JP3047284B2 - 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 capacitance type electromagnetic flowmeter for detecting a flow signal through a capacitance, and more particularly to a capacitance type electromagnetic flowmeter improved so as not to be affected by vibration.

[0002]

2. Description of the Related Art Various attempts have been made to obtain a stable flow signal by removing the influence of noise in an electromagnetic flowmeter. However, there are various causes of this noise, The means of removal is also different, and there are various types of electromagnetic flow meters.

One of the conventional techniques is that the frequency of an exciting current flowing through an exciting coil of an electromagnetic flowmeter is 50 Hz or 6 Hz.
There is an electromagnetic flowmeter having a commercial circumferential waveform that employs a commercial frequency such as 0 Hz. This commercial flow waveform electromagnetic flow meter applies a magnetic field of a commercial frequency generated by an exciting current to a measurement fluid through a metal pipe lined with an insulator on the inner surface, and generates a signal generated by the measurement fluid. A commercial frequency component of the voltage is detected by a detection electrode in contact with the measurement fluid.

More specifically, as shown in FIG. 9, a detection section of this type of electromagnetic flowmeter has a pair of metal detection electrodes 1 and 2 fixed and an inner surface covered with an insulating lining 3. Excitation coils 5 and 6 are arranged outside a metallic pipe 4. The metal pipe 4 is selected to have a sufficiently large size so as to withstand the pressure of the measurement fluid, for example, 10 kg / cm ² or more.

An excitation current _{If1 of a} commercial frequency is supplied to the excitation coils 5 and 6 from an excitation circuit (not shown), and a magnetic flux B is applied to the measurement fluid from the outside of the pipe 4 as shown in the figure. I have. However, a feedback core and a case, which return the magnetic flux B, are not shown.

[0006] The electromagnetic flowmeter having the commercial circumferential waveform has an advantage that it can be inexpensively constructed because it is excited at the commercial frequency, but the zero point fluctuates with time, and the flow signal cannot be detected stably. The causes of the zero point fluctuation in this manner include, for example, the causes (a) and (b) described below.

(A) First, the time variation of the magnetic flux of the commercial frequency
Noise caused by transformer components
There is A metal pipe is used as shown in FIG.
Eddy current i _PIs induced and this vortex
Current i_PCancels the magnetic flux B by the exciting coils 5 and 6
Create a demagnetizing field in the direction Therefore, the exciting current I_f1Is a constant value
Has a time derivative component of the magnetic flux B even after reaching
It becomes the noise of the component.

The eddy current i _P is attenuated by a time constant determined by the conductivity of the pipe 4 and the inductance formed by the loop of the eddy current i _P. However, in the case of a metal pipe, this decay takes time, and is substantially 100 Hz. Excitation beyond this level is difficult.

Further, the conductivity of the pipe 4 varies with temperature, and the decay time constant of the eddy current i _P also varies. Therefore, the size of the tail of the time differential component of the magnetic field varies, which causes the zero point to become unstable. It becomes a factor. FIG. 10 illustrates this relationship. Here, FIG. 10 (a) the waveform of the exciting current I _f1, FIG. 10 (b) the waveform of the eddy current i _P, FIG. 10 (c) shows the waveform of a time differential component of the magnetic flux B, respectively.

(B) Next, an eddy current induced in the measurement fluid by electromagnetic induction flows into the detection electrode, and a phase shift is caused by the electrode impedance of the detection electrode. There is a cause.

This will be described with reference to FIG. Since an AC magnetic flux of a commercial frequency is applied to the conductive measurement fluid, an eddy current _ie is induced in the measurement fluid. The eddy current i _e is induced due to the electromotive force e _n0 generated by the time variation of the magnetic flux B, the time change of the magnetic flux B is attenuated rapidly at a time constant of the loop of eddy currents is formed becomes zero.

