JP2021081408A - Electromagnetic flowmeter - Google Patents

Abstract

To provide an electromagnetic flowmeter which has high product performance and improved usability, and which enables the cost thereof to be reduced and the productivity thereof to be improved.SOLUTION: The electromagnetic flowmeter comprises: a measurement pipe 14; excitation coils 15, 16; first and second sub boards 17, 18 through which the measurement pipe 14 penetrates; and first and second joints 21, 22 connected to the measurement pipe 14. The electromagnetic flowmeter further comprises: a case 12 having first and second side walls 23, 24 to which the first and second joints 21, 22 are respectively fixed; and a main board 19 that blocks an opening of the case 12 to form a closed space S1. The closed space S1 includes: a first space S1a which is partitioned by the first and second sub boards 17, 18 and in which the excitation coils 15, 16 are housed; and second and third spaces S1b, S1c which are formed outside the first space S1a, and in which the first and second joints 21, 22 are housed. The first space S1a is formed in such a manner that air flow between the first space S1a: and the second and third spaces S1b, S1c is regulated.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electromagnetic flow meter that measures the flow rate of a fluid flowing through a measuring tube.

In recent years, for example, a small capacitive electromagnetic flowmeter for the FA (Factory Automation) market as described in Patent Document 1 has been put into practical use. The electromagnetic flowmeter described in Patent Document 1 is configured as shown in FIGS. 15 and 16. In the electromagnetic flowmeter shown in Patent Document 1, the measuring tube 5 and the exciting coil are contained in one space sealed by the body (case) 1, the casing (upper lid) 2, and the pair of attachments (connecting joints) 3 and 4. 6. All components including the excitation board 7 and the control board 8 are built-in. The pair of attachments 3 and 4 are formed of a metal material and are connected to the measuring tube 5 in the body 1 to form an integrated flow path in cooperation with the measuring tube 5. The purpose of sealing the inside with the body (case) 1, the casing (upper lid) 2, and the pair of attachments (connecting joints) 3 and 4 is to prevent the intrusion of moisture from the outside, and the respective joints. A sealing means (rubber packing, etc.) (not shown) is applied to the.

Japanese Unexamined Patent Publication No. 2014-202662

In the electromagnetic flowmeter described in Patent Document 1, a part of the pair of attachments 3 and 4 protrudes into a resin case having a sealed structure composed of a body 1 and a casing 2. These attachments 3 and 4 are made of a metal material and have high thermal conductivity. Therefore, when a high-temperature fluid is flowed as the measurement fluid, heat convection occurs in the resin case. Due to this heat convection, the temperature inside the resin case rises, and there is a problem that the temperature of parts such as the exciting coil 6, the exciting substrate 7, and the control substrate 8 rises.

In particular, since the exciting coil 6 generates self-heating due to the exciting current and the coil resistance, the heat-resistant temperature of the insulating material of the electric wire to be used is determined by considering not only the influence of the temperature of the fluid but also the temperature rise due to the self-heating. The exciting current must be limited so that it does not exceed. When the exciting current is lowered, the obtained flow rate signal level is lowered, and the S / N ratio is deteriorated, that is, the product performance (accuracy and stability of the flow rate measurement value) is deteriorated.

Further, with respect to the circuit components mounted on the exciting board 7 and the control board 8, the allowable operating temperature range of the circuit parts is also taken into consideration in consideration of the temperature rise due to the above-mentioned thermal convection and the temperature rise due to the heat generation of the exciting coil 6. The product specifications had to be restricted so as not to exceed the upper limit of. For example, the upper limit of the temperature range of the measurement fluid is 85 ° C., and the upper limit of the product operating temperature range is 50 ° C. Therefore, the conventional electromagnetic flowmeter as shown in Patent Document 1 is not easy to use.

In order to eliminate such restrictions, as circuit parts, circuit parts whose upper limit of the allowable operating temperature range is higher than those used in general industrial equipment, for example, special specification parts whose upper limit temperature reaches 125 ° C. It is possible to use it. However, many of these types of special specification parts are expensive and have poor distribution. Therefore, when special specification parts are used, it is inevitable that the cost of the product will increase and the productivity will deteriorate. Even if the temperature is below the upper limit temperature of the component specifications, the life of the components with a limited life such as LCD, LED, non-volatile memory, electrolytic capacitor, etc. is shortened by using them for a long time near the upper limit temperature.

An object of the present invention is to make it less susceptible to the influence of heat transferred from a fluid through a joint into a case, thereby improving product performance and usability, reducing costs and improving productivity. Is to provide an electromagnetic flowmeter capable of

In order to achieve this object, the electromagnetic flowmeter according to the present invention has a measuring tube formed of a material having a low thermal conductivity and through which a fluid to be measured flows, and an excitation that forms a magnetic circuit so as to pass through the measuring tube. The coil, a pair of sub-boards that penetrate the measuring tube and extend in a direction intersecting the longitudinal direction of the measuring tube, a pair of joints connected to both ends of the measuring tube, and the pair of joints penetrate. It has first and second side walls to be fixed, and closes the box-shaped case for accommodating the measuring tube, the exciting coil and the sub-board, and the opening of the case, and closes inside the case. The closed space is formed outside the first space and the first space in which the exciting coil is housed, which is partitioned by the pair of sub-boards. The first space includes a second space and a third space in which the pair of joints are housed, and the first space is formed so as to regulate the flow of air with the second and third spaces. Is.

The present invention further comprises a shield case that surrounds the measuring tube in cooperation with the pair of sub-boards in the electromagnetic flow meter, and the shield case accommodates the measuring tube in the first space. It may be divided into an inner space and an outer space around the inner space.

In the present invention, in the electromagnetic flowmeter, circuit components having relatively low heat resistance may be mounted at positions on the main board other than the second and third spaces.

