A thickness measurement method

Abstract

The invention discloses a detector based on beta rays, a thickness gauge and a thickness measurement method. The method comprises: when unloaded, a central photoelectric sensor unit and a plurality of peripheral photoelectric sensor units respectively collect a first central ray intensity signal and a plurality of first peripheral ray intensity signals, and calculate a first comprehensive ray intensity; an object to be measured is placed between a beta ray source and a detector; a second central ray intensity signal and a plurality of second peripheral ray intensity signals are respectively collected by the central photoelectric sensor unit and the plurality of peripheral photoelectric sensor units after the beta rays pass through the object to be measured, and a second comprehensive ray intensity is calculated according to the second central ray intensity signal and the plurality of second peripheral ray intensity signals; and the thickness of the object to be measured is calculated according to the first comprehensive ray intensity and the second comprehensive ray intensity. The method can effectively solve the problem of thickness measurement value fluctuation caused by height change of the object to be measured during on-line detection of a traditional ionization chamber.

Description

Technical Field

[0001] The invention relates to the field of thickness measurement, and in particular to a thickness measurement method. Background Art

[0002] Currently, in various online detection systems for the surface density and thickness of thin films, metals, papermaking and other sheet materials, X-ray or β-ray penetration detection methods are commonly used. For example, patent text CN100588960C discloses a battery pole surface density measurement system that uses β-ray measurement equipment. In this type of equipment, based on the principle that the ray intensity attenuation ratio after the ray penetrates the pole piece to be measured is negatively exponentially related to the surface density of the object being measured, the ray attenuation ratio is detected by the sensor during the detection process to calculate the surface density value or thickness value of the pole piece. The thickness of the object being measured and the ray intensity obey the following relationship:

[0003] ;

[0004] Among them, I represents the intensity of the ray detected after passing through the object being measured, I 0 represents the initial intensity of the ray, u represents the mass absorption coefficient of the object being measured, and X represents the thickness of the object being measured.

[0005] The above formula is transformed to obtain the calculation formula for the thickness of the object being measured:

[0006] .

[0007] In the film, paper and metal industries, the thickness and surface density of the objects being measured are generally small, and their β rays are generally obtained through the natural nuclear fission process of Kr85 radioactive gas. According to the characteristics of Kr85, its half-life is as long as 10.7 years, and the average energy of the emitted β rays is relatively constant, so the initial intensity of the ray I in the above formula is 0 The mass absorption coefficient u of the object being measured can be regarded as a fixed value in the short-term detection process. Therefore, during the thickness gauge detection process, the intensity I detected after the ray passes through the object being measured has a decisive influence on the detection accuracy.

[0008] The β-rays generated by Kr85 are actually high-speed electron streams, but the energy of the electrons in the rays is continuously distributed. In addition to absorption, they will also undergo elastic scattering with the atoms of the material they encounter on their path, changing their direction of motion many times, making their motion paths complex and curved. Therefore, when the online thickness measurement system is working, the change in the distance between the object being measured and the β-ray generator will greatly affect the projection distribution of the rays on the detector receiving plane after penetrating the object being measured: refer to Figure 1 , the beta rays emitted by Kr85 radiation source 1 are received by the receiving plane 2 of the detector, refer to Figure 2aWhen there is no object between the Kr85 radiation source 1 and the detector 3, the intensity distribution of the radiation received by the detector 3 is as follows: Figure 2b As shown; Reference Figure 2c When the object 4 is close to the Kr85 radiation source 1, that is, the object 4 is at a high position, the intensity distribution of the radiation received by the detector 3 is as follows: Figure 2d As shown; Reference Figure 2e When the object 4 is close to the detector 3, that is, the object 4 is at a low position, the intensity distribution of the radiation received by the detector 3 is as follows: Figure 2f As shown in the figure, it can be seen that the projection intensity of the ray on the detector receiving plane is different when the distance between the object under test and the β-ray generator is different.

[0009] In addition, the cylindrical gas ionization chamber is the mainstream thickness gauge radiation detector. Due to its internal structure, the radiation detection efficiency of each area on the receiving surface is inconsistent, which is reflected in the fact that the center is significantly stronger than the periphery, such as Figure 3 As shown. In summary, when the intensity distribution of the β-ray projected on the receiving plane changes, although the overall beam flux remains unchanged, the signal intensity of the ionization chamber detection output will also change. The maximum signal change is even close to 10%, which has a great negative impact on the measurement accuracy of the thickness gauge. Most thickness gauges deal with this by limiting the up and down jitter of the object being measured and reducing the sensor spacing, which makes the thickness gauge unable to adapt to products with high production speeds and severe jitters. A few thickness gauges will add distance sensors to assist in compensation, but the actual application effect is not satisfactory. Summary of the invention

[0010] The present invention provides a detector, a thickness gauge and a thickness measurement method based on beta rays, which can effectively solve the problem of thickness measurement value fluctuation caused by height change of the object to be measured during the on-line detection process of a traditional ionization chamber.