However, when the detection electrodes 1 and 2 are in contact with the measurement fluid, the capacitors C ₁ , C ₂ , C ₃ and C ₄ formed on the surfaces of the detection electrodes 1 and ₂ and the fluid resistances R ₁ and R are formed. ₂ , R ₃ , R ₄ ,
The charges are accumulated and discharged by the eddy current i _{e on} the surfaces of the detection electrodes 1 and 2 by R ₅ and R ₆ , and a noise voltage having a phase delayed with respect to the eddy current i _e is generated on the detection electrodes 1 and 2. .

The values of these capacitors C ₁ and C ₄ are 1 m
Even a detection electrode having a diameter of m has an order of about 1 μF, and the zero point changes due to the noise voltage having the lag phase. Moreover, since these impedance components are unstable, they cause the zero point to change with time.

In order to avoid the drawbacks of the commercial frequency type electromagnetic flowmeter in which the detection electrode is in contact with the liquid, for example, a low frequency excitation type electromagnetic flow meter disclosed in Japanese Patent Application Laid-Open No. 49-29676 is used. Flow meters have been proposed.

In this method, the commercial frequency is set to 6.25 Hz, for example, which is frequency-divided by 1/8, and this is passed through an exciting coil to produce a low-frequency magnetic flux, which is applied to a measurement fluid. is there.

[0016] Thus, by lowering the excitation frequency, reduce the eddy current i _e with reducing differential noise generated due to electromagnetic induction, causes described in the preceding (a), (b) To secure a stable zero point.

However, this low-frequency excitation type electromagnetic flowmeter has the advantage that the excitation frequency is low, so that the induction noise is reduced and the fluctuation of the zero point is greatly improved as compared with the conventional one. Is reduced, which causes a new occurrence of noise attributable to another cause.

First, the flow of the measurement fluid causes a potential fluctuation called a low-frequency streaming potential (flow noise) to occur in the measurement fluid, and this phenomenon is particularly remarkable when the measurement fluid has low conductivity. . Since this potential fluctuation is similar to the excitation frequency of the low-frequency excitation, it is output as disturbance of the flow signal. FIG. 12 shows an actual measurement example of this noise spectrum.
And FIG.

In each case, the horizontal axis represents the frequency, and the vertical axis represents the spectrum of the noise power. FIG. 12 shows a case where a surface electrode is used as a detection electrode, and FIG. 13 shows a case where a point electrode is used as a detection electrode. ing. While corner frequency f _c by the shape of the detection electrode is different, it is understood that the 1 / f _c characteristics.

In addition, for example, output instability with respect to low-frequency noise generated when a slurry fluid containing a solid substance in a measurement fluid collides with a detection electrode, or responsiveness to a change in flow rate due to a low excitation frequency is also deteriorated. A new problem has arisen. Therefore, for example, FIG.
4 has been proposed.
Hereinafter, this summary will be described with reference to FIG.

Reference numeral 7 denotes a pipe for flowing a measurement fluid,
This pipe 7 is made of an insulating material such as ceramics or vinyl chloride resin. Reference numerals 8 and 9 denote detection electrodes for detecting a signal voltage generated in the measurement fluid. These detection electrodes 8 and 9 are DC-insulated from the measurement fluid and are provided on the outer surface of the pipe 7 or inside the pipe wall. It is embedded and placed.

A pair of exciting coils 10 and 11 are arranged on the outer surface of the pipe 7 in a direction perpendicular to the line connecting these detecting electrodes 8 and 9. The outer surfaces of the exciting coils 10 and 11 are both electrostatically shielded and connected to a ground electrode G which is a reference potential.

Guard electrodes 12 and 13 are disposed outside the detection electrodes 8 and 9 so as to cover the entirety of the detection electrodes 8 and 9 while maintaining insulation between the detection electrodes 8 and 9. . The pipe 7 is provided with a liquid contact electrode E, which determines a reference potential of a signal voltage generated by the measurement fluid, and is connected to a ground electrode G.