In the electromagnetic flow meter, the present invention further comprises a lid that is attached to the opening side end of the case to form a sealing space in cooperation with the case, and the sealing space inside the lid as the main substrate. A lid-side substrate that partitions a fourth space on the side and a fifth space on the opposite side is provided, and heat resistance mounted on the main substrate is provided in a portion of the lid-side substrate that is included in the fifth space. A circuit component having a relatively low heat resistance as compared with a circuit component having a relatively low heat resistance may be mounted.

In the present invention, the heat convection generated in the case using the pair of joints as a heat source is limited to the second and third spaces. Therefore, the inside of the first space is less susceptible to the heat of the measurement fluid. Therefore, since the temperature rise of the exciting coil due to the heat of the measuring fluid is suppressed, the exciting current can be increased accordingly. As a result, according to the present invention, it is possible to provide an electromagnetic flow meter having high product performance such as accuracy and stability of flow rate measurement values.

Further, since the heat convection in the case is restricted to the second and third spaces, the temperature rise of the main board is suppressed, so that the heat of the fluid is less likely to be transferred to the circuit components mounted on the main board. .. Therefore, since the temperature rise of the circuit parts can be suppressed, the upper limit of the fluid temperature range of the product specifications can be raised, and the upper limit of the operating temperature range of the product can be raised, so that an electromagnetic flowmeter that is easy to use is provided. it can. Moreover, since it is possible to use inexpensive and well-distributed circuit parts generally used in industrial equipment as circuit parts, it is possible to reduce the cost of the electromagnetic flowmeter and increase the productivity. be able to.

It is sectional drawing which shows the structure of the electromagnetic flowmeter which concerns on 1st Embodiment. It is a top view of the case part of the electromagnetic flowmeter which concerns on 1st Embodiment. It is a block diagram which shows the circuit structure of the electromagnetic flowmeter which concerns on 1st Embodiment. It is sectional drawing of the electromagnetic flowmeter which concerns on 1st Embodiment. It is an assembly drawing of the electromagnetic flowmeter which concerns on 1st Embodiment. It is a top view which shows the detector which concerns on 1st Embodiment. It is a side view which shows the detector which concerns on 1st Embodiment. It is a front view which shows the detector which concerns on 1st Embodiment. It is a figure explaining the structural example of the differential amplifier circuit using a preamplifier. It is sectional drawing which shows the structure of the electromagnetic flowmeter which concerns on 2nd Embodiment. It is sectional drawing which shows the structure of the electromagnetic flowmeter which concerns on 3rd Embodiment. It is a top view of the case part of the electromagnetic flowmeter according to the 3rd Embodiment. It is an assembly drawing of the electromagnetic flowmeter which concerns on 3rd Embodiment. It is sectional drawing which shows the structure of the electromagnetic flowmeter which concerns on 3rd Embodiment. It is sectional drawing seen from the side for explaining the structure of the conventional electromagnetic flowmeter. It is sectional drawing seen from the front for explaining the structure of the conventional electromagnetic flowmeter.

Next, an embodiment of the present invention will be described with reference to the drawings.
[First Embodiment]
First, the electromagnetic flowmeter 11 according to the first embodiment of the present invention will be described with reference to FIGS. 1 and 2. The electromagnetic flowmeter 11 is configured by attaching various parts described later to a bottomed square tubular case 12. The opening 12a of the case 12 is closed by the lid 13. The lid 13 is attached to the opening-side end of the case 12 and cooperates with the case 12 to form a sealing space S.

The parts to be attached to the case 12, which will be described in detail later, include a measuring tube 14 extending from one end side to the other end side of the case 12, and a pair of exciting coils 15 and 16 arranged on both sides of the measuring tube 14. A pair of sub-boards (first sub-board 17 and second sub-board 18) through which the measuring tube 14 penetrates, a main board 19 attached to the opening 12a of the case 12, and the like. The measuring tube 14, the exciting coils 15, 16 and the first and second sub-boards 17 and 18 are housed in the case 12.

A fluid as a measurement target flows into the measuring tube 14 from the upstream end located on the left side in FIG. 1 to the downstream end located on the right side in FIG. The upstream end of the measuring tube 14 is supported by the case 12 via a first joint 21. The downstream end of the measuring tube 14 is supported by the case 12 via a second joint 22. The first joint 21 penetrates the first side wall 23 of the case 12 and is fixed to the first side wall 23. The second joint 22 penetrates the second side wall 24 of the case 12 and is fixed to the second side wall 24.
The first and second sub-boards 17, 18 and the main board 19 are electrically connected by a conductive means (not shown). Further, the first and second sub-boards 17 and 18 and the main board 19 are provided with an electric circuit as shown in FIG.

FIG. 3 is a block diagram showing a circuit configuration of the electromagnetic flowmeter 11 according to the first embodiment. In the following, a capacitive electromagnetic flowmeter 11 in which a pair of detection electrodes does not directly contact the fluid as a measurement target flowing in the measuring tube 14 will be described as an example, but the present invention is not limited to this, and the detection electrodes are used. The present invention can be similarly applied to a liquid contact type electromagnetic flowmeter that is in direct contact with a fluid.
As shown in FIG. 3, the capacitive electromagnetic flowmeter 11 has a detection unit 31, a signal amplification circuit 32, a signal detection circuit 33, an excitation circuit 34, and electricity for measuring conductivity (electrical conductivity) as main circuit units. It includes a circuit 35, a transmission circuit 36, a setting / display circuit 37, and an arithmetic processing unit (CPU) 38.

The detection unit 31 includes a measuring tube 14, an exciting coil 15 and 16 forming a magnetic circuit so as to pass through the measuring tube 14, a pair of surface electrodes 41 and 51, and a preamplifier 61, and the inside of the measuring tube 14 is provided. It has a function of detecting electromotive forces Va and Vb according to the flow velocity of the fluid flowing through the flow path 14a by the surface electrodes 41 and 51 and outputting an AC detection signal Vin corresponding to these electromotive forces Va and Vb. ..

