JPS6255622B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bipolar current probe that simultaneously and separately measures positive ion current density and negative ion current density in an electric field where both positive ions and negative ions coexist.

For example, in an electrostatic precipitator that collects dust with extremely high electrical resistance, the voltage drop of the dust layer deposited on the dust collection electrode becomes excessive, causing dielectric breakdown, and from this, negative polarity is emitted. So-called reverse ionization, which causes an abnormal positive corona discharge toward the electrode, has been a factor that significantly inhibits dust collection performance. This is because the negative charge of the dust charged by the impact of the negative ion current from the negative corona discharge of the discharge electrode is neutralized and reduced by the positive ion current supplied by the abnormal positive corona discharge. This is because the Coulomb force required for dust collection is greatly reduced.
In this case, the electric charge Q of the dust is the ratio β of the positive ion current density i+ to the negative ion current density i- with respect to the ideal value Q _O obtained by negative ions from the discharge electrode during normal operation without the occurrence of back ionization. Even if i- is only 10%, it will drop to 50%, and β will be 20%, 30%, 40
%, the charge Q becomes 30% of Q _O , 20
%, it decreases by a wide range of 10%, resulting in a significant decrease in dust collection performance. In order to investigate such abnormal phenomena, understand the extent of their inhibition, and appropriately control the voltage and current of the precipitator based on this, it is necessary to investigate the electric field where both positive and negative ion currents coexist. Among them, it is necessary to separately measure the positive ion current density i+ and the negative ion current density i-.
However, in the past, such separate measurements have been considered impossible, and as a result, major difficulties remain unresolved to this day.

The present invention provides a means that enables separate measurement of positive and negative ion current densities in an electric field, which was previously impossible. The present invention thus accomplishes this with a bipolar current probe device as described below.

That is, the novel bipolar current probe device according to the present invention has a small imaginary surface having a plane-symmetrical shape with respect to a certain plane of symmetry, and a rectangular shape having a small width on the intersection line S where the plane of symmetry intersects. A center electrode C is insulated and arranged on the imaginary planes on both sides thereof, symmetrically with respect to the intersection line S, so as to substantially cover the entire imaginary planes on both sides, and with a constant distance from the center electrode C. Measuring electrodes A and B are insulated and arranged at a small interval to form one three-electrode probe, which is insulated and supported by a supporting hollow metal column, and an insulated conductor wire is connected to each of the electrodes C, A, and B. These conductors are insulated through the interior of the support metal pillar, and the other ends of these conductors are connected to _the terminals of microammeters _{D C} , D _A , and D _B , respectively _. The other terminal and the supporting hollow metal column are connected to a common conductive wire, and this is connected to a variable DC power source to configure one measurement system,
Insert the three-electrode probe into a measurement point in an electric field where positive ion current and negative ion current coexist, and point one of the A and B electrodes toward the negative ion source and the other toward the positive ion source so that they are symmetrical. The probe is arranged so that its surface is perpendicular to the direction of the electric field, and by changing the voltage V of the variable DC power supply, the potential of the electrodes C, A, and B of the three-electrode probe and the supporting hollow metal pillar can be changed. Center electrode C
Make sure that the current I _C of the ammeter D _C connected to the electrode becomes substantially zero, and then find the readings of the currents I A and I B of the ammeter D _A and D _B connected to the electrodes _A and _B at that time. I
_The present invention is characterized in that the positive and negative ion current densities are measured simultaneously and separately from the values of I _A and I _B by utilizing the fact that the values of A and I _B are each substantially proportional to the positive and negative ion current densities.

In this case, the electrodes A, B, and C may be insulated from each other with a suitable insulator and held in a predetermined shape. It may be used as a carrier, and electrodes A, B, and C may be further deposited, plated, or
The deposit may be formed by thick film technology, application of conductive paint, or the like. In addition, three microcurrent meters D _C , D
Instead of using _A and D _B , only one ammeter is used,
Switch this to I _C , I _A , I _B
may be measured. Also, instead of determining the equilibrium point of I _C =O by manually changing V while looking at I _C , the output signal of D _C is fed to the variable DC power supply, and V is changed by automatic control to determine I _C =O may be set. Furthermore, instead of determining the positive and negative ion current density using I _C =O, the relationship curve between V and I _C may be determined manually or automatically, and the positive and negative ion current density may be determined from this using the method described below.

