WO2001011324A1

WO2001011324A1 - A method for precisely measuring the weight of mass material and a nucleonic weigher employing this method

Info

Publication number: WO2001011324A1
Application number: PCT/CN2000/000229
Authority: WO
Inventors: Shengcai Di
Original assignee: Shengcai Di
Priority date: 1999-08-10
Filing date: 2000-08-10
Publication date: 2001-02-15

Abstract

The present invention discloses a method for precisely measuring the weight of mass material and a nucleonic weigher employing this method. It is characterised in that the coefficient K in the nucleonic weigher's weighing formula F=KLn(Ui/Uo) is dynamically modified, based on the variations of the parameters including the flowrate, the position on the conveying device, and the piled shape of the weighed mass material and the scattering of η radiation, thus improving the measuring precision. The nucleonic weigher manufactured with a completely enclosed framework has the merits of high measuring precision, wide application, good stability, reliable safety, small maintenance, and low cost.

Description

Method for high-precision measurement of material weight and nuclear scale using the same TECHNICAL FIELD

The present invention relates to a method for measuring the weight of materials, and in particular, to a method for measuring the weight of materials with nuclear radiation with high accuracy and a high-precision nuclear scale using the measurement method. Background technique

The nuclear scale is developed based on the principle of absorption of Y-rays by matter. The working principle of the existing nuclear scale is shown in Figure 1. In the figure, 1 is a Y radiation source, 2 is a γ-ray detector, 3 is a γ-ray irradiation area, 4 is a speed measuring device, 5 is a data processing device, and 6 is a scale body. Bracket and protective cover, 7 is belt and material. A Y-ray source is placed above the bracket of the nuclear scale, and a Y-ray detector is placed below the bracket. The conveyor belt and the material pass through the middle of the bracket. The Y-ray source steadily emits Y-rays, whose intensity is constant. When there is no material on the belt, the Y-rays received by the Y-ray detector are also constant. At this time, the voltage output by the Y-ray detector is U. When there is material on the belt, part of the Y-rays emitted by the radiation source is absorbed by the material, and the rest passes through the material and is received by the Y-ray detector. At this time, the output voltage of the γ-ray detector is. According to the law of y-ray absorption of matter:

U ₀ and Ui have the following relationship with the material:

U ^ Ue ^ ^d (1)

Where μ _ρ -mass absorption coefficient of material to γ-rays

Ρ-material density

d-material thickness

Shift the term and multiply the exponent by S / S

U — μ _n pd S / S

W = P d s

½a _p - ^WIS (2) Where S-the area occupied by the material on the belt will be logarithmic on both sides of (2), and let W / S = F, κ = -1 / μ _ρ :

F = K Ln ^ (3)

Where F-material load

K-material calibration coefficient The speed V of the conveyor belt can be measured using the speed sensor. The material flow rate P on the conveyor belt is:

P = F V

The cumulative amount of material conveyed by the conveyor belt over a period of time w _h is −

In the existing nuclear scale, when formula (3) is used, K is regarded as a constant, but in fact K is not a constant, and it changes with the change of the belt load. The main reason is that the existing nuclear scales made two approximations when applying the law of absorption of Y-rays by substances:

1) Set the scattering factor to 1 to ignore the effect of Y-ray scattering. In fact, the larger the density of the material and the thicker the material, the greater the effect of scattering.

2) The law of absorption of Y-rays by matter requires that the Y-rays are parallel beams. In fact, the existing nuclear scales use point sources, and the Y-rays emitted by them are fan beams. As shown in Figure 2, when the material is at A When the absorbed Y-ray is at the plane where ab is, and when the material is at B, the absorbed Y-ray is at the plane where cd is, obviously c-d> ab. It can be seen that the changes in the material flow (load), the shape of the material stack, the location of the material, and the influence of scattering factors are the main reasons that restrict the accuracy of the existing nuclear scales. At present, the nuclear scale products produced by nuclear scale manufacturers at home and abroad use the total weight of materials. Coefficient K, such as Chinese patent ZL95106808.3 (publication number CN1039160C). When the coefficient K is calibrated by this method, the nuclear scale only records the weight of the material, but does not record the change of the material load. Therefore, the calibrated coefficient K has nothing to do with the amount of material load on the belt, which is not in line with the actual situation. It can be seen that the existing nuclear scale cannot change according to the load