The excitation control unit 38A of the arithmetic processing circuit 38 outputs an excitation control signal Vex for switching the polarity of the excitation current Iex based on a preset excitation cycle. The excitation circuit 34 supplies an alternating current excitation current Iex to the excitation coils 15 and 16 based on the excitation control signal Vex from the excitation control unit 38A of the arithmetic processing circuit 38.
The signal amplification circuit 32 filters the noise component contained in the detection signal Vin output from the detection unit 31, and then outputs the AC flow rate signal VF obtained by amplification. The signal detection circuit 33 sample-holds the flow signal VF from the signal amplification circuit 32, A / D converts the obtained DC voltage into the flow amplitude value DF, and outputs it to the arithmetic processing circuit 38.

The flow rate calculation unit 38B of the arithmetic processing circuit 38 calculates the flow rate of the fluid based on the flow rate amplitude value DF from the signal detection circuit 33, and outputs the flow rate measurement result to the transmission circuit 36. The transmission circuit 36 transmits data to and from 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 38 to the host device.

In the electric circuit 35 for measuring conductivity, for example, the fluid flowing in the measuring tube 14 via the first joint 21 has a common potential of Vcom, and the surface electrode 62 for measuring conductivity is alternating current via a resistance element. A signal is applied, the amplitude of the AC detection signal generated on the surface electrode 62 for measuring conductivity at that time is sampled, and the AC amplitude value data DP obtained by A / D conversion is output to the arithmetic processing circuit 38. It is a circuit.

The conductivity calculation unit 38C of the arithmetic processing circuit 38 has a function of calculating the electrical conductivity of the fluid based on the AC amplitude value data DP from the electric circuit 35 for measuring the conductivity.
The empty state determination unit 38D of the arithmetic processing circuit 38 has a function of determining the presence or absence of the fluid in the measuring tube 14 based on the electric conductivity of the fluid calculated by the conductivity calculation unit 38C.
Generally, the electrical conductivity of a fluid is greater than the electrical conductivity of air. Therefore, the empty state determination unit 38D determines the presence / absence of the fluid by performing threshold processing on the electrical conductivity of the fluid calculated by the conductivity calculation unit 38C.

The setting / display circuit 37 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 38, and outputs from the arithmetic processing circuit 38. The flow rate measurement result and the empty state judgment result are displayed by a display circuit such as an LED or an LCD.

The arithmetic processing circuit 38 includes a CPU and its peripheral circuits, and by executing a preset program on the CPU, the hardware and software are made to cooperate, thereby causing the excitation control unit 38A, the flow rate calculation unit 38B, and conductivity. Various processing units such as a rate calculation unit 38C and an empty state determination unit 38D are realized.

In the circuit shown in FIG. 3, the preamplifier 61 of the detection unit 31 is mounted on the second sub-board 18 of the first and second sub-boards 17 and 18 through which the downstream end of the measuring tube 14 penetrates. ing. The signal amplifier circuit 32, the signal detection circuit 33, the excitation circuit 34, a part of the electric circuit 35 for measuring conductivity, the transmission circuit 36, the setting / display circuit 37, and the arithmetic processing circuit 38 will be described later. It is mounted on the main board 19. The electrical connection between the preamplifier 61 and the signal amplification circuit 32 and the electrical connection between the excitation circuit 34 and the excitation coils 15 and 16 are made by conduction means (not shown), respectively. Among the electric circuits 35 for measuring conductivity, the electric circuit not mounted on the main board 19 is the first of the first and second sub-boards 17 and 18 through which the upstream end of the measuring tube 14 penetrates. It is mounted on the sub-board 17 of the above and is connected to the electric circuit on the main board 19 side by a conductive means (not shown).

[Mounting structure of measuring tube]
Next, the mounting structure of the measuring tube 14 will be described in detail with reference to FIGS. 1, 2 and 4. FIG. 2 is a top view of the electromagnetic flow meter 11 according to the first embodiment. FIG. 4 is a cross-sectional perspective view of the electromagnetic flow meter 11 according to the first embodiment.

In the present embodiment, both ends of the measuring tube 14 are passed through the tube holes 17a and 18a provided in the first and second sub-boards 17 and 18, respectively, and these first and second sub-boards 17 and 18 are formed. Is held in the case 12 and the measuring tube 14 is attached to the case 12. As shown in FIG. 2, the side end portions 17b and 17c of the first sub-board 17 are inserted and fitted into the guide portions 73 and 74 formed on the inner wall portion 12b of the case 12 through the opening portion 12a of the case 12. ing. The side end portions 18b, 18c of the second sub-board 18 are inserted and fitted into the guide portions 75, 76 formed on the inner wall portion 12b of the case 12 through the opening portion 12a of the case 12. The first sub-board 17 is fitted into the guide portions 73 and 74 to hold the case 12, and the second sub-board 18 is fitted into the guide portions 75 and 76 and held by the case 12. , The measuring tube 14 is attached to the case 12.

The measuring tube 14 is formed in a cylindrical shape by a material such as ceramic or resin which is excellent in insulating property and dielectric property and has low thermal conductivity. As shown in FIG. 2, a yoke 77 and a pair of exciting coils 15 and 16 are provided on the outside of the measuring tube 14. The yoke 77 has a substantially C-shaped cross section that is opened toward the opening of the case 12 so that the magnetic flux direction (second direction) Y is orthogonal to the longitudinal direction (first direction) X of the measuring tube 14. It is formed. The pair of exciting coils 15 and 16 are wound and held around the coil bobbins 15a and 16a, respectively, and are attached to the yoke 77 so as to face each other with the measuring tube 14 interposed therebetween. In the following, only the end faces of the opposing yokes 77, that is, only the yoke faces 77A and 77B are shown for the sake of easy viewing.