The features and structure of the present invention will be explained in detail below with reference to embodiments and drawings.

FIG. 1 is a perspective view showing the structure of a cylindrical bipolar current probe in which the above-mentioned virtual surface is a cylindrical surface according to an embodiment of the present invention, particularly the structure of the three-electrode probe part, and FIG. 2 is a longitudinal sectional view thereof. Figure 3 is its cross-sectional view. FIG. 4b is an external view of the three-electrode probe portion. Needless to say, the virtual cylindrical surface described above is plane symmetrical with respect to a plane passing through its central axis, and the intersection lines S thereof become two straight lines on the cylinder that are symmetrical with respect to the central axis. Elongated strip-shaped electrodes C ₁ and C ₂ are provided on the cylindrical surface with this straight line as the center line, and are interconnected by a conductive wire 1 to form one center electrode C. However, in this figure, the insulators that insulate and support all the electrodes are omitted and are not drawn. Two semi-cylindrical measuring electrodes A and B are insulated on the cylindrical virtual surface and spaced apart from each other by a smaller distance on both sides of C ₁ and C ₂ , and the measuring electrodes A and B are placed in the center. Together with the electrode C, a cylindrical three-electrode probe 2 is formed. 3
is a cylindrical supporting hollow metal column in this example which is coaxial with the probe and has the same outer diameter, and supports the three-electrode probe 2 via an insulator not shown in the figure. In addition, 4 is a guard electrode consisting of a metal cup of the same outer diameter installed coaxially and insulated with the three-electrode probe 2 to prevent electric field concentration at the other end of the three-electrode probe 2, and a conductor 5 is connected to the hollow metal pillar for supporting the three-electrode probe 2. Connected to 3.

The center electrodes C ₁ -C ₂ and the measurement electrodes A and B are three conductive wires 6 passing through the interior of the supporting hollow metal column 3.
7 and 8. The conductive wires are guided to the outside of the hollow metal column 3 through the base outlet 9 and are connected to one ends of minute ammeters D _A , D _C , and D _B , respectively.
The other end of the ammeter is connected to conductors 6', 7', 8', and a conductor 10 connected to the supporting hollow metal column 3.
At the same time, it is connected by a common conducting wire 11 to a negative terminal of a variable DC high voltage power supply 12 whose positive terminal is grounded in this example. 13 is a voltmeter that indicates the terminal voltage of the power source 12;

Now, insert the three-electrode probe part 2 through the supporting hollow metal column into a measurement point in an electric field where positive ion flow and negative ion flow coexist, and as shown in FIG.
Electrode A is supported toward the negative ion source and electrode B toward the positive ion source so that the symmetry plane 14 including the center line of electrodes C ₁ -C ₂ of the electrode probe is perpendicular to the electric field E.
Now, the voltage V of the variable DC high voltage power supply 12 is changed to make the potential of the three-electrode probe section 2 equal to the original potential of the space at the insertion point. This state is called an equilibrium state.
The potential at this time is called the equilibrium potential. At this time, the lines of electric force indicated by the contact point 14' are completely vertically symmetrical with respect to the plane of symmetry 14 as shown. However, in this figure, the electric lines of force enter electrode B from below and exit upward from electrode A. In this case, the number of electric lines of force entering electrode B completely matches the number of lines of electric force exiting from electrode A. Further, in electrodes C ₁ and C ₂ , the number of electric lines of force entering and the number of lines of electric force going out are equal, so the total is zero.

Positive ions flow into the electrode B from below along the lines of electric force, and the total positive ion current I+ is indicated on the ammeter D _B as a positive current I _B =I+. Further, the negative ion current flows into the electrode A from above along the lines of electric force, and the total negative ion current I- is indicated to the ammeter D _A as a negative current I _A =I-. Positive and negative ion currents I _B flowing into electrodes B and A under equilibrium conditions
=I _+O , I _A =I _-O is called equilibrium ion current. When the positive ion current density i+ and the negative ion current density i- are different, a small current I _CO flows through the electrodes C ₁ - C ₂ even in an equilibrium state, and I _CO is positive when i+ > i-. , i-<i+, it becomes negative, but in any case, if the width of the center electrode is made sufficiently small, I _CO takes an extremely small value. Under this equilibrium state, the positive and negative ion current densities to be measured i+, i- [A/
m ² ] and the positive and negative balanced ion currents I _+O and I _-O [A] detected at the electrodes B and A, the following relationship holds theoretically.

