JP3458377B2 - Capacitive electromagnetic flowmeter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitive electromagnetic flowmeter which is excited at a high frequency of 60 Hz or higher, and more particularly to a capacitive electromagnetic flowmeter improved so as to reduce the influence of noise.

[0002]

2. Description of the Related Art Various efforts have been made in electromagnetic flow meters to eliminate the influence of noise and obtain a stable flow signal, but there are various causes of this noise, and the corresponding elimination Means are different, and there are various types of electromagnetic flow meters.

As one of them, there is a Japanese Patent Laid-Open No. 8-278175 "Capacitance type electromagnetic flowmeter" as shown in FIGS. 11 and 12. FIG. 11 is a transverse sectional view thereof, and FIG. 12 is a vertical sectional view thereof.

In this example, the insulating pipe 20 is
For example, it is formed of a material such as ceramics and has a cylindrical shape. A concave portion 20A having a thin outer peripheral surface is formed in the central portion of the pipe 20 in the axial direction, and thick end portions 20B and 20C are formed on both outer sides in the axial direction.

For example, the end face portions 21A and 21B of a cylindrical case 21 made of stainless steel are formed in a ring shape, and the space between these end face portions 21A and 21B is a cylindrical portion 21C.
Are fixed by welding.

The pipe 20 is inserted into the case 21, and O-rings 22A and 22B are inserted between the end portions 20B and 20C and the end surface portions 21A and 21B to ensure airtightness. Further, a rectangular connection tube 21D is fixed to the case 21 perpendicularly to its axis, and a converter (not shown) is mounted on the rectangular connection tube 21D.

The detection electrode 23 is formed on the central surface of the recess 20A.
A and 23B are formed to face the axis of the pipe 20 in the radial direction. These detection electrodes 23A and 23B are covered with box-shaped guard cases 24A and 24B.

Further, on the surface of the recess 20A of the pipe 20, conductive guard electrodes 25A, 25B are provided over the entire surface up to the ends 20B, 20C of the pipe 20.
It is formed so as to sandwich the gaps 26 and 27 that are divided into left and right portions at the top and bottom. Then, these guard electrodes 25A, 2
5B is electrically connected to guard cases 24A and 24B, respectively.

Then, in a state of being insulated from the guard electrodes 25A and 25B by an insulating paint or the like so as to cover each of the gaps 26 and 27, a conductive damping foil 28A in a circular arc shape is formed on the peripheral surfaces thereof. 28B is fixed. The damping foils 28A and 28B are fixed to the reference potential point 30 by the lead wires 29, respectively.

The damping foils 28A and 28B are, for example,
Although it is made of copper, brass, stainless steel, etc., when the excitation frequency becomes high, the eddy current generated here becomes large when the thickness of the damping foils 28A, 28B is large,
The demagnetizing field generated by this causes the time constant of the magnetic field fluctuation to increase, and the magnetic field is not settled by the time the signal is sampled, which causes an error factor.

Further, since the damping foils 28A and 28B are formed so as to cover the gaps 26 and 27, the damping foils 28A and 28B are statically transferred from the exciting coils 31A and 32B, which will be described later, to the detection electrodes 23A and 23B through the gaps 26 and 27 via stray capacitance. It also reduces the zero-point fluctuation due to inductive noise generated by electrical coupling and enables stable measurement.

These damping foils 28A and 28B are
At the central part of the surface, a pole piece core 29 laminated in a rectangular shape with laminated cores and fixed integrally with bolts or the like.
It is fixed to one end surface of A and 29B.

And these Paul Peas scores 29
Exciting coils 31A and 31 are provided around A and 29B, respectively.
B is wound, and excitation lead wires 32A and 32B are case 2
It is pulled out to one connection tube 21D.

The exciting coils 31A and 31B have shield foils 33A and 33B for electrostatic shield wound around them, and the reference potential point 30 (ground potential) via the connecting cylinder 21D by the lead wires 34A and 34B. Connected to.