On the other hand, on the outer peripheral surface 14b of the measuring tube 14, a pair of surface electrodes (first) made of thin film conductors are formed in the electrode direction (third direction) Z orthogonal to the longitudinal direction X and the magnetic flux direction (second direction) Y. 41 and the surface electrode (second surface electrode) 51 are arranged to face each other.
As a result, when an alternating current exciting current Iex is supplied to the exciting coils 15 and 16, a magnetic flux Φ is generated between the yoke surfaces 77A and 77B located at the center of the exciting coils 15 and 16, and the fluid flowing through the flow path 14a is affected. An alternating current electromotive force having an amplitude corresponding to the flow velocity of the fluid is generated along the electrode direction Z, and this electromotive force is passed through the electrostatic capacitance between the fluid and the surface electrodes 41, 51 to the surface electrodes 41, 51. Is detected by.

The case 12 has a bottomed square cylinder (box shape) having an opening 12a at the upper side and accommodating the measuring tube 14, the exciting coils 15, 16, the first and second sub-boards 17, 18 and the like inside. It is made of a resin material. As shown in FIG. 2, guide portions 73 to 76 are formed on the pair of inner wall portions 12b parallel to the longitudinal direction X of the inner wall portions of the case 12 at positions facing each other. The guide portions 73 to 76 are composed of two ridges 73a, 73b, 74a, 74b, 75a, 75b, 76a, 76b formed in parallel with the electrode direction Z, respectively, and the fitting portion 78 between the ridges 78. ~ 81 fit with the side ends 17b, 17c, 18b, 18c of the first and second sub-boards 17, 18 inserted through the opening 12a.

The ridges 73a, 73b, 74a, 74b, 75a, 75b, 76a, 76b of the guide portions 73 to 76 do not need to be continuously formed in the electrode direction Z, and the side end portions 17b, 17c, 18b and 18c may be formed separately at intervals of smooth insertion. Further, the guide portions 73 to 76 are formed in the inner wall portion 12b instead of the ridges, and are grooves in which the side end portions 17b, 17c, 18b, 18c of the first and second sub-boards 17, 18 are inserted. There may be.

A metal material (for example, for example) capable of connecting a pipe (not shown) provided outside the electromagnetic flowmeter 11 and a measuring tube 14 to a pair of side surfaces 12c parallel to the magnetic flux direction Y among the side surfaces of the case 12. The tubular first and second joints 21 and 22 made of SUS) are arranged. At this time, the measuring tube 14 is housed inside the case 12 along the longitudinal direction X, and the first joint 21 and the second joint 22 sandwich the O-ring 82 at both ends of the measuring tube 14. Each is connected.

Here, at least one of the first and second joints 21 and 22 functions as a common electrode 83 (see FIG. 3). For example, the first joint 21 not only connects the external pipe and the measuring pipe 14 but also functions as a common electrode 83 by being connected to the common potential Vcom.
As described above, by realizing the common electrode 83 by the first joint 21 made of metal, the area of the common electrode 83 in contact with the fluid is widened. As a result, even if foreign matter adheres or corrodes to the common electrode 83, the area of the portion where the foreign matter adheres or corrodes is relatively small with respect to the total area of the common electrode 83, so that polarization occurs. It is possible to suppress measurement errors due to changes in capacitance.

FIG. 5 is an assembly drawing of the electromagnetic flow meter 11 according to the first embodiment.
The first and second sub-boards 17 and 18 are general printed circuit boards for mounting circuit components (for example, a glass cloth base material epoxy resin copper-clad laminate having a plate thickness of 1.6 mm), and FIG. As shown in the above, tube holes 17a and 18a for passing the measuring tube 14 are formed at substantially the center position. Therefore, the first and second sub-boards 17 and 18 extend in a direction through which the measuring tube 14 penetrates and intersects the longitudinal direction of the measuring tube 14.

The main board 19 is a printed circuit board equivalent to the first and second sub-boards 17, 18 and, as shown in FIG. 1, extends in the longitudinal direction of the measuring tube 14, and the first and second sub-boards 17, It is attached to the opening 12a of the case 12 so as to make substantially contact with 18. The main substrate 19 according to this embodiment closes the opening 12a of the case 12 in a state of substantially contacting the pair of first and second sub-boards 17 and 18, and is formed inside the case 12 and inside the lid 13. The sealed space S is divided into a closed space S1 in the case 12 and a closed space S2 in the lid 13. The main board 19 is fixed to mounting seats 84 provided at four corners of the case 12 by fixing bolts 85.

Further, the main substrate 19 is substantially in contact with each other so that no gap is formed at one end of the electrode directions Z on the first and second sub-boards 17 and 18. The "substantial contact" here means a state in which the main substrate 19 is in contact with a part or all of the first and second sub-boards 17 and 18 at one end in the electrode direction Z, and the main substrate 19 is in contact with the first and first This includes a state in which the second sub-boards 17 and 18 do not come into contact with each other and a minute gap is formed between the main board 19 and the first and second sub-boards 17 and 18. As the main substrate 19 "substantially contacts" the first and second sub-boards 17 and 18 in this way, the pair of first and second sub-boards 19 in a state where the main substrate 19 closes the opening of the case 12. The inside of the case 12 is partitioned into a plurality of spaces in cooperation with the sub-board.

The closed space S1 in the case 12 is partitioned by a pair of first and second sub-boards 17, 18 and accommodates the exciting coils 15 and 16, and the outside of the first space S1a. Includes second and third spaces S1b, S1c formed in the space and accommodating the first and second joints 21 and 22. Almost no gap is formed between the first and second sub-boards 17 and 18 and the measuring tube 14. Almost no gap is formed between the first and second sub-boards 17 and 18 and the main board 19. Therefore, the first space S1a is formed so as to regulate the flow of air with the second and third spaces S1b and S1c.

