JPH0233964B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a β-ray transmission type dust meter.

Conventionally, the method of measuring the dust concentration in the atmosphere using β-rays is to pass through the atmosphere with a tape-shaped paper and collect the dust in the atmosphere on the surface of the paper. Measure the degree of attenuation,
There is a way to calculate the dust concentration from this. That is,
This method applies the fact that the following equation (1) holds between the transmitted β-ray intensity and the thickness of the collected dust.

I = I ₀ exp (-μX) ...... (1) where I: β-ray intensity transmitted through paper and dust I ₀ : β-ray intensity transmitted only through paper μ: Mass absorption coefficient (cm ² /g) X: Dust amount (g/cm ² ) Furthermore, the dust concentration in the atmosphere is expressed by equation (2).

C=A/μQtlnI ₀ /I (2) where A: Collection area (cm ² ) Q: Passing flow rate (cm ³ /min) t: Collection time (min) C: Dust concentration (g/ cm ² ) Therefore, the transmitted β-ray intensity I ₀ and I before and after dust collection
By actually measuring , the dust concentration in the atmosphere can be determined from equation (2). Conventional dust meters based on this principle are shown in FIGS. 1 and 2.

In the case of the dust meter shown in Fig. 1, paper a is unwound from a roll of paper b, passes through a passage c, and reaches a measurement section d, where the paper is irradiated with β-rays emitted from a β-ray source e. and its transmitted β-ray intensity I ₀ is β
It is measured by a line detector f and stored. Then paper a
The part of the paper that was rewound and irradiated with the β-rays and the transmitted β-ray intensity I ₀ was measured is attached to the upper part c. Thereafter, the suction pump is activated, and atmospheric air is sucked downward (in the direction of arrow P in the figure) through the suction tube g, whereby dust in the atmosphere is separated by the paper a. The paper is then unrolled again and
After the excess portion is moved to the measurement part d,
β transmitted through paper and filtered and deposited dust layer
The line intensity I is measured, and the dust concentration C is calculated from I ₀ and I obtained in this way using equation (2). In addition, h is a pinch roller, i is a capstan, and j is a winding roll.

In the case of the dust meter shown in Figure 2, roll paper b
The paper a fed out from the measuring section d first measures the transmitted β-ray intensity I ₀ of the paper a, and then is sent to the transfer section c, where the atmosphere is passed through. Next, the measurement part d is 180 degrees centering on the axis of the suction tube g.
The measuring part d is rotated by
is moved, and paper a is also moved, and the β-ray intensity I transmitted through paper a and the dust layer is measured at the position indicated by the chain line. Using equation (2) from I ₀ and I obtained in this way, The dust concentration C is calculated using the following steps.

In both of the above-mentioned dust meters, moving the same part (over part) of paper a to measuring part d and over part c with good reproducibility is a necessary condition for accurately measuring the amount of dust. On the other hand, it is quite difficult to do so, and there is a problem in that the deviation between the above-mentioned measurement positions and the suction position that occurs when the paper is moved directly causes measurement errors.

A dust meter shown in FIG. 3 has been proposed to solve the above problem (manufactured by Friegeke). In the case of this dust meter, atmospheric air is sucked by a pump k and flows into a suction pipe g, and after the dust is separated by a paper a, it passes through a β-ray irradiation path l and then exits the system through a discharge pipe m. be discharged. Dust n separated in this way and deposited on the top surface of paper a
is irradiated with β-rays emitted by a β-ray source installed at the bottom of the irradiation path, and the transmitted β-ray intensity I is detected by a detector f arranged above the paper. If the transmitted β-ray intensity I ₀ in the case of only paper a is measured beforehand, the dust concentration can be calculated from the above I ₀ and I, and in this case, the movement of the paper in the measurement of I ₀ and I Since there is no
Unlike the former two dust meters, it is unlikely that a measurement error will occur due to a shift in the measurement position of the paper caused by movement of the paper. However, in the case of this dust meter, the air is supplied to the irradiation path 1 from the side of the irradiation path 1 almost parallel to the paper a, and passes through the paper a, so the dust n is distributed non-uniformly on the paper a. Easily deposited. For this reason, there is a problem that measurement accuracy decreases, and
Since the structure is such that the atmosphere is exhausted to the outside through the irradiation path 1, the irradiation path is easily contaminated by fine dust. Therefore, it is necessary to periodically clean this dirt, but this is a complicated process, and furthermore, cleaning is difficult to perform simply due to the structure.