These Paul Peas scores 29A, 29B
The other end surface of the feedback core 3 is formed in a cylindrical shape and is layered.
5 is arranged, and the pole pieces 29A and 29B are integrally screwed by screws 36A and 36B and 37A and 37B.

On the other hand, signal lead wires 38A and 38B are connected from the detection electrodes 23A and 23B, and the guard case 2
4A, 24B and the cylindrical return core 35 are crossed and led out to the converter (not shown) in the upper part via the connecting cylinder 21D of the case 21.

Similarly, also from the guard cases 24A and 24B, the feedback core 35 is crossed and insulated from the signal lead wires 38A and 38B via the connection cylinder 21D, and led to the converter by the lead wires 39A and 39B. .

A shield plate 40 is inserted into the connecting cylinder 21D to physically separate the excitation lead wires 32A and 32B side from the signal lead wires 38A and 38B side. This prevents electrostatic induction from the high voltage excitation lead wires 32A, 32B side to the low voltage signal lead wires 38A, 38B side.

The insides of the guard cases 24A and 24B are filled with, for example, an insulating and self-adhesive silicone resin, and between the case 21 excluding the guard cases 24A and 24B and the outer surface of the pipe 20, and the connection. Tube 21D
The space between and is filled with, for example, an epoxy resin or the like to secure moisture resistance, vibration resistance, and weather resistance.

The same potential as that of the signal lead wires 38A, 38B is applied to the lead wires 39A, 39B from the converter side with low impedance, whereby the surface of the pipe 20 is detected including the guard cases 24A, 24B. Electrode 23
The substantially entire surface except A and 23B has the same potential as the signal potential, and the influence of the stray capacitance including the signal lead wires 38A and 38B is removed. Such consideration is particularly made because these constitute a high impedance circuit.

Next, the operation of the conventional example shown in FIGS. 11 and 12 will be described with reference to the frequency characteristic diagram shown in FIG.

The exciting coils 31A and 31B are connected in series so that the magnetic fields are oriented in the same direction, and a rectangular wave-like exciting current having a frequency higher than the commercial frequency is supplied from the converter side via the exciting lead wires 32A and 32B. Flowed pipe 2
It is applied to the measuring fluid flowing in the zero.

As a result, an electromotive force corresponding to the flow rate of the measurement fluid is generated in the pipe 20, and this electromotive force is an electrostatic force of the pipe 20 formed between the measurement fluid and the detection electrodes 23A and 23B. Detected via the capacitors CP1 and CP2,
It is transmitted to the converter side through the signal lead wires 38A and 38B and converted into a flow rate signal as an electric signal.

In this case, as shown in FIG. 13, the exciting coils 31A and 31B have a resonance point R where the inductance L with respect to the exciting frequency is in the vicinity of 50 KHz, which causes the exciting current If2 to ring. However, in the examples shown in FIGS. 11 and 12, since the conductive and extremely thin damping foils 28A and 28B are inserted in the path of the magnetic field applied to the measurement fluid ,
As a result, the resonance point R disappears and the ringing phenomenon does not occur. The horizontal axis of FIG. 13 is the excitation frequency, and the vertical axis is the excitation coils 31A and 3
The inductance L of 1B is shown.

In general, when a conductive material is placed in the path of a magnetic field, an eddy current flows there to generate a demagnetizing field. Since this demagnetizing field is proportional to the time derivative of the magnetic field B, the higher the frequency component becomes. .

As described above, since the influence of the demagnetizing field becomes larger as the high frequency component increases, the high frequency magnetic field apparently becomes smaller, and the high frequency characteristic is improved by reducing the inductance L of the exciting coils 31A and 31B in the high frequency region. To prevent ringing of the exciting current.