The circuit components constituting the electric circuit mounted on the main board 19, that is, the signal amplification circuit 32, the signal detection circuit 33, the excitation circuit 34, a part of the electric circuit 35 for measuring conductivity, and the transmission circuit 36. Among the circuit components constituting the setting / display circuit 37 and the arithmetic processing circuit 38, the heat resistance of the circuit component 91 in which the upper limit of the allowable operating temperature range is relatively low and the life-long component 92 is relatively low. The circuit components are mounted at positions other than the second and third spaces S1b and S1c. Examples of the circuit component 91 in which the upper limit of the allowable operating temperature range is relatively low include an LCD, a microcomputer, and a semiconductor integrated circuit such as a non-volatile memory. Examples of the life-long component 92 include LCDs, LEDs, non-volatile memories, electrolytic capacitors, and the like. The term "heat resistance" as used herein is a heat resistant temperature at which the performance of semiconductor parts and other general circuit parts can be maintained even when subjected to thermal stress. Further, in a life-long component such as an electrolytic capacitor, an LCD, or an LED, the heat resistance characteristic of the component performance with respect to the operating temperature and the operating time corresponds to "heat resistance". In this case, a component that can operate at a high operating temperature for a long time is a component having high "heat resistance".

FIG. 6 is a top view of the detector, which is a part of the electromagnetic flow meter 11 for measuring the flow rate. FIG. 7 is a side view showing the detector according to the first embodiment. FIG. 8 is a front view showing the detector according to the first embodiment. Note that FIGS. 6 and 7 are drawn with the first sub-board 17 omitted.
The capacitance between the fluid and the surface electrodes 41 and 51 is very small, about several pF, and the impedance between the fluid and the surface electrodes 41 and 51 is high, so that it is easily affected by noise. Therefore, the preamplifier 61 using an operational amplifier IC or the like lowers the impedance of the electromotive forces Va and Vb obtained by the surface electrodes 41 and 51. The preamplifier 61 is mounted on one surface of the second sub-board 18 close to the surface electrodes 41 and 51.

In the present embodiment, the second sub-board is located in a region where the magnetic flux Φ is generated between the yoke surfaces 77A and 77B of the exciting coils 15 and 16, that is, the outer position of the magnetic flux region F in the direction intersecting the measuring tube 14. 18 is attached to the measuring tube 14 to mount the preamplifier 61, and the surface electrodes 41 and 51 and the preamplifier 61 are electrically connected via the connection wirings 42 and 52.

In the examples of FIGS. 6 to 8, the mounting position of the second sub-board 18 is a position separated from the magnetic flux region F in the downstream direction of the fluid flowing in the longitudinal direction X (arrow direction). Further, as described above, the mounting direction of the second sub-board 18 is the direction in which the board surface intersects the measuring tube 14, in this case, the direction along the two-dimensional plane composed of the magnetic flux direction Y and the electrode direction Z. .. The mounting position of the second sub-board 18 may be any position outside the magnetic flux region F, and may be a position separated from the magnetic flux region F in the upstream direction opposite to the downstream direction. Further, the mounting direction of the second sub-board 18 is not strictly limited to the direction along the two-dimensional plane, and may have an inclination with the two-dimensional plane.

Further, the surface electrodes 41 and 51, the connection wirings 42 and 52, and the preamplifier 61 are electrically shielded by a shield case 93 made of a metal plate connected to the ground potential. The shield case 93 has a substantially rectangular cross section extending along the longitudinal direction X, and as shown in FIG. 1, openings for the measuring tube 14 to penetrate the inside are formed in the upstream direction and the downstream direction from the magnetic flux region F. It is provided in. One end of the shield case 93 is closed by the first sub-board 17, and the other end is closed by the second sub-board 18. The shield case 93 according to this embodiment is fixed in a state where the other end is in contact with the second sub-board 18. As shown in FIG. 1, the shield case 93 provided between the first sub-board 17 and the second sub-board 18 accommodates the measuring tube 14 in the first space S1a of the case 12. It is divided into an inner space S3 and an outer space S4 around the inner space S3.

Since the measuring tube 14 is housed in the shield case 93, the entire circuit portion having high impedance is shielded by the shield case 93, and the influence of external noise is suppressed. In this embodiment, from the grounding pattern (solid pattern) connected to the grounding potential on the other surface (the surface opposite to the mounting surface) of the second subboard 18 of the second subboard 18. Shield pattern 94 is formed. As a result, among the planes constituting the shield case 93, all the planes in contact with the second sub-board 18 may be open, and the structure of the shield case 93 can be simplified.

The connection wirings 42 and 52 are wirings for connecting the surface electrodes 41 and 51 and the preamplifier 61, and since the whole is shielded by the shield case 93 as described above, even if a general pair of wiring cables is used. Good. At this time, both ends of the wiring cable may be soldered to the pads formed on the surface electrodes 41 and 51 and the second sub-board 18, respectively.
In the present embodiment, as shown in FIGS. 6 to 8, tube-side wiring patterns 43 and 53 formed on the outer peripheral surface 14b of the measuring tube 14 are used as the connection wirings 42 and 52.

That is, the connection wiring 42 has a pipe-side wiring pattern 43 formed on the outer peripheral surface 14b and one end connected to the surface electrode 41, and a substrate side formed on the second sub-board 18 and one end connected to the preamplifier 61. It is composed of a wiring pattern 44, and a jumper wire 45 connecting the pipe-side wiring pattern 43 and the board-side wiring pattern 44. The jumper wire 45 is soldered to a pad 43a formed at the other end of the pipe-side wiring pattern 43 and a pad 44a formed at the other end of the substrate-side wiring pattern 44.

Further, the connection wiring 52 has a pipe-side wiring pattern 53 formed on the outer peripheral surface 14b and one end connected to the surface electrode 51, and a substrate side formed on the second sub-board 18 and one end connected to the preamplifier 61. It is composed of a wiring pattern 54 and a jumper wire 55 connecting the pipe-side wiring pattern 53 and the board-side wiring pattern 54. The jumper wire 55 is soldered to a pad 53a formed at the other end of the pipe-side wiring pattern 53 and a pad 54a formed at the other end of the substrate-side wiring pattern 54.

