8th Asian Particle Technology Symposium APT2021
Osaka, Japan

排ガス中の粉塵濃度と帯電量を同時に測定可能なダストサンプラー
A Dust Sampler Capable of Simultaneously Measuring
Dust Concentration and Electric Charging
in Flue Gas from Stationary Sources
Masashi Wada1 , Masashi Tsuji2
1

Research Institute of Environment Agriculture and Fisheries Osaka Prefecture, Japan
2

KANSAI Automation Co., Ltd., Japan*E-mail: WadaM@mbox.kannousuiken-osaka.or.jp
ダストモニタは、粒子状物質（PM）の濃度を連続的に測定できる装置であるため、多くの国で汚染物質の排出を監視する CEMS（Continuous Emission Monitoring System）として使用されています。PM のモニタリングには、オパシティ、光散乱、ベータ線減衰、プローブ帯電（摩擦電気、エレクトロダイナミック）などの技術がよく使われています。これらの技術に基づいて開発された PM-CEMS は、実際の濃度を得るためには、重量測定や等速度サンプリングによる校正が必要であり、粉塵濃度（mg/m3）を連続的に出力することができる唯一の方法です。そのため、これらの装置は、現場で行われる重量法サンプリングによるフィッティング作業を経て使用されます。しかし、プローブ帯電方式では、粉塵の帯電が測定値に影響を与えるため[1]、粉塵の帯電が不安定な状況では、フィッティング作業が困難になります。そこで本研究では、重量法で使用するダストサンプラーに、帯電量を同時に測定する機能を持たせることを試みました。帯電量の同時測定を可能にするため、ファラデーケージを組み込んだダストサンプラーを製作しました。開発したサンプラーの性能について、ELPI（electrical low pressure impactor）で測定した静電気と、開発したサンプラーを試験ダ
クト装置で動作させて測定した静電気を比較した結果を報告します[2]。

Fig.1 Schematic diagram of a dust sampler that can simultaneously measure the electrical charge
References[1] M. Wada et. al.MATEC Web of Conferences 333(2020)[2] M.Wada et. al. Proc. 11th RESTconf 123-135 (2021)

JIS Performance Evaluation Testing for Automatic
Dust Concentration Measuring Instrument: Effect of
dust charge on measured value

Masashi Wada1, *Masashi Tsuji2, William Averdieck1

Research Institute of Environment, Agriculture and Fisheries, Osaka Prefecture, JAPAN2

KANSAI Automation Co., Ltd, JAPAN

Abstract
The automatic measurements of dust concentration emissions is well developed technology
which is commonly used in industrial processes. To make public use of such technologies forregulatory compliance purposes, a certification system in Japan is needed, and as a part of such
effort, a series of JIS standards were developed in 2020. This study reports on the actual
performance evaluation of JIS-compliant test equipment, and useful knowledge and practicalissues obtained on the validation and operation to the standard. In particular, the problem of not
being able to universally correlate results between gravimetric measurements and probe
electrification type dust meters was analysed and found to be caused by variable charging of
the test dust. The amount of charge on the test dust is influenced by the dust injection method
and the geometry and design of the test section in the ducts was identified. Charging of the test
dust, presumably owing to frictional charging between the agitator plate or the rectifying wire
mesh, was observed. The dust charge was significantly affected by the dust concentration,although not by the velocity, and this relationship was found to be inversely proportional. Whilethe change in dust charge undermined the linear relationship between the gravimetricmeasurements and the dust monitor readings, a linear relationship is possible and can beobtained by compensating for the effect of the differences in the amount of charge. For theprobe electrification type dust meter, it is necessary to focus on changes in the dust charge whencarrying out equivalence tests using a test duct.
Keywords: Particulate emission monitor; Performance evaluation test; Dust charge; JIS B7996; JIS B-7997