[0011] A detector based on beta rays, comprising a detector body, a central photoelectric sensor unit arranged on a detection surface of the detector body, and a plurality of peripheral photoelectric sensor units, wherein the geometric center of the photosensitive surface of the central photoelectric sensor unit coincides with the geometric center of a radiation field formed by beta ray projection, the plurality of peripheral photoelectric sensor units are evenly distributed around the central photoelectric sensor unit, and the photosensitive surfaces of the plurality of peripheral photoelectric sensor units are within the radiation field formed by beta ray projection;

[0012] The central photoelectric sensing unit is used to collect the central radiation intensity signal, and the peripheral photoelectric sensing unit is used to collect the peripheral radiation intensity signal. The central radiation intensity signal and multiple peripheral radiation intensity signals are used to calculate the comprehensive radiation intensity in combination with the pre-calibrated proportional constant of the material of the object being measured, and the comprehensive radiation intensity is used to calculate the thickness of the object being measured.

[0013] Furthermore, the central photoelectric sensing unit and / or the peripheral photoelectric sensing unit are photodiodes.

[0014] Furthermore, the plurality of peripheral photoelectric sensing units are distributed on two mutually perpendicular symmetry lines of the radiation field formed by the β-ray projection.

[0015] Furthermore, the detector also includes a signal processing unit for receiving and processing the central ray intensity signal sent by the central photoelectric sensing unit and the peripheral ray intensity signal sent by the peripheral photoelectric sensing unit.

[0016] Furthermore, the detector also includes a central pre-operational amplifier circuit and multiple peripheral pre-operational amplifier circuits, the central pre-operational amplifier circuit is connected to the central photoelectric sensor unit, and the multiple peripheral pre-operational amplifier circuits are respectively connected to multiple peripheral photoelectric sensor units, the signal processing unit is connected to the central pre-operational amplifier circuit and the multiple peripheral pre-operational amplifier circuits, the central pre-operational amplifier circuit is used to amplify the central ray intensity signal and then send it to the signal processing unit, and the peripheral pre-operational amplifier circuit is used to amplify the peripheral ray intensity signal and then send it to the signal processing unit.

[0017] A thickness gauge comprises the above-mentioned detector based on beta rays and also comprises a beta ray source.

[0018] A thickness measurement method, using the thickness gauge as described above, the method comprising:

[0019] Pre-calibrate the proportional constant of the material of the object to be measured to obtain the proportional constant of the material of the object to be measured;

[0020] When unloaded, the central photoelectric sensor unit and the plurality of peripheral photoelectric sensor units respectively collect a first central ray intensity signal and a plurality of first peripheral ray intensity signals;

[0021] Calculate a first integrated radiation intensity according to the first central radiation intensity signal, a plurality of first peripheral radiation intensity signals and the proportional constant;

[0022] Placing the object to be measured between the beta ray source and the detector;

[0023] The central photoelectric sensor unit and the plurality of peripheral photoelectric sensor units respectively collect a second central ray intensity signal and a plurality of second peripheral ray intensity signals after the β-ray passes through the object to be measured;

[0024] Calculate a second integrated radiation intensity according to the second central radiation intensity signal, a plurality of second peripheral radiation intensity signals and the proportional constant;

[0025] The thickness of the object to be measured is calculated according to the first integrated ray intensity and the second integrated ray intensity.

[0026] Furthermore, the first comprehensive ray intensity is calculated by the following formula:

[0027] I 1 =I a1 +k*I b1 ;

[0028] Among them, I a1 It represents the intensity of the first central ray received by the central photoelectric sensor unit when it is unloaded, I b1 represents the sum of the intensities of the first peripheral rays received by the plurality of peripheral photoelectric sensing units when no-load, I 1 represents the first integrated ray intensity, k represents a pre-calibrated proportional constant corresponding to the material of the object being measured;

[0029] The second comprehensive ray intensity is calculated by the following formula:

[0030] I 2 =I a2 +k*I b2 ;

[0031] Among them, I a2 It represents the intensity of the second central ray sensed by the central photoelectric sensor unit after the β ray passes through the object to be measured, I b2 represents the sum of the intensities of multiple second peripheral rays sensed by multiple peripheral photoelectric sensing units after the β-ray passes through the object to be measured, k represents a pre-calibrated proportional constant corresponding to the material of the object to be measured, and I 2 Represents the second integrated ray intensity.

[0032] Furthermore, the thickness of the object to be measured is calculated by the following formula:

[0033] ;

[0034] Where X represents the thickness of the object being measured, u represents the mass absorption coefficient of the object being measured, and I 1 Represents the first integrated ray intensity, I 2 Represents the second integrated ray intensity.

[0035] Furthermore, the proportional constant of the material to be measured is calibrated in advance, including:

[0036] Placing samples of known thickness and the same material as the object to be measured at different heights between the β-ray source and the detector;

[0037] At each height, respectively, the central photoelectric sensing unit and the plurality of peripheral photoelectric sensing units are used to collect a calibrated central ray intensity signal and a plurality of calibrated peripheral ray intensity signals after the beta ray passes through the sample;

[0038] The least square method is used to fit the calibrated central ray intensity at multiple heights and the sum of multiple calibrated peripheral ray intensities to obtain the calibrated fitting straight line equation;

[0039] Obtaining a linear proportionality coefficient between a calibrated central ray intensity and a sum of a plurality of calibrated peripheral ray intensities according to the calibrated fitting straight line equation;

[0040] The proportionality constant is obtained according to the first-order linear proportionality coefficient.