I _+O = 4alCos (d/2a) i + [A] (1) I _-O = 4alCos (d/2a) i - [A] (2) where a = cylinder radius [m], d = center electrode C ₁ ,C ₂
width [m], l = axial length of electrodes A, B, C ₁ , C ₂ [m].

In other words, the equilibrium ion currents I _+O and I _-O are i+, i
-, and immediately i from the measured values of I _+O and I _-O
+, i- can be obtained. Next, there are the following methods for setting the equilibrium state. The first method is extrapolation. Currents from electrodes C, A, and B while changing V, I _C , I _A =I-, I _B =I
When + is measured, the curves I _C , I _A , and I _B shown in FIG. 5 are obtained. Each of these curves consists of two straight parts and a curved part in between. and the curve I _C
The intersection point _P of the _{extrapolation of} the straight line _part of Give accurate equilibrium ion currents I _+O and I _-O . At this time, as shown in the figure, a small equilibrium ion current I _CO flows through the electrodes C ₁ -C ₂ . I _+O , I by extrapolation
_-O determination can be immediately and automatically performed by a pre-programmed computer.

Another method for setting an equilibrium state is the pseudo-equilibrium method. That is, the equilibrium potential V _O has a potential V _O ' (point Q) at which the current I _C from the center electrode C is zero
Approximate. This is called a pseudo-equilibrium potential. The values of I _{B and} I _A at this time I _+O ′, I _-O ′ are called pseudo-equilibrium ion currents, and the true equilibrium ion currents I _+O , I _-O
As approximate values of , i− and i+ are obtained by substituting them into equations (1) and (2). The accuracy of this method increases as the width of the center electrode C becomes narrower, but the detection sensitivity of I _C=O decreases accordingly. Therefore, as a way to solve this problem, the width of electrode C is increased to a certain extent, and the values of positive and negative pseudo-equilibrium ion currents I _+O ′ and I -O ′ obtained at measurement electrodes B and _A when _{I C=O} are The correct positive and negative equilibrium ion currents I _{+ O = k + I +O ' are obtained by multiplying them by the theoretically determined correction coefficients k + and k -} (given theoretically as a function of the ratio of I _B and I _A ), respectively. A method for determining I-=k _- I _-O ' can be used. Furthermore, the determination of I _+O and I _-O by the pseudo-equilibrium method, including this correction operation, can be immediately executed by a pre-programmed computer.

FIG. 6 is a longitudinal cross-sectional view of a spherical bipolar current probe, which is an example in which the present invention can be practiced using a spherical surface as the above-mentioned virtual surface, and FIG. 4a is a side view of the three-electrode probe portion thereof. In the figure, 2 is a three-electrode probe part, and the intersection line S where the spherical virtual surface intersects with one symmetry plane 14 forms one equatorial curve, and with this as the center, a small annular central electrode C, Hemispherical measurement electrodes A and B, which are symmetrical to each other on both sides of the virtual spherical surface, are insulated and spaced apart from the center electrode C by an equal small distance. The names and functions of the elements numbered 3 to 13 in the figures are shown in Figure 1, Figure 2,
It is the same as that of the elements with the same numbers in FIGS. 3 and 4b. The principle and operation of this embodiment are the same as those of the cylindrical type described above, and are self-evident from the above explanation, so the explanation thereof will be omitted. However, in this spherical bipolar current probe, there is no guard electrode 4, and when V is made to match the equilibrium potential V _O , the positive and negative equilibrium ion currents detected by both measurement electrodes B and A are I _B =I _+O [A], I _A =I _-O There is the following theoretical relationship between [A] and the positive and negative ion current densities i+, i- [A/m ² ].