The present invention was made to improve the above situation, and includes a β-ray source and a β-ray source emitted from the β-ray source.
a line irradiation path; a material supplied to the irradiation path;
a detector that detects the amount of β-rays that passes through the material;
It consists of an amplification section that amplifies and outputs the signal detected by the detector, and a gas flow path to be measured that intersects the material, and the gas flow path is passed through the gas flow path through the material. At the same time as collecting floating dust in the gas to be measured, the detector detects the amount of attenuation of β-rays passing through the material due to the collected dust, and this detection signal is amplified by the amplifier and output. In a dust meter that determines the amount of suspended dust in a gas, a β-ray irradiation path is connected to the intersection of the material and the gas flow path to be measured by intersecting the gas flow path to be measured at an angle of 70 degrees or less, A dust meter is provided in which a β-ray irradiation path is closed with a β-ray permeable thin film at the intersection with a gas flow path to be measured.

In the present invention, since the intersection angle between the gas flow path to be measured and the β-ray irradiation path is 70 degrees or less, the angle between the gas flow path and the material surface and the angle between the β-ray irradiation path and the material surface are are closer to the right angle, and as a result, the dust deposited layer on the material surface is formed uniformly on the material surface, and the dust deposited layer is irradiated with the β rays at an angle close to the right angle, so that the transmitted β The linear intensity I corresponds accurately to the amount of deposition, and the measurement accuracy is improved.

In other words, when collecting dust in a gas using a material, it is desirable to flow the gas at an angle as close to perpendicular to the surface of the material as possible in order to deposit the dust uniformly on the material. When the path angle becomes smaller, more dust is deposited on a part of the periphery of the material, causing a shift in dust distribution. Particularly, when the gas flow velocity exceeds the laminar region and enters the turbulent region, such a shift becomes noticeable. If the above-mentioned deviation occurs in the distribution of the amount of dust deposited, the β-ray transmission type dust meter will detect a value smaller than the amount of dust actually deposited.

On the other hand, in the present invention, the gas flow path and β
By forming the intersecting angle θ with the beam irradiation path to 70 degrees or less, the angle of the gas flow path to the material surface can be increased and made closer to a right angle, which allows dust to be collected uniformly on the material surface. , it has become possible to measure dust concentration with high accuracy.

Furthermore, when irradiating a dust deposited layer on a material with β-rays, it is desirable to irradiate the β-rays at an angle as close to perpendicular to the material surface as possible in order to improve measurement accuracy. By forming the intersection angle θ between the beam and the β-ray irradiation path to 70 degrees or less, the angle of the β-ray irradiation path with respect to the material surface can be increased to be closer to a right angle, making it possible to measure dust concentration with high accuracy. It has become possible to do so.

Furthermore, in the present invention, by blocking the β-ray irradiation path with a β-ray permeable thin film at the intersection with the gas flow path, it is possible to prevent dust from entering and accumulating in the β-ray irradiation path. This has resulted in improved accuracy and simplified maintenance.

Hereinafter, one embodiment of the present invention will be described with reference to FIG. 4.

In the figure, 1 is a material wound into a roll, and the material 1a fed out from this roll-shaped material 1 is detected by a detection unit 2 disposed in front of the traveling direction (direction of arrow A in the figure).
supplied to The detection section 2 is formed using a block main body 3 in the shape of a rectangular parallelepiped, and the block main body 3 consists of two blocks 3a and 3b horizontally divided into two at the center. The main body 3 has a gas flow path 4 to be measured and a β-ray irradiation path 5 having diameters smaller than the width of the material 1a from the upper end surface to the lower end surface of the main body 3, respectively.
3b are intersectingly bored at the joint,
The angle θ formed by the flow path 4 and the irradiation path 5 is approximately 60 degrees, which is an acute angle, and the β-ray irradiation path 5 at the intersection with the flow path 4 is made of synthetic resin, metal, etc. that is transparent to β-rays. It is closed by a thin film 6.
The upper side of the flow path 4 is connected to one end of the sampling pipe 7, and the lower side is connected to a suction pump 9 through a suction pipe 8. When the pump 9 is operated under the control of the arithmetic control section 10, The gas to be measured is sucked in from the other end of the sampling pipe 7 , passes through the flow path 4 and the suction tube 8 in sequence, and then is discharged to the outside from the discharge portion 11 of the suction pump 9 .