Summary of the Invention

The purpose of the present invention is to solve the above-mentioned problems, and provide a dynamic high-precision measurement method that reduces and eliminates changes in flow, stacking shapes and different positions of materials, and scattering and other factors that affect the measurement accuracy, thereby manufacturing a method using the method. High-precision nuclear scale. To achieve the above objective, the present invention adopts the following technical solutions:

A method for high-precision measurement of materials, including steps:

(1) Set up multiple Y-radiation sources and corresponding Y-ray detectors, and set up a material conveying device between them;

(2) The output voltage U of the Y-ray detector is measured when there is no material and when there is material. And Ui, and input it to the data processing device connected to the Y-ray detector;

(3) Use the speed measuring device to measure the conveying speed Vi of the conveyor belt on the conveying device, and input its value to the data processing device (PLC) connected to it;

(4) Data processing device according to formula

Calculate the cumulative amount W of the material transported in a certain period of time,

Among them, the material calibration coefficient K in the formula is based on the material

Y-ray scattering and other influencing factors are dynamically modified in real time. The material calibration coefficient κ value is determined by the physical calibration method according to the change of the material flow. The steps are as follows:

(1) The material weight w _{a fe is} weighed with a standard scale, and the material conveying device conveys the material with a stable flow load; (2) The output voltage of the Y-ray detector collected by the data processing device in real time

Ui, the conveying speed Vi output by the speed measuring device, and the conveying time ti, calculate-

, / U,

Yin _M

Mark

F standard ( ^w T) average ―

And use the F standard as the ordinate and LnUAJo as the abscissa to establish a coordinate system. According to the average value of F _{¾ a} and (LnUi / U ₀ ) _a calculated above, determine the point a in the coordinate system to obtain K _a , That is the slope of Oa;

(3) For different material weights W _b , W _c , W _{d ¾} ~, using the same method described above, the point b, c, and d in the coordinate system can be determined, so that K _b and K can be obtained. _e , K _d- , and P = functional relations of ί · (ΐΛυ υ ₀ ). As shown in Figure 3. Use the linear relationship of multiple line segments F = bj + kjLnOJ UQ) to fit the function F = f (LnUi / U.), Where j is the number of line segments, and its steps are −

(1) Connect 0a, ab, bc, cd, ... to obtain each line segment;

(2) Use 0, a, b, c, d ... to calculate b '' and k of each line segment using the coordinate values of each point, or fit the function F ^ -fCLnU / Uo with a polynomial method). Points a, b, c, d ... The coordinates of each point can be obtained by the least square method.

F = ao + a 'Lnl Uo a ^ LnUi / Uo + + a LnUi / UJk coefficient a. , A ,, a ₂ ,…, a _k , where k = 0, 1, 2, 3, '·· 1ς. A nuclear scale using the above method, comprising

1-N tritium radioactive sources, where N = 2-10;

A radon detector, corresponding to a radon radiation source, can convert the intensity of the radon radiation received into a voltage parameter, and a material transport device can be set between the radon radiation source and the radon radiation source; Speed measuring device for measuring the conveying speed on the material conveying device;

A microcomputer and a data processing device (PLC) are connected to the Y-ray detector and the speed measuring device, and can calculate the accurate amount of materials based on the above data. The Y radiation source can be selected from ¹³⁷ C _S and ^6Q C according to the measured material. , ²⁴¹ A _m , the number of which can be determined according to the width of the material conveying device, preferably 2-7. The y-radiation source and the Y-ray detector can be fixed at corresponding positions on a fully enclosed weighing frame. For the linear relationship of the multi-segment fitting function F ^^ flLnl V. :), the nuclear scale works according to the broken line position determination flowchart of FIG. 4. The invention has the advantages that the dynamic high-precision measurement method eliminates the influence of factors such as flow changes, different positions of materials, material stacking shape, and Y-ray scattering on measurement accuracy, and greatly improves measurement accuracy. The nuclear scale using this method has high measurement accuracy, a large applicable flow range, a wide range of applications, good stability, and a wide range of use of radioactive sources, which can reduce costs and improve measurement accuracy, and is safe and reliable to use. Brief description of the drawings

FIG. 1 is a schematic diagram of a prior art nuclear scale;

Figure 2 is a schematic diagram of the Y-ray absorption of the material at different positions;

Figure 3 shows the relationship between the F standard and Ln (lVU.) Function;

FIG. 4 is a flowchart for determining a position of a broken line;

FIG. 5 is a relationship curve between the F standard and the Ln (Ui / U.) Function in the embodiment; FIG.