Therefore, the damping foil 2 is placed in the path of the magnetic field.
8A and 28B are inserted. In this case, if the damping foils 28A and 28B are made thicker, the settling time of the magnetic field becomes longer as described above, which causes an error factor. Therefore, the damping foils 28A and 28B are made of a conductive material. And make it extremely thin.

Furthermore, since a frequency higher than the commercial frequency is used as the excitation frequency, it is not possible to use solid mild steel or iron such as the pole pie score of an electromagnetic flowmeter that excites at a low excitation frequency of about 10 Hz, A laminated iron core with good magnetic properties will be used.

However, Paul Peascore 29A,
When the laminated core is used as 29B, the frequency characteristic of the magnetic circuit is improved, and the magnetic permeability of the pole pee scores 29A and 29B with respect to the frequency has the resonance point R in the high frequency region, resulting in the ringing of the exciting current. Becomes

Therefore, as a countermeasure against this, FIG. 11 and FIG.
The damping foils 28A and 28B shown in 2 can be expected to have an effect, and further, the above-described effect that the magnetic field is settled early by the time of signal sampling with respect to the magnetic field fluctuation can be expected.

Further, the size of the damping foils 28A, 28B is adjusted in the range from the size of the pole pee scores 29A, 29B to the outer peripheral edges of the exciting coils 31A, 31B so that high-order frequency characteristics can be obtained as necessary. Can be improved.

Further, as shown in FIG. 14, FIG. 11 and FIG.
The same applies when the positions of the damping foils 28A and 28B shown in 2 are changed. In the example shown in FIGS. 11 and 12, the damping foils 28A and 28B are arranged in the magnetic flux path between the excitation coils 31A and 31B and the guard electrodes 25A and 25B so as to cover the gaps 26 and 27, and the damping foils 28A and 28B are provided at the reference potential point 30. In the case of FIG. 13, the damping foils 41A and 41B are arranged in the magnetic flux path between the pole cores 29A and 29B and the feedback core 35 to which the magnetic field is fed back.
Is configured to connect to. With such a configuration, the same effect as described above can be obtained.

Further, in the example shown in FIG. 15, the structure of the guard electrodes 42A and 42B is changed from the structure of FIG. In this case, the guard electrodes 42A and 42B are configured to overlap while insulating so that the gaps 26 and 27 shown in FIGS. 11 and 12 do not occur. With such a configuration, the same effect as described above can be obtained.

[0034]

In the conventional electromagnetic flowmeter as described above, the damping foils 28A and 28B shown in FIGS. 11 and 12 and the damping foils 41A and 41B shown in FIGS. , And both are connected to the common potential point 30.

These damping foils are used for the excitation coil 31.
Since the magnetic fields generated in A and 31B are both arranged at positions orthogonal to this magnetic field, it is a place where an eddy current is generated by the largest magnetic field in this device. Further, since the damping foil has a large area, the generated eddy current causes a potential distribution on the damping foil.

Even if the damping foil is connected to the common potential point, the grounding is performed only at the point, so the damping foil may not be completely at the common potential or the ground potential.

If the damping foil does not completely reach the common potential (ground potential), the unstable potential of the damping foil is directly superposed on the detection electrode through the gap between the pair of detection electrodes and the guard electrode. There is a problem that it becomes noise and correct measurement cannot be performed.

In the example of FIG. 15, the guard electrodes 42A,
Although the structure of eliminating the gap of 42B is adopted, such a structure easily causes a problem that the potential of one guard electrode adversely affects the other guard electrode.

Further, although it has been described that the laminated cores are used for the pole pieces cores 29A and 29B, the apparatus using such laminated cores also has a problem of high cost.

The present invention solves the above problems, and an object thereof is to secure a common potential point so that noise generated on the damping foil will not be propagated to the detection electrode even if the damping foil is installed. In addition to the above, the objective is to further reduce costs.