[0041] The beta-ray based detector, thickness gauge and thickness measurement method provided by the present invention have at least the following beneficial effects:

[0042] (1) The photoelectric sensor unit is used to replace the traditional ionization chamber, so that the detection efficiency on the entire detection surface is basically the same, which can avoid the disadvantage of the detector output signal change caused by the change of β-ray projection intensity distribution. On this basis, the central and peripheral photoelectric sensor units form a multi-channel signal output, which can obtain the two-dimensional distribution of the ray intensity within the radiation field, and calculate the comprehensive ray intensity. The thickness of the object to be measured is calculated based on the comprehensive ray intensity, so as to adapt to the different ray intensity distributions at different heights of the object to be measured, and effectively solve the problem of measurement value fluctuation caused by the change of the height of the object to be measured during the online detection of the traditional ionization chamber;

[0043] (2) The layout of the photoelectric sensor unit can be set according to actual needs, thereby effectively saving production costs;

[0044] (3) The photoelectric sensing unit based on the photodiode requires much less energy to form electrons and holes than the ionization energy of electron pairs in the gas ionization chamber. Therefore, when the irradiated area and the radiation flux are the same, the efficiency of the detector proposed by the present invention is at least one order of magnitude higher than that of the gas ionization chamber. With the improvement of detection efficiency, the detector can detect weaker radiation signals after penetrating the object to be measured, which greatly improves the measurable range of the detector. The maximum measurable thickness of common paper and film objects can be increased by more than double.

[0045] (4) Limited by the signal detection efficiency and stability, the distance between the radiation source and the detector of the traditional thickness gauge is generally controlled within 25mm. During the online detection process, the sheet will vibrate greatly when it is running at high speed. The smaller probe spacing is very likely to cause the sheet to contact and scratch the probe, which will lead to damage to the sheet or the sensor. The detector proposed in the present invention can achieve a larger detection area by adjusting the layout and the number of photoelectric sensor units, so as to adapt to the radiation field of the β-rays that is enlarged after the probe spacing is increased. At the same time, combined with the provided thickness measurement method, the vibration of the object to be measured in the height direction can also be effectively and actively adapted, ultimately meeting the detection conditions of high-speed and large-vibration products. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The figure is a schematic structural diagram of an embodiment of a thickness gauge in the prior art.

[0047] Figure 2a The present invention is a schematic diagram of an embodiment of a beta ray beam of an existing thickness gauge when there is no object to be measured.

[0048] Figure 2b The present invention is a schematic diagram of an embodiment of the intensity distribution of rays received by the detector of an existing thickness gauge when there is no object to be measured.

[0049] Figure 2c The present invention is a schematic diagram of an embodiment of a β-ray beam of an existing thickness gauge when the object to be measured is close to a ray source.

[0050] Figure 2d The present invention is a schematic diagram of an embodiment of the intensity distribution of radiation received by the detector of an existing thickness gauge when the object to be measured is close to the radiation source.

[0051] Figure 2e The present invention is a schematic diagram of an embodiment of a β-ray beam of an existing thickness gauge when the object to be measured is far away from the ray source.

[0052] Figure 2f The present invention is a schematic diagram of an embodiment of the intensity distribution of radiation received by the detector of an existing thickness gauge when the object to be measured is far away from the radiation source.

[0053] Figure 3 The present invention is a schematic diagram of an embodiment of the detection efficiency of a gas ionization chamber detector of an existing thickness gauge.

[0054] Figure 4 A schematic structural diagram of an embodiment of a beta-ray based detector provided by the present invention.

[0055] Figure 5 This is a schematic diagram of a first distribution of peripheral photoelectric sensing units in a beta-ray based detector provided by the present invention.

[0056] Figure 6This is a schematic diagram of a second distribution of peripheral photoelectric sensing units in a beta-ray based detector provided by the present invention.

[0057] Figure 7 A schematic structural diagram of another embodiment of a beta-ray based detector provided by the present invention.

[0058] Figure 8 A schematic structural diagram of an embodiment of a thickness gauge provided by the present invention.

[0059] Fig. 9 The present invention provides a flow chart of an embodiment of the thickness measurement method.

[0060] Fig.10a This is a schematic diagram of the light spot state obtained by the detector when there is no object to be measured in an application scenario.

[0061] Fig.10b This is a schematic diagram of the light spot state obtained by the detector when the PI film is close to the side of the radiation source in an application scenario.

[0062] Fig.10c This is a schematic diagram of the light spot state obtained by the detector when the PI film is close to the side of the detector in an application scenario.

[0063] Fig.11 A schematic diagram of the layout of a photoelectric sensor unit in an application scenario of the thickness detection method provided by the present invention.