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1

Introduction

An automated concentration monitoring instrument (dust meter) is an instrument that cancontinuously measure the concentration of particulate matter (PM) and is therefore used as acontinuous emission monitoring system (CEMS) to monitor pollutant emissions in manydifferent countries. The most commonly used technologies for PM monitoring are opacity, lightscattering, beta attenuation, and probe electrification (triboelectric effect, electrodynamic
device) (Castellani, 2004). The PM-CEMS developed based on these technologies must be
calibrated through gravimetric and isokinetic sampling, which is the only way to obtain theactual concentration and provide a continuous output of the dust concentration (mg/m3).
Therefore, measurement methods and quality standards for the equivalence of devices andgravimetric sampling have been determined, and a certification system has been establishedand is currently in operation (EN 14181:2014, VDI 4203:2017, U.K. Environment Agency
2012, U.S. EPA 2016, M.E.P. China 2017). CEMSs are being used not only for PM in flue gas,
but also for various components, and many countries are actively using such systems foremission control and research (Levy et al., 2002, Jang et al., 2009, Zhao et al., 2010,
Krittayakasem et al., 2011, Kristanto et al., 2018, Tang et al., 2020). In Japan, however, thesetechnologies have not yet been officially recognised as methods for PM emission control. The
main reasons for this have been an inadequacy of the relevant JIS standards and a lack ofscientific evidence to properly assess the reliability of dust meters distributed throughout Japan.
Regarding the former, ISO 10155:1995, i.e. “Stationary source emissions - Automatedmonitoring of mass concentrations of particles - Performance characteristics, test methods andspecifications,” has already been established as an international standard. For example, in
Europe, EN 14181 has been established in response to this standard, and dust meters are usedas CEMS tool for emission monitoring regulations of stationary sources. This situation issimilar in many other countries. For these reasons, there have been strong calls for the active
use of dust meters in air pollution control systems in Japan. In response to this request, JIS Z
8852:2013 was published based on ISO 10155:1995 to provide an overview of automatic dust
measurement technology (Tamori, 2014). JIS B 7996:2020 was established in 2018 for detailsof the instrumental functions and performance test methods of the instruments. In addition, toallow the method to become an official approach used for emission control under the Air
Pollution Control Law, it was necessary to establish a system allowing third parties to recognise
continuous measurement data. As a precondition for this, it was considered necessary toestablish product standards. In 2020, JIS B 7997:2020, i.e. “Automated concentration
monitoring instrument of dust in flue gas,” was published, which specifies the measurement
principles, composition and structure, specified values, formal tests, and performance tests. For
the first time worldwide, provisions for stability under changing flow velocities have been
introduced in the standard. With these standards in place, the construction of a certification
system is now underway.
Regarding the latter, initially, there was no test duct equipment for evaluating theperformance of dust meters in Japan. The authors have been working on the development of atest duct equipment (Wada et al., 2021). To examine the content of the specifications, the JIS
drafting committee for preparing JIS B 7997:2020 conducted round-robin tests using two test
duct equipment in Japan, including the authors’ own equipment. During the tests, there was agood agreement between the results obtained by the two types of device in the case of lighttransmission and when applying light scattering dust meters. However, the trends of the results
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obtained for the probe electrification type dust meter were quite different (Wada et al., 2019).
In particular, the trend of the results obtained differed when the flow velocity condition waschanged, and the reason for the difference could not be identified. Therefore, it was concluded
that the test ducts could not be used to make an accurate evaluation. Therefore, we decided to
exclude the performance test items from the stability test during the velocity fluctuations in thestandard used for the probe electrification type instruments.
With the probe electrification method (Fig. 1), three different effects are detected whenparticles hit or pass near a conductor placed in the exhaust gas stream: (i) When the particles
hit the probe, they rub the surface and cause a frictional charge, (ii) when the particles hit theprobe, a charge transfer occurs, and (iii) when charged particles pass near the probe, they induce
charges of equal and opposite magnitude in the conductor. The amount of charge generated by
the first two effects depends on the velocity of the particle, its mass, and the charge history of
the particle. The third effect is the induced charge, and the magnitude of the charge depends on
the proximity of the particle to the conductor and the charge history of the particle (Matsusaka
et al., 2010). The triboelectric device measures the DC current in such a way that the first two
effects are detected.
The electrodynamic device is a method for detecting only the third effect (electrostaticinduction), which filters the DC current produced by the particle impact on the rod and measures
the RMS signal within an optimised frequency bandwidth resulting from particles passing
through the probe (Averdieck, 1995). The signal is independent of the probe surface conditionand has a stable and repeatable relationship with dust concentration in many types of industrial
applications. Because the signal does not depend on particle collisions (unlike a triboelectriceffect), the associated problems of rod contamination and velocity dependence are minimised(Averdieck, 1999). It is known that these probe electrification methods do not work well when
the particles are subjected to varying charges (Castellani, 2014). Therefore, they are notrecommended to be installed at locations where the dust charge is highly variable, such as in
the immediate vicinity downstream of the EP. This means that, even for the same dust
concentration, the indicated value will increase in proportion to the dust charge.
Figure 1: Operating principles of probe electrification method