I _+O = 3πa ² cos ² (d/2a) i + [A] (3) I _-O = 3πa ² cos ² (d/2a) i - [A] (4) where a = sphere radius [m], d=width of center electrode C [m]. Therefore, i+ and i- can be obtained immediately from the measured values of I _+O and I _-O . The method for setting the equilibrium state is exactly the same as for the cylindrical bipolar current probe described above. This spherical bipolar current probe has a 3-electrode probe part 2 that is spherical, so i+, i- at a certain point in a three-dimensional electric field.
However, since the supporting hollow metal column 3 causes disturbances in the electric field and ion current, it is necessary to make the column 3 as thin as possible.

FIG. 4 is a diagram showing examples of various three-electrode probe sections 2, and in FIG.
B is constituted by circular electrodes with a radius slightly smaller than that provided on the circular planes above and below. In addition, in Figure d, the virtual plane is a square prism, and the center electrodes C ₁ and C ₂ are rectangular electrodes provided on both sides, and measurement electrodes A and B.
has rectangular electrodes provided on its upper and lower surfaces, and in this example, the guard electrode 4 and the supporting hollow metal column 3 are both square prisms.

By using the bipolar current probe according to the present invention, it is possible to detect the occurrence of back ionization and its degree of failure with extremely high sensitivity and accuracy, so this can be used to automatically control various electrostatic precipitators to suppress back ionization. It can be performed.

FIG. 7 shows an example of this, in which a new cylindrical bipolar current probe according to the present invention is shown in another invention of the present inventor, ``Pulse Charging Type Electrostatic Precipitator'' (Patent Application No. 51-073004).
Fig. 1 shows a system diagram of a device that can be used as a detection unit for optimal control of the invention (Japanese Patent Application Laid-open No. 52-156473). In the figure, 15 and 15' are grounded dust collecting electrodes, 16
A negative DC high voltage Vdc, which is slightly lower than the corona starting voltage V _C , is applied by a DC high voltage power supply 17 via a conductor 18 to a discharge electrode that is insulated between the two electrodes, and a dust collection space 19 is created between the two electrodes. , 19' is the main electric field E
Create. At the same time, a negative pulse voltage 20 having a pulse width τ _P , a peak value V _P , and a frequency _P is supplied to the discharge electrode 16 from the pulse power source 21 via the conductor 22 and the coupling capacitor 23 superimposed on Vdc. As a result, a pulsed corona discharge occurs in the discharge electrode 16 only when the pulse is applied, and a negative ion current flows toward the dust collecting electrode 15.
Therefore, the dust particles that have entered the dust collection space 19 are bombarded with this negative ion current and become negatively charged.
The dust is driven and removed by the dust collection electrodes 15, 15' under Coulomb force by the action of the main electric field E, and is deposited thereon to form dust layers 24, 24'. 25 is a rectifying element that prevents the pulse voltage 20 from entering the DC high voltage power supply 17. If the electrical resistance of the dust to be collected is high, the dust layers 24 and 24' will act as an insulating layer against the negative ion current, and a significantly large voltage drop will occur between both ends, eventually leading to dielectric breakdown. A positive corona is generated from there toward the dust collection space, and a reverse ionization phenomenon occurs. As a result, a positive ion current flows from here, which neutralizes the dust negative charge necessary for dust collection, significantly impairing the dust collection performance. In order to operate the above-mentioned pulse charging type electrostatic precipitator while completely preventing this reverse ionization phenomenon, the occurrence of reverse ionization is detected, and the pulse width τ _P of the pulse voltage 20, the pulse wave peak voltage V _P , or By controlling the pulse frequency _P , the negative ion current density i- is narrowed down,
The average value - is set to -xρd<Eds (5) (where Eds = dielectric breakdown electric field strength of the dust layer) with respect to the electrical resistivity ρd of the dust layer, thereby preventing dielectric breakdown of the dust layer.

The DC voltage Vdc is controlled so that the main electric field strength E is always kept below a constant value E _p that suppresses the growth of back ionization and its propagation over a wide area.

It is necessary to drive while satisfying the following two conditions.