The detection electrodes 8 and 9 are respectively connected to non-inverting input terminals (+) of preamplifiers 14 and 15 having high input impedance, and their inverting input terminals (-) are connected to guard electrodes 12 and 13, respectively. The output terminals of these preamplifiers 14 and 15 are connected. The detection electrodes 8 and 9, the guard electrodes 12 and 13, and the preamplifiers 14 and 15 are connected by a pair of signal lines CA and CB. The output terminals of the preamplifiers 14 and 15 are connected to the input terminals of the differential amplifier 16, respectively.

The exciting circuit 17 receives the control signal Vc from a timing circuit (not shown) and sends the control signal Vc to the exciting coils 10 and 11.
An excitation current _If2 having a steady value equal to or greater than the value is supplied. The exciting current _If2 is a square wave having a frequency that is an even multiple of the commercial power supply frequency, for example, 200 Hz.

More specifically, the signal lines CA and CB have a configuration as shown in FIG. In FIG. 15, the signal line CA is representatively shown, but the signal line CB has a similar configuration. C ₁ , C ₂ and C ₃ are conductors such as copper, and I ₁ ,
I ₂ and I ₃ are insulators such as tetrafluoride resin.

The conductor C ₁ is connected to the detection electrode 8, the conductor C ₂ is connected to the guard electrode 12, and the conductor C ₃ is connected to the common potential point COM. The insulators I ₁ , I ₂ and I ₃ cover the conductors C ₁ , C ₂ and C ₃ and insulate them from each other.

Next, these operations will be described. When a square wave exciting current _If2 having an even multiple of the frequency of the commercial power supply is applied to the exciting coils 10 and 11 from the exciting circuit 17, a square wave magnetic flux having the same frequency as the exciting current _If2 is applied to the measurement fluid. Applied.

Here, when the measurement fluid flows into the insulating pipe 7, a signal voltage having a square wave shape and a frequency higher than the commercial frequency is generated on the inner surface of the pipe 7 corresponding to the detection electrodes 8, 9. This signal voltage is detected by the detection electrodes 8 and 9 via a capacitor formed by the insulating pipe 7.

Therefore, the detected signal voltage is received by the preamplifiers 14 and 15 having a high input impedance, is subjected to impedance conversion, and is output to the differential amplifier 16. At this time, the same voltage as the signal voltage is driven from the output terminals of the preamplifiers 14 and 15 to the guard electrodes 12 and 13 with low impedance.

For this reason, the detection electrodes 8 and 9 and the guard electrode 1
The reduction of the signal voltage due to the capacitance formed between the terminals 2 and 13 is prevented. Then, the differential amplifier 16 calculates the difference between the voltages generated at the detection electrodes 8 and 9 and outputs the result to the output terminal 18 as a flow rate signal.

This capacitive type electromagnetic flow meter applies a magnetic flux to the measurement fluid from outside the insulating pipe, and furthermore, a signal is applied to a detection electrode disposed outside the insulating pipe so as not to contact the measurement fluid. Since the voltage is detected, it is possible to solve the various problems described above caused by the detection electrode coming into contact with the measurement fluid.

[0033]

However, the capacity type electromagnetic flow meter as described above has the following problems.

First, since the output impedances of the detection electrodes 8 and 9 are several MΩ to several hundred MΩ, the input impedance of the preamplifier is equal to the expression 1 even if an error of 1% is allowed.
A high value of about 00 MΩ to several 10,000 MΩ is required.

Next, since the electromagnetic flowmeter is installed on site, it may be subjected to large piping vibration. In particular, in the case of a capacitive electromagnetic flow meter, since the impedance of the circuit connected by the signal lines CA and CB forms a high impedance circuit as described above, the conductor C ₂ and the insulator I shown in FIG. _{When the} pipe ₁ is separated from the pipe by the vibration of the pipe, triboelectricity is induced between them.