6 is a flowchart of determining a position of a broken line in the embodiment;

7 (a) is a schematic diagram of an embodiment of a nuclear scale of the present invention (built-in linear gamma radiation source);

FIG. 7 (b) is a schematic diagram of another embodiment of the nuclear scale of the present invention (multiple gamma radiation sources); FIG. 8 is a schematic structural diagram of a fully enclosed weighing frame; Figure 9 is a side view of Figure 8;

Figure 10 is a perspective view of a fully enclosed weighing frame. Best practice

The invention is further described below with reference to the drawings. Use the load method to calibrate the material calibration coefficient K on the nuclear scale:

Assume that the physical calibration timing data processing device measures the nuclear scale U _Q = 5 volts, 1 ^ = 4.5 belt speed V = 1 m / s, conveying time t = 180 seconds, and the weight of the material weighed by the standard scale

W _{a fi;} = 1800Kg, according to the standard. One

Calculate F _{¾ a} and

And belt length, material calibration factor K. With F f _t as the ordinate and LnOVUo) as the abscissa, a coordinate system is established. according to? ^ And ^ !!!;, /!;. ; ^ Determines point a. Then change the material flow in turn, and use the same method to determine points b, c, and d. The data is shown in Table 1: Table 1

1) Fit using the polyline method. Connect the line segments of 0a, ab, b _C , and cd, and use two points to determine the straight line method, and obtain the intercept and slope of each line segment. See Table 2 and Figure 5.

The calculation formula of high-precision nuclear scale: F-bj + kjLnO Uo), where bj, represents the intercept and slope of each line segment. The nuclear scale works according to the broken line position judgment flowchart shown in Figure 6.

2) Fit with a polynomial. For polynomial F

+ a ₂ (LnUi / U.) ² +… + a _k (LnU, / U ₀ ) ^k (k = 0.1, 2, ~ k), assuming the coordinate points are still 0, a, b, c, d, use Quadratic trinomial fit. Find a using the least squares method. , A,, a ₂ are:

a ₀ = 0.019324

a] = 95.3145

a ₂ = -6.62383

Bay ij

a ₂ (LnUj / U ₀ ) ²

= 0.019324 + 95.3145 ^ ηυ _; / υ _ο ) + (-6.62383) ^ ηυ / υ _ο ) ² Nuclear scales work according to this formula. Use the polynomial F = a. + _ai (LnUi / U.) + a ₂ (LnlVU.) ² and the result calculated by the formula F = Kln (U, / U ₀ ) used in existing nuclear scales for comparison:

a) Use the polynomial to calculate the load F, the cumulative weight W _h and the error δ at each point of a, b, c, and d. The data are shown in the right half of Table 3.

b) Calculate the loads at points a, b, c, and d using the formula of the existing nuclear scale? The cumulative weight of the material W _h and the error S are shown in the left half of Table 3. W Table 3

It can be seen that the accuracy of the high-precision nuclear scale using this method is greatly improved compared with the accuracy of the existing nuclear scale. Fig. 7 (a) shows a specific embodiment of the nuclear scale for implementing the above method according to the present invention. The radiation source in the nuclear scale is a built-in linear source, wherein the same reference numerals as in Fig. 1 represent the same components. Fig. 7 (b) shows another specific embodiment of the nuclear scale of the present invention, in which a plurality of point radiation sources are arranged in a line. According to the situation of the measured materials, y radioactive source can choose one of three different radioactive sources, ¹³⁷ C _S (Cesium-137), ^0Q C _Q (Cobalt-60), 2 ⁴¹ A _m (Rhenium-241), and its use form You can choose a point source or a line source. Figures 8 to 10 are schematic diagrams of fully enclosed weighing racks. In the figure, 8 is the main bracket, 9 is the panel, 10 is the rear panel, 1 is the safety cover, 12 is the bottom plate, 13 is the end box, and 14 is the feet. . The fully enclosed weighing frame has a good sealing effect on y-rays, making the high-precision nuclear scale safe and reliable. As the data processing device used in the present invention, those conventionally used in the art can be used, such as a PLC manufactured by Siemens. The performance comparison between the high-precision nuclear scale using the inventive measuring method and the existing nuclear scale, see 4

Table 4

Nuclear scale Existing nuclear scale Inventive nuclear scale Name item

1. The scale body has a single radiation source, and the Y-ray is a fan of multiple radiation sources or a linear radial beam. Therefore, the source of measurement accuracy of the scale makes the chirped rays closer to the shape of the material pile and the flow flux, which can reduce the Or eliminate the change of flow and the location where the material is located. And the impact of different locations on measurement accuracy.

