JP7294875B2 - capacitive electromagnetic flowmeter - Google Patents

Description

The present invention relates to a flow rate measuring technique for measuring the flow rate of fluid flowing through a measuring tube based on an electromotive force generated in a plane electrode formed on the outer peripheral surface of the measuring tube.

Conventionally, as one of the electromagnetic flowmeters, a capacitive electromagnetic flowmeter has been proposed that measures the flow rate of a fluid flowing through a measuring tube based on the electromotive force generated in a surface electrode formed on the outer peripheral surface of the measuring tube ( For example, see Patent Document 1). FIG. 10 is a front view showing a detection section of a conventional capacitive electromagnetic flowmeter. FIG. 11 is a side view showing a detecting portion of a conventional capacitive electromagnetic flowmeter. FIG. 12 is a top view showing a detecting portion of a conventional capacitive electromagnetic flowmeter.

As shown in FIGS. 10 to 12, a conventional capacitive electromagnetic flowmeter 50 includes a pair of surface electrodes 52A and 52B formed on the outer peripheral surface of a measuring tube 51, and an exciting current flowing through a pair of exciting coils 53A and 53B. The flow rate of the fluid flowing through the measurement tube 51 is measured by detecting the electromotive force generated between the surface electrodes 52A and 52B while alternately switching the polarities of the electrodes 52A and 52B.

JP 2018-077118 A

In the above-described conventional capacitive electromagnetic flowmeter, the measuring tube 51 is made of a dielectric material such as resin or ceramic, and is a dielectric with a property of storing electricity. It may cause some type of electrostatic charge.

[Electrification due to fluid temperature change]
If the temperature of the fluid flowing through the measuring tube 51 changes significantly in a short period of time, the outer peripheral surface of the measuring tube 51 may be charged due to the pyroelectric effect. The pyroelectric effect is a phenomenon in which when a dielectric crystal is heated, the crystal structure changes and an electric charge called pyroelectricity appears on the surface. This heating includes, for example, heating by infrared rays emitted from the human body, and even such slight heating may generate an electric charge due to the pyroelectric effect. The generated charge is normally neutralized by ions in the air adhering to the surface, but if the temperature of the fluid changes significantly in a short time, a large amount of charge is generated and the outer peripheral surface of the measuring tube 51 is charged. It will be.

[Electrification by fluid pressure change]
When the pressure of the fluid flowing through the measuring tube 51 changes, the measuring tube 51 is distorted, and the outer peripheral surface of the measuring tube 51 may be charged due to the piezoelectric effect. The piezoelectric effect is a phenomenon in which, when pressure is applied to a dielectric, the crystal structure changes and becomes polarized, and an electric charge called piezoelectricity appears on the surface. The generated charge is charged on the outer peripheral surface of the measuring tube 51 .
[Electrification by fluid friction]
When a low-conductivity fluid such as ultrapure water is passed through the measuring tube 51, static electricity is generated due to friction between the inner peripheral surface of the measuring tube 51 and the fluid, and the outer peripheral surface of the measuring tube 51 is charged. .

Since these charges occur on the outer peripheral surface of the measuring tube 51, they may appear as a DC voltage (potential difference) between the surface electrodes 52A and 52B (and between the wiring patterns). Moreover, the DC voltage generated at this time may be several tens of mV or more depending on the conditions. On the other hand, the electromotive force (AC voltage signal) generated between the surface electrodes 52A and 52B in accordance with the flow velocity of the fluid is within several mV (pp). For this reason, there is a possibility that the flow rate measurement value may drift due to the influence of the DC voltage generated between the surface electrodes 52A and 52B due to the charging.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a capacitive electromagnetic flowmeter capable of reducing the influence of electrification generated on the outer peripheral surface of a measuring tube on flow measurement.

In order to achieve such an object, the capacitive electromagnetic flowmeter according to the present invention includes a dielectric measuring tube in which a fluid to be measured flows, and a measuring tube facing each other on the outer peripheral surface of the measuring tube with the measuring tube interposed therebetween. and a dielectric thin film formed to cover at least the entire outer surface of the pair of surface electrodes.

Further, in one configuration example of the capacitive electromagnetic flowmeter according to the present invention, the pair of surface electrodes are made of conductors patterned on the outer peripheral surface of the measurement tube, and the thin film is formed on the pair of surface electrodes. It consists of a film that is attached to the outer peripheral surface of the measuring tube so as to cover it all.