In this case, the conductor C ₂ is connected to the preamplifier 14.
Because of being connected to the output terminal, the triboelectrically directly, or bonded conductors C ₁ and capacitor, is output to the output terminal 18, there is a problem that results in output swing.

Therefore, as a countermeasure, for example, it is conceivable that the signal lines CA and CB are firmly fixed to the input terminals of the preamplifiers 14 and 15 so as not to move. However, if such measures are taken, the preamplifiers 14, 15
In the event of a failure, this cannot be repaired, causing a new problem that maintenance becomes extremely difficult.

[0038]

According to the present invention, as a main structure for solving the above-mentioned various problems, a pipe made of an insulating material for flowing a measurement fluid and a pole piece core are provided.
Detected via wound around the A and the exciting coil for applying a magnetic field from the outside of the pipe ahead of the measurement fluid, the capacitance formed a signal voltage generated in the previous measurement fluid in the previous pipe A pair of detection electrodes, a pair of guard electrodes that are separated from the detection electrodes and are spaced apart from each other in the circumferential direction and are arranged at least in two parts, and a detection electrode connected to these guard electrodes and connected to the guard electrodes A pair of guard cases that cover the input signal and the signal voltage of the previous signal are input to convert the impedance and output with a low output impedance, while driving the guard electrode with a low impedance and a guard voltage that is almost the same potential as the previous signal voltage. It has a preamplifier, a core wire, and a guard wire. At least one surface of the guard wire coating is covered with a conductive rubber layer, and the signal voltage is advanced by the guard wire. It is obtained so as to include a signal line for transmitting a guard voltage.

[0039]

The pipe is made of an insulating material and flows the measuring fluid.
Then, the exciting coil is wound around the pole piece core for applying a magnetic field from the outside of the pipe ahead of the measurement fluid. The pair of detection electrodes detects the signal voltage generated in the measurement fluid via the capacitance formed by the pipe.

The pair of guard electrodes are separated from the detection electrodes and are divided into at least two parts while keeping a gap therebetween in the circumferential direction, and the pair of guard cases are connected to these guard electrodes. Cover the detection electrode.

Further, the preamplifier receives the previous signal voltage, performs impedance conversion and outputs the same with a low output impedance, and drives the previous guard electrode with a low impedance and a guard voltage having substantially the same potential as the previous signal voltage.

The signal wire has a core wire and a guard wire, and at least one side of the guard wire coating is covered with a conductive rubber layer to discharge the electric charge caused by the vibration, thereby making the output signal less affected by noise. I do.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing a cross section of one embodiment of the present invention, and FIG. 2 is a configuration diagram showing a vertical cross section corresponding to FIG. 1, respectively.

Reference numeral 20 denotes an insulating pipe. The pipe 20 is formed of a material such as ceramics and has a cylindrical shape. The central portion in the axial direction of the pipe 20 is formed as a concave portion 20A whose outer peripheral surface is thin, and thick ends 20B and 20C are formed on both outer sides in the axial direction.

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

Then, a pipe 20 is inserted into the inside of the case 21, and its ends 20B and 20C and the end face 21 are formed.
A and 21B between O-rings 22A and 22B, respectively.
Is inserted to ensure airtightness. In addition, Case 2
A rectangular connection cylinder 21D is fixed to 1 perpendicular to the axis thereof, and the conversion unit TRM is integrally mounted thereon.

On the center surface of the concave portion 20A of the pipe 20, detection electrodes 23A and 23B are formed in a planar shape so as to be opposed to the axis of the pipe 20 in the radial direction and closely contact the conductor. On the detection electrodes 23A and 23B, box-shaped guard cases 24A and 24B are fixed to the outer surface of the pipe 20 so that the detection electrodes 23A and 23B are separated from each other and cover them.