[0064] Fig.12 A schematic diagram of a calibrated fitting straight line equation obtained by fitting in an application scenario of the thickness detection method provided by the present invention. DETAILED DESCRIPTION

[0065] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0066] refer to Figure 4 In some embodiments, a detector based on beta rays is provided, comprising a detector body 101, a central photoelectric sensor unit 102 and a plurality of peripheral photoelectric sensor units 103 arranged on a detection surface of the detector body 101, wherein the geometric center of the photosensitive surface of the central photoelectric sensor unit 102 coincides with the geometric center of a radiation field formed by projection of beta rays, the plurality of peripheral photoelectric sensor units 103 are evenly distributed around the central photoelectric sensor unit 102, and the photosensitive surfaces of the plurality of peripheral photoelectric sensor units 103 are within the radiation field formed by projection of beta rays;

[0067] The central photoelectric sensing unit 102 is used to collect the central radiation intensity signal, and the peripheral photoelectric sensing unit 103 is used to collect the peripheral radiation intensity signal. The central radiation intensity signal and multiple peripheral radiation intensity signals are used to calculate the comprehensive radiation intensity in combination with the proportional constant of the material of the object to be measured which is calibrated in advance. The comprehensive radiation intensity is used to calculate the thickness of the object to be measured.

[0068] In the above embodiment, a photoelectric sensor unit based on the photoelectric effect is used to replace the traditional gas ionization chamber as a direct receiving device for β rays. Due to the internal structure of the traditional gas ionization chamber, the ray detection efficiency of each area of ​​its receiving surface is uneven, with a stronger central area and gradually weakening towards the sides. For details, see Figure 3 The detection efficiency of the photoelectric sensing unit based on the photoelectric effect is basically the same on the entire detection surface, which can avoid the disadvantage of the change of the detector output signal caused by the change of the β-ray projection intensity distribution.

[0069] In some embodiments, the central photoelectric sensing unit 102 and / or the peripheral photoelectric sensing unit 103 may be a photodiode.

[0070] In some embodiments, the central photoelectric sensing unit 102 and / or the peripheral photoelectric sensing unit 103 may be Si-PIN photodiodes.

[0071] Specifically, the beta rays emitted by the beta ray source form a projection spot onto the detection surface of the detector body 101. The central photoelectric sensor unit 102 and multiple peripheral photoelectric sensor units 103 form multiple channels to respectively collect multiple ray intensity signals. After obtaining the multiple ray intensity signals, the system analyzes them and can approximately know the two-dimensional distribution of the ray intensity within the radiation field. Then, the comprehensive ray intensity is calculated in combination with the proportional constant of the material of the object to be measured which is calibrated in advance. The thickness of the object to be measured is calculated based on the comprehensive ray intensity, taking into account the two-dimensional distribution of the ray intensity within the radiation field. This can adapt to different ray intensity distributions at different heights of the object to be measured, and effectively solve the problem of measurement value fluctuations caused by changes in the height of the object to be measured during online detection of traditional ionization chambers.

[0072] Further, refer to Figure 5 and Figure 6 , a plurality of peripheral photoelectric sensing units 103 are distributed on two mutually perpendicular symmetry lines of the radiation field formed by the β-ray projection.

[0073] Specifically, the central photoelectric sensor unit 102 and multiple peripheral photoelectric sensor units 103 are arranged in a specific manner within the radiation field formed by the β-ray projection. The central photoelectric sensor unit 102 is located at the geometric center of the radiation field formed by the β-ray projection, and the geometric center of its photosensitive surface coincides with the geometric center of the radiation field formed by the β-ray projection, so as to detect the intensity of the central area of ​​the β-ray beam. With the geometric center of the photosensitive surface of the central photoelectric sensor unit 102 as the center of the circle, one or two circles of peripheral photoelectric sensor units 103 are arranged around it, and each peripheral photoelectric sensor unit 103 is arranged evenly. The distance between the β-ray source and the detector is different, and different β-ray geometric radiation fields will be obtained on the detection surface of the detector. Generally, the larger the distance, the larger the radiation field, and the radiation field gradually weakens radially outward with the center of the circle as the center. According to this characteristic, when the distance between the β-ray source and the detector is small, when the radiation field is small, four peripheral photoelectric sensor units 103 in the outer circle are selected to be arranged along the horizontal symmetry line and the vertical symmetry line of the radiation field, such as Figure 5 When the distance between the β-ray source and the detector is large, the outer periphery is two circles of 8 outer photoelectric sensor units 103 arranged along the horizontal symmetry line and the vertical symmetry line of the radiation field, as shown in FIG. Figure 6 Arrangement along the horizontal symmetry line and the vertical symmetry line of the radiation field can achieve the use of fewer peripheral photoelectric sensor units to represent the two-dimensional distribution of the β-ray intensity of the entire detection surface, which is highly efficient and cost-saving.

[0074] Further, refer to Figure 7 In some embodiments, the detector further includes a signal processing unit 104 for receiving and processing a central ray intensity signal sent by the central photoelectric sensing unit 102 and a peripheral ray intensity signal sent by the peripheral photoelectric sensing unit 103 .

