JPH03239948A - Characteristic measuring method for sheet-like substance - Google Patents

Abstract

PURPOSE:To eliminate an error caused by a fluctuation of an X-ray tube applied voltage by deriving in advance in the correction quantity of an analytical curve related to the fluctuation of the X-ray tube applied voltage. CONSTITUTION:In a state that an X-ray tube applied voltage HV is stable, plural reference samples whose basis weight (weight per sheet unit area) BW is different are placed between an X-ray tube 1 and an X-ray detector 4, and an analytical curve in which the basis weight BW and an output I (intensity of transmission X rays) are taken in the horizontal axis and the vertical axis, respectively is generated. In such a state, the reference sample of the basis weight BW in a range used actually is placed between the X-ray tube 1 and the detector 4, and by fluctuating a voltage HV a little, the fluctuated voltage is led to an arithmetic means 8 through a voltage dividing circuit 6 and a voltage detecting means 7, and a relation of the voltage HV and an output fluctuation quantity DELTAI is derived by the arithmetic means 8, and stored in the arithmetic means 8 as the correction quantity of the analytical curve. In such a way, at the time of actual measurement, the fluctuation quantity from a set value is derived by always monitoring the voltage HV, and by adding the correction quantity of the analytical curve to the output I at that time, a correct measured value can be obtained.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for measuring properties of a sheet-like material using an X-ray tube.6 <Prior Art> Sheet material characteristic devices that use X-rays emitted from an X-ray tube include a thickness meter that measures the thickness of a metal plate, and an ash meter that measures the amount of ash in paper. X! using the X-ray tube used here! ! The means of generation is as follows.

The conventional technology will be explained below with reference to the drawings.

FIG. 3 is a schematic diagram of an X-ray generating means using a conventional X-ray tube.

In Fig. 3, reference numeral 1 indicates a filament F as an electron generation source that generates thermoelectrons, an electron lens G that controls (focuses) the generated thermoelectrons, and a metal (1) that generates X-rays by collision of thermoelectrons.
This is an X-ray tube consisting of a target), a tube body B, and a window W for housing the targets in a vacuum atmosphere. 2 is an X-ray tube drive circuit that drives the XIl tube 1. For example, when one end of the filament F is used as a cathode, a DC power supply E is supplied between the cathode and the electron lens G, and a DC power supply E is supplied between the cathode and the target T, for example. It has a structure in which high voltages (referred to as X-ray tube applied voltage or target applied voltage) HV of ~8 KeV are connected to each other.

In such a configuration, when a current is passed through the filament F, thermoelectrons are generated. These thermoelectrons are accelerated by an electric field caused by a high voltage V applied between the cant and the target T, are focused by an electron lens G, and hit the target T. As a result, bremsstrahlung X-rays having an energy spectrum continuous with a characteristic X-ray of a specific energy are emitted.

There is an apparatus as shown in FIG. 4 that uses X-rays obtained with such a configuration to measure properties of sheet-like materials.

FIG. 4 is a diagram for explaining a conventional sheet-like material characteristic measuring apparatus constructed using FIG. 3.

FIG. 5 is a diagram for explaining FIG. 4.

In Figures 4 and 5, 3 is a sheet-like material (hereinafter referred to as "sheet") that is the object to be measured by irradiating X-rays and measuring its characteristics, and 4 is a material such as an ionization chamber that detects transmitted X-rays. 5 is an amplifier circuit.

According to this, the sheet 3 is irradiated with X-rays from the X-ray tube 1, and the transmitted X-rays are detected by the X-ray detector 4 and obtained via the amplification circuit 1i5. Characteristics can be measured.

At this time, the intensity of transmitted X-rays (output of
). However, μ represents an absorption coefficient, and Io represents a value at the maximum intensity of transmitted X-rays (intensity before transmission).

FIG. 5 shows a calibration curve with the basis weight BW on the tank axis and the output I on the vertical axis as an X-ray energy distribution based on this relationship.

By the way, the output I is the rays of the bremsstrahlung X-rays to be irradiated.
It varies depending on the rugi. That is, when the X-ray tube applied voltage applied between the target cathode of the X-ray tube 1 changes, the X-ray energy distribution, that is, the calibration curve (solid line in Figure 5) changes from the broken line α (large applied voltage) to β (applied voltage voltage (low voltage).

<Problem to be Solved by the Invention> As described above, in the conventional technology, during actual online measurement, there is an output error due to fluctuations in the output voltage of the high voltage source due to temperature fluctuations. As a way to prevent this, it is necessary to adjust the temperature as necessary or install a device to measure the properties of the sheet material! Depending on the conditions of the location, etc., it may be difficult to take such considerations, and in some cases, it may be disadvantageous in use, such as having to expect a certain amount of output error. There was a point.

The present invention was made in view of the shortcomings of the conventional technology, and its purpose is to simply add a simple circuit of 1,000 F2 without performing any special temperature adjustment. , provides a method for measuring characteristics of a sheet-like material that can eliminate output errors caused by changes in the voltage applied to the X-ray tube between the target cathode of the X@ tube.

Means for Solving the Problems> In order to achieve the above object, the present invention provides an X-ray generating means that is provided on one side of a sheet-like material and irradiates the sheet-like material with X-rays; In the apparatus for measuring the properties of the sheet-like material from the amount of transmitted X-rays, the apparatus includes an X-ray detector provided on the other side of the sheet-like material and detects the X-rays transmitted through the sheet-like material. Prior to the above
The amount of variation with respect to the set value of the voltage applied to the X-ray tube of the radiation generating means and the supplement 1Eji of the calibration curve related to this amount of variation are determined in advance for each basis weight to be measured, and the voltage applied to the X-ray tube is monitored during measurement. By understanding the amount of variation from the set value, the amount of correction of the calibration curve in the output of the X-ray detector is obtained each time, and the amount of correction of the calibration curve is used to compensate for the output of the X-ray detector each time. This is a method for measuring the characteristics of the sheet-like material.