Further, above the β-ray irradiation path 5, a β-ray source 12 is provided.
A β-ray source container 13 containing a
The line is being irradiated. Furthermore, a β-ray detector 14 is installed at the bottom of the β-ray irradiation path 5, and the β-rays that have reached this detector 14 are converted into electrical signals according to the amount of the β-rays that have arrived at the arithmetic control unit 10. transmitted to.

The detection unit 2 is unrolled from the roll-shaped material 1.
The material 1a supplied to the blocks 3a, 3
b, and at this time, it is attached to the detection unit 2 while covering the flow path 4. And this material 1
To move the material, open the blocks 3a and 3b vertically, move the material 1a, and then open the blocks 3a and 3b.
This is done by closing channel b; in this case, channel 4
It is closed using known means such as rubber packing to prevent air leakage from outside. Next, the material 1a passes between the pinch roller 15 and the capstan 16 and is wound onto the take-up roll 17, but the movement of the material 1a is controlled by the pinch roller 15 driven according to instructions from the control section 10. It is done. Note that 18 is a display unit connected to the control unit 10, on which measurement results and the like are displayed.

Next, a case will be described in which the dust concentration in the atmosphere is measured using the dust meter. First, the other end of the sampling pipe 7 (not shown) is installed at the air sampling location to be measured. Next, in this state β
The β-ray dose emitted from the radiation source 12, transmitted through the material 1a and reaching the detector 14 is measured, and this measured value
I ₀ is temporarily stored in the calculation control unit 10. after that,
The suction pump 9 is activated and atmospheric sampling begins. That is, the air sucked in from the other end of the sampling pipe 7 flows into the upper part of the channel 4 and moves downward in the channel 4, but at this time, the material 1a stretched across the channel 4 As a result, dust in the atmosphere is separated and a deposited dust layer 19 is formed on the upper surface of the material 1a. Next, the air from which the dust has been separated by the material 1a flows further down the flow path 4 to the suction pipe 8.
The water flows into the pump 9 and is discharged from the discharge section 11 to the outside through the pump 9. When the pump 9 operates for a predetermined period of time and a predetermined amount of air is sucked, the pump 9 is stopped and the collection of air is stopped. The intensity of β-rays from the β-ray source 12 reaching the target is measured. The obtained measured value I is sent to the arithmetic control section 10, where the dust concentration is calculated by the above equation (2) using the measured value _I0 stored in advance, and the dust concentration is displayed on the display section 1.
8 is displayed. Thereafter, the blocks 3a and 3b are moved up and down, respectively, and the pinch roller 15 is driven to move the material 1a a predetermined distance forward in the advancing direction (in the direction of arrow A in the figure). As a result, the deposited layer 19 moves outside the flow path 4, and a new material portion on which no dust is deposited is supplied into the flow path 4.
In this state, the gap between the blocks 3a and 3b is closed, returning to the initial state. Thereafter, similar operations are repeated to continue measuring the dust concentration, but all of these operations are automatically performed according to instructions from the arithmetic control section 10.

In the dust meter of this embodiment, the flow path 4 and the irradiation path 5 intersect, and the material 1a is supplied to this intersection, so that the material 1a is supplied to the material 1a at this intersection.
The measurement of the β-ray intensity _I0 transmitted through the dust deposited layer 19 formed on the material surface by passing through the dust in the atmosphere, and the β-ray intensity I transmitted through the material 1a. You can do it without having to do it. Therefore, there is no reduction in measurement accuracy due to material movement errors in the conventional method, and the measurement accuracy of this dust meter is high. In addition, since the intersection angle θ between the flow path 4 and the irradiation path 5 is formed at an acute angle of 60 degrees, the dust deposition layer 19 on the material surface is formed uniformly on the material surface, and the β rays are The beam is irradiated at an angle close to perpendicular to the material surface. For this reason,
The transmitted β-ray intensity I accurately corresponds to the amount of deposition, improving measurement accuracy. Further, at the intersection between the flow path 4 and the irradiation path 5, the irradiation path 5 is separated from the flow path 4 by a thin film 6. Therefore, dust is reliably prevented from entering and accumulating in the β-ray irradiation path 5, and improvement in measurement accuracy and simplification of maintenance are achieved. To explain this point in more detail, the dust meter of this example has the following effects by providing the β-ray transparent thin film 6.