[0075] Furthermore, in some embodiments, the detector also includes a central pre-amplifier circuit 105 and multiple peripheral pre-amplifier circuits 106, the central pre-amplifier circuit 105 is connected to the central photoelectric sensor unit 102, the multiple peripheral pre-amplifier circuits 106 are respectively connected to the multiple peripheral photoelectric sensor units 103, the signal processing unit 104 is connected to the central pre-amplifier circuit 105 and the multiple peripheral pre-amplifier circuits 106, the central pre-amplifier circuit 105 is used to amplify the central ray intensity signal and then send it to the signal processing unit 104, and the peripheral pre-amplifier circuit 106 is used to amplify the peripheral ray intensity signal and then send it to the signal processing unit 104.

[0076] Specifically, the signal processing unit 104 receives the amplified central radiation intensity signal and the peripheral radiation intensity signal for analysis, and can approximately obtain the two-dimensional distribution of the radiation intensity within the radiation field, and then calculate the comprehensive radiation intensity, and calculate the thickness of the object under test based on the comprehensive radiation intensity.

[0077] Further, refer to Figure 8 In some embodiments, a thickness gauge is provided, comprising the above-mentioned β-ray based detector 100 , and also comprising a β-ray source 200 .

[0078] Specifically, the β-ray source 200 is used to emit β-rays to form a radiation field of a projected light spot on the detection surface of the detector body 101 of the detector 100 .

[0079] refer to Fig. 9 In some embodiments, a thickness measurement method is provided, using the above-mentioned thickness gauge, the method comprising:

[0080] S1. Pre-calibrate the proportional constant of the material to be measured to obtain the proportional constant of the material to be measured;

[0081] S2, when no-load, collecting a first central ray intensity signal and a plurality of first peripheral ray intensity signals respectively through the central photoelectric sensor unit and the plurality of peripheral photoelectric sensor units;

[0082] S3, calculating a first comprehensive ray intensity according to the first central ray intensity signal, a plurality of first peripheral ray intensity signals and a proportional constant;

[0083] S4, placing the object to be measured between the β-ray source and the detector;

[0084] S5, collecting, through the central photoelectric sensing unit and the plurality of peripheral photoelectric sensing units, a second central ray intensity signal and a plurality of second peripheral ray intensity signals after the β-ray passes through the object to be measured;

[0085] S6, calculating a second integrated ray intensity according to the second central ray intensity signal, a plurality of second peripheral ray intensity signals and a proportional constant;

[0086] S7. Calculate the thickness of the object to be measured according to the first comprehensive ray intensity and the second comprehensive ray intensity.

[0087] Specifically, in step S2, when unloaded, that is, no object is set between the β-ray source and the detector, the β-ray source is turned on, and the central photoelectric sensor unit and multiple peripheral photoelectric sensor units respectively collect the first central ray intensity signal and multiple first peripheral ray intensity signals.

[0088] In some embodiments, after the central photoelectric sensing unit and the multiple peripheral photoelectric sensing units respectively collect the first central ray intensity signal and the multiple first peripheral ray intensity signals, the first central ray intensity signal and the multiple first peripheral ray intensity signals can also be amplified by the central pre-amplifier circuit and the peripheral pre-amplifier circuit respectively.

[0089] Furthermore, in step S3, after obtaining the first central ray intensity signal and multiple first peripheral ray intensity signals, they are analyzed to obtain the first central ray intensity sensed by the central photoelectric sensor unit when no-load and the multiple first peripheral ray intensities sensed by each peripheral photoelectric sensor unit, and the first comprehensive ray intensity is calculated based on the first central ray intensity, the multiple first peripheral ray intensities and the proportional coefficient.

[0090] Specifically, the first comprehensive ray intensity is calculated by the following formula:

[0091] I 1 =I a1 +k*I b1 ;

[0092] Among them, I a1 It represents the intensity of the first central ray received by the central photoelectric sensor unit when it is unloaded, I b1 represents the sum of the intensities of the first peripheral rays received by the plurality of peripheral photoelectric sensing units when no-load, I 1 represents the first integrated ray intensity, k represents a pre-calibrated proportional constant corresponding to the material of the object being measured;

[0093] I b1 It is obtained by adding the intensities of multiple first peripheral rays.

[0094] Furthermore, in step S4, the object to be measured is placed between the β-ray source and the detector. The object to be measured can be located at any height between the β-ray source and the detector.

[0095] Furthermore, in step S5, a second central ray intensity signal and multiple second peripheral ray intensity signals are respectively collected by the central photoelectric sensor unit and multiple peripheral photoelectric sensor units after the β-rays pass through the object to be measured. In some embodiments, after the central photoelectric sensor unit and multiple peripheral photoelectric sensor units respectively collect the second central ray intensity signal and multiple second peripheral ray intensity signals, the second central ray intensity signal and multiple second peripheral ray intensity signals can also be amplified by the central pre-operational amplifier circuit and the peripheral pre-operational amplifier circuit.