As a result, among the connection wirings 42 and 52, the pipe-side wiring patterns 43 and 53 formed on the outer peripheral surface 14b are used in the section from the surface electrodes 41 and 51 to the vicinity position of the second sub-board 18. Become. Therefore, as in the case of using the pair of wiring cables described above, the installation work such as routing and fixing of the wiring cables can be simplified, and the cost of connection wiring and the burden of wiring work can be reduced.

Further, the surface electrodes 41, 51 and the tube-side wiring patterns 43, 53 are made of a non-magnetic metal thin film such as copper, and are integrally formed on the outer peripheral surface 14b of the measuring tube 14 by a metallizing process, thus simplifying the manufacturing process. It also leads to reduction of manufacturing cost. The metallizing treatment described above may be a plating treatment, a vapor deposition treatment, or the like, and may be further attached to a pre-molded non-magnetic metal thin film body. When attaching the non-magnetic metal thin film body, jumper wires 45 and 55 are not used, and the tip of the non-magnetic metal thin film body (the other end side of the pipe side wiring patterns 43 and 53) is directly connected to the pads 44a and 54a, respectively. can do.

Further, as shown in FIGS. 6 and 7, the tube-side wiring pattern 43 includes a longitudinal wiring pattern 46 formed linearly along the longitudinal direction X on the outer peripheral surface 14b of the measuring tube 14, and is a tube-side wiring. The pattern 53 includes a longitudinal wiring pattern 56 formed linearly along the longitudinal direction X on the outer peripheral surface 14b of the measuring tube 14.

Since a part of the connection wirings 42 and 52 is arranged inside or near the magnetic flux region F, when a pair of wiring cables are used as the connection wirings 42 and 52, between the two wirings viewed from the magnetic flux direction Y. A signal loop is formed due to the misalignment of the above, which causes magnetic flux differential noise. By using the wiring pattern formed on the outer peripheral surface 14b of the measuring tube 14 as in the present embodiment, the positions of the connecting wirings 42 and 52 can be accurately fixed. Therefore, the positional deviation between the two wirings as seen from the magnetic flux direction Y can be avoided, and the generation of magnetic flux differential noise can be easily suppressed.

Further, as shown in FIGS. 6 and 7, the tube-side wiring pattern 43 is a measuring tube 14 from the first end 41a of the surface electrodes 41 along the longitudinal direction X to one end of the longitudinal wiring pattern 46. A circumferential wiring pattern 47 formed along the circumferential direction W of the measuring tube 14 is included in the outer peripheral surface 14b of the measuring tube 14.
Further, the tube-side wiring pattern 53 includes the circumference of the measuring tube 14 on the outer peripheral surface 14b of the measuring tube 14 from the second end 51a along the longitudinal direction X to one end of the longitudinal wiring pattern 56 of the surface electrodes 51. The circumferential wiring pattern 57 formed along the direction W is included.

At this time, the longitudinal wiring pattern 56 is formed at a position overlapping the longitudinal wiring pattern 46 when viewed from the magnetic flux direction Y, on the outer peripheral surface 14b on the opposite side of the measuring tube 14 from the longitudinal wiring pattern 46. There is. That is, the longitudinal wiring patterns 46 and 56 are formed at positions symmetrical with respect to the plane along the electrode direction Z passing through the tube axis J on the outer peripheral surface 14b.

In the examples of FIGS. 6 and 7, the longitudinal wiring patterns 46 and 56 are respectively on the intersecting lines JA and JB where the plane passing through the tube axis J of the measuring tube 14 intersects the outer peripheral surface 14b along the magnetic flux direction Y, respectively. It is formed. Further, one end of the circumferential wiring pattern 47 is connected to the central position of the surface electrode 41 in the longitudinal direction X in the first end portion 41a of the surface electrode 41. Similarly, one end of the circumferential wiring pattern 57 is connected to the center position of the surface electrode 51 in the longitudinal direction X in the second end portion 51a of the surface electrode 51.

As a result, since the longitudinal wiring patterns 46 and 56 are formed at overlapping positions when viewed from the magnetic flux direction Y, the formation of a signal loop can be accurately avoided, and the generation of magnetic flux differential noise can be easily suppressed. Can be done.
The connection points between the circumferential wiring patterns 47 and 57 and the surface electrodes 41 and 51 are connected at symmetrical positions with respect to the tube axis J, that is, at the same positions in the longitudinal direction X of the surface electrodes 41 and 51. It does not have to be the center position of the surface electrodes 41 and 51.

Further, by forming the longitudinal wiring patterns 46 and 56 on the intersecting lines JA and JB, the lengths of the circumferential wiring patterns 47 and 57 become equal, and the lengths of the pipe side wiring patterns 43 and 53 as a whole become equal. Therefore, it is possible to suppress an imbalance such as a phase difference and an amplitude of the electromotive forces Va and Vb from the surface electrodes 41 and 51, which are caused by the difference in the lengths of the pipe-side wiring patterns 43 and 53. If these imbalances can be ignored in terms of measurement accuracy, the longitudinal wiring patterns 46 and 56 do not have to be on the intersecting lines JA and JB, and are formed at overlapping positions when viewed from the magnetic flux direction Y. Just do it.

FIG. 9 is a configuration example of the differential amplifier circuit 101 using the preamplifier 61. As shown in FIG. 9, the preamplifier 61 includes two operational amplifiers UA and UB that individually lower the impedance of the electromotive forces Va and Vb from the surface electrodes 41 and 51 and output them. These operational amplifiers UA and UB are sealed in the same IC package (dual operational amplifier). Further, these differentially amplify the input Va and Vb, and output the obtained differential output as a detection signal Vin.