26 is a new bipolar current probe according to the present invention used for this reverse ionization detection, and the discharge electrode 1
6. It is inserted from above into the dust collecting space 19' between the dust collecting electrodes 24' in parallel thereto. However, the three-electrode probe part 2 is shielded from the electric field by a wire mesh 27 connected to the supporting hollow metal column 3, while allowing the passage of positive and negative ion currents, and the induced noise voltage caused by the pulse voltage 20 is transmitted to each probe A, This prevents B and C from being detected. Further, a negative DC voltage is applied to the probe 26 from the variable DC power supply 12 via the conductor 10, but a bypass capacitor 28 is connected in parallel to the power supply 12, and a pulse voltage is applied to the wire mesh 27 and the supporting hollow metal column 3. The noise voltage induced by the sensor 20 is dissipated to the ground, so that the noise voltage does not substantially interfere with the measurement results. In this case, in order to completely prevent noise, it is preferable to adopt a double shield system in which the supporting hollow metal column 3 and the wire mesh 27 have a double structure. Now, the three-electrode probe section 2 at the tip of this probe is positioned at the measurement point, and the plane of symmetry containing the center electrode C is made perpendicular to the electric field as described above. At this time, the ion current I _C flowing into the center electrodes C ₁ and C ₂ is detected and amplified by the current detection control device D _C ', and its output signal is fed back to the voltage adjustment section of the variable DC power supply 12 via the conductor 29. The output voltage V is automatically controlled so that I _C becomes zero, achieving a pseudo-equilibrium state. At this time, the positive and negative pseudo-balanced currents I _B =I _+O ′, I _A =I _-O ′ flowing into the measurement electrodes B and A are detected by minute current detection devices D _B ′ and D _A ′, and their output signals are Furthermore, the signal processing conversion device 3 is connected by conductors 30 and 31.
2, and after calculating the correction coefficients k+ and k- according to the ratio I _+O ′/I _-O ′, the correct equilibrium ion current I
_+O =k ₊ I _+O ' and I _-O =k-I _-O ' are calculated, and these positive and negative ion current densities i+ and i- are determined.
In order to transmit these from the signal processing conversion device 32 at a high potential to the control section at ground potential, i+ and i- are converted into optical signals, which are sent to the power supply control section 34 via the optical fiber 33. The control unit 27 uses the value of i+ or the ratio of i+/i- as a control variable, and sends a control signal to the conductor 3 so that this value is zero or less than a predetermined constant value close to zero.
5 and 36 to the DC high-voltage power supply 17 applying DC voltage to the discharge electrode 16 and the pulse power supply 21 supplying pulse voltage to the discharge electrode, and transmitting the DC voltage Vdc and the peak value V _P of the pulse voltage. , pulse width τ _P , or pulse frequency _P are automatically controlled so as to provide optimum values, that is, the largest main electric field strength and negative ion current density i- within the range that suppresses the occurrence of back ionization.

In addition, the novel bipolar current probe device according to the present invention can be used for automatic control of all types of electrostatic precipitators (for example, three-electrode electrostatic precipitators having a third electrode in addition to the discharge electrode and the collection electrode). It can be used to control body coating systems, electrostatic separation, etc.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the main structure of an embodiment of the novel bipolar current probe device according to the present invention;
The figure is a longitudinal cross-sectional view thereof, and FIG. 3 is a cross-sectional view thereof. FIG. 4 is an external view showing various configurations of the three-electrode probe section which is the main part of the present invention, FIG. FIG. 2 is a vertical cross-sectional view showing one embodiment. FIG. 7 is a system diagram of a system in which optimal control of a pulse charging type electrostatic precipitator can be realized by using the novel bipolar current probe device according to the present invention as a reverse ionization detection device. The main parts in the figure are as follows. 1, 5, 6, 6', 7, 7', 8, 8', 10,
11, 18, 22, 29, 30, 31, 33, 3
5, 36...Conducting wire, 2...3 electrode probe part,
A, B...Measurement electrode, C, _C1 , _C2 ...Center electrode, 3...Hollow metal column for support, 4...Guard electrode, D _A , D _B , D _C ... Microcurrent meter, D _A ′、D _B ′
...Minute current detection device, D _C ′ ...Current detection control device, 12 ...Variable DC power supply, 13 ...Voltmeter, 1
4... Symmetry plane, 15, 15'... Dust collection pole, 16...
...Discharge electrode, 17...DC high voltage power supply, 19, 19'
... Dust collection space, 21 ... Pulse power supply, 23 ... Coupling capacitor, 24, 24' ... Dust layer, 2
5... Rectifying element, 26... Bipolar current probe device, 27... Shield wire mesh, 28... Bypass capacitor, 32... Signal processing conversion device, 33
...Optical fiber, 34...Power control unit.

