing part 11 for computing a thickness of the measured object 2 based on an output signal from the detector 6, and a tube current setting part 14 for controlling the leakage dosage leaked from the X-ray source. A distance from the X-ray source to a prescribed position and the leakage dosage in the prescribed position are input by the tube current setting part 14, a tube current is found from a tube current setting table preliminarily stored, and the tube current is controlled to be brought into a prescribed leakage dosage in the prescribed position. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an X-ray thickness measuring apparatus, and more particularly to an X-ray thickness measuring apparatus provided with a means for controlling a leakage dose so that a control area and a change of a leakage dose can be easily set.
[0002]
[Prior art]
In the rolling process of a steel sheet, a radiation thickness measuring device that irradiates a rolled metal sheet with radiation and measures the thickness from the amount of transmitted radiation is used. There are gamma-ray thickness measuring devices that use radioisotopes such as gamma-ray sources and X-ray thickness measuring devices that use X-ray sources. The measuring device is used particularly in a process that requires a high-accuracy response speed.
[0003]
The radiation protection management of workers in these radiation thickness measuring devices is carried out in accordance with the recommendations of the International Commission on Radiological Protection (ICRP), and radiation protection standards are set by regulatory authorities in each country. The latest ICRP recommendation is ICRP Pub60 issued in 1990, and the laws and regulations in Japan have been revised accordingly.
[0004]
The use of X-ray thickness measurement equipment is not subject to the Radiation Hazard Prevention Law, but the appointment of the chief of X-ray work and the X-ray source It is obligatory to provide a controlled area around the equipment that is inaccessible during the irradiation.
[0005]
The measurement principle of the X-ray thickness measuring apparatus utilizes that when transmitted X-rays pass through a substance, transmitted X-rays are attenuated by scattering and absorption in the substance. It is known that the intensity I of transmitted X-rays after passing through a substance is a function of the thickness t of the substance. In other ^{_{words, I = I 0 · e -}} μt ··· (1)
Is established. Therefore, the thickness of the object to be measured is obtained from the following equation by taking the logarithm of both sides.
[0006]
t = 1 / μ · (logI ₀ −logI) (2)
Here, since the absorption coefficient μ is a value inherent to the substance, the thickness t of the substance is calculated from the equation (2) by measuring the intensity I ₀ of the irradiated X-ray and the intensity I of the transmitted X-ray transmitted through the substance. Can be obtained by
[0007]
Hereinafter, a conventional X-ray thickness measuring apparatus will be described with reference to FIG.
[0008]
The X-ray thickness measuring device includes a detection unit 101 that detects an X-ray transmission amount of an object to be measured 102, and a control unit 110 that calculates a thickness t of the object to be measured 102 from a detected detection signal. Consists of
[0009]
The detection unit 101 detects an X-ray source 103, which is disposed below one of the arms of the C-shaped frame 200 and irradiates X-rays, and is disposed above the other of the arms of the C-shaped frame 200, and detects transmitted X-rays. , A preamplifier 107 for amplifying the signal of the detector 106, and a reference plate setting unit 105 used for calibration.
[0010]
The control unit 110 includes a calculation unit 111 that calculates the thickness t of the measured object 102 from a detection signal from the detector 107, a reference plate driving unit 112 that drives the reference plate setting unit 105 during calibration, and an X-ray source An X-ray control unit 113 for stabilizing and controlling the intensity of the irradiated X-rays 104 emitted from 103.
[0011]
Such an X-ray thickness measuring apparatus has a measurement mode for measuring the thickness t of the measurement target object 102 and a mode for calibrating the measurement accuracy of the thickness t. The arithmetic unit 111 sets the measurement mode, Each unit of the detection unit 101 and the control unit 110 is controlled according to a program incorporated in the calculation unit 111 (not shown) depending on the measurement mode.
[0012]
When used as an X-ray thickness measuring device, an X-ray scattering intensity distribution diagram (hereinafter referred to as a “leakage distribution diagram”) as shown in FIG. 9 is created. Set.
