JPH09218154A - Method for calibratig dust densitometer, and calibrating standard jig - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure dust of a low concentration less than a specified value with high precision by providing a standard jig having a reflecting means having a reflecting surface formed of an irregular surface, and calibrating the indicated value of a densitometer by use of this. SOLUTION: A standard jig 6 has optical filters 63, 64 for covering a luminous flux having a diameter of about 10mm on the incident and emitting sides and a reflecting surface 61a irregularly provided on the surface, and this jig is set in a measuring chamber. An incident light 62 is reduced by the filter 63, and the scattered light scattered by the reflecting surface 61a is again reduced by the filter 65, and received by a light receiving part as an emitted light 64. A dust densitometer is calibrated in the same manner as in the past by use of the jig 6 having the combination of the irregular reflecting surface 61a and the filters 63, 65. Even in a narrow measuring concentration range of 0-200, 100, 50, 10mg/Nm<3> or less, a direct calibration can be performed. Thus, the dust concentration in such a low concentration area can be measured with high precision.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an object to be measured containing dust.
Irradiating a constant gas with light and measuring the intensity of the scattered light.
Dust densitometer instrument instructions to measure dust concentration by
Method for calibrating values and calibration standard tools used therefor
Related to ingredients, especially 20mg / Nm ^ThreeLess than or equal to
A calibration of the indicated value of a densitometer that accurately measures low-concentration dust.
The present invention relates to a positive method and a standard jig for calibration.

[0002]

2. Description of the Related Art As a device for measuring the concentration of dust such as incinerator ash, dust or coal dust in exhaust gas from an incinerator, a firing furnace, a boiler, a blast furnace, etc., a light scattering type dust concentration as shown in FIG. The meter is widely used. This device utilizes the property that the amount of light scattering is proportional to the weight of dust, that is, the concentration, if the shape, color, composition, etc. of dust particles are constant. In FIG. 3, first, the gas to be measured is continuously circulated in the measurement chamber 2. Then measuring room 2
From a light source 11 such as a near-infrared light emitting diode provided in the light emitting unit 1 provided orthogonal to
Near-infrared light having a wavelength of nm is intermittently applied to the gas to be measured as a pulse wave. Here, the incident light is absorbed, transmitted, and scattered by the dust particles contained in the gas to be measured, but this densitometer uses this scattered light.
Scattered light is introduced into the light-receiving unit 3 provided at an angle of 0 °, and the sensor 33 such as a silicon photodiode converts the scattered light into an electric signal, which is then calculated to display the concentration instruction value, and the dust concentration is displayed in real time. Is to measure. The trap 4 is for removing light harmful to the measurement, and the optical system 5 is for appropriately converging incident light and scattered light.

Next, a method of calibrating the concentration instruction value in such a light scattering type dust densitometer will be described. Since this concentration indication value displayed in digital or analog is based on the above principle and does not directly indicate the actual dust concentration, it is necessary to indicate the correct dust concentration using a gas of known dust concentration. The value needs to be calibrated. As the calibration method, the following method has been conventionally used. First, in the case where the actual dust concentration is set to 0, clean air is circulated in the measurement chamber, the output of the electric signal is adjusted, and calibration (hereinafter referred to as zero calibration) is performed to match the concentration instruction value to 0. Then, by performing a calibration (hereinafter, referred to as span calibration) in which a gas having a known actual dust concentration value is circulated through the measurement chamber and the measured value obtained by measurement is matched with the actual dust concentration value, at least 0 to 0 is obtained. Between known density values, the density indication value can directly display the actual dust density.

The span calibration that has been conventionally performed will be described in detail. As a measured gas of known concentration used for calibration, dust particles of 10 μm are generated by a dust generator.
Disperse some calcium hydroxide powder in air to 700
Prepare air containing ˜1000 mg / Nm ³ . Regarding the absolute value of the dust concentration of the measured air, a predetermined amount of the air is sucked through the filter paper to collect the dust (calcium hydroxide powder) on the filter paper, and the weight of the dust is weighed to calculate the concentration. It is possible to know by measuring each time by the filter paper collecting and weighing method. For convenience of explanation, in this example, the actual dust concentration (absolute value) of the measured air whose concentration is known is 700.
It was assumed to be mg / Nm ³ .