[0041]

The present invention, which has solved the above problems, is as follows. According to the invention of claim 1, a pipe made of an insulating material for flowing a measurement fluid, an exciting coil for applying a magnetic field having a frequency higher than a commercial frequency to the measurement fluid from the outside of the pipe, and the measurement fluid. A pair of detection electrodes for detecting the signal voltage generated in the area through the capacitance formed by the pipe, and a pair of detection electrodes that are separated from the detection electrodes and maintain a gap in the circumferential direction and are divided into at least two. A pair of guard electrodes arranged, a pair of shield cases connected to the guard electrodes and covering a pair of the detection electrodes, and a resonance in the frequency characteristic of the inductance of the exciting coil provided in the magnetic flux path to which the magnetic field is applied. A capacitive electromagnetic flowmeter comprising a conductive damping foil thinly connected to a common potential point so as to eliminate points, wherein the guard electrode and the damper pin are provided. An insulating layer between the foil is provided, the thickness of the insulating layer (d2) is previously Roh
Before the above pipe diameter for which anti-noise effect is known
The pipe axis length (Lbase) of the insulating layer and the insulating layer
Using the thickness (dbase), the length in the axial direction of the pipe (L)
So that d2 = dbase · L / Lbas
It is a capacitive electromagnetic flow meter characterized in that it is set to e .

According to a second aspect of the present invention, the thickness of the insulating layer is
The thickness according to claim 1, wherein only a gap between the pair of guard electrodes is provided.
2. The capacitive electromagnetic flowmeter according to claim 1, wherein a calculation formula of the height (d2) is applied .

According to a third aspect of the invention, the thickness of the insulating layer is
The capacitive electromagnetic flowmeter according to claim 1, wherein the thickness is increased in proportion to a distance from the common potential point .

According to a fourth aspect of the present invention, the thickness of the insulating layer is
The thickness according to claim 1, wherein only a gap between the pair of guard electrodes is provided.
(D2) Applying the formula, the distance from the common potential point
The capacity type electromagnetic flowmeter according to claim 1, wherein the capacity type electromagnetic flowmeter is made thicker in proportion to .

According to a fifth aspect of the present invention, the insulating layer is foamed.
Claim from claim 1 characterized by using a resin 4
It is the described capacitive electromagnetic flow meter.

The invention of claim 6 is connected to the exciting coil.
The lead wire that connects to
Electromagnetic shield plate or electrostatic seal on the part to be pulled out
Claim from claim 1, characterized in that it has established a de plate 5
The described capacity type electromagnetic flow meter.

The invention of claim 7 is for flowing a measuring fluid.
From a pipe made of insulating material and from the outside of this pipe
A magnetic field having a frequency higher than the commercial frequency is applied to the measuring fluid.
The exciting coil to be applied and the signal current generated in the fluid to be measured.
Detect pressure via capacitance formed by the pipe
A pair of detection electrodes and these detection electrodes are separated from each other in the circumferential direction.
And maintain a gap between each other and divide into at least two
A pair of guard electrodes placed on the
A pair of shield cases that are connected to cover the pair of detection electrodes
And the excitation field provided in the magnetic flux path to which the magnetic field is applied.
The resonance point in the frequency characteristic of the inductance of the coil
Conductive that is thin enough to disappear and is connected to the common potential point
Damping foil and lead wire and connecting to the exciting coil
And a metal pipe covering the lead wire connected to the detection electrode
And a connecting tube for pulling out the metal pipe to the outside.
In the capacitive electromagnetic flowmeter provided with the metal pipe
A capacitive electromagnetic flow meter characterized in that the damping foil is connected to a common potential connection line .

According to an eighth aspect of the present invention, the metal pipe is
The capacitive electromagnetic flow meter according to claim 7, wherein the connection cylinder is connected by a common potential connection line .

According to a ninth aspect of the present invention, the exciting coil is made of resin.
Claim 7 or contract , characterized in that it is fixed by filling.
The capacitive electromagnetic flowmeter according to claim 8 .