[0013]
For example, in FIG. 9, FIG. 9A is a plan view of the detection unit 101, and FIG. 9B is a front view of the detection unit 101. It shows a leakage distribution due to scattered X-rays of X-rays 104t. A dashed line 104d in the figure shows a leakage distribution diagram when the X-ray source 103 has the maximum output.
[0014]
A broken line 104d indicates a spatial position where the intensity of the predetermined leaked X-ray to be managed is the same, and is displayed in the three-dimensional x, y, and z directions.
[0015]
There are many known applications in which the X-ray thickness measuring device is installed on a steel rolling line or the like to measure the thickness t of the measured object 102 to be rolled. For example, there is an example in which it is installed between rolling mills in a cold rolling line (for example, see Patent Document 1).
[0016]
Even when installed in such a small space, when using an X-ray thickness measuring device, measure the distribution of leakage, set up a controlled area based on laws and regulations, and control by an operator during X-ray irradiation. It is necessary to keep out of the area. In addition, a technique for improving reliability in such a small space in a bad environment having dust, heat, and the like is also known (for example, see Patent Document 2).
[0017]
[Patent Document 1]
Japanese Patent Publication No. 63-52964
[Patent Document 2]
Japanese Utility Model Publication No. 4-29365
[Problems to be solved by the invention]
In recent years, opportunities such as consolidation and abolition of equipment have increased, and demands for relocation of an X-ray thickness measuring device have increased. In this case, it is necessary to satisfy the protection standard at the installation location where the X-ray thickness measuring device in use is also relocated. In addition, if there is a revision of the protection standard, it is necessary to re-establish a controlled area that satisfies the revised protection standard.
[0020]
Conventionally, when such relocation or changes in protection standards have been made, it has been necessary to add a protective wall at the relocation site or to significantly change the management area so as to comply with the protection standards.
[0021]
As described above, when the equipment at the installation place is changed or the measurement range of the object to be measured is changed after the installation of the X-ray thickness measuring device, the setting of the management area needs to be changed, and the protection wall is required. And the size of the management area changes.
[0022]
However, there has not been known a conventional measuring device that can easily change equipment that satisfies a protection standard complying with laws and regulations when such installation conditions are changed.
[0023]
The present invention has been made in order to solve the above-described problems.Changes of the object to be measured, changes in the installation location of the device, and even when there is a change in the protection standard, etc. It is an object of the present invention to provide an X-ray thickness measuring device capable of easily changing a management area.
[0024]
[Means for Solving the Problems]
In order to achieve the above object, an X-ray thickness measuring apparatus of the present invention is arranged so as to be opposed to and spaced apart from an object to be measured, and an X-ray source for irradiating the object to be measured with X-rays and the X-ray thickness measuring apparatus. Detecting means for detecting transmitted X-rays transmitted through the object to be measured, tube voltage control means for controlling the tube voltage of the X-ray tube of the X-ray source, and controlling the tube current of the X-ray tube of the X-ray source A tube current control unit, a reference plate setting unit between the X-ray source and the detection unit for setting a thickness reference, and a calculation for calculating a thickness of the object to be measured from an output signal of the detection unit Means, and a tube current setting means for controlling a leak dose leaked from the X-ray source, wherein the control of the leak dose is performed by setting a predetermined distance or a predetermined distance to a predetermined position with the irradiation port of the X-ray source as an origin. While inputting the set leakage dose at the position to the tube current setting means, By the tube current calculated and inputted to the tube current control means, characterized by being adapted to control the tube current to a predetermined leak dose at a predetermined position.
[0025]
Therefore, according to the present invention, since the leak X-ray can be easily controlled and set by the tube current setting means, even when the installation location of the X-ray thickness measuring device is changed or the protection standard is changed, It is possible to provide an X-ray thickness measuring device capable of easily adding a protective wall and changing a management area.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment according to the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing a configuration of an embodiment relating to an X-ray thickness measuring apparatus of the present invention.
