JPH0629758B2 - How to calibrate the basis weight - Google Patents

Description

The present invention relates to a method for calibrating a grammage meter capable of compensating for drifts due to causes other than bank deposition, radiation source attenuation, or temperature change.

<Prior Art> Conventionally, an apparatus as shown in FIG. 4 is used as an apparatus for measuring the basis weight of a sheet-shaped material such as paper or film. That is, the radiation source 2 and the detector 3 facing each other at a predetermined interval are provided on the frame 1, and the sheet-shaped material 4 is made to run in the direction of the arrow A between them, and the radiation source 2 and the detector 3 are connected to this sheet. Detection is performed by reciprocating the material in the width direction (direction of arrow B).

In the case of such an apparatus, since the radiation of the radiation source 2 is reduced and dust is accumulated in the radiation passage between the radiation source 2 and the detector 3 to cause drift, it is necessary to perform calibration at a predetermined cycle.

There is the following method as such a calibration method. First, a radiation source 2 provided with a shutter mechanism for blocking radiation is used, and at the time of factory shipment, the following calibration work is performed using various standard samples of known grammage in a state where dust is not accumulated.

Measurement performed with the shutter mechanism closed (radiation intensity at that time: I _Bo ), measurement performed with the shutter mechanism open only in the air layer (radiation intensity at that time: I _Bo )
_Ao ), measurement with the standard sample with the shutter mechanism open (radiation intensity at that time: I
_s ).

Thereby, I _Bo represents the electrical drift of the detector 3, I _Ao −I _Bo represents the full span of the detected signal,
I _s -I _Bo represents the signal change measured using the standard sample. From these measurement results, a calibration curve C _o shown in FIG. 5 is obtained.

After the measurement, the measurement is interrupted at a predetermined cycle to perform the next calibration.
Measurement under the above conditions (radiation intensity at that time: I
_B ), measurement under the above-mentioned conditions (radiation intensity at that time: I _A ).

A β-ray source is used as the radiation source 2, but the attenuation continues with the elapsed time t from the time of the first calibration (A _{1 in} FIG. 5 is the attenuation amount at that time), and I _A −I _B is expressed by the following equation. Can be expressed as It should be noted that there is no temperature change for the sake of simplification of the description.

_{I A -I B = (I Ao} -I Bo) -λt ... (1) where: base of natural logarithm, lambda: corresponding to the half-life of β-ray source constant.

If the relationship of the expression (1) is not established, it is considered that the attenuation A ₂ due to the accumulation of dust is added, and the dust D is calculated by the calculation based on the following expression.

_{I A -I B = (I Ao} -I Bo) -λt · -μD ... (2) However, μ: absorption coefficient.

After the dust correction is performed in this way, the measurement is performed in this state until the next calibration is performed, and the basis weight X of the sheet material 4 is measured based on the following equation.

_{I-I B = (I Ao} -I Bo) -λt · -μ (D + X) ... (3) where, I: detection output of the normal measurement.

Japanese Examined Patent Publication No. 54-18148 discloses a method for correcting dust in a grammometer, which has a different configuration from the above-mentioned conventional device.

<Problems to be Solved by the Invention> However, in these conventional methods, the source 2 and the detector 3 are used.
Drift caused by the accumulation of dust in the radiation path between and, drift caused by the decay of the radiation source 2 over time,
Alternatively, the drift due to the temperature change can be compensated, but the drift caused by other causes cannot be compensated.

The technical problem to be solved by the present invention is to compensate drift in the grammometer caused by dust accumulation, source attenuation, or a cause other than temperature change.

<Means for Solving Problems> The method of the present invention comprises steps a to d below.

a. At the time of the first calibration, a step of performing a measurement with a shutter of the radiation source closed, a state of only an air layer, and a state of using various standard samples of known basis weights to obtain a calibration curve b. After a lapse of a predetermined time from the time of the first calibration, the shutter mechanism of the radiation source is closed and the measurement is performed only in the air layer, and the theoretical value of the radiation source attenuated according to the elapsed time is obtained, while the theoretical value is obtained. Calculating the amount of dust accumulation in the radiation path based on the measured value and the measured value c. After a lapse of a predetermined time from the time of the first calibration, measurement is performed using a built-in standard sample having a known basis weight (S), and the measurement value, the attenuation correction of the radiation source, and the accumulation correction of the dust are performed. Determining an incorrect basis weight S ′ based on the equation, and d. A step of obtaining an error coefficient from the basis weights S and S'of the built-in standard sample, correcting the arithmetic expression thereby, and using this equation to obtain the true basis weight of the sheet-shaped material.

<Operation> The above-mentioned technical means operates as follows. That is, if the calibration curve is unchanged, the measurement value I of the built-in standard sample is measured when the measurement is performed after a predetermined time has elapsed from the time of the first calibration.
_S and grammage S should satisfy the following calculation formulas in which radiation source attenuation correction and dust accumulation correction are performed.

