JPH0429022B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a β-ray transmission type dust monitor for measuring the concentration of dust contained in the atmosphere or the like.

[Prior art and problems to be solved by the invention] Conventionally, as a method for measuring the concentration of dust contained in the atmosphere or factory smoke, etc., a constant flow rate of the gas to be measured is measured using a filter paper drawn out from a roll of filter paper. Dust in the gas to be measured is collected on the surface of the filter paper by filtration for a certain period of time, and the collected dust layer is irradiated with β-rays to measure the amount of transmitted β-ray attenuation due to the collected dust layer. A method is known in which the dust concentration in the gas to be measured is calculated by determining the thickness of the dust collection layer. Among the β-ray transmission type dust monitors using these methods, those shown in Figures 1 and 2 are those that continuously measure the transmitted β-ray attenuation while collecting dust and output measured values continuously. There are some things shown below.

That is, in the dust monitor shown in FIG. 1, a is a suction pump, and by operating this pump a, the air that has passed through the particle sizer b passes through the sample tube c and reaches the detection part d, where it is filtered by the filter paper e. Dust in the atmosphere is filtered out by the filter and then discharged to the outside of the system through the discharge pipe f. g is a β-ray source, and the β-rays emitted from it pass through the filter paper e and the dust layer h deposited on the filter paper surface, and its intensity is measured by an ionization chamber i, and this measurement signal is sent to an amplifier j. After being amplified, it is sent to a recorder k and the measurement results are displayed. Note that g' is a compensating β-ray source, 1 is a metal foil, and i' is a compensating electrode box, which compensate for fluctuations in measured values due to changes in pressure and temperature. That is, as dust collection progresses, the permeability of the atmosphere through the filter paper decreases due to the dust layer deposited on the surface of the filter paper, and the suction pressure (pressure from filter paper e to suction pump a) changes. Temperature changes due to pressure changes and temperature fluctuations greatly fluctuate the β-ray intensity measurement value, giving rise to measurement errors due to pressure and temperature.In order to compensate for this influence, this dust monitor uses a compensation β-ray source. A compensating section consisting of g' metal foil 1 and ionization chamber i' is provided. Measurement of dust concentration using this dust monitor can be carried out as soon as atmospheric suction begins, and the measurement results are displayed on the recorder k over time. g′, ionization chamber i′, etc. are required, resulting in a complicated structure and high manufacturing cost.

The dust monitor shown in Fig. 2 has almost the same structure as the above-mentioned dust monitor, but the β-ray source g for measurement and compensation is shared, which reduces the number of β-ray sources used. We are trying to simplify the process. However, the detectors are expensive, and since two detectors m and m' are used in this case, there is a problem in that the manufacturing cost is high, as in the case of the dust monitor shown in FIG.

Furthermore, since the apparatuses shown in FIGS. 1 and 2 use a plurality of β-ray sources or detectors, there is a problem in measurement accuracy. That is, since dust enters and adheres to locations other than the collection surface, if the measured value for compensation is influenced by the dust attached to locations other than the collection surface, a measurement error occurs. In addition, the device in Figure 1 uses two β-ray sources and two detectors, and the device in Figure 2 uses two detectors, but measurement errors occur due to individual differences in these detectors. .

The present invention has been developed in view of the above circumstances, and is capable of compensating for measurement errors caused by pressure changes and temperature changes using one line source and one detector, and has high measurement accuracy and a simple structure. The purpose of the present invention is to provide a β-ray transmission type dust monitor.