Calculation formula F = Kln (UyUo) F bj + kjLn Ui / Uo) Coefficient K κ = Constant K- f (F), the variable parameter flow range is only when the flow rate when κ is calibrated is in the (0-100%) maximum flow range And applicable within a certain range. Applicable within the fence.

Accuracy The measurement accuracy is generally 1-3%. The accuracy can be improved to 0.5%. Safety The weighing racks are all open, and the radiation source is a fully enclosed scale body bracket. The radiation is exposed and the safety is poor. The source is placed in the weighing rack for safety

Claims

Rights request

1. A method for high-precision measurement of materials, comprising the steps:

(1) Install multiple gamma radiation sources and their corresponding gamma-ray detectors, and place a material transport device between them;

(3) Use a speed measuring device to measure the conveying speed Vi of the conveyor belt on the conveying device, and input its value to the data processing device connected to it;

(4) Data processing device according to formula

Calculate the cumulative amount W of the material transported within a certain period of time,

Among them, the material calibration coefficient K in the formula is dynamically modified in real time according to the change of the material flow, that is, the load change and Y-ray scattering.

~

2. The measurement method according to claim 1, characterized in that the value of the material calibration coefficient K is determined by a physical calibration method according to the change of the material flow rate, and the steps are:

(1) The material weight W _{a ¾ is} weighed with a standard scale, and the material conveying device conveys the material with a stable flow load;

(2) The data processing device uses the real-time collected output voltage of the Y-ray detector I to measure the conveying speed Vj output from the speed measuring device and the conveying time t ,. to calculate:

With F as the ordinate and LnUi / U _Q as the abscissa, a coordinate system is established, and F _{¾ a} and _η ννυ are calculated based on the above. ) _A mean value is determined in the coordinate system point & give K _a, i.e., the slope of 0a;

(3) For different material weights W _b , W _c , W _d , etc., using the same method described above, the point b, c, and d in the coordinate system can be determined, so that K _b and K can be obtained. _e , K _d- , and the functional relationship of F = f (LnU Uo).

3. The measuring method according to claim 2, characterized in that a linear relationship F = b ′ + kjLn J Uo) is used to fit the function F = f (LnU Uo), wherein j is the number of line segments, and the step For:

(1) Connect 0a, ab, bc, cd, ... to obtain each line segment;

(2) Use 0, a, b, c, d ... coordinate values of each point to obtain bj and

4. The measuring method according to claim 2, characterized in that the function F _fe = f (LnU / Uo) is fitted by a polynomial method, for points a, b, c, d in the coordinate system ... Coordinates, the polynomial can be obtained by least squares

F = a. + a ₁ (LnU ₁ / U.) + a ₂ (LnU _i / U.) ² + "'+ a _k (LnU _i / U.) ^k

The coefficient a. , Ap a ₂ ,…, a _k , where k = 0, 1, 2, 3, ··· ¼.

5. A nuclear scale including

1-N Y radioactive sources, where N = 2-10,

The Y-ray detector, corresponding to the Y-radiation source, can convert the intensity of the received Y-rays into a voltage parameter, and a material transport device can be set between the Y-ray detector and the Y-ray source;

Speed measuring device for measuring the conveying speed on the material conveying device;

The data processing device is connected to the Y-ray detector and the speed measuring device, and can calculate the accurate amount of materials based on the above data.

6. The nuclear scale according to claim 5, wherein the Y radiation source is selected from the group consisting of ¹³⁷ C _S and ^6Q C according to the measured material. , ²⁴¹ A _m .

7. The nuclear scale according to claim 5, wherein the Y radiation source and the Y-ray detector can be fixed at corresponding positions on a fully enclosed weighing frame.

The nuclear scale according to claim 5, characterized in that the number of said Y radiation sources is 2-7.