JP2006162581A - Capacity measuring device for measuring particulates - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the precise measurement of the amount of fine particles by eliminating the influence of a relative dielectric constant by a pressure applying to air or gas for transferring the fine particles. <P>SOLUTION: A measurement electrode is mounted on a fine particle transferring pipe with the pressure of air or gas applied thereto and a reference electrode is mounted closely thereto. Both the measuring electrode and reference electrode undergo the changes of the relative dielectric constant by changes in air pressure. Both the measurement electrode and reference electrode are a same length along the passage of the fine particles. The electrode area of the reference electrode is N times as large as the electrode area of the measurement electrode. By increasing a voltage or a current signal obtained from the measurement side by N, a difference between the increased voltage or the current signal and a voltage or a current signal obtained from the reference electrode side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a capacitance measuring device for powder measurement that measures the flow rate of powder conveyed by compressed air or compressed gas as a change in capacitance, and in particular, the dielectric constant of air or gas due to pressure applied to air or gas. The present invention relates to a technique for accurately measuring the amount of powder by removing the influence of rate change.

  A capacitance measuring device for measuring powder that passes the amount of powder between electrodes and measures the change in capacitance is the relative permittivity of air or gas due to the pressure applied to the air or gas carrying the powder. There is a problem that the amount of powder cannot be accurately measured because of a large change, and an accurate capacitance measuring device for powder measurement that is not affected by the pressure of air or gas is desired.

  The capacitance sensor used for measuring the amount of powder obtains the amount of powder by calculating the difference in capacitance between the measurement electrode and the reference electrode. The measurement electrode and reference electrode shown in FIG. 14 constitute an AC bridge circuit. When the powder enters the measurement electrode side, the capacitance changes to C + ΔC. The capacitance on the reference electrode side does not change. The amount of powder can be determined from ΔC for the difference in capacitance between the measurement electrode and the base electrode.

However, as shown in FIG. 15, compressed air is introduced into the powder supply tank, and the powder is often conveyed by opening and closing the valve. For this reason, the reference electrode is not subjected to a pressure change, but a high air pressure is applied to the measurement electrode side, and the relative dielectric constant of the air is greatly changed.
It is very difficult to calculate the capacitance precisely in consideration of the electric polarization of the powder when the powder is in the capacitance sensor. And not.

となる。上式の３項と４項は非常に大きな誤差となる。
空気の圧力変化がない時、上式はε_ｍ１、＝ε_ｒ１＝ε_１なので、以下のようになる。

一般的に粉体による、測定電極の静電容量の変化は数％程度であり、粉体が微小になるとさらに小さい変化となる。16 and 17 show a measurement electrode and a reference electrode for simple calculation. In FIG. 16, assuming that a square columnar powder having a length of t is parallel to the electrode on the measurement electrode, the composite capacitance is obtained by simple calculation by dividing each capacitance. In the figure, the electrostatic capacity of air and powder in the t portion are connected in series, and the electrostatic capacity of air other than the t portion is calculated as parallel connection.
If the relative permittivity of air on the measurement electrode side is ε _m1 and the relative permittivity of air on the reference electrode side is ε _r1 , the difference Δ in capacitance between the measurement electrode and the base electrode is

It becomes. The terms 3 and 4 in the above formula are very large errors.
When there is no change in pressure of air, the above equation is ε _m1 , = ε _r1 = ε _1, so that

Generally, the change in the capacitance of the measurement electrode due to the powder is about several percent, and the change becomes smaller as the powder becomes finer.

Ｎは電気双極子密度（気体分子密度）、ｅは電子の電荷、ｘは＋ｅと−ｅの電荷対間の距離

となり、これを、
Ｄ＝ε_０ε_ｒＥ
とすると、比誘電率ε_ｒは

となる。

従って、電気双極子の密度Ｎが大きいほど比誘電率ε_ｒは大きくなる。From the literature of electromagnetism, the electric flux density D in a gas, ₀ the dielectric constant of vacuum _epsilon, the electric polarization of the gas molecules to P D = ε _{0 E} + P
The electric polarization P in the above equation is

N is the electric dipole density (gas molecule density), e is the electron charge, x is the distance between the + e and -e charge pairs.