[Means and effects for solving the problem] In order to achieve the above-mentioned object, the present invention includes a β-ray source and a β-ray source through which β-rays emitted from the β-ray source pass.
a radiation irradiation path, a filter medium supplied to the irradiation path to intersect with the irradiation path, a detector that detects the intensity of β-rays passing through the filter medium, and a control calculation unit that processes the signal detected by the detector; A gas to be measured intake path connected to an irradiation path between the filter medium and the β-ray source, and a gas discharge path connected to the irradiation path between the filter medium and the detector, The gas to be measured drawn into the irradiation path from the gas inlet path is filtered to collect dust in the gas to be measured, and the attenuation of β-rays passing through the filter medium due to the collected dust is measured by the detector. In a dust monitor that determines the dust concentration in the gas to be measured by calculating and outputting the detection signal through a control calculation section, and a temperature sensor for detecting the temperature of the gas to be measured; The temperature of the gas to be measured at the time of detecting the transmitted β rays is measured by the temperature sensor, and the pressure measurement value and temperature measurement value obtained by the measurement are sent to the control calculation unit, and the control calculation unit From the pressure measurement value and temperature measurement value, the mass per unit area of the β-ray permeable air layer before dust collection X _SO and the mass per unit area of the β-ray permeation air layer after dust collection X _S can be calculated using the following formulas. X _S =1.293×k/1+0.00367t _N・H _N /760 (mg/cm ² ) X _SO =1.293×k/1+0.00367t _O・H _O /760 (mg/cm ² ) k: β rays penetrate Thickness of the air layer H _O : Pressure of the β-ray permeable air layer before dust collection (mmHg) H _N : Pressure of the β-ray permeable air layer after dust collection (mmHg) t _O : Before dust collection Temperature of the β-ray permeable air layer (°C) t _N : Calculated from the temperature of the β-ray permeable air layer after dust collection (°C), and using these X _SO and X _S , the following formula (1) X _n = ln(I _O /I) + (X _SO −X _S )/μm …(1) μm: Mass absorption coefficient I: β-ray intensity that has passed through the filter medium and dust I _O : The β-ray intensity that has passed only through the filter medium Mass of dust per unit area above x _n
A β-ray transmission type dust monitor is provided, characterized in that the dust concentration is determined from this X _n .

That is, in the β-ray transmission type dust monitor, the dust concentration C is calculated by the following formula (2).

C=A/QTX _n (μg/cm ³ )...(2) A: Area of filter medium (cm ² ) Q: Flow rate of gas to be measured (cm ³ /min) T: Collection time (min) X _n : Filter medium The mass of dust per unit area above (g/cm ³ ) In _this case, _{X n} is conventionally calculated as I'm looking for it.

However, the attenuation of β rays occurs only when they pass through an air layer, and in this case, the amount of attenuation when β rays pass through an air layer changes depending on the density of the air layer, and the higher the density, the attenuated it becomes. Although the amount is large, the density D of air at a temperature of t℃ and a pressure of HmmHg is generally expressed by the following formula (4) D=1.293/1+0.00367t・H/760 (mg/cm ³ )...(4) The density of the air layer and thus the density of the air layer changes with changes in pressure and temperature.

On the other hand, I _O and I are represented by the following formulas (5) and (6).

I=I _{a exp} {−μm(X _n +X _P +X _S )} …(5) I _O =I _{a exp} {−μm(X _P +X _SO )} …(6) I _a : β-ray intensity of the source X _P : Mass of filter medium per unit area (g/cm ² ) X _S : Mass per unit area of β-ray permeable air layer before dust collection (g/cm ² ) X _SO : β after dust collection Mass per unit area of the line-transmission air layer (g/cm ² ) In this case, since X _P is constant, if the pressure and temperature of the air in the β-ray transmission path are constant, X _S and X _SO
are equal, and the dust concentration C can be determined accurately even if the measured I _O and I are used without compensation.

However, in reality, as mentioned above, part of the β-ray transmission path is under negative pressure, and the degree of negative pressure depends on the dust concentration, variations in the ventilation resistance of the collection filter, and changes in temperature. Possible, so X _S
and X _SO fluctuates. Therefore, the dust concentration C cannot be accurately determined unless the values of I _O and I are compensated based on the fluctuations of X _S and X _SO .

Therefore, in the present invention, the pressure in the irradiation path between the filter medium and the detector and the temperature of the gas to be measured are detected during the detection of transmitted β-rays, and dust collection is performed based on these pressure measurement values and temperature measurement values. Mass per unit area of β-ray permeable air layer before x Mass per unit area of β-ray permeable air layer after _SO and dust collection
While calculating X _S , X _n is determined using the above equation (1) using these X _SO and X _S , and the dust concentration C is calculated from this X _n using the above equation (2).

That is, _both X _S and X _SO are expressed by ^the following formula (7 ₎ : , X _S and X _SO are expressed by the following formulas (8 ₎ and (9), respectively, based on ^the _above formula (4 ₎ . _{) _ _} ^_ _{_ _} Pressure of the β-ray permeable air layer after dust collection (mmHg) t _O : Temperature of the β-ray permeable air layer before dust collection (°C) t _N : Temperature of the β-ray permeable air layer after dust collection (°C) It can be calculated accordingly. On the other hand, I _O and I are (5) above,
As shown in equation (6), the following calculation ln(I _a /I)=μm(X _n +X _P +X _S )...(10) ln(I _a /I)=μm(X _P +X _SO )...( 11) From (10)−(11), ln(I _a /I) − ln(I _a /I _O ) = μmX _n + μm(X _S −X _SO ) …(12) ∴ln(I _O /I) ₌ μmX _n + μm (X _S − X _{SO )} …(13) X _n = ln (I _O / _I ) + μm (X _{SO − ) / μm _} Therefore, according to the present invention, by calculating X _n by equation (1) using X _S and X _SO , the measurement error due to pressure and temperature fluctuations included in the transmitted β-ray attenuation can be reduced. can be compensated using pressure and temperature measurements.