[0027]
In the figure, an X-ray thickness measuring device calculates a thickness t of a measured object 2 from a detection unit 1 for detecting a transmitted X-ray from the measured object 2 and a detection signal of the detected transmitted X-ray. And a control unit 10.
[0028]
The detection unit 1 is disposed below one of the arms of the C-shaped frame 100 with the object 2 to be measured sandwiched therebetween, and is provided with an X-ray source 3 for irradiating X-rays and an X-ray source 3 above the other. A detector 6 for detecting X-rays transmitted through the object 2 to be measured by the irradiated X-rays 4, a preamplifier 7 for amplifying the transmitted X-ray signal detected by the detector 6, and a thickness reference for calibration. And a reference plate setting section 5 for setting a reference plate on the optical path of the irradiated X-rays 4.
[0029]
The control unit 10 further includes a calculation unit 11 for obtaining the thickness t of the DUT 2 from the detection signal of the preamplifier 7, a reference plate driving unit 12 for driving the reference plate setting unit 5 during calibration, and An X-ray controller 13 for stabilizing the tube voltage and the tube current of the X-ray tube so that the intensity of the irradiated X-ray emitted from the X-ray source 3 to be described later becomes constant, and the scattered X-rays from the irradiated X-rays 4 It comprises a tube current setting unit 14, which will be described in detail later, for controlling scattered X-rays leaking around the detection unit 1.
[0030]
Usually, the X-ray thickness measuring device has at least two types of operation modes. One is a measurement mode for measuring the thickness of the object 2 to be measured, and the other is a calibration mode for calibrating the thickness measurement accuracy of the X-ray thickness measuring device. The calibration mode is performed using an idle time when the measured object 2 does not exist.
[0031]
Since this apparatus is a measurement for directly measuring transmitted X-rays, it is necessary to suppress the temperature drift of the irradiated X-rays 4 and each component of the detection unit 1 for high-accuracy thickness measurement. Calibration to maintain is performed frequently and at short intervals.
[0032]
These controls are performed by controlling each of the above-described calibration elements of the detection unit 1 and the control unit 10 by a calculation CPU (not shown) incorporated in the calculation unit 11 and a control program of this device.
[0033]
Next, the setting of the irradiated X-rays 4 and the control of the leakage distribution of the scattered X-rays of the X-ray thickness measuring device will be described, for example, in a case where the X-ray thickness measuring device is used for measuring the thickness of a steel material in a steel rolling line. FIG. 2 shows a configuration for setting and controlling the irradiation X-ray 4.
[0034]
In the figure, an X-ray source 3 is composed of an X-ray tube 3a, a collimator 3b for determining a beam diameter of the irradiated X-ray 4 at an irradiation port 4a, and a case 3c in which these are fixedly arranged. A predetermined tube voltage e is applied to the anode 3a1 of the X-ray tube 3a from the constant voltage circuit 13b via a high voltage cable, and a predetermined constant current i is applied to the cathode 3a2 from the constant current circuit 13a. Connected.
[0035]
The arithmetic unit 11 is connected to the constant current circuit 13a and the constant voltage circuit 13b, and a predetermined tube voltage e and a predetermined tube current i are set in advance according to a measurement range of the thickness t of the object 2 to be measured. . Further, a tube current setting unit 14 is connected to the constant current circuit 13a, and is set so as to control the amount of scattered X-rays at a predetermined position around the detection unit 1.
[0036]
Next, the setting of the irradiation X-ray 4 will be described. When the thickness t and the material of the object 2 to be measured are determined, the intensity and the beam diameter of the irradiation X-rays 4 from the X-ray source 3 are set so as to obtain a predetermined transmitted X-ray intensity.
[0037]
The X-ray intensity Ix is generally determined by a tube voltage e and a tube current i applied to the X-ray tube 3a, and the following relational expression is known. Here, k is a ratio constant.
[0038]
Ix = kie ² (3)
For example, when the measured object 2 is a steel plate having a diameter of about 10 mm or less, an X-ray tube 3a having a rated tube voltage of 100 kv and a rated tube current of about 2 mA is selected to obtain a predetermined detection signal. .