Therefore, the unexplained measurement results that occurred in the round-robin test aresuspected to be due to the change in the dust charge in the test duct. However, the confirmationof the phenomenon and the magnitude of the effect are unclear and need to be studied. In thisstudy, the issue in which the equivalence with gravimetric measurements cannot be universally125

measured was verified when the probe electrification type device, one of the main types of dust
monitors, was tested using a test duct. Dust charging in the ducts was identified owing to thestructure of the test ducts, and changes in such charging from changes in the test conditions of
the flow velocity and dust concentration were measured. The influence of the dust chargechange on the evaluation test results of the dust meter was then examined.

2

Experimental Equipment and Methods

2.1 Test duct equipment
In this study, the test duct equipment developed by the authors was used (Wada et al., 2021).
This test duct can generate dust-containing air at any flow velocity and dust concentration
conditions. A schematic diagram of the test duct is shown in Fig. 2. A blower locateddownstream of the duct causes air to flow horizontally in the duct at a constant velocity. Dustcontaining air is generated at the dust generator upstream of the duct (left side of Fig. 2), andparallel measurements with a dust meter and gravimetric can be conducted at the measurement
section downstream. The flow velocity are continuously monitored by a pitot tube. The flow
velocity can be set arbitrarily by the inverter control of the blower.
Figure 2: Test equipment for performance evaluation of dust monitors

Figure 3: Dust generation mechanism

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The dust generation mechanism is shown in Fig. 3. A screw type dust feeder (MF15A-C1.5L,
Alpha, Japan) was used to feed the powder. The storage hopper was heated to 100 °C to prevent
dust agglomeration owing to moisture absorption during storage. There is a rotating brush at
the outlet of the feeder, which allows continuous feeding of powder with minimal pulsation.
The dust is fed into a hopper connected to the ejector. The dust suctioned from the top of theejector is mixed with compressed air, and well-dispersed dust-containing air is ejected from theejector. The agitator plate (a stainless steel disc with a diameter of 20 cm and numerous roundholes of 5 mm in diameter and perforated metal with an aperture ratio of 35.4%) installed in
front of the ejector mixes the ejected dust-containing air with the airflow in the duct to generate
dust uniformly in the test duct. Furthermore, a wire mesh and a rectifying grid are installed
downstream for rectification, which can homogenise the airflow and dust concentration over ashort distance. The dust concentration can be set arbitrarily by controlling the screw rotation
speed of the feeder. By contrast, during some tests, dust-containing air generated by a fluidized
bed dust generator (Model 3216, Kanomax, Japan) was used instead of the above dust generator.
A stainless steel suction tube was installed at the same position as the nozzle for a gravimetricmeasurement and introduced into an electrical low-pressure impactor (ELPI) (ELPI, DEKATI,
Finland) to measure the charge of dust in the duct based on particle size.
2.2 Charge measurement of the test dust generated in the test duct
The charge of the dust in the measurement section of the test duct was measured using an
ELPI. The ELPI is an instrument that can measure the particle size distribution and the numberof particles in real time, and is composed of three main parts: a particle charging part, aclassification part (cascade impactor), and a high-sensitivity current detection part. Particles arecharged to saturation in the corona charging section, and then collected based on the particle
size (6 nm to 10 µm in 11 stages) in a cascade low-pressure impactor consisting of multiple
electrically insulated collection stages. The number concentration can be measured bymeasuring the amount of charge carried by the particles in each impactor stage with anextremely sensitive ammeter. In addition, by turning off the charging section, the charge
distribution of the particles can be measured. For the test dust, JIS Class 10 fly ash (JIS Z
8901:2006) was dried at 110 °C for 1 h and then cooled in a desiccator. The test conditions arelisted in Table 1. The measurements were conducted at the same velocity and dust concentration,with and without the use of an ejector, with and without a rectification wire mesh (downstreamside), and with different dispersing air pressures introduced into the ejector. Measurements werealso conducted when the dust generation mechanism was changed from the ejector system tothe fluidized bed system.
Table 1: Test conditions for measuring the amount of charged dust generated in the test duct
Comparison
conditions