[Example] Hereinafter, an example of the present invention will be described with reference to FIG. 3, but the present invention is not limited to the following example.

In the figure, reference numeral 1 denotes a filter medium wound into a roll, and the filter medium 1a unwound from the roll-shaped filter medium 1 is supplied to a filter medium cutting monitoring sensor 2 disposed forward in the transfer direction (direction of arrow z in the figure). . This sensor 2 detects when the filter medium 1a is cut due to an accident and sends a signal to an input/output port (not shown) of a control calculation section 3 consisting of a microcomputer, etc., and uses this signal to perform measurements. is canceled. The filter medium 1a is then supplied to a detection unit 4 disposed at the front in the direction of movement. The detection section 4 is formed using a block main body 5 in the shape of a rectangular parallelepiped, and the block main body 5 consists of two blocks 5a and 5b horizontally divided into two at the center. The main body 5 has a gas flow path 6 to be measured and a β-ray irradiation path 7 having diameters smaller than the width of the filter medium 1a from the upper end surface to the lower end surface of the main body 5, respectively.
a and 5b are intersectingly bored at the junction, and the angle θ formed by the flow path 6 and the irradiation path 7 is formed at an acute angle, and the β-ray irradiation path 7 at the intersection with the flow path 6 is β due to synthetic resin, metal, etc.
It is closed by radiolucent thin films 8,8. The upper side of the flow path 6 is connected to one end of a sampling pipe 9. Also, the lower side of the flow path 6 is the suction pipe 1
0 is connected to the suction part of a suction pump 12 via a flow meter 11, and when the pump 12 is operated under the control of the control calculation part 3, the gas to be measured is sucked from the other end of the sampling pipe 9, and the flow path 6,
After successively passing through the suction pipe 10, flow meter 11, and suction pump 12, the measured gas is discharged outside the system from the discharge pipe 12' connected to the discharge part of the pump 12. In this case, the flow rate of the measured gas is 11, the signal is measured, converted into an electrical signal, and sent to the input/output port of the control calculation section 3. Further, a detection end 13 of a pressure detector and a temperature sensor 14 are respectively attached to the inner circumferential wall downstream of the filter medium 1a of the flow path, and their output signals are transmitted to the input/output ports of the control calculation section 3, respectively. Ru.

A β-ray source container 16 containing a β-ray source 15 is inserted into the upper side of the β-ray irradiation path 7, and β-rays are constantly irradiated into the irradiation path 7 from the β-ray source 15. ing. Furthermore, a β-ray detector 17 is installed on the lower side of the β-ray irradiation path 7, and the β-rays that have reached this detector 17 are converted here into electrical signals according to the amount of the β-rays that have arrived, and are sent to an amplifier 18. The signal is transmitted to the input/output port of the control calculation unit 3 via the input/output port.

The detection unit 4 is unrolled from the rolled filter medium 1.
The filter medium 1a supplied to both blocks 5a,
The filter medium 1a is mounted between the blocks 5a and 5b so as to cover the flow path 6.
This is done by moving blocks 5a and 5b up and down to open the space between them, moving the filter medium 1a, and then closing the space between blocks 5a and 5b. In this case, the flow path 6
In order to maintain airtightness, known means such as rubber packing may be used to close the space between the flow path 6 and the outside.

Next, the filter medium that has passed through the detection section 4 is further moved and wound up by a take-up roll 19, but this movement of the filter medium is performed under the control of the control calculation section 3. Note that 20 is a display unit connected to the input/output port of the control calculation unit 3, and the measured dust concentration etc. are displayed on this display unit.