Claims (1)

[Claims] 1. An elongated central electrode C having a small width is insulated and disposed on a cross line S where a small virtual surface having a plane-symmetrical shape with respect to a plane of symmetry intersects the plane of symmetry. Measurement electrodes are placed on the imaginary planes on both sides thereof, symmetrically with respect to the intersection line S, so as to substantially cover the entire imaginary planes on both sides, and spaced apart from the center electrode C by a certain small distance. A and B are arranged insulated to form one three-electrode probe, which is insulated and supported by a hollow metal pillar for support, and insulated conductive wires are connected to electrodes C, A, and B, respectively, and these are connected to the support. The insulation is penetrated through the interior of the hollow metal column, and the other ends of these conductors are connected to the terminals of minute current meters D _C , D _A , and D _B , respectively.
Another terminal of _C , D _A , D _B and the supporting hollow metal column are connected to a common conductive wire, and this is connected to a variable DC power supply to configure one measurement system, and the three-electrode probe Insert the electrode into a measurement point in an electric field where positive ion current and negative ion current coexist, and point one of the A and B electrodes toward the negative ion source and the other toward the positive ion source so that the plane of symmetry is in the electric field. arranged perpendicular to the direction,
By changing the voltage V of the variable DC power supply, the potentials of the electrodes C, A, B of the three-electrode probe and the supporting hollow metal column are changed, and the current of the microammeter D _C connected to the center electrode C is changed. Make sure that I _C becomes substantially zero, and then obtain the readings of the currents I A and I B of the microammeters D _A and D _B connected _to electrodes _A and B, and calculate the values of I _A and I _B. I _A and I _B are substantially proportional to the positive and negative ion current densities, respectively.
A bipolar ion current probe device characterized in that positive and negative ion current densities are measured simultaneously and separately from the values of . 2. An elongated center electrode C having a small width is insulated and arranged on the intersection line S where a small virtual plane having a plane-symmetrical shape with respect to the plane of symmetry intersects the plane of symmetry, and Measuring electrodes A and B are insulated and arranged on the virtual plane symmetrically with respect to the intersection line S so as to substantially cover the entire virtual plane on both sides and spaced apart from the center electrode C by a certain small distance. This is insulated and supported by a supporting hollow metal column, and insulated conductive wires are connected to each of the electrodes C, A, and B, and these are passed through the inside of the supporting hollow metal column. Penetrate the insulation and connect the other ends of these conductors to the terminals of microcurrent meters D _C , D _A , and D _B , respectively.
Another terminal of _C , D _A , D _B and the supporting hollow metal column are connected to a common conductive wire, and this is connected to a variable DC power supply to configure one measurement system, and the three-electrode probe Insert the electrode into a measurement point in an electric field where positive ion current and negative ion current coexist, and point one of the A and B electrodes toward the negative ion source and the other toward the positive ion source so that the plane of symmetry is in the electric field. arranged perpendicular to the direction,
By changing the voltage V of the variable DC power supply, the potentials of the electrodes C, A, B of the three-electrode probe and the supporting hollow metal column are changed, and the current of the microammeter D _C connected to the center electrode C is changed. Make sure that I _C becomes substantially zero, and then obtain the readings of the currents I A and I B of the microammeters D _A and D _B connected _to electrodes _A and B, and calculate the values of I _A and I _B. I _A and I _B are substantially proportional to the positive and negative ion current densities, respectively.
A bipolar ion current probe device, which is characterized by simultaneously and separately measuring positive and negative ion current densities from the values of An automatic control device for electrostatic precipitators that automatically controls the output of the power supply that applies voltage to the device.