Prevention of contamination of the β-ray source and detector Since dust does not enter the β-ray irradiation path 5,
The β-ray source 12 and detector 14 are not contaminated by dust, which prevents deterioration in measurement accuracy due to contamination of the β-ray source 12 and detector 14, and facilitates maintenance of the device. become.

Protection of β-ray Source and Detector When the pump 9 is operated and measurement is performed, the β-ray irradiation path 5 is at almost atmospheric pressure on the β-ray source 12 side, and the pump 9 is under suction on the detector 14 side. It is in a negative pressure state due to the force. Therefore, during measurement, there is a risk that negative pressure will be applied to the detector 14 due to the suction force of the pump 9, making the measurement operation unstable, but this is prevented by the thin film 6. Also, during measurement, the sampling pipe 7
If a foreign object, such as a plant leaf, adheres to the end of the pipe 7 and blocks the pipe 7, the entire β-ray irradiation path 5 becomes extremely negative pressure due to the suction force of the pump 9, and the β-ray
This negative pressure is applied to both the radiation source 12 and the detector 14, destroying the sealing of the β-ray source, etc.
Although there is a risk of contamination with radioactive isotopes and destruction of the detector, the thin film 6 prevents these. Therefore, this device using radioactive isotopes is highly safe. Furthermore, since dust is collected and measured without moving the material 1a at the intersection, a complicated and highly accurate movement mechanism for the material is not required, and the configuration is simplified.

In this example, the intersection angle between the channel 4 and the irradiation channel 5 was formed at 60 degrees, but the intersection angle is not limited to this, and any intersection angle of 70 degrees or less can be adopted. Although the irradiation path 5 is formed with a downward slope along the direction of movement of the material 1a, and the irradiation path 5 is formed with a downward slope along the direction opposite to the direction of movement of the material 1a, the irradiation path 5 is not limited to this. The flow path 4 and the irradiation path 5 may be formed with a downward slope along a direction of an arbitrary angle. Furthermore, in this example, the case of measuring with β rays after dust deposition was explained, but when using this dust meter, the amount of deposited each moment can be measured continuously or at regular intervals, and the measurement can also be displayed. Various modifications may be made without departing from the gist of the present invention.

Therefore, in the present invention, the β-ray irradiation path and the gas flow path to be measured are connected to each other at an angle of 70 degrees or less at the intersection between the material and the gas flow path to be measured, so that the gas flow path and the material surface are connected to each other at an angle of 70 degrees or less. The angle between the β-ray irradiation path and the material surface becomes closer to a right angle, making the deposited layer of dust uniform, and the angle between the β-ray irradiation path and the material surface becomes closer to a right angle, which improves measurement accuracy. In addition, since the opening of the irradiation path is closed with a thin film at the intersection of the irradiation path and the flow path, the inside of the irradiation path will not be contaminated with dust, which will greatly improve measurement accuracy and simplify maintenance. It has characteristics.

[Brief explanation of drawings]

1 to 3 are explanatory diagrams showing the configuration of a conventional dust meter, respectively, and FIG. 4 is a partially sectional side view showing an embodiment of the present invention. 1a... Material, 4... Gas flow path to be measured, 5...
β-ray irradiation path, 6... thin film, 10... calculation control unit,
12...β-ray source, 14...β-ray detector, 19...
Deposited layer.

Claims (1)

[Claims] 1. A β-ray source, an irradiation path for β-rays emitted from the β-ray source, a material supplied to the irradiation path, a detector for detecting the amount of β-rays transmitted through the material, and detection by the detector. It consists of an amplification unit that amplifies and outputs a signal to be measured, and a gas flow path to be measured that intersects with the material, and the material passes through the gas flowing through the gas flow path to detect floating air in the gas to be measured. At the same time as collecting dust, the amount of attenuation of β-rays passing through the material due to the collected dust is detected by the detector, and this detection signal is amplified by the amplifier and output, thereby determining the amount of suspended dust in the gas to be measured. In the dust meter that determines the A dust meter characterized in that the intersection with a measurement gas flow path is blocked with a β-ray permeable thin film.