JPH01153917A - Calibrating method for area weigher - Google Patents

Abstract

PURPOSE:To compensate even a drift caused except by the deposit of dust between a ray source and a detector and the attenuation of the ray source by taking measurements at the time of 1st calibration and a specific time later in a state wherein the shutter of the ray source is closed, a state wherein there is only an air layer, a state wherein various standard samples which are already weighed are used, etc. CONSTITUTION:The radiation ray source 2 and detector 3 are arranged opposite each other across a sheet material 4 to constitute the device which measures the area of the material 4. For the purpose, a calibration curve is obtained by measuring various standard samples which are already measured while no dust is deposited between the ray source 2 and detector 3 at the time of the 1st calibration in factory shipment. Then measurements are taken in the state wherein the shutter of the ray source 2 is closed the specific time later and the state wherein there is only the air layer to correct the attenuation of the ray source 2 and also correct the deposit of the dust. Then a measurement is taken by using an internal standard sample whose weight is already known and an error coefficient is found from values obtained from the measured value and an area-known quantity by the attenuation correction of the ray source 2 and the deposit correction of the dust, thereby compensating the drift caused by other factors.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for calibrating a basis weight meter capable of compensating for drift I due to causes other than dust accumulation, source attenuation, or temperature changes. .

<Prior Art> Conventionally, an apparatus as shown in FIG. 4 has been used as an apparatus for measuring the basis weight of sheet-like materials such as paper and films. That is, a radiation source 2 and a detector 3 are provided facing each other at a predetermined interval on a frame 1, and a sheet material 4 is placed between them in the direction of arrow A.
Detection is performed by moving the radiation source 2 and detector 3 back and forth in the width direction (direction of arrow B) of the sheet 1-shaped material.

In the case of such a device - due to the attenuation of the radiation source 2 and the accumulation of dust in the radiation path between the radiation source 2 and the detector 3, which causes drifts, it is necessary to carry out calibration at regular intervals.

Examples of such calibration methods include the following.

First, the radiation source 2 is equipped with a shutter mechanism that blocks radiation.
The following calibration work is carried out using various standard samples of known weight when shipped from the factory, with no lumps accumulated.

■Measurement performed with the shutter mechanism closed (radiation m intensity at that time: Iaa), ■Measurement performed with the shutter mechanism open only in the air layer (radiation intensity at that time: IA)
o), ■Measurement performed using the standard sample with the shutter mechanism open (radiation intensity at that time: Is
).

Thereby, IaO' represents the electrical drift of the detector 3, IAOiao represents the full span of the detection signal,
Is IaO represents the signal change measured using the standard sample. From these measurement results, a calibration curve C0 shown in FIG. 5 is obtained.

After measurement, the measurement is interrupted at a predetermined interval and the next calibration is performed.
A1 constant in the state of ■ (radiation intensity at that time:
Ia), Measurement in the state of (2) above (radiation intensity at that time: Ia).

A β-ray source is used as the radiation source 2, and it continues to attenuate with the elapsed time from the time of the first calibration (A1 in Figure 5 is the attenuation company at that time), and IA-Ia is expressed by the following formula. can be done. Note that, to simplify the explanation, it is assumed that there is no temperature change.

IA Ia=(IAo Iao 're-”...(
1) However, e: the base of natural logarithm, λ: a constant corresponding to the half-life of the β-ray source.

If the relationship in equation (1) does not hold, it is assumed that attenuation A2 due to dust accumulation has been added, and stiffness D is calculated based on the following equation.

IA Ia=(IAo Iao)e-”・e-
μp... (2) tn L, μ: Absorption coefficient.

After the dust has been corrected in this manner, measurement is performed in this state until the next calibration is performed, and the basis weight χ of the sheet material f=) 4 is measured based on the following equation.

I ra = (IAo Iaa) e-λ, e-μ
(p) ... (3) However, ■ = detection output during normal measurement.

Japanese Patent Publication No. 54-18148 discloses a method for correcting dust in a basis weight meter, although the structure is different from the conventional device described above.

<Problems to be solved by the invention> However, in these conventional methods, the radiation source 2 and the detector 3
Drift 1 caused by dust accumulating in the radiation path between
~, Drift 1- that occurs as the radiation source 2 attenuates over time
Although it is possible to compensate for drift caused by temperature change or temperature change, drift caused by other causes cannot be compensated for.

The technical problem to be solved by the present invention is to compensate for drifts caused by causes other than dust accumulation, source attenuation, or temperature changes in the basis weight meter.

Means to solve problems〉 The method of the present invention is comprised of the following steps a to d.

a,! & At the time of the first calibration, step (b) of obtaining a calibration curve by performing measurements with the shutter of the radiation source closed, with only an air layer, and with various standard samples of known tsuboli; After a predetermined period of time has elapsed from the time of calibration, measurements are taken with the side of the shutter n of the source closed and with only an air layer, and the theoretical value of the source attenuated according to the elapsed time is determined. Step C1: Calculate the amount of dust deposited in the radiation path based on the actual measurement value. After a predetermined period of time has elapsed since the first calibration, this measurement is performed using a built-in standard sample with a known weight (S), and this measurement value is calculated. and a step of determining an incorrect basis weight S' based on an arithmetic expression in which the radiation source attenuation correction and the dust accumulation correction are performed;
and d, determining an error coefficient from the basis weight iS and S' of the built-in standard sample, correcting the calculation formula based on this, and determining the true basis weight of the sheet material using this formula.