Further, in one configuration example of the capacitive electromagnetic flowmeter according to the present invention, a pair of tube sides formed opposite to each other on the outer peripheral surface of the measurement tube and electrically connected to the pair of surface electrodes, respectively. A wiring pattern is further provided, and the thin film is formed so as to cover the outer surfaces of the pair of pipe-side wiring patterns.

In one configuration example of the capacitive electromagnetic flowmeter according to the present invention, the thin film is made of an insulating tape having a resin film as a base material.

In one configuration example of the capacitive electromagnetic flowmeter according to the present invention, the thin film is made of an insulating tape having a two-layer structure of a resin film substrate and an adhesive.

In one configuration example of the capacitive electromagnetic flowmeter according to the present invention, the thin film is a film formed by applying an insulating liquid coating agent and drying it.

Further, in one structural example of the capacitive electromagnetic flowmeter according to the present invention, the thin film is made of an insulating coating that annularly covers all of the pair of surface electrodes over the entire circumference of the measuring pipe.

In one configuration example of the capacitive electromagnetic flowmeter according to the present invention, the insulating film is made of a heat-shrinkable tube.

In one configuration example of the capacitive electromagnetic flowmeter according to the present invention, the thin film is formed in an annular shape over the entire circumference of the measurement tube.

In one configuration example of the capacitive electromagnetic flowmeter according to the present invention, the thin film is divided into two in the circumferential direction of the measuring pipe.

According to the present invention, the dielectric thin film is formed on the outer peripheral surface of the measuring tube to cover the entire outer surface of the plane electrode. will move to For this reason, electrification does not appear as a DC voltage between the electrodes of the surface electrodes, and the drift of the flow rate measurement value can be suppressed. Therefore, it is possible to reduce the influence of electrification generated on the outer peripheral surface of the measuring tube on the flow rate measurement.

FIG. 1 is a block diagram showing the circuit configuration of the capacitive electromagnetic flowmeter according to the first embodiment. FIG. 2 is a front view of a detection unit according to the first embodiment; FIG. 3 is a side view of the detector according to the first embodiment; 4 is a top view of the detection unit according to the first embodiment; FIG. FIG. 5 is a configuration example of a differential amplifier circuit using a preamplifier. FIG. 6 is a side view of the detector according to the second embodiment; FIG. 7 is a top view of a detector according to a second embodiment; FIG. 8 is a front view of a detector according to a third embodiment; FIG. 9 is a side view of the detector according to the third embodiment; FIG. 10 is a front view showing a detection section of a conventional capacitive electromagnetic flowmeter. FIG. 11 is a side view showing a detecting portion of a conventional capacitive electromagnetic flowmeter. FIG. 12 is a top view showing a detecting portion of a conventional capacitive electromagnetic flowmeter.

Next, embodiments of the present invention will be described with reference to the drawings.
[First embodiment]
Next, a capacitive electromagnetic flowmeter 100 according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the circuit configuration of the capacitive electromagnetic flowmeter according to the first embodiment.

[capacitance electromagnetic flowmeter]
In the capacitive electromagnetic flowmeter 100, the electromotive force generated in the fluid to be measured flowing in the measuring tube by the magnetic flux applied from the exciting coil is generated by the surface electrodes provided on the outer peripheral surface of the measuring tube. The flow rate of the fluid is measured without bringing the electrodes into contact with the fluid by detecting the electromotive force obtained through the capacitance between the electrodes and amplifying the resulting electromotive force, followed by sampling and signal processing.

As shown in FIG. 1, the capacitive electromagnetic flowmeter 100 includes, as main circuit portions, a detection portion 20, a signal amplification circuit 21, a signal detection circuit 22, an excitation circuit 23, a transmission circuit 25, a setting/display circuit 26, and a An arithmetic processing circuit (CPU) 27 is provided. Among them, the arithmetic processing circuit 27 includes a CPU and its peripheral circuits. 27B and other processing units.

The detection unit 20 mainly includes a measurement tube 2, excitation coils 3A and 3B, surface electrodes 10A and 10B, and a preamplifier 5U. It has a function of detecting Va and Vb by the surface electrodes 10A and 10B and outputting an AC detection signal Vin corresponding to these electromotive forces Va and Vb.

The signal amplifier circuit 21 filters noise components contained in the detection signal Vin output from the detection unit 20, and then outputs an AC flow rate signal VF obtained by amplification.
The signal detection circuit 22 samples and holds the flow rate signal VF from the signal amplification circuit 21, A/D-converts the obtained DC voltage into a flow rate amplitude value DF, and outputs the flow rate amplitude value DF to the flow rate calculation section 27B.