The surface of the recess 20A around the guard cases 24A, 24B is provided with the ends 20B, 2B of the pipe 20.
Guard electrode 25 which is conductive over the entire surface up to 0C
A and 25B are formed with gaps 26 and 27 formed by being divided into right and left at the top and bottom of the pipe 20.
The guard electrodes 25A and 25B are electrically connected to the guard cases 24A and 24B by soldering or the like.

To cover each of the gaps 26 and 27,
Guarding electrodes 25A and 25B are insulated from the guard electrodes 25A and 25B by an insulating paint or the like, and conductive damping foils 28A and 28B are fixed to these peripheral surfaces in an arc shape. These damping foils 28A and 28B are respectively It is fixed to a reference potential point 30 by a lead wire 29.

[0050] These damping foils 28A, 28B are:
For example, it is made of copper, brass, stainless steel or the like.
When the thickness of B is large, the eddy current generated here becomes large, and the demagnetizing field generated thereby increases the time constant of the magnetic field fluctuation and the magnetic field is not settled until the signal is sampled, thus causing an error factor. 200μ thick
m or less.

The damping foils 28A and 28B are formed so as to cover the gaps 26 and 27. As a result, the damping foils 28A and 28B are electrostatically coupled to the detection electrodes 23A and 23B through the gaps 26 and 27 from the excitation coil described later via the floating capacitance. This reduces the zero-point fluctuation caused by induced noise, and enables stable measurement.

These damping foils 28A, 28B
A pole piece core 2 which is laminated in a rectangular shape with a laminated iron core and fixed integrally with bolts at the center of the surface.
9A and 29B are fixed to one end face.

Then, these pole piece cores 29
Exciting coils 31A, 31A around A, 29B, respectively.
B is wound, and the excitation lead wires 32A and 32B are
It is drawn out to one connection cylinder 21D.

The excitation coils 31A and 31B are wound around the shielding foils 33A and 33B for electrostatic shielding, and are connected to the reference potential point 30 (ground potential) via the connection tube 21D by the lead wires 34A and 34B. It is connected to the.

These pole piece cores 29A, 29B
A return core 35, which is formed in a cylindrical shape and is layered, is arranged on the other end surface of FIG.
The two pole piece cores 29A and 29B are screws 36A and 3
6B, and are screwed together by 37A and 37B, respectively.

On the other hand, lead wires 38A and 38B as core wires from the detection electrodes 23A and 23B are
4A and 24B cross the cylindrical return core 35 and are led out to the conversion unit TRM via the connection tube 21D of the case 21.

Similarly, from the guard cases 24A and 24B, the return core 35 is crossed to connect the connecting cylinder 21D of the case 21.
Are insulated from the lead wires 38A and 38B and are connected to the conversion unit TRM as lead wires 39A and 39 as guard wires.
B.

The lead wire 38A and the lead wire 39A
The signal line SA is connected to the lead wire 38B and the lead wire 39B.
The signal lines SB are respectively formed as described above, and their specific configurations will be described later with reference to FIGS.

The signal lines SA and SB are connected to each other in the connecting tube 21D, as shown in an enlarged view in FIG. Conversion unit TRM stored in 40, 41
Is derived.

By storing the signal lines SA and SB in the flexible tubes 40 and 41 as described above, the portions of the signal lines SA and SB led to the conversion unit TRM can be freely moved. In addition, the signal lines SA and SB can be freely connected to the preamplifier in the conversion unit TRM while reducing the vibration transmitted to the signal lines SA and SB due to the pipe vibration.

A shield plate 42 is inserted into the connection tube 21D to physically separate the excitation lead wires 32A, 32B from the signal lead wires 38A, 38B. This prevents electrostatic induction from the high voltage excitation lead wires 32A, 32B to the low voltage signal lead wires 38A, 38B.