[0039]
FIGS. 3 and 4 show examples of energy distribution characteristics and wavelength distribution characteristics of continuous X-rays emitted from the X-ray tube 3a. In FIGS. 3 and 4, E1, E2, and E3 indicate characteristics when the tube voltage e is 60 kv, 80 kv, and 100 kv, respectively. As shown in FIG. And total energy. In the wavelength distribution characteristics, as the tube voltage increases, short wavelength components increase.
[0040]
From such a characteristic of the continuous X-ray intensity Ix, as shown in FIG. 5, the tube voltage e of the X-ray tube 3a is changed according to the thickness measurement range of the object 2 so that a predetermined detection signal can be obtained. On the other hand, the tube voltage is set to be higher in the case where the thickness t of the measured object 2 in which the transmitted X-rays decrease is larger.
[0041]
When the X-ray intensity Ix of the irradiated X-rays 4 is set to a predetermined value, next, a leak distribution diagram of the scattered X-rays around the detection unit 1 and a tube current setting table are created. The measurement of the leakage distribution and creation of the tube current setting table will be described with reference to FIGS.
[0042]
First, the measurement of the leakage distribution of scattered X-rays by the X-ray thickness measuring device will be described with reference to FIG. FIG. 1A is a plan view of the leakage distribution of the X-ray thickness measuring device, and FIG. 1B is a front view thereof.
[0043]
An X-ray source 3 is arranged below the arm of the C-shaped frame 100 sandwiching the object 2 to be measured, and irradiation X-rays 4 radiated from the X-ray source 3 are radiated to the lower part of the object 2 to be measured. The transmitted X-ray 4t transmitted through the C-frame 2 is incident on the detector 6 arranged in the upper arm of the C frame.
[0044]
At this time, the irradiated X-rays 4 are absorbed in the object 2 to be measured, and at the same time, some are radiated as scattered X-rays and distributed around the detection unit 1. A leakage distribution diagram is obtained by measuring the X-ray intensity distribution with a survey meter or the like.
[0045]
Reference numerals 4d1 and 4d2 denote leakage distribution diagrams starting from the Pe point of the irradiation port 4a of the irradiation X-ray 4. At the same tube voltage, the tube current i is reduced from id1 (mA) to id2 (mA) and changed to a predetermined same value. Is plotted at a position where the absorbed dose Sm (μS: microsievert) is obtained. The unit of the leak distribution measurement is the absorbed dose (μS: microsievert) for setting the control area.
[0046]
As shown in the figure, when the tube current i is reduced from id1 to id2 at the same tube voltage e, the shape of the leakage distribution changes substantially similar.
[0047]
That is, as described with reference to FIGS. 3 and 4, when the tube voltage e is changed, the energy distribution and the wavelength distribution of the irradiated X-rays 4 are changed, so that the distribution shape of the scattered X-rays is largely changed, but the tube voltage e is the same. Then, as shown in Expression (3), the intensity of the irradiated X-rays 4 is proportional to the tube current i, and only the intensity of the scattered X-rays changes.
[0048]
Since this leakage distribution diagram is a characteristic inherent to the X-ray thickness measuring device, it is measured in advance in the range of use of the maximum tube voltage and the maximum current of the device, and this leakage distribution diagram is used as a tube current setting table as a tube current setting section. 14 is stored.
[0049]
Next, a method of creating the tube current setting table will be described with reference to FIGS. 1 and 7 again. The tube current setting table is created by the tube current setting unit 14. In FIG. 1, a tube current setting unit 14 includes an input unit 14 a for inputting a tube current setting value, a memory 14 b for storing a tube current setting table, and a connection between the tube current setting unit 14, the calculation unit 11, and the X-ray control unit 13. And a tube current calculation circuit 14c for performing an interface.
[0050]
FIG. 7 is a diagram illustrating a method of creating a tube current setting table. In the same figure, x, y, and z, like x, y, and z shown in FIG. 6, indicate a leak distribution with the Pe point of the irradiation port 4a of the irradiation X-ray 4 of the detection unit 1 as the coordinate origin. .