[0096] Furthermore, in step S6, after obtaining the second central ray intensity signal and multiple second peripheral ray intensity signals, they are analyzed to obtain the second central ray intensity sensed by the central photoelectric sensor unit after the β-ray passes through the object to be measured, and the multiple second peripheral ray intensities sensed by each peripheral photoelectric sensor unit. Based on the second central ray intensity and the multiple second peripheral ray intensities, the second comprehensive ray intensity is calculated.

[0097] Specifically, the second comprehensive ray intensity is calculated by the following formula:

[0098] I 2 =I a2 +k*I b2 ; (2)

[0099] Among them, I a2 It represents the intensity of the second central ray received by the central photoelectric sensor unit after the β ray passes through the object to be measured, I b1 represents the sum of the intensities of multiple second peripheral rays received by multiple peripheral photoelectric sensing units after the β-ray passes through the object to be measured, k represents a pre-calibrated proportional constant corresponding to the material of the object to be measured, and I 2 Represents the second integrated ray intensity.

[0100] I b2 It is obtained by adding the intensities of multiple second peripheral rays.

[0101] Further, in step S7, after obtaining the first integrated ray intensity when unloaded and the second integrated ray intensity after the object to be measured is placed, the thickness of the object to be measured can be calculated based on the first integrated ray intensity and the second integrated ray intensity. Specifically, the thickness of the object to be measured is calculated by the following formula:

[0102] ; (3)

[0103] Where X represents the thickness of the object being measured, u represents the mass absorption coefficient of the object being measured, and I 1 Represents the first integrated ray intensity, I 2 Represents the second integrated ray intensity.

[0104] In some embodiments, in step S1, the proportional constant of the material of the object to be measured is calibrated in advance, specifically including:

[0105] S11, placing samples of the same material as the object to be measured and of known thickness at different heights between the β-ray source and the detector;

[0106] S12, at each height, respectively collecting a calibrated central ray intensity signal and a plurality of calibrated peripheral ray intensity signals after the β-ray passes through the sample through the central photoelectric sensing unit and the plurality of peripheral photoelectric sensing units;

[0107] S13, fitting the calibrated central ray intensity at multiple heights and the sum of multiple calibrated peripheral ray intensities using the least squares method to obtain a calibrated fitting straight line equation;

[0108] S14, obtaining a linear proportionality coefficient between a calibrated central ray intensity and a sum of a plurality of calibrated peripheral ray intensities according to the calibrated fitting straight line equation;

[0109] S15. Obtain the proportional constant according to the first-order linear proportional coefficient.

[0110] Specifically, the linear proportional coefficient is the slope of the calibration fitting straight line equation, and the relationship between the proportional constant and the linear proportional coefficient is as follows:

[0111] ; (4)

[0112] Among them, k is the proportional constant and r is the linear proportional coefficient.

[0113] The method provided in the above embodiment is further described below through specific application scenarios.

[0114] The T1001 cylindrical Kr85 sold by German IUT company is used as the β-ray source (activity 500mCi). The active area of ​​the source is a circle with a diameter of 22mm. The detector is kept about 45mm away from the active area of ​​the β-ray source for vertical imaging, and the exposure is adjusted to obtain a clear image of the main spot of the β-ray projection. The size and brightness of the main spot represent the distribution of the β-ray beam in the radiation field. A PI film with a thickness of 50um is used to keep it in three states: close to the detector side, close to the ray source side, and without the object to be measured. A dynamic flat panel is used to expose once at a frame rate of 30fps to obtain the main spot image as shown in the figure. Figures 10a to 10c As shown, Fig.10a When there is no object to be measured, the spot width is 300 pixels, about 25.5mm. Fig.10b This is the state when the PI film is close to the radiation source side. The spot width is 350 pixels, about 29.75mm. Fig.10c This is the state when the PI film is close to the detector side, and the spot width is 229 pixels, about 19.5mm.

[0115] according to Figures 10a to 10c It can be determined that the diameter of the main light spot is about 25mm when there is no object to be measured. When the object to be measured is close to the side of the ray source and at the maximum height, Fig.10bThe diameter of the main light spot is about 30 mm. Therefore, the distance between the inner edge of the four peripheral photoelectric sensor units in the first circle and the center of the beam is about 25 / 2=12.5 mm. Fig.10b It can be seen that the maximum projection distribution of the ray beam has a radius of 15mm, which has covered the first peripheral photoelectric sensor unit, so it is necessary to add another circle of 4 peripheral photoelectric sensor units to supplement the detection of the ray intensity outside the main spot. The distribution of ray intensity in the horizontal and vertical directions of the projection plane is consistent, so only the peripheral photoelectric sensor units are arranged on the horizontal and vertical symmetry lines of the radiation field. The basic layout of the inner and outer peripheral photoelectric sensor units is as follows: Fig.11 As shown: eight peripheral photoelectric sensor units 103 are distributed on the horizontal symmetry line and the vertical symmetry line of the radiation field, and the central photoelectric sensor unit 102 is arranged at the geometric center of the radiation field.