With respect to the air to be measured whose concentration is known, a normal measurement operation is performed using the dust densitometer whose measurement concentration range is set to 0 to 1000 mg / Nm ^3. Dust concentration is 70
Adjust the output sensitivity of the electrical signal to indicate 0 mg / Nm ³ . By this operation, the span calibration referred to in the present invention is performed. Further, in this case, when the zero value fluctuates, zero calibration and span calibration are appropriately repeated to improve the calibration accuracy. Thus, in this measurement concentration range of 0 to 1000 mg / Nm ³ , the dust concentration of the gas to be measured can be directly read.

However, although the calibration method using the measured air having a known concentration obtained from the dust generator as the measured gas for calibration has the feature of high accuracy and reliability, it is troublesome to handle the dust generator. It is very inconvenient because it takes a lot of time, requires skill, and it is indispensable to measure the actual dust concentration by the filter paper collection and weighing method each time.Therefore, in the field where the dust concentration meter is used, the following simple calibration method is used. Is used.

In this simple method, a calibration standard jig having a light-reflecting surface that appropriately scatters light is used in place of the calibration gas to be measured whose concentration is known in the measurement chamber in which the gas to be measured is circulated. This is a method of inserting and arranging it. An example of the calibration standard jig is shown in FIG. 4, which shows a vertical cross section of the calibration standard jig inserted and arranged in the measurement chamber of the dust densitometer. 63, 6
5, a standard jig 6 having a flat reflecting surface 61
Is disposed in the measurement chamber 2, and the incident light 62 from the light emitting portion (not shown) is reduced by the optical filter 63, and the reflection surface 6
The light is scattered by 1, and the scattered light is further reduced by the optical filter 65, and is received by the light receiving portion (not shown) as the emitted light 64.

In this case, the standard jig 6 having the flat reflecting surface 61 is made of metal such as aluminum alloy, and the flat reflecting surface 61 is coated with so-called non-reflective paint whose reflectance is as low as possible. And the optical filter 6
Filters that are commercially available as 3, 65 and have practical strength and a minimum transmittance of 10% (for example, Neutr manufactured by Kenko Co., Ltd.)
al Density Filter: ND-03) was prepared, and it was set on the calibrated dust densitometer whose zero calibration and span calibration had been completed, and the emitted light was measured. A value corresponding to a dust concentration in the range of 500 to 1000 mg / Nm ³ is obtained, although it varies depending on the property. The dust concentration value thus obtained is referred to as a dust concentration conversion value of the standard jig in the present invention.

Here, if the dust concentration conversion value is 80
Assuming that the standard jig 6 is 0 mg / Nm ³ ,
Equal to the concentration produce an equivalent scattered light and the measurement gas is 800 mg / Nm ^3, it is possible to use this standard jig 6 for calibration as a substitute of the calibration measurement gas concentration 800 mg / Nm ³ . That is, for a dust densitometer that has been zero-calibrated but has not been span-calibrated, the standard jig 6 is set in the measurement concentration range of 0 to 1000 mg / Nm ³ , and the normal measurement operation is performed to obtain the value. The span calibration can be performed by adjusting the output sensitivity of the electric signal so that the density instruction value of the measured instrument matches the dust density conversion value of the standard jig 6 of 800 mg / Nm ³ . By this operation, it becomes possible to extremely easily perform the same calibration as the span calibration using the above-mentioned calibration measurement gas.

By the way, in recent years, this dust concentration meter has been used.
Along with the remarkable improvement of management technology for incinerators, boilers, etc.
The dust concentration in the exhaust gas that is
Nearly several mg / Nm^ThreeAccurately measures low concentration gas
The need has arisen. So, comparing the dust densitometer,
Measured concentration range 0-10mg / Nm^ThreeAt span
If you try to calibrate it
Calibration standard as shown in FIG. 4 with a planar reflective surface
For jigs, lower transmittance filters and reflections
Reasons such as low availability of paints from the market
And the dust concentration conversion value is 400mg / Nm^ThreeThe following
I couldn't make it stably. Therefore, the spa
Calibrated measurement concentration range 0-1000 or 500m
g / Nm ^ThreeBased on, adjust the output sensitivity electrically
0-100mg / Nm^ThreeOr 0 to 50 mg / Nm^ThreeAbout
I set the measurement concentration range of the degree to correspond,
There is a problem that the measurement accuracy is reduced.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and in order to make it possible to accurately measure a low dust concentration, for example, several mg / Nm ³ , Provided are a calibration method of a dust densitometer and a calibration standard jig applicable in a measurement concentration range of about 10 mg / Nm ³ .