Commonconditions

Test No.
Dust generator
Ejector

(a)

(b)

(c)
(d)
Screw type

(e)

(f)

(g)
(h)
Fluidized bed type

None
Yes
None
Yes
Dispersion air
0.2
0.2
0.4
0.4
0.2
pressure (Mpa)
Rectification
Yes
None
Yes
None
Yes
None
None
Yes
wire mesh
Measurement point: Center of the duct in the measurement section; flow velocity, 12 ⅿ/s;
dust concentration, 10 mg/m3

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2.3 Measurement of changes in the status of dust charge owing to changes in the test
conditions
The charge of the test dust, which varied with changes in the test condition settings (flowvelocity and dust concentration), was measured at different flow velocities and powder feed
rates. Among the facilities of the test ducts, the rectifying wire mesh on the downstream side
was not installed here.
The test dust used was JIS Class 10 fly ash. The gravimetric measurement was conducted inaccordance with JIS Z 8808:2013. A Type II dust sampler (ERH-A-32H, Okano, Japan)
equipped with a 90° stainless steel vent nozzle and an automatic dust sampling device (ESA703, Okano, Japan) was used. A quartz fibre circular filter (3200QAT-UP, 32 mmφ, ~60 mg,
Advantec, Japan) was used as the collection filter. Before and after dust sampling, the filters
were dried at 110 °C for 1 h and kept in a thermostatic room (room temperature, 21 ± 1.5 °C;
relative humidity, 35 ± 5 %) for 1 day. The filters were weighed on an electronic balance (XS205, maximum capacity, 81 mg; minimum display, 0.01 mg, Metler Toledo, Japan). Both thelaboratory blank and travel blank were 0.02 mg.
A nozzle was inserted at the centre point of the duct, and dust was collected using isokinetic
sampling. The diameter of the nozzle and the sampling time were determined by the following
factors: dust collection volume of 2.5 mg or higher (0.5 mg or more for each square centimetre
collection area, i.e. 5.3 cm2 collection area).
The charge of the dust was obtained as follows.
(1) Total charge (q)Turn off the particle charger of the ELPI, measure the detection current of each impactor
stage, and then integrate the detection current with the measurement time t to obtain the dust
charge of stage i. Then, sum the total charge of the 11 stages to obtain the total charge q.
𝑡𝑞𝑖 = ∫0 𝐼𝑖 𝑑𝑡(1)

𝑞 = ∑11𝑖=1 𝑞𝑖(2)(2) Total amount of particles collected using the ELPI (m).
The amount of particles collected using the ELPI was determined from the dust
concentration value through a gravimetric measurement. In this calculation, it was assumed that
there was no loss in the ELPI (α = 1).
𝑚 = 𝛼𝐶𝑄𝐸𝐿𝑃𝐼(3)

where m is total mass of particles collected by ELPI (mg), α is loss in the ELPI ( - ), C is dust
concentration by gravimetric measurement (mg/m3), and QELPI is suction rate of ELPI (m3/s)(3) Charging amount per unit mass (q)The amount of charge per unit mass was calculated by dividing the total charge q measured
using the ELPI by the amount of collected dust.
𝑞̅ = 𝑞 ⁄𝑚