The flow rate calculator 27B calculates the flow rate of the fluid based on the flow rate amplitude value DF from the signal detection circuit 22 and outputs the flow rate measurement result to the transmission circuit 25 .
The transmission circuit 25 performs data transmission with the host device via the transmission line L, thereby transmitting the flow rate measurement result and the empty state determination result obtained by the arithmetic processing circuit 27 to the host device.

The excitation control unit 27A outputs to the excitation circuit 23 an excitation control signal Vex for controlling excitation switching of the excitation coils 3A and 3B.
The excitation circuit 23 supplies an alternating excitation current Iex to the excitation coils 3A and 3B based on the excitation control signal Vex from the excitation control section 27A.
The setting/display circuit 26 detects, for example, an operator's operation input, outputs various operations such as flow rate measurement, conductivity measurement, and empty state determination to the arithmetic processing circuit 27, and outputs from the arithmetic processing circuit 27, A display circuit such as an LED or LCD displays the flow rate measurement result and the empty state determination result.

[Structure of detector]
Next, the configuration of the detector 20 will be described in detail with reference to FIGS. 2 to 4. FIG. FIG. 2 is a front view of a detection unit according to the first embodiment; FIG. 3 is a side view of the detector according to the first embodiment; 4 is a top view of the detection unit according to the first embodiment; FIG.

As shown in FIG. 2, the measuring tube 2 is made of a cylindrical ceramic, resin, or other material having excellent insulating and dielectric properties. A substantially C-shaped yoke and a pair of excitation coils 3A and 3B are arranged to face each other with the measurement tube 2 interposed therebetween so that the magnetic flux direction (second direction) Y is orthogonal to the direction X of the magnetic flux. 2 to 4, only the yoke end faces facing each other, that is, only the yoke faces 4A and 4B are shown in order to make the drawings easier to see.

On the other hand, on the outer peripheral surface 2A of the measuring tube 2, a pair of plane electrodes (first A plane electrode) 10A and a plane electrode (second plane electrode) 10B are arranged to face each other.
As a result, when an alternating excitation current Iex is supplied to the excitation coils 3A and 3B, a magnetic flux Φ is generated between the yoke surfaces 4A and 4B located at the center of the excitation coils 3A and 3B. Alternating current electromotive forces Va and Vb having an amplitude corresponding to the flow velocity of the fluid are generated along the electrode direction Z, and these electromotive forces Va and Vb are generated via the capacitance between the fluid and the surface electrodes 10A and 10B. are detected by the surface electrodes 10A and 10B.

This electrostatic capacitance is very small, on the order of several pF, and the impedance between the fluid and the surface electrodes 10A and 10B is high, making it susceptible to noise. Therefore, the impedance of the electromotive forces Va and Vb obtained by the plane electrodes 10A and 10B is lowered by a preamplifier 5U using an operational amplifier IC or the like.
In this embodiment, as shown in FIGS. 3 and 4, plane electrodes 10A and 10B are connected by a pair of connection wires 11A and 11B including a wiring pattern formed on the outer peripheral surface 2A of the measuring tube 2. and the preamplifier 5U are electrically connected.

That is, the connection wiring 11A includes a tube-side wiring pattern 12A formed on the outer peripheral surface 2A and having one end connected to the surface electrode 10A, and a substrate-side wiring pattern 5A formed on the preamplifier substrate 5 and having one end connected to the preamplifier 5U. and a jumper wire 15A connecting the tube-side wiring pattern 12A and the substrate-side wiring pattern 5A. The jumper wire 15A is soldered to a pad 16A formed at the other end of the tube-side wiring pattern 12A and a pad 5C formed at the other end of the substrate-side wiring pattern 5A.

The connection wiring 11B includes a tube-side wiring pattern 12B formed on the outer peripheral surface 2A and having one end connected to the surface electrode 10B, and a substrate-side wiring pattern 5B formed on the preamplifier substrate 5 and having one end connected to the preamplifier 5U. and a jumper wire 15B connecting the tube-side wiring pattern 12B and the substrate-side wiring pattern 5B. The jumper wire 15B is soldered to a pad 16B formed at the other end of the tube-side wiring pattern 12B and a pad 5D formed at the other end of the substrate-side wiring pattern 5B.

As a result, the tube-side wiring patterns 12A and 12B formed on the outer peripheral surface 2A are used in the section from the surface electrodes 10A and 10B to the position near the preamplifier substrate 5 among the connection wirings 11A and 11B. Therefore, it is possible to simplify installation work such as routing and fixing of the wiring cable, and reduce the cost of connection wiring and the burden of wiring work.