The invention of claim 10 covers the exciting coil.
The capacitive electromagnetic flowmeter according to claim 7, further comprising a feedback core .

[0051]

[0052]

[0053]

[0054]

[0055]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a capacitive electromagnetic flow meter embodying the present invention. In this figure, components having the same reference numerals as those of the conventional capacitive electromagnetic flowmeter shown in FIGS. 11 and 12 have the same functions, and therefore their description is omitted.

Here, noise due to the eddy currents generated in the damping foils 28A and 28B and the exciting coils 31A and 31B.
The noise given from the damping foils 28A, 28B
Common potential connection point in proportion values (noise voltage value) distance from (common potential point 30 shown in FIG. 1 2) increases the. The equivalent circuit is shown in FIG.

In FIG. 2, the noise on the damping foil is VN, C1 is the capacitance between the damping foil 28A generating the eddy current and point A in FIG. 1, the potential at point A is VA, and C2 is point A. And the end face portion Q (earth ring) of the pipe 20 shown in FIG.
Between them, C3 is the capacity between the point A and the measurement fluid, C4 is the capacity of the detection electrodes 23A and 23B, R is the fluid resistance, and HA is the head amplifier. Among them, the capacitance C1 between the damping foil 28A and the point A (guard electrode 25A) is the largest capacitance. Therefore, if the capacitance C1 is configured to be small, the damping foil 28 is provided correspondingly to the guard electrode 25A.
The noise voltage from A becomes difficult to propagate.

That is, VA = VN (C1 / (C1 + C
2)), C1 = ε · S / d (S is the area of the gap 26, ε
Is the dielectric constant, d is the damping foil thickness), and the capacitance value C
Reducing 1 reduces the noise propagated to the point A. To reduce the capacitance value C1, the thickness of the damping foil 28A may be increased. However,
If the damping foils 28A and 28B are made too thick, as described above, the settling time of the magnetic field becomes long and an error factor is generated.

Therefore, in the present invention, the guard electrode 25A
So as to cover the gaps 26 and 27 between the guard electrode 25B and
It is characterized in that insulating films F1 and F2 are newly provided as insulating layers.

Specifically, the insulating layers F1 and F2 are provided between the damping foils 28A and 28B and the guard electrodes 25A and 25B in the structure described below. As shown in FIG. 3, the thickness d2 of the insulating films F1 and F2 is determined in proportion to the pipe axial length L of the insulating layers F1 and F2 .

For example, a pipe having a certain diameter is verified to confirm that no problem occurs, and the length Lbase and the thickness dbase of the insulating film at that time are used, and the insulation used for the corresponding pipe diameter is basically used. The film length L 1 and thickness d 2 are determined. That is, d2 = dbase
The L / Lbase equation is adopted, which determines the thickness of the insulating film.

Alternatively, as shown in FIG. 4, the thickness of the insulating film may be determined by using the above formula only for the portion d2 covering the gap portion of the guard electrode, and the thickness d1 of other portions may not be considered. .

Further, as shown in FIG. 5, the insulating film may be made thicker in thickness d2 in proportion to the distance from the common potential point. In this case, the thickness d1 is thin only near the common potential point, and the thickness d2 becomes thicker toward the end.

Further, by combining the two examples shown in FIGS. 4 and 5, only the portions of the guard electrodes 25A and 25B which cover the gaps 26 and 27 are adjusted to have the thickness d2 = dbase.L / Lbase. The thickness of the other portion may be determined in proportion to the distance from the common potential point.

As the material of the insulating film as described above, a foamed resin is used and the dielectric constant ε of the insulating film is
May be lowered, and as a result, the capacitance C1 may be reduced.

Next, in order to reduce the influence of external noise superimposed on the damping foils 28A, 28B, the damping foils 28A, 2 are provided on the outer side portions of the exciting coils 31A, 31B.
An electrostatic shield plate or electromagnetic shield plates P1 and P2 may be installed so as to cover 8B.