Next, a case will be described in which the dust concentration in the atmosphere is monitored using the dust monitor. First, the other end (not shown) of the sampling pipe 9 is installed at the air sampling location to be measured. Next, in this state, the intensity of the β rays emitted from the β ray source 15, transmitted through the filter medium 1a, and reaching the detector 17 is measured, and this measured value I _p is temporarily stored in the control calculation unit 3. Thereafter, the suction pump 12 is activated, and atmospheric sampling begins. That is, the air sucked in from the other end of the sampling pipe 9 flows into the upper side of the flow path 6 and moves downward in the flow path 6, but at this time, the filter medium 1a stretched over the flow path 6 The dust is filtered out, thereby forming a dust deposit layer 21 on the upper surface of the filter medium 1a, the thickness of which increases with the passage of time. For this reason, the deposited layer 2
The β-ray intensity that passes through 1 and the filter medium 1a and reaches the detector 17 continues to gradually decrease, but this decreasing β-ray intensity is detected by the detector 17 and the measured value I is constantly stored in the control calculation unit 3. Sent to input/output ports.

On the other hand, the pressure and temperature in the flow path 6 on the downstream side of the filter medium 1a are measured by the detection end 13 of the pressure detector and the temperature sensor 14, and each measured value is sent to the control calculation unit 3.
At the same time, the measured value of the atmospheric flow rate is sent from the flowmeter 11 to the input/output port. The measured values of pressure, temperature, and flow rate in the downstream flow path 6 sent to the input/output port in this way are sent to the control calculation section 3, and these measured values are used to calculate I _p at each measurement time. The control calculation section 3 compensates for measurement errors based on fluctuations in pressure, temperature, and flow rate included in the values of and I.

In the apparatus shown in Figure 3, the thickness of the air layer that creates a negative pressure in the β-ray irradiation path between the filter medium and the detector is approximately 5 mm, but in this case, the measured temperatures t _O , t _N and From ^the pressure H _O and H _N , the following _formula ( _{8 ' )} , (9') Calculate X S and X _SO by 0.5/1 + 0.00367t _O・H _O /760 (mg/cm ² ) (9′), and use these X _{S and} X _SO to calculate according to equation (1) above. By finding X _n, I _O ,
Compensation for I will be made. Then, using this X _n , the dust concentration C is calculated according to the equation (2) above, and the display unit 2
0 is displayed continuously.

In addition, in the dust monitor of this example, the amount of β-ray transmission measured while the suction pump is operating
The dust concentration C may be calculated using I _O and I.
That is, the I _O is measured for a certain period of time at the beginning of pump startup (accumulating the number of transmitted β rays), and then the I O is measured for the same period of time as I _O.
In addition to repeating the measurement of these I _O ,
The dust concentration C, which varies from moment to moment, may be calculated using the above equation (2) using I.

After a predetermined period of time has elapsed, the measurement is interrupted, the blocks 5a and 5b are moved up and down to open a space between them, and the filter medium 1a is moved a predetermined distance forward in the direction of movement (in the direction of arrow z in the figure).
As a result, the deposited layer 21 is moved out of the flow path 6, and a new filter medium portion in which no dust is deposited is supplied into the flow path 6, and in this state, the gap between the blocks 5a and 5b is closed and the filter is initially filtered. The state will be restored. Thereafter, the same operation is repeated to measure the dust concentration, and the measurement results continue to be recorded on the display section 20, but all of these operations are automatically performed under the control of the control calculation section 3.

The dust monitor of this embodiment has a filter medium 1 in the flow path 6.
A detection end 13 of a pressure detector is disposed downstream of a, thereby constantly measuring the pressure on the downstream side of the flow path 6, and using this pressure measurement value to compensate for I _O and I. Therefore, unlike the conventional dust monitor, there is no need to provide a compensation section, the structure is simplified, and the number of expensive detectors used can be reduced to one, which is economical. In other words, in conventional dust monitors, when dust in the atmosphere is collected using a filter medium, the filter medium becomes clogged with the collected dust and the pressure on the suction side gradually decreases, but this pressure change occurs as described above. This greatly affects the intensity of β-rays reaching the detector and reduces measurement accuracy.
For this reason, in conventional dust monitors that continuously measure dust concentration while collecting dust, it is essential to include a compensation section to prevent the effects of pressure changes, which requires two expensive detectors. This is used to construct the compensation section. In this dust monitor, the structure of the dust monitor can be simplified and the measurement accuracy can be improved by measuring pressure changes and compensating I _O and I using the measured values. Furthermore, on the downstream side of the filter medium 1a,
A temperature sensor 14 is disposed in the flow path 6 to measure the atmospheric temperature, and this temperature measurement value is used to compensate for I _O and I. Measured values are unaffected by atmospheric temperature changes and are accurate even when they vary greatly. That is, in the β-ray transmission type dust monitor of this example, the pressure in the β-ray irradiation path normally fluctuates in the range of about 610 to 410 mmHg, and the dust concentration varies by 0.1 to 0.2 mg/ There will be an error of about m ³ , but
By determining X _n using X _S and X _SO as described above, such errors can be compensated for and accurate dust concentration can be determined.