Further, the surface electrodes 10A, 10B and the tube-side wiring patterns 12A, 12B are made of a non-magnetic metal thin film such as copper, and are integrally formed on the outer peripheral surface 2A of the measuring tube 2, thereby simplifying the manufacturing process. This also leads to a reduction in product costs.

[Thin film]
Next, the thin film 7 formed on the outer surfaces of the plane electrodes 10A and 10B will be described.
As shown in FIGS. 2 to 4, in the present embodiment, a dielectric thin film 7 covering at least the entire outer surface of the surface electrodes 10A and 10B is formed on the outer peripheral surface 2A of the measuring tube 2. It is formed in an annular shape over the entire circumference. Specifically, since the plane electrodes 10A and 10B are conductors pattern-formed on the outer peripheral surface 2A, the thin film 7 is a dielectric thin film that is attached to the outer peripheral surface 2A so as to cover all of the plane electrodes 10A and 10B. film may be used.

As described above, when the measuring tube 2 is made of a dielectric material such as a resin or a ceramic and has a property of storing electricity, the outer peripheral surface 2A of the measuring tube 2 has a polarizing effect caused by fluid temperature changes. Electrification occurs due to the electrical effect, electrification due to the piezoelectric effect due to changes in fluid pressure, or electrification due to fluid friction when a low-conductivity fluid such as ultrapure water is flowed.

Since these charges occur on the outer peripheral surface 2A of the measuring tube 2, they may appear as a DC voltage (potential difference) between the surface electrodes 10A and 10B (and between the wiring patterns). Moreover, the DC voltage generated at this time may be several tens of mV or more depending on the conditions. On the other hand, the electromotive forces Va and Vb generated between the plane electrodes 10A and 10B according to the flow velocity of the fluid are within several mV (pp). For this reason, there is a possibility that the flow rate measurement value may drift due to the influence of the DC voltage generated between the surface electrodes 10A and 10B due to the charging.

In this embodiment, since the dielectric thin film 7 is formed on the outer peripheral surface 2A of the measuring tube 2 so as to cover the entire outer surface of the plane electrodes 10A and 10B, electric charges due to electrification are applied to the outer surfaces of the plane electrodes 10A and 10B. does not occur and moves to the thin film 7 outside it. Therefore, the charge does not appear as a DC voltage between the surface electrodes 10A and 10B, and the drift of the flow rate measurement value can be suppressed. Therefore, it is possible to reduce the influence of electrification generated on the outer peripheral surface 2A of the measuring tube 2 on the flow rate measurement.

The thin film 7 may be an insulating tape whose base material is a resin film that has a wide heat-resistant temperature range and is readily available, such as polyester, acrylic, epoxy, fluorine, or silicon. An insulating tape having a two-layer structure of a material and an adhesive such as a thermosetting rubber may be used. Also, when a thin film or insulating tape is used as the thin film 7, in order to secure a sufficient distance between the charge charged on the outer surface of the thin film 7 and the surface electrodes 10A and 10B, the thin film 7 is laminated so as to have a constant thickness. good too.

The thin film 7 is not limited to a sheet member attached to the outer surface of the plane electrodes 10A and 10B, and is formed by applying an insulating liquid coating agent such as electrical insulating varnish and drying the coating agent. It may be a thin film. Alternatively, an insulating coating such as a heat-shrinkable tube that annularly covers all of the surface electrodes 10A and 10B over the entire circumference of the measuring tube 2 may be used.

[About wiring pattern]
As shown in FIGS. 3 and 4, the tube-side wiring pattern 12A includes a longitudinal wiring pattern 13A linearly formed along the longitudinal direction X on the outer peripheral surface 2A of the measuring tube 2, and a plane electrode 10A. A circumferential wiring pattern 14A formed along the circumferential direction W of the measuring tube 2 on the outer peripheral surface 2A of the measuring tube 2 from an end along the longitudinal direction X to one end of the longitudinal wiring pattern 13A. .
The tube-side wiring pattern 12B includes a longitudinal wiring pattern 13B formed linearly along the longitudinal direction X on the outer peripheral surface 2A of the measuring tube 2, and an end portion of the surface electrode 10B along the longitudinal direction X. to one end of the longitudinal wiring pattern 13B.