Further, in order to reduce the influence of inductive noise and electrostatic coupling noise from a converter section (not shown) connected to the connecting cylinder 21D, an electromagnetic shield plate (iron / silicon steel plate) is provided on the top of the connecting cylinder 21D. Alternatively, an electrostatic shield plate (SUS, brass, etc.) S may be provided.

Another example is as follows. As described above, the damping foil 28A,
28B noise due to eddy currents, exciting coil 31
The noise given from A and 31B is the damping foil 28.
The value (noise voltage value) increases in proportion to the distance from the common potential connection point (ground point) of A and 28B.

Therefore, in the conventional capacitive electromagnetic flowmeter shown in FIGS. 11 and 12, the pole pie score 29A,
29B and the damping foils 28A and 28B are electrically connected, the damping foils 28A and 28B are connected to the common potential point on the converter (not shown) side with low impedance, so that the pole piece scores 29A and 29B are connected. Will be grounded in the plane.

As shown in FIG. 6, when a conductive magnetic material such as a laminated iron core is used for the pole pieces 29A and 29B, the pole pieces 29A and 29B and the damping foils 28A and 28B are separated from each other. As indicated by the arrow a, the conductive adhesive is used for adhesion and electrical connection.

Further, as shown in FIG. 7, since the adhesive strength of the conductive adhesive is weaker than that of a normal resin adhesive by about 1/3, the pole piece 29 is fixed after conducting with the conductive adhesive.
A resin adhesive (B) may be applied around A and 29B so as to have strength.

As a result, the damping foils 28A, 28B
Is grounded with low impedance on the surface, and the influence of noise voltage such as eddy current distributed on the damping foils 28A and 28B and external noise can be reduced.

Another example is as follows. As described above, the damping foils 28A, 28B
Due to eddy currents generated in the magnet, exciting coils 31A, 3
The noise given from 1B is the damping foil 28A, 2
The value (noise voltage value) increases in proportion to the distance from the common potential connection point (ground point) of 8B.

Here, the potentials of the damping foils 28A and 28B are the most standard potential in this capacitive electromagnetic flowmeter (potential of the casing of the device, etc.), and the influence of the eddy current due to the magnetic field with low impedance. Damping foil 28A, 28B by connecting with a small loop so as not to receive
The electric potential of is coincident with the common electric potential point on the converter side.

Specifically, it has the following configuration. As shown in FIG. 8, the common potential line E1 is shortened from the central portion DO of the damping foils 28A and 28B, and the lead wires 38A and 38B are connected to the metal pipe U so as to minimize the loop. . Further, as shown in FIG. 9, the metal pipe U is connected to the connection tube 21D by the common potential housing connection line E2.
Connected to the top of the device (the case side of the device), this connection rattan 21D
Is connected to a common potential point on the converter side (not shown).

Further, in the capacitive electromagnetic flowmeter, it is necessary to improve the frequency characteristic of the magnetic circuit in order to excite the exciting coils 31A and 31B at a high frequency. Therefore, the frequency characteristics of the pole piece scores 29A and 29B are improved. However, the larger the volume of such a laminated iron core, the more expensive it becomes.

For example, in a capacitive electromagnetic flowmeter, if the pipe diameter is relatively large, the exciting coils 31A, 31
The distance between B does not have to be accurately defined, and therefore, there is no hindrance to the measurement even if the pole pee scores 29A and 29B for positioning are omitted.

If the pole piece scores 29A and 29B are not used, it is possible to eliminate the magnetic circuit delay that occurs in this pole piece score portion. Therefore, as shown in FIG. 9, the pole pieces 29A and 29B may be omitted, the exciting coils 31A and 31B may be temporarily fixed, and the positions may be fixed by filling the inside with resin. .

Further, in such a capacitive electromagnetic flowmeter which does not employ the pole pee score, the leakage magnetic field is confined in the electromagnetic flowmeter and the exciting coils 31A and 31B are covered in order to enhance the efficiency of the magnetic circuit. The return core 35 is installed.