[0116] The proportional constant k is calibrated as follows:

[0117] Keep the distance between the radiation source and the detector at 40mm, use a PI film (polyimide) with a thickness of 50um as the sample, use a clamp to fix the PI film and lift it horizontally, the heights are 2, 12, 20, 24, 29, and 34mm respectively. Record the radiation intensity signals output by all photoelectric sensor units through the preamplifier circuit, including the calibrated central radiation intensity I in the central area. a , add the calibrated peripheral radiation intensities sensed by all 8 peripheral photoelectric sensor units to obtain the total peripheral calibrated peripheral radiation intensity I b . refer to Fig.12 , to calibrate the central ray intensity I a is the horizontal axis, and the peripheral calibrated peripheral ray intensity sum I b The least square method is used for fitting, and the calibration fitting straight line equation y = -0.5787x + 9831.1 is obtained. The linear proportional coefficient between the two is r = -0.5787, that is, the slope of the calibration fitting straight line equation. According to formula (4), the proportional constant k is calculated to be 1.728.

[0118] So far, for the current 40mm probe spacing and the film with the composition of PI, the proportional constant k has been obtained to be 1.728. Save this parameter and apply it to this type of product. When measuring the thickness of this type of object again, first obtain the first integrated ray intensity when no load is applied, then place the object between the β-ray source and the detector to obtain the second integrated ray intensity, and then calculate the thickness of the object according to formula (3).

[0119] The following is a verification of the effect of the method provided in the above embodiment:

[0120] Again, a PI film with a thickness of 50um was used as a sample, and a clamp was used to lift it horizontally, with the heights being 2, 12, 20, 24, 29, and 34mm respectively. The thickness value X calculated and displayed by the thickness gauge was recorded, and the range of the measured value was calculated. The results are shown in Table 1:

[0121] Table 1

[0122]

[0123] A detector based on an ionization chamber was used, and a PI film with a thickness of 50 um was used as the object to be measured. The height of the detector was changed when the probe spacing was 40 mm. The experimental results show that the intensity I of the ray detected by the ionization chamber after penetrating the object and the thickness value X are affected by the probe spacing and the height of the object to be measured, as shown in Table 2. The maximum change rate of the thickness value is 59.6%.

[0124] Table 2

[0125]

[0126] By comparing Table 1 and Table 2, it can be seen that using the detector provided in the above embodiment to replace the ionization chamber and using the calculation method of formulas (1) to (4) to convert the radiation intensity and thickness value can effectively avoid the influence of height. The detector and thickness measurement method provided in the above embodiment have a maximum measurement value fluctuation rate of only 0.44% when the height change of the measured object reaches 32 mm.

[0127] The beta-ray based detector, thickness gauge and thickness measurement method provided in the above embodiments have at least the following beneficial effects:

[0128] (1) The photoelectric sensor unit is used to replace the traditional ionization chamber, so that the detection efficiency on the entire detection surface is basically the same, which can avoid the disadvantage of the detector output signal change caused by the change of β-ray projection intensity distribution. On this basis, the central and peripheral photoelectric sensor units form a multi-channel signal output, which can obtain the two-dimensional distribution of the ray intensity within the radiation field, and calculate the comprehensive ray intensity. The thickness of the object to be measured is calculated based on the comprehensive ray intensity, so as to adapt to the different ray intensity distributions at different heights of the object to be measured, and effectively solve the problem of measurement value fluctuation caused by the change of the height of the object to be measured during the online detection of the traditional ionization chamber;

[0129] (2) The layout of the photoelectric sensor unit can be set according to actual needs, thereby effectively saving production costs;

[0130] (3) The photoelectric sensing unit based on the photodiode requires much less energy to form electrons and holes than the ionization energy of electron pairs in the gas ionization chamber. Therefore, when the irradiated area and the radiation flux are the same, the efficiency of the detector proposed by the present invention is at least one order of magnitude higher than that of the gas ionization chamber. With the improvement of detection efficiency, the detector can detect weaker radiation signals after penetrating the object to be measured, which greatly improves the measurable range of the detector. The maximum measurable thickness of common paper and film objects can be increased by more than double.

[0131] (4) Limited by the signal detection efficiency and stability, the distance between the radiation source and the detector of the traditional thickness gauge is generally controlled within 25mm. During the online detection process, the sheet will vibrate greatly when it is running at high speed. The smaller probe spacing is very likely to cause the sheet to contact and scratch the probe, which will lead to damage to the sheet or the sensor. The detector proposed in the present invention can achieve a larger detection area by adjusting the layout and the number of photoelectric sensor units, so as to adapt to the radiation field of the β-rays that is enlarged after the probe spacing is increased. At the same time, combined with the provided thickness measurement method, the vibration of the object to be measured in the height direction can also be effectively and actively adapted, ultimately meeting the detection conditions of high-speed and large-vibration products.