128

(4)

The test conditions are listed in Table 2. The dust concentration to be generated was set tothree different concentration ranges from 5 to 30 mg/m3, considering the dust concentration at
the actual source.
Table 2: Test conditions for measuring changes in the status of dust charging owing to changes
in test condition settings
Item
Description
Total number ofmeasurements
Low (8 m/s), standard (12 m/s), high (16 m/s) × 3
3
Flow velocity
Low (5 mg/m3 ), medium (10 mg/m3 ), high (20 mg/m3 )×3
Dust*The value is the reference concentration at 12 m/s. The setting
concentrationfor each concentration range is controlled by the feeder voltage,
and the same setting value is used for each concentration range.
3×3 = 27 times
Number ofmeasurements

2.4 Measurement of the effect of change in charge of the test dust on the readings of thedust meter
The gravimetric and dust meter measurements were carried out in parallel. A probe
electrification type dust meter (an electrodynamic device) manufactured by Kansai Automation(VIEW 370) was used. The dust meter is a measuring instrument used in a relative concentration
indication method, and does not directly measure the mass concentration. Therefore, it isnecessary to conduct parallel measurements with gravimetric measurements to obtain theconversion factor for the mass concentration. For the the detected AC current, the dust
concentration is expressed through the following equation; where C is dust concentration(mg/m3), I is AC current (A), V is Flow velocity (m/s), Z is factor, dp is particle size (µm), andk is particle-specific coefficients.
𝑑𝑝

𝐶 = 𝑘 𝑣𝑍 𝐼

(5)

The AC current and dust concentration have a proportional relationship when the velocity,
particle size, and particle-specific coefficients do not vary. Therefore, when using the dust meter,
the readings converted using Eq. (6) can be obtained by setting the reciprocal of the sensitivity
ratio (dust concentration meter indication (primary value) divided by gravimetric measurement)
obtained by the user at each site as the conversion factor; where Ku is conversion factors to be
set by the user, Km is manufacturer’s device constant, R is indicated value of dust meter (primaryvalue) (mg/m3 RC), and R' is indicated value of dust meter (mg/m3 RC).
𝐶 = 𝐾𝑢 𝐾𝑚 𝐼 = 𝐾𝑢 𝑅 = 𝑅′
(6)
The value used to convert the indicated value includes the conversion factor Ku, which is set
by the user using the gravimetric measurement value in the field, and the device constant K m,which is set by the manufacturer, the latter of which is a black box in most cases. The readingsof the dust meter during this test indicate the amount (primary value) of dust. (Hereinafter, thereadings refer to the indicated value (primary value) of the dust meter, i.e., the value measured
without setting a conversion factor (Ku = 1). The unit of the measured value in this study ismilligrams per cubic meter of relative concentration (RC), because the measured value of thedust meter is a relative concentration and does not represent the actual concentrated mass.)
The measured value output (output at 4–20 mA) of the dust meter installed upstream of themeasurement section of the test duct was recorded using a data logger. The sampling period of
129

the data logger was set to 1 s, and the average value of the trend indicated during the sampling
period of the gravimetric measurement was taken as the readings of the dust meter. The dust
concentration through gravimetry, the value output by the dust meter, and the electrostatic
charge using the ELPI were measured simultaneously in parallel and treated as one set ofmeasurement data.