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

As shown in FIG. 8, the same potential as the potential of the lead wires 38A, 38B is applied to the lead wires 39A, 39B with low impedance from the preamplifiers 14, 15 of the conversion unit TRM. A substantially the entire surface except for the detection electrodes 23A and 32B including the guard cases 24A and 24B has the same potential as the signal potential, and the influence of the stray capacitance including the lead wires 38A and 38B is eliminated.

Then, the lead wire 38A and the lead wire 39A
The outer shields C _3A, lead 38B and the lead wire 3
The outside of 9B is a shield C _3B and has a common potential point COM.
It is connected to the.

Next, the feedback core 35 and the pole piece cores 29A and 29B shown in FIG. 1 will be specifically described with reference to FIGS. Figure 3 is fed back core 35 to expand and the pole piece core 29A, 29B, the exciting coils 31A, shows the positional relationship, such as 31B, FIG. 4 shows the pole peak score was represented by Paul P. score 29A FIG. 4A is a perspective view, and FIG. 4B is a top view.

As shown in FIG. 3, square notches X and Y are provided in a portion of the return core 35 extending in a band shape, which faces the guard cases 24A and 24B.
The magnetic resistance is increased so that a part of the main magnetic field passing through 9B does not leak to the notches X and Y, so that the magnetic field can be used effectively. If there is a magnetic material close to the magnetic material, a lattice-shaped hole may be provided in a part of the feedback core 35 as necessary.

As shown in FIG. 4, the pole piece core 29A is formed by stacking thin layered cores insulated on both sides. These layered cores are simply joined by, for example, an adhesive or the like and returned to the core. Core 35 with screws 36A, 36B,
If the screw holes 36a, 36b, 36c, 36d for fixing with (not shown, 36C, 36D) or the like are formed, there is a problem that the stratified cores come off.

The return core 35 is connected to the pole piece core 2.
If not fixed to 9A, the feedback core 35 forms a diaphragm by the changing magnetic field and vibrates like a speaker. Therefore,
As shown in FIG. 4, the bolt 43 (45) and the nut 44 (4
6, not shown) to solve the vibration problem by binding stratified iron cores.

Next, the signal lines shown in FIG. 5 will be described. Note that, for portions having the same functions, reference numerals shown in FIG. 15 are appropriately used as necessary. And
Since the configuration of the signal line SA and the configuration of the signal line SB are the same, the signal line SA will be described as a representative.

The lead wire 38A is connected to the detection electrode 23A.
Conductor and lead wire 39A are in contact with guard case 24A.
Connected conductor, C_3AIs a shielded wire. And re
Inside the wire 39A, rubber such as silicon and carbon
Conductive rubber layer CR made of throat _AIs coated
An insulator I such as a highly insulating tetrafluoride resin is interposed between them.₁,
I_Two, I_ThreeInsulated.

[0071] With this configuration, between the insulator I ₁ and the lead wire 39A becomes more difficult adhesion to peeling by external vibrations occur, as a result, friction electricity caused by external vibration hardly occurs .

Further, by making the portion where friction occurs conductive, a friction voltage generated by friction can be discharged, and a stable output can be ensured even when there is external vibration.

FIG. 6 shows another modification of the signal line shown in FIG. Note that portions having the same functions as those of the signal line SA illustrated in FIG. 5 are denoted by reference numerals illustrated in FIG. The signal line SC in this case is different from where the structure provided a conductive rubber layer CR _C on the outside as well as inside of the lead wire 39A is a signal line SA shown in FIG. With such a configuration, the structure is more resistant to external vibration.

[0074]

As described above, according to the first embodiment of the present invention, at least one side of the guard wire is covered with the conductive rubber. Therefore, even in a capacitive electromagnetic flowmeter in which the signal detection unit is an extremely high impedance circuit, output fluctuations due to triboelectricity caused by vibration such as pipe vibration can be significantly reduced, and a highly accurate and stable flow rate can be achieved. A signal can be obtained.