And this
D = ε ₀ ε _r E
Then, the relative dielectric constant ε _r is

It becomes.

Therefore, the relative dielectric constant ε _r increases as the density N of the electric dipole increases.

気体の比誘電率を圧力の関係式で表すと

となり、気体の比誘電率は圧力に比例して変化する。空気の比誘電率は２０°Ｃ、１気圧で１．０００６である。Next, when the pressure P is expressed by a relational expression of gas molecule motion,

When the relative dielectric constant of gas is expressed by the relational expression of pressure,

Thus, the dielectric constant of the gas changes in proportion to the pressure. The relative dielectric constant of air is 1.0006 at 20 ° C. and 1 atmosphere.

  Both the measurement electrode and the reference electrode are configured to receive a change in relative dielectric constant due to a change in air pressure. The measurement electrodes and the reference electrodes have the same length along the powder flow path. The electrode area of the reference electrode is set to twice the electrode area of the measurement electrode. Further, the voltage or current signal obtained from the measurement electrode side is doubled to obtain a difference from the voltage or current signal obtained from the base electrode side. As a result, it is possible to obtain only a change in capacitance due to the powder without being subjected to a change in air pressure.

This will be described below with reference to FIG. In the t portion of the measurement electrode, the capacity of air with a dielectric constant ε ₁ is C ₁ , and the capacity of powder with a dielectric constant ε ₂ is C ₂ . capacitance C ₀ of the total and the capacitance other than t parts and C ₃ is

基準電極の電極面積は測定電極の電極面積の２倍である。同様に基準電極側の全体の容量をＣ_ｒ０とすると

となる。If the total capacitance on the measurement electrode side is C _m0

The electrode area of the reference electrode is twice the electrode area of the measurement electrode. Similarly, if the total capacitance on the reference electrode side is C _r0

It becomes.

測定電極と基準電極には同じ圧力が加わるので比誘電率ε_１は同じである。従って、圧力変化のない時と同じとなる。The capacitance C _m0 of the measurement electrode is doubled, and the difference Δ from the capacitance C _r0 of the reference electrode is calculated.
Δ = 2C _m0 −C _r0

Since the same pressure is applied to the measurement electrode and the reference electrode, the relative dielectric constant ε ₁ is the same. Therefore, it is the same as when there is no pressure change.

  According to the present invention, it is possible to eliminate the influence of the change in the dielectric constant due to the change in the pressure of the air that carries the powder. Therefore, even if the powder is conveyed by applying a high air pressure, the amount of the powder can be stabilized. It can be measured.

BEST MODE FOR CARRYING OUT THE INVENTION

  As shown in FIG. 1, a base electrode is attached adjacent to the measurement electrode attached to the powder transport pipe. The closer the mounting interval is, the better. The measurement electrode and the reference electrode have the same length along the powder flow path. The electrode area of the reference electrode is doubled compared to the measurement electrode. Next, the electric signal on the measurement electrode side is doubled.

  FIG. 2 is a schematic view of a capacitance sensor formed in a spiral shape. 1 is a measurement electrode and 2 is a reference electrode. In these, the measurement electrode pattern 4, the reference electrode pattern 6, the guard electrode patterns 3, 3 ', 5, 5' and the earth electrode 7 formed on the measurement electrode and the base electrode are formed in a cylindrical pipe. The pattern width of the reference electrode is twice the pattern width of the measurement electrode. The length in the direction that the powder passes is the same.

FIG. 3 is a schematic diagram of a circuit of the capacitance sensor. In this example, the resistance 10 on the measurement electrode side is 2R, and the resistance 10 ′ on the reference electrode side is R, thereby doubling the signal voltage on the measurement electrode side. From these signal voltages, the difference between the measurement electrode and the reference electrode is calculated to obtain the difference Δ in capacitance.
In the case of a spiral shape as shown in FIG. 4, it is considered that the opposing electrode pattern is formed by continuously forming approximately rhombic parallel plane plate capacitors with the central axis of the cylinder symmetrical as shown in FIG. I can do it. It also shows that when the pattern width is doubled, the area is also doubled.