Since a part of the connection wirings 11A and 11B is arranged inside or near the magnetic flux region F, when a pair of wiring cables are used as the connection wirings 11A and 11B, the distance between both wirings when viewed from the magnetic flux direction Y A signal loop is formed due to the positional deviation of , which causes the magnetic flux differential noise to occur as described above.
By using the wiring pattern formed on the outer peripheral surface 2A of the measuring tube 2 as in this embodiment, the positions of the connection wirings 11A and 11B can be accurately fixed. Therefore, it is possible to avoid the positional deviation between both wirings when viewed from the magnetic flux direction Y, and to easily suppress the occurrence of magnetic flux differential noise.

At this time, the longitudinal wiring pattern 13B is formed at a position overlapping the longitudinal wiring pattern 13A when viewed from the magnetic flux direction Y on the outer peripheral surface 2A on the side opposite to the longitudinal wiring pattern 13A across the measuring tube 2. there is That is, the longitudinal wiring patterns 13A and 13B are formed at symmetrical positions with respect to a plane along the electrode direction Z passing through the tube axis J on the outer peripheral surface 2A.

In the examples of FIGS. 3 and 4, longitudinal wiring patterns 13A and 13B are formed on intersection lines JA and JB where a plane passing through the tube axis J of the measuring tube 2 along the magnetic flux direction Y intersects the outer peripheral surface 2A. formed. Also, one end of the circumferential wiring pattern 14A is connected to the central position of the plane electrode 10A in the longitudinal direction X among the ends 17A of the plane electrode 10A. Similarly, one end of the circumferential wiring pattern 14B is connected to the center position of the plane electrode 10B in the longitudinal direction X among the ends 17B of the plane electrode 10B.

As a result, since the longitudinal wiring patterns 13A and 13B are formed at overlapping positions when viewed from the magnetic flux direction Y, it is possible to accurately avoid the formation of signal loops as described above, and to prevent the occurrence of magnetic flux differential noise. can be easily suppressed.

Further, by forming the longitudinal wiring patterns 13A, 13B on the crossing lines JA, JB, the lengths of the circumferential wiring patterns 14A, 14B become equal, and the lengths of the tube-side wiring patterns 12A, 12B as a whole become equal. Therefore, it is possible to suppress the imbalance of the phase difference and amplitude of the electromotive forces Va and Vb from the plane electrodes 10A and 10B, which is caused by the difference in the length of the tube-side wiring patterns 12A and 12B. In terms of measurement accuracy, the longitudinal wiring patterns 13A and 13B do not have to be on the intersection lines JA and JB, and are formed at overlapping positions when viewed from the magnetic flux direction Y, as long as these imbalances can be ignored. All you have to do is

[About the preamplifier board]
The preamplifier board 5 is a general printed wiring board for mounting electronic components, and as shown in FIG. It is Therefore, the preamplifier board 5 is attached along the direction intersecting the measuring tube 2 . The preamplifier board 5 can be easily attached to the measuring tube 2 by fixing the outer peripheral surface 2A of the measuring tube 2 penetrating the tube hole 5H and the end of the tube hole 5H with an adhesive. In the example of FIG. 2, the tube hole 5H does not open toward the board end of the preamplifier board 5, but a part of the periphery of the tube hole 5H opens directly toward the board end of the preamplifier board 5. Alternatively, it may be opened indirectly through a slit.

3 and 4, the mounting position of the preamplifier board 5 is a position away from the magnetic flux region F in the downstream direction of the fluid flowing in the longitudinal direction X (arrow direction). The mounting direction of the preamplifier board 5 is the direction in which the board surface intersects the measuring tube 2, as described above, which is the direction along the two-dimensional plane defined by the magnetic flux direction Y and the electrode direction Z here. The mounting position of the preamplifier board 5 may be any position outside the magnetic flux area F, or may be a position separated from the magnetic flux area F in the upstream direction opposite to the downstream direction. Moreover, the mounting direction of the preamplifier board 5 is not strictly limited to the direction along the two-dimensional plane, and may have an inclination with respect to the two-dimensional plane.

The plane electrodes 10A and 10B, the connection wirings 11A and 11B, and the preamplifier 5U are electrically shielded by a shield case 6 made of a metal plate connected to the ground potential. The shield case 6 has a substantially rectangular shape extending along the longitudinal direction X, and is provided with openings in the upstream and downstream directions from the magnetic flux region F, through which the measuring tube 2 passes.

As a result, the entire circuit portion with high impedance is shielded by the shield case 6, thereby suppressing the influence of external noise. At this time, a shield pattern 5G composed of a ground pattern (solid pattern) connected to a ground potential may be formed on the solder surface of the preamplifier substrate 5 opposite to the mounting surface of the preamplifier 5U. As a result, of the planes forming the shield case 6, all the planes in contact with the preamplifier board 5 may be open, and the structure of the shield case 6 can be simplified.