[0051]
4d shows, in a three-dimensional space, a leakage distribution in which a predetermined absorbed dose is obtained at the maximum tube voltage Em when the tube current ip is the maximum tube current Ipm and when the tube current ip is α% of the maximum tube current. is there. Thus, it is desirable to confirm the shape of the leakage distribution in advance in the range of the tube voltage and the tube current to be controlled.
[0052]
Such a three-dimensional leakage distribution map is measured in advance, and the plotted data is stored in the memory 14b for each predetermined tube voltage using the data. The tube current setting table thus created is used as follows.
[0053]
In the same figure, when the control area of the X-ray thickness measuring device is changed from the point Pm to the linear Px point connecting the Pe point of the irradiation port 4a, the same absorbed dose (μS) is required at the Px point. In this case, the tube current ip may be changed from Ipm to Ipx. At this time, the tube current Ipx to make a predetermined absorbed dose (μS) at the point Px is as follows: lm is the distance from the Pe point to the Pm point of the irradiation port 4a, and lx is the distance from the Pe point to the Px point of the irradiation port 4a. , And is represented by the following equation.
[0054]
Ipx = Ipm · (lx / lm) ² (4)
Therefore, the absorbed dose (μS) at the predetermined position Px can be changed by changing it to Ipx obtained by the equation (4).
[0055]
When the absorbed dose at the point Px is changed from the initially set Sm (μS) to Sx (μS), the setting of the tube current Ips is as follows.
Ipx = Ipm · Sx / Sm (5)
Thus, the leakage dose (μS) managed at a predetermined position can be changed by changing the tube current Ipx obtained by the equation (5).
[0056]
That is, when the management area is changed, the distance lx to the position is set, and when the management of the absorbed dose (μS) is changed, the absorbed dose Sx is set in the input unit 14a. In the circuit 14c, a tube current corresponding to the equations (4) and (5) is calculated. The value can be changed by setting the value from the tube current calculation circuit 14c to the constant current circuit 13a.
[0057]
Next, the operation of the X-ray thickness measuring apparatus in which the leak distribution is measured and the tube current setting table is created will be described. Although this device has been described as generally having two operation modes, measurement mode and calibration mode, it is desirable to add a tube current setting mode for changing the tube current.
[0058]
When the tube current is to be changed, a tube current setting mode is instructed from the calculation unit 11 and input to the tube current calculation circuit 14c.
[0059]
The tube current calculation circuit 14c extracts the calculation parameters shown in the equations (4) and (5) stored in the tube current setting table from the set distance lx and the absorbed dose Sx, and calculates the calculated tube current. Input to the constant current circuit 13a.
[0060]
When the processing in the tube current setting mode is completed, the calculation unit 11 performs the processing in the calibration mode. In this process, the reference plate is set for the changed tube current, the thickness measurement is calibrated, and the noise component included in the detection signal at this time is processed by the arithmetic unit 11 and displayed on the display unit of the arithmetic unit 11 (not shown). Output.
[0061]
The setting of the reference plate is performed by the arithmetic unit 11 instructing the reference plate driving unit 12 to set the reference plate, the reference plate driving unit 12 instructing the setting of the reference plate built in the reference plate setting unit 5, and performing a predetermined calibration process. I do.
[0062]
When the above is completed, the calculation unit 11 enters the measurement mode. The X-ray intensity I ₀ of the irradiation X-ray 4 is set from the calculation unit 13 via the X-ray control unit 13 based on the thickness measurement range of the measurement target object 2. Then, when the measured object 2 is inserted into the detection unit 1, the transmitted X-ray I is detected. The calculation unit 11 calculates the thickness of the measured object 2 from the transmitted X-ray I based on the above-described equation (2).
[0063]
By measuring the leak distribution in advance and creating a tube current setting table in this way, even if a change in the protection standard or a change in the management area occurs, a new protection wall can be manufactured or installed. The device can be used without changing the equipment environment.