In FIG. 6, the spiral pattern is approximately replaced with a parallel plane plate capacitor so that the calculation can be easily performed as a parallel plane plate capacitor with uniform electric field strength.
Capacitance sensor is a spiral structure formed in a cylindrical pipe, and because it is not uniform electric field strength, it is difficult to produce an accurate capacitance, but the electrode area of the measurement electrode and the base electrode It is sufficient that the ratio is approximately doubled. For errors such as manufacturing variations in the electrode area ratio, the amplification factor of the signal voltage may be adjusted.

In this example, the outside of the capacitance sensor shown in FIG. 2 is covered with a guard shield electrode shown in FIG. 7 and connected to the guard shield.
By configuring the guard shield electrodes 3a and 5a in the vicinity of the cylindrical pipe, the guard electrode patterns 3, 3 'and 5, 5' can be omitted as shown in FIG.

Next, an outline of the operation of the capacitance sensor circuit shown in FIG. 3 will be described. The capacitances of the measurement electrode and the reference electrode constitute resistors 10 and 10 ', respectively, and differential circuits.
Voltage drop _{e m} and _{e r} of the resistor 2R and R of the output voltage and the _e osc _{= E} m _sinωt measuring electrode side and the reference electrode side of the AC oscillator 19

となる。交流発振器１９から流れる電流は各々の静電容量インピーダンスに比例する。従って、測定電極側の信号電圧は基準電極側の信号電圧の２倍になる。電極面積比の製造バラツキ誤差による静電容量インピーダンスのバラツキ誤差は図示していないが前述の抵抗の１部を可変抵抗にする事により調整出来る。The frequency of the AC oscillator 19 is set to be 1 >> jωC _m0 2R, 1 >> jωC _r0 R.

It becomes. The current flowing from the AC oscillator 19 is proportional to each capacitance impedance. Therefore, the signal voltage on the measurement electrode side is twice the signal voltage on the reference electrode side. Although the variation error of the capacitance impedance due to the manufacturing variation error of the electrode area ratio is not shown, it can be adjusted by making a part of the aforementioned resistance variable.

Signal voltage _{e m} and _{e r} is detected by the non-inverting amplifier 11 and 11 '. These outputs are connected to the guard electrode patterns 3, 3 ′ and 5, 5 ′ of the measurement electrode and the reference electrode. Although not shown, it is also connected to the shield side of the coaxial cable connecting them.
The outputs of the non-inverting amplifier are connected to the first switch circuit 13, amplified by the amplifier 14, and connected to the modulator or multiplier 15. The other input of the modulator or multiplier is connected through a phase advance circuit 20 that advances the phase of the AC voltage of the AC oscillator 19 by 90 degrees. The output of the modulator or multiplier is amplified by the filter & amplifier 16 while cutting the frequency of the AC oscillator 19. The output of the modulator or multiplier has a non-inverted output and an inverted output, but the following description is on the non-inverted output side.

上式、ｃｏｓ２ωｔの成分をフィルター＆アンプ１６でカットすると

The output of the modulator or multiplier, the signal voltage e _m of the measuring electrode side and the reference electrode _side, the AC oscillator and e _r

When the component of cos2ωt is cut by the filter & amplifier 16

ｅ_Ｍ−ｅ_Ｒ＝（２Ｃ_ｍ０−Ｃ_ｒ０）Ｋ
ｅ_Ｍ−ｅ_Ｒ＝ΔＫ

この出力は第２スイッチ回路１７とフィルター＆アンプ１８により同期検波及び増幅されて出力される。第１スイッチ回路１３及び第２スイッチ回路１７は電源周波数の整数倍の矩形発振器により駆動されている。The difference signal voltage by the first switch circuit 13 is the difference between e _M and e _{R in} the above equation.

e _M −e _R = (2C _m0 −C _r0 ) K
e _M −e _R = ΔK

This output is synchronously detected and amplified by the second switch circuit 17 and the filter & amplifier 18 and output. The first switch circuit 13 and the second switch circuit 17 are driven by a rectangular oscillator that is an integral multiple of the power supply frequency.

9 and 10 show the switching filter circuit and its frequency characteristics. As shown in FIG. 10, the synchronous detection operation has an infinite amount of attenuation at a frequency that is an integral multiple of the switching frequency. The constant decay curve is when there is no switch.
The frequency of the first switch circuit 13 and the second switch circuit 17 is synchronized with the power supply frequency, and the switching cycle is an integral multiple of the power supply frequency. As a result, it is possible to remove the induction noise from the largest power source and the noise having an integer multiple of the induced noise.