_{I S -I B = (I Ao} -I Bo) -λt · -μ (D + S) ... (4) Wakashi, (4) If equation is not satisfied, the damping of the source, or other dust deposition Indicates that the calibration curve has changed due to.

Therefore, the erroneous basis weight S ′ is calculated from the measured value I _S using the above equation, and the error coefficient k = S ′ / is calculated from S and S ′.
S is obtained, the above equation is corrected, and the correct basis weight X is obtained by the following equation during normal measurement.

<Example> An example of the present invention will be described below with reference to the drawings. FIG. 1 is a flow chart for explaining the method of the present invention, and FIG. 2 is a plan view of a radiation source 2 used for carrying out the method of the present invention. First, in FIG. 2, 201 is a box for accommodating a β-ray source, 202 is a radiation irradiation window, 203 is a sample holder, and a built-in standard sample 204 is placed by an arm 206 pivotally supported by a drive motor 205. Enter and exit the irradiation window 202. 207 is a sample holder 2
03's guide. Reference numeral 208 denotes a drive motor for a shutter mechanism, which is not shown in the figure, and this shutter mechanism also operates similarly to the sample holder 203.

Next, the method of the present invention will be described with reference to the flowchart of FIG. 1 and the explanatory view of FIG. In step (1), at the time of initial calibration such as factory shipment, the source and detector 3
With no dust accumulated in the radiation passage between
The basis weight of various known standard sample was measured against the irradiation window 202 parts, obtaining a calibration curve C _o in Figure 3.

In step (2), after a lapse of a predetermined time, measurement with the shutter mechanism closed and measurement of only the air layer are performed, and as described in the expressions (1) and (2),
Correction of radiation source attenuation and dust accumulation.

In step (3), the measurement is performed using the built-in standard sample 204 whose basis weight is known (S). Measured value _{I s} and basis weight S
Is supposed to satisfy the equation (4) with the attenuation correction of the radiation source and the dust accumulation correction, but if not,
This indicates that drift has occurred due to other causes, and as shown in FIG. 3, the calibration curve changes from _Co to C ₁ .
Incidentally, C ₂ represents a curve of the measured values.

In Fig. 3, built-in standard sample 2 at the first calibration
The measurement point using 04 is at P ₁ on the calibration curve C _O. P ₂
Is a measurement point measured with the built-in standard sample 204 in a state where dust D is deposited after the lapse of t time. This point should return to the point P ₁ if the radiation source attenuation correction (A ₁ ) and dust accumulation correction (A ₂ ) are performed, but an error E ₁ due to some cause is added to the point P ₃ That is the case of returning to.

In such a case, in step (4), the measured value I _S
And the equation (4), the erroneous basis weight S ′ is obtained, and in step (5), the error coefficient k = S ′ is obtained from S and S ′.
/ S is calculated.

Then, the error coefficient k is corrected in the equation (4), and the true basis weight X of the sheet-shaped material 4 is obtained from the measured value I using the equation (5) during the normal measurement (step (6)).

<Advantages of the Invention> According to the present invention, a drift caused by accumulation of dust in the radiation passage between the radiation source and the detector, a drift caused by decay of the radiation source with time, or a drift caused by a temperature change. Can be corrected, and drift caused by other causes can be compensated.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining the method of the present invention,
FIG. 2 is a plan view of a radiation source used for carrying out the method of the present invention, FIG. 3 is an explanatory view for explaining the method of the present invention,
FIG. 4 is an overall perspective view of the grammage measuring device, and FIG. 5 is an explanatory diagram for explaining a conventional method. 2 ... Ray source, 204 ... Built-in standard sample, 3 ... Detector, 4 ... Sheet material, _C0 ... Calibration curve at the first calibration, D ... Dust accumulation, S ... Built-in standard Sample basis weight

Claims (1)

[Claims] 1. A method for calibrating a grammometer in which a radiation source and a detector are arranged to face each other across a sheet material and the basis weight of the sheet material is measured, and the steps a to d below are performed. The calibration method of the grammage featured. a. At the time of the first calibration, a step of performing a measurement with a shutter of the radiation source closed, a state of only an air layer, and a state of using various standard samples of known basis weights to obtain a calibration curve b. After a lapse of a predetermined time from the time of the first calibration, the shutter mechanism of the radiation source is closed and the measurement is performed only in the air layer, and the theoretical value of the radiation source attenuated according to the elapsed time is obtained, while the theoretical value is obtained. Calculating the amount of dust accumulation in the radiation path based on the measured value and the measured value c. After a lapse of a predetermined time from the time of the first calibration, measurement is performed using a built-in standard sample having a known basis weight (S), and the measurement value, the attenuation correction of the radiation source, and the accumulation correction of the dust are performed. Determining an incorrect basis weight S ′ based on the equation, and d. A step of obtaining an error coefficient from the basis weights S and S'of the built-in standard sample, correcting the arithmetic expression accordingly, and using this equation to obtain the true basis weight of the sheet-shaped material.