(a) First, the amount of variation in the voltage applied to the X-ray tube between the target cathode of the X-ray tube with respect to the initially set value, and the amount of correction of the calibration curve caused by this amount of variation, are determined for each basis weight to be measured. Find it in advance.

(b) Next, the voltage applied to the X-ray tube is constantly monitored to determine the amount of variation from the set value.

(c) Then, the correct measured value is determined by adding the correction amount of the calibration curve determined in advance to each output value.

<Example> Examples will be described with reference to the drawings.

In the following drawings, parts that overlap with those in FIGS. 3 to 5 are given the same numbers, and the explanation thereof will be omitted.

FIG. 1 is a schematic diagram of a specific embodiment of an apparatus for explaining the method for measuring properties of sheet-like materials according to the present invention. Further, FIG. 2 is a diagram used to explain FIG. 1.

In Figure 1, -6 is a voltage divider circuit, 7 is a voltage detection + stage, and 8
is an i-calculation means. The voltage dividing circuit i6 and the voltage detecting means 7 are circuits that constantly monitor the voltage applied to the X-ray tube, and at this time, the voltage dividing circuit 6 is a high voltage of several KeV as described above, so that the voltage applied to the X-ray tube is HV. This circuit is provided to appropriately divide and detect the voltage according to the voltage specifications (therefore, this circuit is provided as necessary).

The operating functions of such blocks will be explained below with reference to FIG. 2.

(2) When the X-ray tube applied voltage HV is stable, a plurality of reference samples with different basis weights BW are sandwiched between the X-ray tube 1 and the X-ray detector 4, and the X-ray tube applied voltage is applied to the reference samples. Create a calibration curve for changes in output (■) based on HV, as shown in Figure 2 (A), with basis weight BW on the horizontal axis and output (intensity of transmitted X-rays) on the vertical axis. do.

■1st, the basis weight in the range actually used, that is, the basis weight in the range shown in Figure 2 (A
A reference sample of "BW," near the middle of the horizontal axis basis weight of Circuit 6. The voltage is guided to the calculation means 8 via the voltage detection means 7, and the relationship between the fluctuation 1ΔI of the output ■ from the X-ray detector 4 at that time is calculated by the calculation means 8.
Find it with

This relationship can be expressed as the X-ray tube applied voltage Hv on the horizontal axis and the output variation ΔI on the 6th axis, as shown in FIG. 2(B).

As a result, the variation amount Δ■ of the output I corresponding to the variation amount with respect to the set value of the X-ray tube applied voltage HV is determined. This is the amount of variation in the output, that is, the amount of correction of the calibration curve caused by the output I.

The graph obtained in this manner is stored in the memory element of the calculation means 8 as a correction amount of the calibration curve, for example, as a graphed numerical value or in the form of a function.

■During actual measurements, it is necessary to constantly monitor the voltage applied to the X-ray tube and understand the amount of variation from the set value.In order to obtain correct measured values, the amount of calibration curve correction is added to the output value each time. Specifically, based on the output I of the X-ray detector 4/amplifying circuit 5 and the output of the X-ray tube applied voltage (Hvf) voltage detection means 7, the calculation means 8 calculates a calibration curve from the amount of variation in the X-ray tube applied voltage. The correct output value is calculated by calculating the correction amount and adding this correction amount to the output value.

As described above, it is possible to obtain the correct basis weight in a form that always corrects applied voltage fluctuations caused by temperature fluctuations and the like.

It should be noted that more accurate correction can be achieved if the correction amounts that are created first are calculated in advance for several basis weights, not just those near the middle of the measurement range.

<Effects of the Invention> Since the present invention performs measurements as described above, it is possible to eliminate the influence of errors caused by fluctuations in the voltage applied to the X-ray tube, which was one of the error factors in actual online measurements. , sufficient practical effects can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block system diagram of a specific embodiment of the device for explaining the method for measuring properties of sheet-like materials according to the present invention, FIG. 2 is a diagram used to explain FIG. 1, and FIG. A schematic diagram of an X-ray generating means using an X-ray tube, FIG. 4 is a diagram used to explain a conventional property measuring device for sheet-like materials configured using FIG. 3, and FIG. It is a figure provided for explanation. DESCRIPTION OF SYMBOLS 1...X-ray tube, 2...X-ray tube drive circuit, 3...sheet-like material (sheet), ...detector, ...amplification circuit, ...voltage dividing circuit, ...voltage detection means , ... calculation means.

Claims (1)

[Claims] An X-ray generating means provided on one side of the sheet-like material to irradiate the sheet-like material with X-rays, and an X-ray generating means provided on the other side of the sheet-like material to irradiate the sheet-like material In an apparatus that is equipped with an X-ray detector that detects the transmitted X-rays and measures the characteristics of a sheet material from the amount of transmitted X-rays, prior to the measurement, the setting value of the voltage applied to the X-ray tube of the X-ray generating means is The amount of variation and the correction amount of the calibration curve related to this amount of variation are determined in advance for each basis weight to be measured, and during measurement, the voltage applied to the X-ray tube is monitored to understand the amount of variation from the set value. Obtaining the correction amount of the calibration curve in the X-ray detector output, and using the correction amount of the calibration curve to correct the X-ray detector output each time to measure the characteristics of the sheet-like material. Characteristic measurement method.