Further, in the dust monitor of this embodiment, the flow path 6 and the irradiation path 7 intersect at an acute angle, and a filter material is stretched at the intersection, so there is no bend in the flow path. Therefore, there is no possibility of accidents such as accumulation of dust at the bending portion and the accumulation of dust causing measurement errors.

Note that in this example, the flow path 6 and the irradiation path 7 intersect at an angle of about 60 degrees, but the invention is not limited to this.
For example, the irradiation path and the flow path may be connected orthogonally as in a conventional dust monitor, or β
When the radiation-transparent thin film 8 has air permeability, the detection end 13 may be arranged in the irradiation path 7 between the thin film 8 and the β-ray detector 17, and the mounting location of the temperature sensor 14 may also be changed. It is not limited to the inside of the flow path 6. In addition, although a microcomputer was used as the control calculation unit 3,
The present invention is not limited to this, and various modifications may be made without departing from the gist of the present invention.

[Effects of the Invention] As explained above, the β-ray transmission type dust monitor of the present invention has the above-described configuration, so that the β-ray transmission type dust monitor of the present invention has the above-mentioned structure. Errors can be compensated for and therefore highly accurate dust concentration measurements can be obtained, and the compensation for such errors can be
Since this can be carried out by using only one radiation source, the measurement accuracy can be further improved and the structure can be simplified.

[Brief explanation of drawings]

1 and 2 are partially sectional side views showing a conventional dust monitor, respectively, and FIG. 3 is a schematic configuration diagram showing an embodiment of the present invention. 1a: filter medium, 3: control calculation section, 6: gas flow path to be measured, 7: β-ray irradiation path, 13: detection end, 15: β
Radiation source, 17: β-ray detector, 21: Deposition layer.

Claims (1)

[Scope of Claims] 1. A β-ray source, a β-ray irradiation path through which β-rays emitted from the β-ray source pass, a filter medium supplied to the irradiation path across the irradiation path, and a Transparent β
a detector that detects radiation intensity; a control calculation unit that processes signals detected by the detector; a gas inlet path to be measured connected to an irradiation path between the filter medium and the β-ray source; and a gas discharge path connected to the irradiation path, and the filter medium filters the gas sucked into the irradiation path from the gas suction path to remove dust in the gas. At the same time, the detector detects the amount of attenuation of the β-rays transmitted through the filter medium due to the collected dust, and this detection signal is processed by the control calculation unit and outputted, thereby determining the dust concentration in the gas to be measured. The dust monitor to be determined is equipped with a pressure detector disposed in the irradiation path or exhaust path between the filter medium and the β-ray detector, and a temperature sensor that detects the temperature of the gas to be measured, and detects the transmitted β-rays. The pressure in the irradiation path between the filter medium and the β-ray detector at the time of detection is detected by the pressure detector, and the temperature of the gas to be measured at the time of detection of transmitted β-rays is measured by the temperature sensor, and the measurement The pressure measurement value and temperature measurement value obtained are sent to the control calculation unit, and the control calculation unit calculates the mass per unit area of the β-ray permeable air layer before dust collection from the pressure measurement value and temperature measurement value _. And the mass _per unit area of the β-ray permeable _air layer after dust collection X _S is calculated using ^the _{following formula} : k/1+0.00367t _O・H _O /760 (mg/cm ² ) k: Thickness of the air layer through which β rays pass H _O : Pressure of the air layer through which β rays pass before dust collection (mmHg) H _N : Pressure of the β-ray permeable air layer after dust collection (mmHg) t _O : Temperature of the β-ray permeable air layer before dust collection (°C) t _N : Temperature of the β-ray permeable air layer after dust collection (°C) ), and using these X _SO and X _S , the following formula (1 ₎ X _n = ln (I _O /I) + (X _SO − : β-ray intensity transmitted through the filter medium and dust I _O : Mass of dust per unit area on the filter medium X _n by β-ray intensity transmitted only through the filter medium
A β-ray transmission type dust monitor characterized in that the dust concentration is calculated from this X _n .