3

Results

3.1 Charging status of the test dust generated in the test duct
It is known that the readings of the dust meter in the probe electrification method are affectedby the charge of the dust in addition to the dust concentration. It is necessary to investigate thecharging conditions and causes of the dust in the test duct. Therefore, the charging of the test
dust was measured using the ELPI under different dust generation conditions.
Fig. 4 shows the measurement results of the amount of charge based on the particle size.
Focusing on the coarse particles (right side of the graph), where the dust charge (absolute value)is large, it can be seen that the charge is larger for particles (c)–(f) with an ejector than forparticles (a) and (b) without an ejector, and that it increases as the dispersion air pressure of theejector increases. In addition, when comparing those with the same ejector conditions, it can beseen that the amount of charge is larger when the wire mesh for rectification is present(comparison of (a) and (b), (c) and (d), and (e) and (f)). When a fluidized bed is used, thecharging is comparable to that of direct injection (comparison of (a) and (g)). By contrast, theaerosol generated using the fluidized bed also shows an increase in charging when passed
through the ejector (comparison of (c) and (h)). It is considered that the dust generated using
the fluidized bed can be tested in a close to uncharged state, and is less affected by fluctuationsin the amount of charge.
To summarise the confirmed phenomena, (ⅰ) the amount of charge of fine particles is small,and changes depending on the generation conditions are also small. (ⅱ) The charging amountof coarse particles increases when the dispersion air pressure of the ejector increases. (iii) The
presence of a wire mesh for rectification in the flow path of the test dust increases the amountof charging. Based on these phenomena, the confirmed charging of dust is assumed to be as
follows. The dust is mixed with the ejected air in the ejector, ejected at high speed with theejected air, and blown to the agitator plate. Coarse particles with high inertia collide and rub
against obstacles owing to inertia. The dust particles collide, and friction with the obstacle ischarged through frictional static electricity. The amount of charging is correlated with thecollision speed of the dust. The same phenomenon occurs in the rectification wire mesh.
From the above results, it was confirmed that the test dust generated in the test duct waselectrically charged, and it was assumed that this was due to frictional charging by the agitator
plate and rectifying a wire mesh.

130Without Ejector(Direct imput)

Figure 4: Effects of ejector and wire mesh for rectification on dust charging status
With wire meshWithout wire meshWith wire mesh
(a)
(b)
(g)

(d)

(e)

(f)

(h)

With Ejector(0.4 MPa)

With Ejector(0.2 MPa)(c)

3.2 Status change of dust charging by changing the settings of the test conditions
The test duct was used to evaluate the equivalence between the dust meter and gravimetricmeasurements by setting the dust concentration and flow velocity. Fig. 5 shows the relationshipbetween the concentration and charge of the test dust generated by changing the flow rate andthe dust supply rate. Fig. 4 shows the relationship between the dust concentration and dust
charge of the test dust generated at different flow velocities and dust feed rates. The equationin the figure is an approximation obtained after a logarithmic conversion. Within the range of−5 to −15 µC/g, the higher the dust concentration, the lower the dust charge. This trend was
also observed in a report that investigated the particle charging in a pipe. Suzuki et al. (2001)
reported that the specific charge was larger when the feed rate was smaller and when the flow
velocity was higher. It is thought that the specific charge increases not only because theprobability of individual particles colliding with the collision plate or tube wall increases, butalso because the collision area also increases as the spatial concentration of the powder
decreases with a decrease in the feed rate, which is consistent with the results obtained in thisstudy. Similar results were obtained when the amount of electric charge in a pipe was measured
using JIS 10 type fly ash (Masuda et al., 1997). By contrast, the dust concentration and amountof charge, regardless of the flow velocity, are on the same curve. Frictional charging owing to131collisions is inversely proportional to the collision speed because the contact area changes withthe collision speed (Masuda et al. 2002). During this measurement, the rectifying wire mesh in
the downstream was not installed, and the collision between the particles and the agitator plate
downstream of the ejector was the main cause of the dust charging. These collisions were notaffected by the velocity of the flow in the duct because the velocity of the exhaust gas from theejector was constant.
It was found that when the dust feed rate was adjusted to change the dust concentration, thedust charge was also unchanged. For the relationship between the dust concentration value andthe amount of charge, a relationship equation specific to this test duct was obtained.
27.0
𝑞𝑎 = 𝐶 0.4(7)𝑚