According to such an embodiment, the damping foil 2
The influence of eddy currents distributed on 8A and 28B and external noise can be reduced. This is the damping foil 28A, 2
By connecting the potential of 8B to the most standard potential (casing potential) in the electromagnetic flowmeter with a small loop that has low impedance and is not affected by the eddy current due to the magnetic field, the common potential of the converter circuit is obtained. It is a connected effect.

Further, since the capacitive electromagnetic flowmeter is constructed so that the laminated core is not used for the pole piece core, the cost can be reduced.

[0082]

According to the invention of claim 1, since the insulating layer is interposed between the gap of the guard electrode and the damping foil,
During this time the volume is reduced, Ri noise voltage on the damping foil hardly propagated to the detection electrodes, also, the thickness of the insulating layer
Use a pipe whose diameter is known to be effective
Therefore, it is possible to realize a noise countermeasure without waste.

[0083]

According to the invention of claim 2 , the thickness (d2) calculation formula is applied only to the gap between the pair of guard electrodes for the thickness of the insulating layer. Can be realized.

According to the invention of claim 3 , the thickness of the insulating layer is increased in proportion to the distance from the common potential point.
It is possible to reduce noise that increases in proportion to the distance from the ground point.

According to the invention of claim 4 , the thickness of the insulating layer is applied only to the gap portion of the guard electrode, and the thickness is increased in proportion to the distance from the common potential point. Measures can be realized.

According to the invention of claim 5 , since the foamed resin is used for the insulating layer, the dielectric constant of the insulating layer can be reduced.

[0088]

According to the sixth aspect of the invention, since the electrostatic shield plate or the electromagnetic shield plate is installed at the location where the lead wire connected to the exciting coil and the lead wire connected to the detection electrode are pulled out to the outside, the damping foil is used. The influence of external noise that is directly coupled can be reduced.

[0090]

[0091]

According to the seventh aspect of the invention, since the metal pipe and the damping foil are connected by the common potential connection line, the influence of noise distributed on the damping foil can be reduced.

According to the eighth aspect of the invention, since the metal pipe is connected to the connection cylinder by the common potential connection line, the influence of noise distributed on the damping foil can be reduced.

According to the invention of claim 9 , the exciting coil is
Since the configuration does not adopt the pole piece score, the cost can be reduced.

According to the tenth aspect of the invention, since the feedback core that covers the exciting coil is attached, the leakage magnetic field can be confined in the electromagnetic flowmeter and the efficiency of the magnetic circuit can be improved.

[Brief description of drawings]

FIG. 1 is a view showing a cross section of a capacitive electromagnetic flow meter of the present invention.

FIG. 2 is an equivalent circuit representing noise generation.

FIG. 3 is a diagram showing an example of an insulating layer in the present invention.

FIG. 4 is a diagram showing an example of an insulating layer in the present invention.

FIG. 5 is a diagram showing an example of an insulating layer in the present invention.

FIG. 6 is a diagram when the insulating layer and the pole piece according to the present invention are bonded together.

FIG. 7 is a diagram when the insulating layer and the pole piece according to the present invention are bonded together.

FIG. 8 is a diagram when the insulating layer and the metal pipe in the present invention are connected by a common potential line.

FIG. 9 is a view showing a cross section of the capacitive electromagnetic flow meter of the present invention.

FIG. 11 is a view showing a cross section of a conventional capacitive electromagnetic flow meter.

FIG. 12 is a view showing a vertical section of a conventional capacitive electromagnetic flow meter.

FIG. 13 is a diagram showing frequency characteristics of an exciting coil in a conventional capacitive electromagnetic flow meter.

FIG. 14 is a view showing a cross section of a conventional capacitive electromagnetic flow meter.

FIG. 15 is a view showing a cross section of a conventional capacitive electromagnetic flow meter.