[0064]
In addition, since the noise of the detection signal is monitored after the change, it can be confirmed that the thickness can be measured with a predetermined measurement accuracy.
[0065]
【The invention's effect】
As described above, according to the present invention, since the leak current setting means for setting and controlling the tube current of the X-ray source is provided, the X-ray thickness measurement which can easily set the control area and the change of the leak dose can be easily performed. Equipment can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration according to an embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of an X-ray source and an X-ray control unit that controls the X-ray source.
FIG. 3 is an explanatory diagram of an energy distribution of an X-ray source.
FIG. 4 is an explanatory diagram of a wavelength distribution of an X-ray source.
FIG. 5 is a diagram illustrating switching of a tube voltage depending on the thickness of an object to be measured.
FIG. 6 is a diagram illustrating a leakage dose distribution of the X-ray thickness measuring device.
FIG. 7 is a view for explaining a tube current setting table of an X-ray source.
FIG. 8 is an explanatory view of a conventional X-ray thickness measuring device.
FIG. 9 is an explanatory diagram of a leakage distribution of a conventional X-ray thickness measuring device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Detecting part 2 Object under test 3 X-ray source 3a X-ray tube 3a1 Anode 3a2 Cathode 4 Irradiation X-ray 4t Transmission X-ray 4d, 4d1, 4d2 Leakage distribution 5 Reference plate setting part 6 Detector 7 Preamplifier 10 Control part Reference Signs List 11 calculation unit 12 reference plate driving unit 13 X-ray control unit 13a constant current circuit 13b low voltage circuit 14 tube current setting unit 14a input unit 14b memory 14c tube current calculation circuit 101 detection unit 102 object to be measured 103 X-ray source 104 irradiation X-ray 104t Transmission X-ray 104d Leakage distribution 105 Reference plate setting unit 106 Detector 107 Preamplifier 110 Control unit 111 Operation unit 112 Reference plate driving unit 113 X-ray control unit

Claims (5)

An X-ray source for irradiating the measured object with X-rays and a detecting means for detecting a transmitted X-ray transmitted through the measured object;
Tube voltage control means for controlling a tube voltage of an X-ray tube of the X-ray source;
Tube current control means for controlling the tube current of the X-ray tube of the X-ray source;
A reference plate setting unit that is provided between the X-ray source and the detection unit and sets a thickness reference;
Computing means for computing the thickness of the object to be measured from the output signal of the detecting means, and a tube current setting means for controlling a leakage dose leaked from the X-ray source,
The control of the leak dose is performed by inputting a set leak dose at a predetermined distance or a predetermined position from the irradiation port of the X-ray source to a predetermined position or at a predetermined position to the tube current setting means, and calculating a predetermined tube current. An X-ray thickness measuring apparatus characterized in that a tube current is controlled so that a predetermined leakage dose is obtained at a predetermined position by inputting to the tube current control means. The tube current setting means, input means for inputting a distance to a predetermined position or a leakage dose at a predetermined position with the irradiation port of the X-ray source as an origin,
A memory for storing a tube current setting table for setting the tube current,
2. The X-ray thickness measurement according to claim 1, further comprising: a tube current calculation unit configured to set a value input by the input unit and a predetermined tube current value obtained from the tube current setting table. apparatus. The tube current setting table is a table obtained by measuring a leakage distribution with the irradiation port of the X-ray source as an origin, using a tube voltage and a tube current of an X-ray tube of the X-ray source as parameters, and tabulating the table. The X-ray thickness measuring device according to claim 1 or 2, wherein: The tube current setting table is a table in which a leakage distribution in a three-dimensional space with the irradiation port of the X-ray source as an origin is tabulated using a tube voltage and a tube current of an X-ray tube of the X-ray source as parameters. The X-ray thickness measuring device according to any one of claims 1 to 3, wherein: The calculation means performs a thickness calibration process by the reference plate setting means every time the tube current setting means sets the tube current, and outputs a noise value included in the detection signal at this time. Item 2. The X-ray thickness measuring device according to item 1.

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