where qa is the actual charge (µC/g ), and Cm is the dust concentration based on the gravimetricmeasurement (mg/m3).
3.3 Effect of change in charge of the test dust on the dust meter readings
The results are shown in Fig. 6. An approximate line was added as an eye guide. There wasno linear relationship between the gravimetric measurements and the dust meter readings, butrather a curvilinear relationship where the higher the concentration, the lower the indicatedvalue. With the regression curve at a flow rate of 12 m/s as a reference, the regression curve at
a flow rate of 16 m/s was comparable, whereas the regression curve at a flow rate of 8 m/s
tended to be slightly lower. These were most likely caused by the difference in dust chargeduring the test. Therefore, because there is a relationship between the dust concentration andthe dust charge during the test, as shown in Eq. (7), and according to the detection theory of theelectrostatic detection method shown in Eq. (5), the indicated values of the dust meter andcharge have a proportional relationship, i.e. the relationship between the readings obtained
under the standard charging conditions (qs = −10 µC/g is used) and the readings obtained fromthe actual test can be expressed as follows:|𝑞 |𝑅𝑎 = |𝑞𝑎 | 𝑅𝑠𝑠(8)

where Rs indicates the dust meter reading obtained under the reference charging condition(mg/m3 RC), Ra is the dust meter reading obtained during the actual test (mg/m3 RC), qs is thereference charge (µC/g), and qa is the actual charge (µC/g ).
Fig. 7 shows the results of removing the effect of charge variation from the respective
readings using the correction equation for removing the effect of the charge variation, i.e. Eq.
(8). A linear relationship between the gravimetric measurements and the converted dust meterreadings was found to be normal. It can be seen that the change in the charge of the test dust
caused by the change in the test condition settings of the test duct has a non-negligible effecton the dust meter readings. It was found that the higher the dust concentration, the lower the
charge per particle, and the curvilinear nature of the relationship made it impossible to evaluate
the equivalence through a gravimetric measurement. It was thought that if the relationshipbetween the amount of charge of the test dust and the dust concentration specific to each duct
was obtained in advance, it would be possible to evaluate the equivalence based on gravimetricmeasurements by measuring the amount of charge of the test dust during the test and removing
the effect of any charge fluctuations from the dust meter readings.
132

Figure 7: Relationship between
dust concentration and dust meterreadings with the effect of charge
variation removed

Figure 5: Relationship between
dust concentration and dust
charge4

Figure 6: Relationshipbetween dust concentration anddust meter readings

Conclusion

In this study, the relevance of the standard and operational considerations for the performance
evaluation of dust meters using the test ducts specified in the newly developed JIS standard are
discussed. In this paper, we focus on the issues in the measurement of a probe electrification
type dust meter. As a result, the following points are found:・It was confirmed that the test dust in the test duct was electrically charged. The cause of thiswas assumed to be the structural origin i.e. the frictional charging of the agitator plate andthe rectifying wire mesh.
・The dust charge changes as the test conditions are changed. The effect of changing the dust
concentration was larger than that of changing the flow rate, and there was an inverse
proportional relationship between the dust concentration and the charge.
・The change in the dust charge undermined the linear relationship between the dust meterreadings and the gravimetric measurement, and a curvilinear relationship was observed inwhich the higher the dust concentration, the lower the dust readings.
・By removing the effect of the difference of dust charges, a linear relationship was obtained.
In summary, it was found that it is necessary to measure the dust charge and compensate it
appropriately when conducting the equivalence test when using this test duct. In addition, it isdesirable to take measures to fundamentally reduce the dust charge generated.
Acknowledgment
Prof. Lenggoro of Tokyo University of Agriculture and Technology provided the equipment
for the ELPI measurements. We would like to express our gratitude to the reviewers. This study
was supported by a JSPS Grant-in-Aid for Scientific Research 19K12375.

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133

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