[0012]

A method for calibrating a dust densitometer that solves the above-mentioned problems is provided by a light emitting section having a light source, a measuring chamber in which a gas to be measured is circulated while intersecting with incident light from the light source, A light receiving unit having a sensor for receiving scattered light due to dust in the gas to be measured, converting the amount of light received by the sensor into an electric signal, and measuring the concentration of the dust having a correlation with the amount of light received. In such a dust densitometer, in the measurement chamber, provided with a reflection surface formed by a concave-convex surface or a curved surface that scatters incident light, and provided with a light reflection means whose dust concentration conversion value is known, The scattered light from the light reflecting means is received by the light receiving unit, and the instrument indicating value of the electric signal obtained by conversion is made to match the dust concentration conversion value by adjusting the output sensitivity. It is a thing.

A standard jig for calibrating a dust densitometer which solves the above problem is used as a light reflecting means in the above calibrating method for a dust densitometer, and the upper limit of the measured concentration range is 20 mg / Nm ³ or less. Is a standard jig for calibrating a dust densitometer, which is characterized in that an optical filter is provided on the incident side and the outgoing side, and a reflecting surface formed of an arc surface is provided.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a calibration method for a dust densitometer of the present invention will be described together with an embodiment of a calibration standard jig of the present invention. The dust densitometer targeted by the method of the present invention is typically the light scattering type dust densitometer shown in FIG. 3, as described above. And, the characteristic feature of the calibration method of the present invention is that, instead of using a calibration target gas whose concentration is known, the calibration standard calibration provided with a reflection means having a light scattering performance whose dust concentration conversion value is known. Specifically, a standard jig having a reflecting surface formed by a concave-convex surface or a curved surface that scatters incident light, as shown in FIGS. 1 and 2, is used.

FIGS. 1 and 2 showing an example of the calibration standard jig are vertical sections of a calibration standard jig having an outer diameter of 20 mm according to the present invention inserted and arranged in a measuring chamber having an inner diameter of 28 mm of a dust concentration meter. Is shown. There, an optical filter 6 for covering a light beam having a diameter of about 10 mm on each of the incident side and the emitting side is provided.
A standard jig 6 provided with a reflecting surface 61a (FIG. 1) having concave and convex surfaces 3 and 65, or a reflecting surface 61b (FIG. 2) having a curved surface is provided in the measurement chamber 2. The incident light 62 from the light emitting portion (not shown) is attenuated by the optical filter 63 and scattered by the reflection surface 61, and the scattered light is further attenuated by the optical filter 65, and the emitted light 6
4 is formed so that it is received by a light receiving portion (not shown). Note that these reflective surfaces are coated with the same non-reflective paint as conventional products.

As the reflecting surface as described above, the degree of unevenness is 3
Table 1 shows the densitometer indicated values obtained by setting and measuring a standard jig using a type and a curved surface with an arc having a curvature radius of 5.5 mm in a calibrated dust densitometer. put it here,
The respective densitometer indicated values are apparently converted into the dust concentration by the amount of light scattered by the reflecting surface, and are values used as the dust concentration converted value. According to this result, even when the conventional smooth flat reflecting surface shows a densitometer indication value of 400 (mg / Nm ³ ) or more, it is about 200 to about 70 (mg / Nm for fine unevenness to rough unevenness). ³ ) Furthermore, in the case of an arcuate reflecting surface, it depends on the transmittance of the filter, but it is about 20 to 1 (mg
/ Nm ³ ) It can be seen that a significantly low concentration densitometer reading can be obtained as follows.

[0017]

[Table 1] Note: * 1 indicates that measurement is impossible due to exceeding the full scale (500 mg / Nm ³ ). Note ND03, ND13 and ND25 are manufactured by Kenko. The average transmittances are 10%, 12.5% and 25%, respectively. Note The measured gas of known concentration used for span calibration of 0 to 100 mg / Nm ³ and 0 to 10 mg / Nm ³ ranges of the used dust densitometer is 0.1 to 1.0 μm salt particles obtained by the standard particle generator, Air containing polystyrene latex particles of 0.3-1.0 μm was used. The absolute concentration was determined by a filter paper collection weighing method or a particle count method.