Function> The above technical means works as follows. That is, if the calibration curve remains unchanged, when measurement is performed after a predetermined period of time has elapsed since the first calibration - the measured value t of the built-in a semi-sample
s and the basis weight S should satisfy the following calculation formula, which is corrected for attenuation of the m source and corrected for dust accumulation.

Is IB=(IAO-1ao)e-", e-
μtossun (4) If equation (4) is not satisfied, this indicates that the calibration curve has changed due to a cause other than the attenuation of the radiation source or the accumulation of dust.

Therefore, the incorrect basis weight S' is calculated using the above formula from the measured value IS, and the error EJA number is calculated from S and S' = s
', /S are determined, the above formula is corrected, and the correct basis weight χ is determined using the following formula during normal measurement.

1 1a=(IAo Iaa)e−λru, e −
μ(0−脣ん...(5) Figure 1 is a flowchart for explaining the method of the present invention, and Figure 2 is a plan view of the radiation source 2 used to carry out the method of the present invention. First, In FIG. 2, 201 is a box containing a β-ray source, 202 is a radiation irradiation window, and 203 is a sample holder, in which a built-in standard sample 204 or fi is placed and irradiated by an arm 206 pivotally supported by a drive claw motor 205. Reference numeral 4207 that goes in and out of the window 202 is a guide for the sample boulder 203. Reference numeral 208 is a drive claw motor of a shutter mechanism (not shown in this figure), and this shutter Rm also moves in the same way as the sample holder 203.

Next, the method of the present invention will be explained with reference to the flowchart of FIG. 1 and the explanatory diagram of FIG. 3. In step (1), at the time of initial calibration such as at the time of factory shipment, dust is not accumulated in the radiation path between the radiation source and the detector 3;
Measurement is performed by applying various standard samples of known basis weight to the irradiation window 202 to obtain a calibration curve Co shown in FIG.

In step (2), after a predetermined period of time has elapsed, measurement is performed with the shutter mechanism closed, and measurement is performed with the air layer only.
As explained in equation 11(2),
Perform source attenuation correction and dust accumulation correction.

In step (3), four measurements are performed using the built-in standard sample 204 with known basis weight (S) @IS and basis weight S.
should satisfy Equation (4) with 6JA attenuation correction and dust accumulation correction for the source, but if it is not satisfied, drift may occur due to other factors, and as shown in Figure 3. As shown, the calibration curve changes from 00 to Ct. Note that C2 indicates a curve of measured values.

In Figure 3, the built-in standard sample 2 is used for the first calibration.
The measurement point using 04 is located at P on the test fl WR= Co. P2 is the measurement point taken using the built-in ridge quasi-sample 204 in a state where the lump D has accumulated after L time has elapsed. This point should return to point 21 if radiation source attenuation correction (A1) and dust accumulation correction (A2) are performed, but with the addition of error E due to some cause, it returns to point P. This is a case of putting it away.

In such a case, in step (-1), the measured value I
From s and equation (4), find the incorrect tsubo iS', and further, in step (5), calculate the error coefficient \& from S and S' =
Find s'/S.

Next, the error coefficient is corrected in equation (4), and the true basis lχ of the sheet material 4 is determined from J1 constant ff1I to j using equation (5) during normal measurement (step (6N)).

<Effects of the Invention> According to the present invention, the drift caused by dust accumulation in the radiation path between the radiation source and the detector, the drift caused by the radiation source attenuating over time, or the drift caused by temperature changes. In addition to correcting drift, it is also possible to compensate for drift caused by other causes.

[Brief explanation of the drawing]

FIG. 1 is a flowchart for explaining the method of the present invention,
FIG. 2 is a plan view of a radiation source used to carry out the method of the present invention, and FIG. 3 is an explanatory diagram for explaining the method of the present invention.
FIG. 4 is an overall perspective view of the basis weight measuring device, and FIG. 5 is an explanatory diagram for explaining the conventional method. 2...Radiation source, 204...Built-in standard sample, 3...
・Detector, 4...Sheet material, Co...Calibration curve at the time of first calibration, D...Dust accumulation, S...Built-in a
Figure 1: Basis weight of semi-samples

Claims (1)

[Scope of Claims] A method for calibrating a basis weight meter that measures the basis weight of a sheet-like material by sandwiching a sheet-like material and arranging a radiation source and a detector facing each other, the method comprising performing steps a to d below. A method for calibrating a basis weight meter. a. At the time of the first calibration, measurements are taken with the shutter of the radiation source closed, only an air layer, and various standard samples of known basis weight are used to obtain a calibration curve. b. The first calibration After a predetermined period of time has elapsed, measurements are taken with the shutter mechanism of the radiation source closed and with only an air layer present, and the theoretical value of the radiation source attenuated according to the elapsed time is determined. step (c) of calculating the amount of dust deposited in the radiation passage based on the above, after a predetermined period of time has elapsed from the first calibration, a measurement is performed using a built-in standard sample with a known basis weight (S), and this measurement value and d) calculating an error coefficient from the basis weights S and S' of the built-in standard sample; a step of determining the true basis weight of the sheet-like material by correcting the arithmetic formula and using this formula;