Next, FIG. 11 shows a state in which the powder flows as the valve 31 is opened and closed. FIG. 12 shows a timing chart of each operation according to the powder flow on the measurement electrode side and the reference electrode side.
When the valve 31 of (1) is opened, a high air pressure is applied. The change in the relative dielectric constant of air is indicated by the shaded area. This change has no time delay and occurs simultaneously on the measurement electrode and the reference electrode.
The response of measurement electrode (2) shows a slight delay in the change due to powder. The blackened area shows the change due to powder.
(3) is obtained by doubling the signal voltage of the measurement electrode, and the change in the dielectric constant due to the air pressure is the same as that on the base electrode side. The signal voltage due to the powder is doubled.
(4) The response on the reference electrode side is shown.
(5) indicates the difference between (3) and (4). Since the change in the relative permittivity of air is the same on both the measurement electrode side and the base electrode side, the difference is zero. However, since the amount of change in the powder is twice as large as that on the reference electrode side on the measurement electrode side, the difference can obtain the original value of one time.
(6) indicates the measurement time.

Next, the valve 31 is closed, and the measurement time is ended after the powder passes through both electrodes. The relative permittivity of air changes back, but this change is unaffected because it occurs simultaneously on the measurement and reference electrodes.
Since the total amount of powder that has passed through the measurement electrode and the total amount of powder that has passed through the reference electrode are the same, the amount of powder can be determined.

The actual amount of powder must be calculated from the flow rate, but the method for measuring the powder flow rate is not included in the present invention.
In this example, the electrode area ratio between the measurement electrode and the reference electrode is practically twice, but theoretically, it can be N times other than one.

In the second embodiment, as shown in FIG. 13, the first and second measurement electrodes are arranged with one reference electrode by arranging the measurement electrode as the first measurement electrode and the second measurement electrode on the powder conveying pipe. The amount of powder is obtained from the difference in output.
The electrode area of the second measurement electrode is doubled with respect to the first measurement electrode. The electrode area of the reference electrode may be the same as the electrode area of the second measurement electrode.
The electric signal on the first measurement electrode side is doubled, the electric signal on the second measurement electrode side is multiplied by 1, and the difference between the electric signals of the reference electrodes is taken. Find the amount.
The capacitance of the first measuring electrode C _m1, when the capacitance of the first measuring electrode C _{m @ 2,} the capacitance of the reference electrode and C _r

The difference between the first measurement electrode and the reference electrode is Δ ₁ = C _m1 −C _r
The difference between the second measurement electrode and the reference electrode is Δ ₂ = C _m2 −C _r
The difference between Δ ₁ and Δ ₂ is Δ ₀ = Δ ₁ −Δ ₂ = (2C _m1 −C _r ) − (C _m2 −C _r ) = 2C _m1 −C _m2
It becomes. Since C _m1 and C _m2 are environments with the same air pressure, they are the same as when there is no change in the dielectric constant.
In this example, the electrode area ratio between the measurement electrode and the reference electrode is practically twice, but theoretically, it can be N times other than one.

  As described above, as is apparent from the description of the embodiments with reference to the drawings, according to the present invention, a minute amount of powder is accurately measured without being affected by the pressure of air or gas conveying the powder. I can do it.

It is the schematic which shows the powder conveyance system of this invention, a measurement electrode, and a reference electrode. It is the schematic which shows the electrostatic capacitance sensor of this invention. It is the schematic which shows the electrostatic capacitance sensor circuit of this invention. It is the schematic which simplified the measurement electrode and reference electrode of this invention. It is a figure which shows the counter electrode of the helical structure of this invention. The figure which simplified the measurement electrode and reference electrode of this invention to the parallel plane plate capacitor | condenser is shown. It is the schematic which shows the structure which has the guard shield electrode and guard electrode pattern of this invention. It is the schematic which shows the structure of having removed the guard shield electrode and guard electrode pattern of this invention. The conceptual diagram of the switching filter which shows the synchronous detection operation | movement of this invention is shown. The frequency characteristic of a switching filter is shown. It is a figure which shows the condition where powder passes a measurement electrode and a base electrode through a valve | bulb. It is a figure which shows the relationship between the signal opening and measurement time of the valve opening / closing of this invention, and a measurement electrode and a base electrode. It is the schematic which shows the 3rd Example of this invention. It is a figure which shows the conventional bridge circuit. It is the schematic which shows the conventional powder conveyance system, a measurement electrode, and a base electrode. The figure which simplified the measurement electrode is shown. The figure which simplified the base electrode is shown.