FIG. 5 is a configuration example of a differential amplifier circuit using a preamplifier. As shown in FIG. 5, the preamplifier 5U includes two operational amplifiers UA and UB that individually reduce the impedance of the electromotive forces Va and Vb from the plane electrodes 10A and 10B and output the resultants. These operational amplifiers UA and UB are sealed in the same IC package (dual operational amplifier). Further, they differentially amplify the input Va and Vb, and output the obtained differential output as the detection signal Vin to the signal amplifier circuit 21 in FIG.

Specifically, Va is input to the non-inverting input terminal (+) of UA, and Vb is input to the non-inverting input terminal (+) of UB. In addition, the inverting input terminal (-) of UA is connected to the output terminal of UA via a resistance element R1, and the inverting input terminal (-) of UB is connected to the output terminal of UB via a resistance element R2. It is The inverting input terminal (-) of UA is connected to the inverting input terminal (-) of UB via a resistance element R3. At this time, the amplification factors of UA and UB are matched by equalizing the values of R1 and R2. The gain is determined by the values of R1, R2 and R3.

Since the electromotive forces Va and Vb from the surface electrodes 10A and 10B are signals showing phases opposite to each other, by configuring such a differential amplifier circuit on the preamplifier substrate 5 using UA and UB, the excitation coil Even if temperature drift occurs in Va and Vb under the influence of heat from 3A, 3B and measurement tube 2, Va and Vb are differentially amplified. As a result, in the detection signal Vin, these in-phase temperature drifts are canceled and Va and Vb are added, so that a good S/N ratio can be obtained.

[Effects of the first embodiment]
In the capacitive electromagnetic flowmeter 100, when the measurement tube 2 is made of a dielectric material such as a resin or a ceramic and has a property of storing electricity, the outer peripheral surface 2A of the measurement tube 2 has a fluid temperature change. electrification due to the pyroelectric effect associated with fluid pressure change, electrification due to the piezoelectric effect due to changes in fluid pressure, or electrification due to fluid friction when a low-conductivity fluid such as ultrapure water is flowed.

In this embodiment, since the dielectric thin film 7 is formed on the outer peripheral surface 2A of the measuring tube 2 so as to cover the entire outer surface of the plane electrodes 10A and 10B, electric charges due to electrification are applied to the outer surfaces of the plane electrodes 10A and 10B. does not occur and moves to the thin film 7 outside it. Therefore, the charge does not appear as a DC voltage between the surface electrodes 10A and 10B, and the drift of the flow rate measurement value can be suppressed. Therefore, it is possible to reduce the influence of electrification generated on the outer peripheral surface 2A of the measuring tube 2 on the flow rate measurement.

In the present embodiment, the pair of plane electrodes 10A and 10B are made of conductors patterned on the outer peripheral surface 2A of the measuring tube 2, and the thin film 7 covers all of the plane electrodes 10A and 10B. A film attached to the outer peripheral surface 2A of the tube 2 may be used. As a result, there is no concern that the thickness of the thin film 7 will vary. In addition, it is possible to cut the sheet to a required size in advance, so that the sticking operation can be easily performed.

Moreover, in the present embodiment, an insulating tape having a resin film as a base material may be used as the thin film 7 . Specifically, as the thin film 7, an insulating tape having a two-layer structure of a resin film substrate and an adhesive may be used. As a result, there is no concern that the thickness of the thin film 7 will vary. Moreover, the sticking work is facilitated, and peeling of the thin film 7 after sticking can be prevented. Furthermore, since the surface electrodes 10A and 10B can also be moisture-proofed, deterioration of insulation between the electrodes 10A and 10B due to humidity can be prevented.

Further, in the present embodiment, a film formed by applying an insulating liquid coating agent and drying it may be used as the thin film 7 . As a result, peeling of the thin film 7 after coating can be prevented. Furthermore, since the surface electrodes 10A and 10B can also be moisture-proofed, deterioration of insulation between the electrodes 10A and 10B due to humidity can be prevented.

Moreover, in the present embodiment, the thin film 7 may be formed in a ring shape over the entire circumference of the measuring tube 2 . As a result, peeling of the film 7 after sticking can be prevented.

Further, in the present embodiment, an insulating coating that annularly covers the entire circumference of the measuring tube 2 may be used as the thin film 7 for the pair of surface electrodes 10A and 10B. Specifically, a heat-shrinkable tube may be used as the thin film 7 . As a result, there is no concern that the thickness of the thin film 7 will vary. Moreover, the sticking work is facilitated, and peeling of the thin film 7 after sticking can be prevented. Furthermore, since the surface electrodes 10A and 10B can also be moisture-proofed, deterioration of insulation between the electrodes 10A and 10B due to humidity can be prevented.