Specifically, Va is input to the non-inverting input terminal (+) of the UA, and Vb is input to the non-inverting input terminal (+) of the UB. Further, the UA inverting input terminal (-) is connected to the UA output terminal via the resistance element R1, and the UB inverting input terminal (-) is connected to the UB output terminal via the resistance element R2. Has been done. The UA inverting input terminal (−) is connected to the UB inverting input terminal (−) via the resistance element R3. At this time, the amplification factors of UA and UB are the same by making the values of R1 and R2 equal. The amplification factor is determined by the values of R1 and R2 and the value of R3.

Since the electromotive forces Va and Vb from the surface electrodes 41 and 51 are signals showing opposite phases to each other, such a differential amplifier circuit 101 is configured on the second sub-board 18 by using UA and UB. As a result, even if temperature drift occurs in Va and Vb under the influence of heat from the exciting coils 15 and 16 and the measuring tube 14, 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.

As shown in FIG. 9, the preamplifier 61 has four wiring patterns 44 and 54, which are inputs from the surface electrodes 41 and 51, as well as a power supply, a signal 1, a signal 2, and a common (circuit GND). Wiring is connected. These four wires are connected to the main board 19 by a conductive means (not shown). Of the four wirings, the common wiring can be configured to include the shield pattern 94 of the second sub-board 18.

The surface electrode 62 for measuring the conductivity is provided on the side (upstream side) of the measuring tube 14 opposite to the second sub-board 18 from the pair of surface electrodes 41 and 51 for measuring the flow rate.
On one surface of the first sub-board 17 close to the surface electrode 62 for measuring conductivity, an electric circuit that is a part of the electric circuit 35 for measuring conductivity is provided. As shown in FIG. 1, a part of the electric circuit 35 for measuring the conductivity is electrically connected to the surface electrode 62 for measuring the conductivity by, for example, a jumper wire 102. A shield pattern 103 made of a solid pattern is provided on the other surface of the first sub-board 17.

[Effect of the first embodiment]
In the electromagnetic flowmeter 11 according to this embodiment, the first and second joints 21 and 22 are heated by the heat of the fluid due to the flow of the high-temperature fluid. When the temperature of the first and second joints 21 and 22 rises, heat convection occurs in the case 12 using these first and second joints 21 and 22 as a heat source. This heat convection is limited to the second space S1b and the third space S1c in the case 12, and does not occur in the first space S1a. Therefore, the inside of the first space S1a is less likely to be affected by the heat of the fluid, and the heat of the fluid is less likely to be transferred to the exciting coils 15 and 16 housed in the first space S1a. Therefore, since the temperature rise of the exciting coils 15 and 16 due to the heat of the fluid is suppressed, the exciting current can be increased accordingly. As a result, according to this embodiment, it is possible to provide an electromagnetic flow meter having high product performance such as accuracy and stability of the flow rate measurement value.

Further, since the heat convection in the case 12 is restricted to the second and third spaces S1b and S1c, the temperature rise of the main board 19 is suppressed, so that the circuit component mounted on the main board 19 has a fluid. It becomes difficult for heat to be transferred. Therefore, since the temperature rise of the circuit parts can be suppressed, the upper limit of the fluid temperature range of the product specifications can be raised, and the upper limit of the operating temperature range of the product can be raised, so that an electromagnetic flowmeter that is easy to use is provided. it can. Moreover, since it is possible to use inexpensive and well-distributed circuit parts generally used in industrial equipment as circuit parts, it is possible to reduce the cost of the electromagnetic flowmeter and increase the productivity. be able to.

The electromagnetic flowmeter 11 according to this embodiment includes a shield case 93 that surrounds the measuring tube 14 in cooperation with a pair of first and second sub-boards 17, 18. The shield case 93 divides the inside of the first space S1a into an inner space S3 in which the measuring tube 14 is housed and an outer space S4 around the inner space S3. Therefore, when the temperature of the measuring tube 14 rises due to the heat of the fluid, the heat convection generated in the first space S1a using the measuring tube 14 as a heat source is limited to the inner space S3 in the shield case 93. Therefore, it is possible to make it more difficult for the heat of the fluid to be transferred to the exciting coils 15 and 16.

In the electromagnetic flowmeter 11 according to this embodiment, the circuit component 91 and the life-long component 92 are mounted at positions corresponding to the first space S1a on the main board 19. Therefore, it is possible to reliably prevent the heat of the fluid from being transferred to these circuit components.

[Second Embodiment]
In the above-described embodiment, the electromagnetic flowmeter 11 including one main substrate 19 has been described. However, the electromagnetic flowmeter 11 according to the present invention can be configured as shown in FIG. In FIG. 10, the same or equivalent members as those described with reference to FIGS. 1 to 9 are designated by the same reference numerals, and detailed description thereof will be omitted as appropriate.

The electromagnetic flowmeter 111 shown in FIG. 10 includes a lid-side substrate 112 inside the lid 13. The lid-side substrate 112 is supported by the case 12 in a state of being parallel to the main substrate 19, and divides the closed space S2 in the lid 13 into two spaces. The two spaces are a fourth space S2a located on the main board 19 side and a fifth space S2b located on the opposite side of the main board 19.

In this embodiment, a circuit component 114 having a relatively low heat resistance as compared with the circuit component 113 mounted on the main substrate 19 is mounted on a portion of the lid-side substrate 112 included in the fifth space S2b. ing. The circuit component 114 having a relatively low heat resistance here is a component (semiconductor integrated circuit such as an LCD, a microcomputer, or a non-volatile memory) having a high cost and poor distribution if it is a special specification product, or a component having a limited life. Is.

According to this embodiment, a heat insulating space composed of a fourth space S2a is formed between the first to third spaces S1a to S1c and the fifth space S2b. Therefore, it is possible to reliably prevent the circuit component 114 housed in the fifth space S2b from being affected by the heat of the fluid.
Therefore, as compared with the case where the first embodiment is adopted, the product performance can be improved and the usability is further improved. Moreover, since inexpensive circuit components can be used, further cost reduction and productivity improvement can be achieved.