Claims (10)

(57) [Claims] 1. A pipe made of an insulating material for flowing a measuring fluid, an exciting coil for applying a magnetic field having a frequency higher than a commercial frequency to the measuring fluid from the outside of the pipe, and the exciting coil generated in the measuring fluid. A pair of detection electrodes for detecting the signal voltage through the capacitance formed by the pipe,
A pair of guard electrodes, which are separated from these detection electrodes and are spaced apart from each other in the circumferential direction so as to be divided into at least two, and a pair of shields which are connected to the guard electrodes and cover the pair of detection electrodes. A capacitive electromagnetic field including a case and a conductive damping foil which is provided in a magnetic flux path to which the magnetic field is applied and is thinly connected to a common potential point so as to eliminate a resonance point in the frequency characteristic of the inductance of the exciting coil. In the flowmeter, an insulating layer is provided between the guard electrode and the damping foil, and the thickness of the insulating layer is
As for (d2), the noise countermeasure effect is already known.
Pipe length of the insulating layer in the pipe diameter (Lba
se) and the thickness (dbase) of the insulating layer,
So as to be proportional to the length (L) in the axial direction, d2 = db
A capacity type electromagnetic flowmeter characterized by having as L / L base . 2. The insulating layer has a thickness equal to that of the pair of guard electrodes.
The thickness (d2) calculation formula according to claim 1 is applied only to the gap between the poles.
The capacitive electromagnetic flowmeter according to claim 1, which is applied . 3. The thickness of the insulating layer is measured from the common potential point.
The thickness is increased in proportion to the distance.
The described capacity type electromagnetic flow meter. 4. The thickness of the insulating layer is a pair of the guard electrodes.
The thickness (d2) calculation formula according to claim 1 is applied only to the gap portion of the pole.
Apply and thicken in proportion to the distance from the common potential point
Capacitive electromagnetic flowmeter according to claim 1, wherein the a. Wherein said insulating layer is foamed claim from claim 1 characterized by using a resin 4 5 capacitive electromagnetic flowmeter according. 6. A lead wire connected to the exciting coil and a front portion.
Location where the lead wire connected to the detection electrode is pulled out to the outside
The electromagnetic electromagnetic flowmeter according to any one of claims 1 to 6 , further comprising an electromagnetic shield plate or an electrostatic shield plate . 7. Made of an insulating material for flowing a measuring fluid
The pipe and the measuring fluid from outside of this pipe
Excitation coil for applying a magnetic field with a frequency higher than the frequency
And the signal voltage generated in the measuring fluid is shaped by the pipe.
A pair of detection electrodes for detecting via the formed capacitance,
Separated from these detection electrodes and kept a gap in the circumferential direction
And a pair of gars divided into at least two
And a pair of the above-mentioned detection electrodes connected to these guard electrodes.
A pair of shield cases that cover the output electrodes and the magnetic field is applied
Of the exciting coil provided in the magnetic flux path
It is thin enough to eliminate the resonance point in the frequency characteristics of the impedance.
A conductive damping foil connected to a common potential
Connect the lead wire connected to the excitation coil and the detection electrode.
The metal pipe that covers the continuous lead wire and the metal pipe
Capacitive electromagnetic flow with a connecting tube for drawing to the outside
In the meter, the metal pipe and the damping foil
A capacitive electromagnetic flowmeter characterized by being connected with a common potential connection line . 8. The metal pipe is connected to the connecting cylinder at a common potential.
The capacitive electromagnetic flow meter according to claim 7 , wherein the capacitive electromagnetic flow meter is connected by a connecting line . 9. The method of claim 7 or claim 8 capacitance type electromagnetic flowmeter wherein a <br/> which the excitation coil is fixed by resin filling. 10. A feedback core is attached to cover the exciting coil.
Capacitive electromagnetic flowmeter according to claim 9, wherein the claim 7, characterized in that digit.