According to the second aspect of the present invention, since the outside of the signal line is covered with the metal flexible tube, the vibration transmitted to the signal line due to the vibration of the pipe is reduced to reduce the triboelectricity. The signal line can be freely connected to the preamplifier in the conversion unit while suppressing occurrence.

[0076] According to the invention described in claim 3, between the feedback core and the pole piece core comprising a return magnetic field with binding by the formed core cross bolts to each other pole piece core laminated core in volts Due to the coupling configuration, the vibration generated inside can be effectively removed, and the generation of triboelectricity due to this can be suppressed, and the fluctuation of the magnetic field can be suppressed to obtain a stable output.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a cross section of one embodiment of the present invention.

FIG. 2 is a configuration diagram showing a vertical section corresponding to the embodiment shown in FIG. 1;

3 is a development view showing the positional relationship between the feedback core and the pole piece core and the exciting coil shown in FIG.

4 is a block diagram showing the structure of a pole piece core shown in FIG.

FIG. 5 is a sectional view showing a configuration of a signal line shown in FIG. 1;

6 is a cross-sectional view showing a configuration of a modified example of the signal line shown in FIG.

FIG. 7 is a partial cross-sectional view of a flexible tube housing the signal line shown in FIG.

FIG. 8 is a partial configuration diagram illustrating a circuit configuration near a first stage of the conversion unit illustrated in FIG. 1;

FIG. 9 is an explanatory diagram illustrating a configuration of a detection unit of a conventional electromagnetic flowmeter.

FIG. 10 is a waveform chart for explaining a drawback of a conventional electromagnetic flow meter.

FIG. 11 is an explanatory diagram for explaining a drawback of a conventional electromagnetic flow meter.

FIG. 12 is a first characteristic diagram illustrating frequency characteristics of a streaming potential.

FIG. 13 is a second characteristic diagram illustrating frequency characteristics of a streaming potential.

FIG. 14 is a configuration diagram showing a configuration of a conventional capacitive electromagnetic flow meter.

15 is a cross-sectional view showing a configuration of a signal line shown in FIG.

[Explanation of symbols]

1, 2, 8, 9, 23A, 23B Detection electrode 3 Lining 4, 7, 20 Pipe 5, 6, 11, 31A, 31B Excitation coil 14, 15 Preamplifier 21 Case 24A, 24B Guard case 12, 13, 25A, 25B The guard electrodes 26 and 27 a gap 29A, 29B pole piece core 35 back core 40 flexible tube CA, CB, SA, SC signal line CRA, CRC conductive rubber layer TRM converter unit

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroki Yoshino 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Corporation (58) Field surveyed (Int. Cl. ⁷ , DB name) G01F 1 / 58

Claims (3)

(57) [Claims] 1. A and pipe made of insulating material for the flow of measurement fluid, wound around the pole piece cores and the exciting coil for applying a magnetic field to the measurement fluid from the outside of the pipe, the measurement fluid A pair of detection electrodes for detecting a signal voltage generated in the pipe via a capacitance formed by the pipe, and separated from the detection electrodes and separated into at least two parts while maintaining a gap therebetween in a circumferential direction. a pair of guard electrodes arranged, and a pair of guard casing is connected to these guard electrodes covering the sensing electrode, said guard electrode with the signal voltage and the inputted impedance conversion outputs at a low output impedance low A preamplifier driven by a guard voltage having an impedance and substantially the same potential as the signal voltage, and a core wire and a guard wire, and Capacitive electromagnetic flowmeter characterized by comprising a signal line for transmitting the guard voltage the signal voltage by the guard wire by the core wire surface is covered with a conductive rubber layer. 2. The displacement type electromagnetic flowmeter according to claim 1, wherein the outside of said signal line is covered with a metal flexible tube. Wherein characterized in that the pole piece core that is also coupled by bolts between the pole piece cores and return to become feedback core of the magnetic field with core cross formed by laminated core is joined by bolts to each other The displacement type electromagnetic flow meter according to claim 1, wherein