Explanation of symbols

1, 1 ′ measurement electrode 1a first measurement electrode 1b second measurement electrode 2, 2 ′ reference electrode 3a guard shield electrode 3, 3 ′ guard electrode pattern 4 measurement electrode pattern 5, 5 ′ guard electrode pattern 5a guard shield electrode 6 Reference electrode pattern 7 Ground electrode 10, 10 'Resistance 11, 11' Input amplifier 12, 12 'Guard shield 13 First switch circuit 14 Amplifier 15 Modulator or multiplier 16 First low-pass filter & amplifier 17 Second Switch circuit 18 Second low-pass filter circuit & amplifier 19 AC oscillator 20 π / 4 phase advancer 21 Rectangular oscillator 30 Powder supply tank 31 Valve 32 Powder transfer pipe 33 Powder transfer receiver 34 Arithmetic circuit 1
35 Arithmetic Circuit 2
36, 36 'arithmetic circuit 3
37 Differential amplifier 38 output

Claims (6)

In a powder capacitance measuring device for measuring the amount of powder by changing the capacitance between electrodes by putting and passing between powders of a measured object between opposed electrodes by a gas conveyance system,
Capacitance measuring device for powder, characterized in that it has a measuring electrode having a guard electrode and a reference electrode having a guard electrode, and is configured as a powder conveying pipe       2. The capacitance measuring device for powder according to claim 1, wherein an electrode area ratio of the measurement electrode connected to the powder conveyance pipe and the reference electrode is N times, and the length of each electrode is the same. Capacitance measuring device for powder, characterized in that it is configured       In the capacitance measuring apparatus for powder according to claim 1 and claim 2, the voltage or current signal obtained from the measurement electrode and the reference electrode is amplified to N times the electrode area ratio of the measurement electrode and the reference electrode, Capacitance measuring device for powder, characterized in that it is configured to obtain the difference between the voltage or current signals The capacitance measuring device for powder according to claim 1 to 3, wherein an AC oscillator connected to the measurement electrode and the reference electrode;
A voltage signal obtained from the measurement electrode and the reference electrode is connected to the input side, and further, a non-inverting amplifier with a voltage follower configuration in which the shield side of the guard electrode and the coaxial cable for connection is connected to the output side,
The measurement electrode and the reference electrode are a first switching circuit that alternately switches between an AC voltage on the measurement electrode side and an AC voltage on the reference electrode side;
A phase advance circuit that advances the phase of the frequency of the AC oscillator by 90 degrees; a modulation circuit or a multiplier circuit that modulates or multiplies a signal through which the output of the first switching circuit has passed through an amplifier circuit and a signal that has passed through the phase advance circuit; A first low-pass filtering circuit that allows the output of the modulation circuit or the multiplication circuit to pass a frequency equal to or lower than the switching frequency;
An output of the first low-pass filtering circuit; a second switching circuit connected through an amplifier;
A second low-pass filter circuit connected to the output of the second switching circuit and having a frequency band corresponding to the powder speed;
The output of the low-pass filter circuit is a DC amplifier that amplifies the powder according to the amount of powder to be measured, and a powder capacitance measuring device configured to output a desired DC output voltage.       5. The electrostatic capacitance measuring device for powder according to claim 4, wherein the switching frequency is a frequency that is an integral fraction of a power supply frequency. In a powder capacitance measuring device for measuring the amount of powder by changing the capacitance between electrodes by putting and passing between powders of a measured object between opposed electrodes by a gas conveyance system,
It has a first measurement electrode and a second measurement electrode configured in the powder conveying pipe, the electrode area ratio of the first measurement electrode and the second measurement electrode is N times, and the length of each electrode Are configured identically
Capacitance measuring apparatus for powder, wherein the first measurement electrode and the second measurement electrode are constituted by a common reference electrode

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