[0132] Although preferred embodiments of the present invention have been described, additional changes and modifications may be made to these embodiments by those skilled in the art once the basic inventive concepts are known. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A thickness measurement method, characterized in that: The thickness gauge is used for measurement, and the thickness gauge includes a detector based on beta rays and a beta ray source. The detector based on beta rays includes a detector body, a central photoelectric sensor unit and a plurality of peripheral photoelectric sensor units arranged on the detection surface of the detector body. The geometric center of the photosensitive surface of the central photoelectric sensor unit coincides with the geometric center of the radiation field formed by the projection of the beta rays. The plurality of peripheral photoelectric sensor units are evenly distributed around the central photoelectric sensor unit, and the photosensitive surfaces of the plurality of peripheral photoelectric sensor units are within the radiation field formed by the projection of the beta rays. The method comprises: Pre-calibrate the proportional constant of the material of the object to be measured to obtain the proportional constant of the material of the object to be measured; When unloaded, the central photoelectric sensor unit and the plurality of peripheral photoelectric sensor units respectively collect a first central ray intensity signal and a plurality of first peripheral ray intensity signals; Calculate a first integrated radiation intensity according to the first central radiation intensity signal, a plurality of first peripheral radiation intensity signals and the proportional constant; Placing the object to be measured between the beta ray source and the detector; The central photoelectric sensor unit and the plurality of peripheral photoelectric sensor units respectively collect a second central ray intensity signal and a plurality of second peripheral ray intensity signals after the β-ray passes through the object to be measured; Calculate a second integrated radiation intensity according to the second central radiation intensity signal, a plurality of second peripheral radiation intensity signals and the proportional constant; Calculating the thickness of the object to be measured according to the first comprehensive ray intensity and the second comprehensive ray intensity; The proportional constant of the material to be measured is calibrated in advance, including: Placing samples of known thickness and the same material as the object to be measured at different heights between the β-ray source and the detector; At each height, respectively, the central photoelectric sensing unit and the plurality of peripheral photoelectric sensing units are used to collect a calibrated central ray intensity signal and a plurality of calibrated peripheral ray intensity signals after the beta ray passes through the sample; The least square method is used to fit the calibrated central ray intensity at multiple heights and the sum of multiple calibrated peripheral ray intensities to obtain the calibrated fitting straight line equation; Obtaining a linear proportionality coefficient between a calibrated central ray intensity and a sum of a plurality of calibrated peripheral ray intensities according to the calibrated fitting straight line equation; Obtaining the proportionality constant according to the first-order linear proportionality coefficient; The linear proportional coefficient is the slope of the calibration fitting straight line equation, and the relationship between the proportional constant and the linear proportional coefficient is as follows: ； Among them, k is the proportional constant, r is the linear proportional coefficient; The first comprehensive ray intensity is calculated by the following formula: I1=I a1 +k*I b1 ; Among them, I a1 It represents the intensity of the first central ray received by the central photoelectric sensor unit when it is unloaded, I b1 represents the sum of multiple first peripheral ray intensities received by multiple peripheral photoelectric sensing units when no-load, I1 represents the first comprehensive ray intensity, and k represents a pre-calibrated proportional constant corresponding to the material of the object to be measured; The second comprehensive ray intensity is calculated by the following formula: I2=I a2 +k*I b2 ; Among them, I a2 It indicates the intensity of the second central ray sensed by the central photoelectric sensor unit after the β ray passes through the object to be measured, I b2 It represents the sum of multiple second peripheral ray intensities sensed by multiple peripheral photoelectric sensing units after the β ray passes through the object to be measured, k represents a pre-calibrated proportional constant corresponding to the material of the object to be measured, and I2 represents the second comprehensive ray intensity.

2. The method according to claim 1, characterized in that The central photoelectric sensing unit and / or the peripheral photoelectric sensing unit are photodiodes.

3. The method according to claim 1, characterized in that The plurality of peripheral photoelectric sensing units are distributed on two mutually perpendicular symmetry lines of the radiation field formed by the β-ray projection.

4. The method according to claim 1, characterized in that: The detector further comprises a signal processing unit for receiving and processing a central ray intensity signal sent by the central photoelectric sensing unit and a peripheral ray intensity signal sent by the peripheral photoelectric sensing unit.

5. The method according to claim 4, characterized in that The detector also includes a central pre-operational amplifier circuit and multiple peripheral pre-operational amplifier circuits, the central pre-operational amplifier circuit is connected to the central photoelectric sensor unit, and the multiple peripheral pre-operational amplifier circuits are respectively connected to multiple peripheral photoelectric sensor units, the signal processing unit is connected to the central pre-operational amplifier circuit and the multiple peripheral pre-operational amplifier circuits, the central pre-operational amplifier circuit is used to amplify the central ray intensity signal and then send it to the signal processing unit, and the peripheral pre-operational amplifier circuit is used to amplify the peripheral ray intensity signal and then send it to the signal processing unit.

6. The method according to claim 1, characterized in that The thickness of the object to be measured is calculated by the following formula: ； Wherein, X represents the thickness of the object to be measured, u represents the mass absorption coefficient of the object to be measured, I1 represents the first integrated ray intensity, and I2 represents the second integrated ray intensity.

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