[Second embodiment]
Next, a capacitive electromagnetic flowmeter 100 according to a second embodiment of the present invention will be described with reference to FIGS. 6 and 7. FIG. FIG. 6 is a side view of the detector according to the second embodiment; FIG. 7 is a top view of a detector according to a second embodiment;
In the first embodiment, the width of the thin film 7 along the longitudinal direction X is slightly longer than the width of the surface electrodes 10A and 10B, and the thin film 7 covers only the surface electrodes 10A and 10B. bottom. In the present embodiment, the thin film 7 covers not only the plane electrodes 10A and 10B but also the tube-side wiring patterns 12A and 12B.

That is, in the present embodiment, the capacitive electromagnetic flowmeter 100 includes a pair of pipes formed facing each other on the outer peripheral surface 2A of the measurement pipe 2 and electrically connected to the pair of surface electrodes 10A and 10B, respectively. Side wiring patterns 12A and 12B are further provided, and a thin film 7 is formed so as to cover the outer surfaces of the pair of tube side wiring patterns 12A and 12B.
Other configurations of the capacitive electromagnetic flowmeter 100 according to the present embodiment are the same as those of the first embodiment, and descriptions thereof are omitted here.

As shown in FIGS. 6 and 7, the thin film 7 extends along the longitudinal direction X from the upstream ends of the surface electrodes 10A and 10B to the downstream ends of the tube-side wiring patterns 12A and 12B, that is, the pads 16A and 16B. It is annularly formed over the entire circumference of the measuring tube 2 in the range up to 16B.
As a result, electric charges due to electrification are not generated not only on the surface electrodes 10A and 10B but also on the outer surfaces of the tube-side wiring patterns 12A and 12B, and move to the thin film 7 on the outer side.

Therefore, static electricity does not appear as a DC voltage between the electrodes of the surface electrodes 10A and 10B and between the electrodes of the tube-side wiring patterns 12A and 12B, and the drift of the flow rate measurement value can be suppressed. Therefore, it is possible to further reduce the influence of electrification generated on the outer peripheral surface 2A of the measuring tube 2 on the flow rate measurement.

[Third embodiment]
Next, a capacitive electromagnetic flowmeter 100 according to a third embodiment of the present invention will be described with reference to FIGS. 8 and 9. FIG. FIG. 8 is a front view of a detector according to a third embodiment; FIG. 9 is a side view of the detector according to the third embodiment;
In the first and second embodiments, the case where the thin film 7 is formed in an annular shape over the entire circumference of the measuring tube 2 has been described as an example. In this embodiment, a case where the thin film 7 is formed by dividing it into two in the circumferential direction W of the measuring tube 2 will be described.

That is, in the present embodiment, the thin film 7 is divided in the circumferential direction W of the measuring tube 2 into two thin films 7A and 7B.
Other configurations of the capacitive electromagnetic flowmeter 100 according to the present embodiment are the same as those of the first or second embodiment, and descriptions thereof are omitted here.

As shown in FIGS. 8 and 9, the thin film 7A is formed in an angular range in the circumferential direction W that includes the plane electrode 10A, and the thin film 7B is formed in an angular range in the circumferential direction W that includes the plane electrode 10B. It is As a result, when the thin films 7A and 7B are attached after the surface electrodes 10A and 10B are formed on the outer peripheral surface 2A of the measuring tube 2, the thin films 7A and 7B are attached annularly over the entire circumference of the measuring tube 2 because the thin films are divided into two. Compared to the case, the work load at the time of pasting can be reduced. In addition, the thin films 7A and 7B can be reduced in area to cover the surface electrodes 10A and 10B, and the member cost can be reduced.

In FIGS. 8 and 9, the width of the thin films 7A and 7B along the longitudinal direction X is the range to the downstream ends of the plane electrodes 10A and 10B, and only the plane electrodes 10A and 10B are covered with the thin films 7A and 7B. Although the case has been described as an example, it is not limited to this. For example, as shown in FIGS. 6 and 7, the width of the thin films 7A and 7B along the longitudinal direction X may be set to the downstream ends of the tube-side wiring patterns 12A and 12B, ie, the pads 16A and 16B. good.