The standard jig thus obtained can be used to calibrate the dust densitometer in exactly the same manner as the conventional one, but with the conventional jig having the flat reflecting surface and the ND03 filter combined. , 0-500 or 0-1000
Although it is suitable for calibrating a measurement concentration range of about mg / Nm ^3, it is unsuitable for calibrating a low concentration region required in recent years, whereas the reflection of the shape according to the present invention is not suitable. 0-200, 0 for combination of face and filter
For calibrating the low concentration range that could not be directly calibrated by the standard jig, such as narrow measurement concentration range of -100, 0-50, 0-10 mg / Nm ³ or less. It will be appreciated that it is suitable.

In particular, in the present invention, an optical filter having an appropriate transmittance is selected on the incident side and the emitting side, and it is embodied as a standard jig for calibrating a dust densitometer having a reflecting surface formed by an arc surface. By doing so, the upper limit of the measurement concentration range is 20
mg / Nm ³ or lower low concentration region, for example, 10 mg /
Since the span calibration can be directly performed in the low concentration region of Nm ³ or less, the excellent effect that the dust concentration in the low concentration region can be accurately measured is obtained.

As for the shape of the arc surface in this case, if the radius of curvature is 5.5 mm, span calibration can be performed at about 80% of full scale in the measured concentration range of 0 to 10 mg / Nm ³ . , There is an advantage that the zero point and the span point can be calibrated in good balance with respect to the measurement range. It should be noted that the degree of unevenness of the reflecting surface and the value of the radius of curvature of the arc shown in Table 1 above are only examples, and the present invention is not limited thereto. Further, the optical filter does not need to be of the same type on the incident side and the emitting side, and can be appropriately combined according to a desired dust concentration conversion value.

[0021]

Since the dust concentration meter calibration method of the present invention is configured as described above, it is possible to directly perform span calibration in a low concentration region for dust in exhaust gas from an incinerator or a boiler combustion furnace. Since it can be performed, there is an excellent effect that the dust concentration in such a low concentration region can be accurately measured. Further, the standard jig for calibrating the dust densitometer of the present invention has an upper limit value of 20 m in the measurement concentration range suitable for measuring a very low dust concentration.
It has an excellent effect that it can be used for span calibration of a densitometer with g / Nm ³ or less. Therefore, the present invention has an extremely great industrial value as a calibration method and a calibration jig for a dust densitometer that solves the conventional problems.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part for explaining a calibration standard jig of the present invention.

FIG. 2 is a sectional view of an essential part for explaining another calibration standard jig of the present invention.

FIG. 3 is a perspective view of a main part for explaining the principle of a light scattering dust densitometer.

FIG. 4 is a sectional view of an essential part for explaining a conventional standard jig for calibration.

[Explanation of symbols]

1 light emitting part, 11 light source, 2 measuring chamber, 3 light receiving part, 3
3 sensor, 4 trap, 5 optical system, 6 standard jig main body, 61 reflective surface, 62 incident light, 63, 65 filter, 64 emitted light.

Claims (2)

[Claims] 1. A light receiving section having a light emitting section having a light source, a measurement chamber for passing a gas to be measured intersecting with incident light from the light source, and a sensor for receiving scattered light due to dust in the gas to be measured. In the dust densitometer, which is configured to convert the amount of light received by the sensor into an electric signal and measure the concentration of the dust that is correlated with the amount of received light, the incident light is scattered in the measurement chamber. A light reflecting means having a reflecting surface formed of an uneven surface or a curved surface and having a known dust concentration conversion value is installed, and the scattered light from the light reflecting means is received by the light receiving section and converted. A method for calibrating a dust densitometer, characterized in that the instrument indicated value of the obtained electric signal is made to match the above-mentioned dust concentration converted value by adjusting the output sensitivity. 2. A standard jig for calibrating a dust densitometer, which is used as a light reflecting means of the method for calibrating a dust densitometer according to claim 1, and has an upper limit value of a measurement concentration range of 20 mg / Nm ³ or less. A standard jig for calibrating a dust densitometer, characterized in that an optical filter is provided on each of an incident side and an outgoing side, and a reflecting surface formed of an arc surface is provided.