As a result, electrification does not appear as a DC voltage between the electrodes of the surface electrodes 10A and 10B and between the electrodes of the pipe-side wiring patterns 12A and 12B, thereby suppressing the drift of the flow rate measurement value. Therefore, it is possible to further reduce the influence of electrification generated on the outer peripheral surface 2A of the measuring tube 2 on the flow rate measurement.

[Expansion of Embodiment]
Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, each embodiment can be implemented in any combination within a non-contradictory range.

DESCRIPTION OF SYMBOLS 100... Capacity-type electromagnetic flowmeter 1... Flow path 2... Measuring tube 3A, 3B... Exciting coil 4A, 4B... Yoke surface 5... Preamplifier board 5A, 5B... Board side wiring pattern 5C, 5D... Pad 5G... Shield pattern 5H... Tube hole 5U... Preamplifier 6, 6A, 6B... Shield case 7, 7A, 7B... Thin film 10A, 10B... Surface electrode 11A, 11B... Connection wiring 12A, 12B ... tube-side wiring pattern 13A, 13B ... longitudinal wiring pattern 14A, 14B ... circumferential wiring pattern 15A, 15B ... jumper wire 16A, 16B ... pad 17A, 17B ... end 20 ... detector 21 Signal amplifier circuit 22 Signal detection circuit 23 Excitation circuit 25 Transmission circuit 26 Setting/display circuit 27 Arithmetic processing circuit 27A Excitation control unit 27B Flow rate calculation unit UA, UB Operational amplifier, R1, R2, R3... Resistance element L... Transmission line Va, Vb... Electromotive force Vin... Detection signal Φ... Magnetic flux F... Magnetic flux area X... Longitudinal direction Y... Magnetic flux direction Z... Electrode Direction, W... Circumferential direction, J... Pipe axis, JA, JB, JC, JD... Intersection line.

Claims (10)

a dielectric measuring tube through which the fluid to be measured flows;
a pair of surface electrodes arranged opposite to each other on the outer peripheral surface of the measuring tube with the measuring tube interposed therebetween for detecting an electromotive force generated in the fluid;
a preamplifier board mounted with a preamplifier for amplifying the electromotive force detected by the pair of surface electrodes;
a pair of tube-side wiring patterns integrally formed with the pair of surface electrodes on the outer peripheral surface of the measurement tube and electrically connecting the pair of surface electrodes and the preamplifier, respectively;
A capacitive electromagnetic flowmeter, comprising: a dielectric thin film formed to cover at least all of the outer surfaces of the pair of surface electrodes and the pair of pipe-side wiring patterns . The capacitive electromagnetic flowmeter according to claim 1,
The pair of planar electrodes are made of conductors patterned on the outer peripheral surface of the measuring tube,
The capacitive electromagnetic flowmeter, wherein the thin film is a film attached to the outer peripheral surface of the measuring tube so as to cover all of the pair of surface electrodes. In the capacitive electromagnetic flowmeter according to claim 1 or claim 2,
further comprising a pair of tube-side wiring patterns formed on the outer peripheral surface of the measurement tube so as to face each other and electrically connected to the pair of surface electrodes, respectively;
The capacitive electromagnetic flowmeter, wherein the thin film is formed so as to cover outer surfaces of the pair of pipe-side wiring patterns. In the capacitive electromagnetic flowmeter according to any one of claims 1 to 3,
A capacitive electromagnetic flowmeter, wherein the thin film is made of an insulating tape having a resin film as a base material. In the capacitive electromagnetic flowmeter according to any one of claims 1 to 3,
A capacitive electromagnetic flowmeter, wherein the thin film is made of an insulating tape having a two-layer structure of a resin film substrate and an adhesive. In the capacitive electromagnetic flowmeter according to any one of claims 1 to 3,
A capacitive electromagnetic flowmeter, wherein the thin film is a film formed by applying and drying an insulating liquid coating agent. In the capacitive electromagnetic flowmeter according to any one of claims 1 to 3,
The capacitive electromagnetic flowmeter, wherein the thin film is an insulating film that annularly covers all of the pair of surface electrodes over the entire circumference of the measuring pipe. The capacitive electromagnetic flowmeter according to claim 7,
A capacitive electromagnetic flowmeter, wherein the insulating film is made of a heat-shrinkable tube. In the capacitive electromagnetic flowmeter according to any one of claims 1 to 8,
A capacitive electromagnetic flowmeter, wherein the thin film is annularly formed around the entire circumference of the measuring pipe. In the capacitive electromagnetic flowmeter according to any one of claims 1 to 8,
The capacitive electromagnetic flowmeter, wherein the thin film is divided into two in the circumferential direction of the measuring tube.

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