[Third Embodiment]
In the electromagnetic flowmeters 11 and 111 shown in the first and second embodiments described above, the flow rate range, which is the range of the measurement amount that can be measured, is determined depending on the diameter of the measuring tube 14. Therefore, an electromagnetic flow meter is prepared for each flow range. That is, a plurality of types of electromagnetic flowmeters having different diameters of the measuring tubes 14 are prepared, and an electromagnetic flowmeter including a flow rate range to be measured is selected from these electromagnetic flowmeters. Electromagnetic flowmeters having different diameters of the measuring tubes 14 have different sizes of the case 12. However, it is desirable that the main substrate 19 is commonly used in all electromagnetic flowmeters in order to keep the manufacturing cost low.

When using a common main board 19 in a plurality of types of cases 12 having different sizes, it is necessary to prevent a gap from being generated between the opening 12a of the case 12 and the main board 19 to cause heat convection. There is. An electromagnetic flowmeter that realizes this will be described with reference to FIGS. 11 to 14. In FIGS. 11 to 14, the same or equivalent members as those described with reference to FIGS. 1 to 10 are designated by the same reference numerals, and detailed description thereof will be omitted as appropriate.

The electromagnetic flowmeter 201 shown in FIG. 11 includes a plate-shaped bracket 202 between the main substrate 19 and the pair of sub-boards 17 and 18. The bracket 202 is for attaching the main board 19 to the case 12, and can be formed by a simple rectangular plate (not shown) or a plate having holes 202a as shown in FIGS. 12 and 13. The bracket 202 is fixed to the mounting seat 84 of the case 12 by a fixing bolt 203 (see FIG. 11) in a state of being fitted to the opening 12a of the case 12.

The electromagnetic flowmeter 201 according to this embodiment is configured such that the bracket 202 is "substantially in contact" with the first and second sub-boards 17, 18 by fixing the bracket 202 to the mounting seat 84. ..

Through holes 204 and screw holes 205 are formed at the four corners of the bracket 202, respectively. The through hole 204 is formed outside the screw hole 205. A fixing bolt 203 for fixing the bracket 202 to the mounting seat 84 is passed through the through hole 204. A fixing bolt 206 (see FIG. 11) for fixing the main board 19 to the bracket 202 is screwed into the screw hole 205.

The main board 19 is supported in a state of being overlapped on the surface of the bracket 202 opposite to the measuring tube 14, and is attached to the case 12 via the bracket 202. When the bracket 202 having the hole 202a is used, the hole 202a is closed by the main board 19 by attaching the main board 19 to the bracket 202. Since the hole 202a of the bracket 202 is closed by the main board 19, the opening 12a of the case 12 is closed with the bracket 202 attached to the case 12, and a closed space S1 is formed inside the case 12. To.

When a bracket 202 made of a simple square plate having no holes 202a is used, the entire area of one end (one end facing the bracket 202) of the first and second sub-boards 17 and 18 in the electrode direction Z is covered. It comes into "substantial contact" with the bracket 202.
When the bracket 202 having the hole 202a is used, if the shapes of the first and second sub-boards 17 and 18 are quadrangular, it is inside the hole 202a of the bracket 202 and the main board 19 and the first and second sub-boards 19 and the second. A gap corresponding to the thickness of the bracket 202 is formed between the sub-boards 17 and 18. This gap serves as a passage that communicates the first space S1a with the second and third spaces S1b and S1c. This gap can be closed by forming convex portions 207 on the first and second sub-boards 17 and 18, as shown by the alternate long and short dash line in FIG. The convex portion 207 is inserted into the hole 202a of the bracket 202 and is formed so as to extend to the main substrate 19 and "substantially contact" with the main substrate 19.

Therefore, the bracket 202 provided between the first and second sub-boards 17 and 18 and the main board 19 closes the opening 12a of the case 12 to form a closed space S1 inside the case 12. , The first and second sub-boards 17 and 18 cooperate with each other to form the first to third spaces S1a to S1c. Even in this case, the first space S1a is formed so as to regulate the flow of air with the second and third spaces S1b and S1c, and the heat convection is in the second space S1b and in the third space S1b. It is limited to the space S1c of. Therefore, also in this embodiment, it is possible to provide an electromagnetic flowmeter having high product performance such as accuracy and stability of the flow rate measurement value, as in the first and second embodiments described above.

In the electromagnetic flowmeter 201 according to this embodiment, a plurality of types of brackets 202 that fit into the openings 12a of a plurality of types of cases 12 having different sizes are formed so that the main substrate 19 can be supported by these brackets 202. By forming the through hole 204 and the screw hole 205 in the case 12, the common main substrate 19 can be used in a plurality of types of cases 12 having different sizes. Therefore, according to this embodiment, it is possible to provide a plurality of types of electromagnetic flowmeters having different flow ranges while keeping the manufacturing cost low by sharing the main substrate 19.

The electromagnetic flowmeter 301 shown in FIG. 14 includes a lid-side substrate 112 inside the lid 13. In FIG. 14, the same or equivalent members as those described with reference to FIGS. 11 to 13 are designated by the same reference numerals, and detailed description thereof will be omitted as appropriate. Also in this electromagnetic flowmeter 301, the bracket 202 described above is provided in the opening 12a of the case 12, and the main substrate 19 is supported by the bracket 202. Therefore, it is possible to form a plurality of types of electromagnetic flowmeters 301 having a lid-side substrate 112 inside the lid 13 by changing the flow rate range, while keeping the manufacturing cost low by standardizing the main substrate 19. become.

<< Expansion of embodiment >>
The inventions made by the present inventors have been specifically described above based on the embodiments, but it goes without saying that the present invention is not limited thereto and can be variously modified without departing from the gist thereof. No.

For example, it is desirable that each space described in the above embodiment has as little air permeability as possible, but even if there is some gap between one space and the other space, heat convection is limited to some extent. Therefore, the effect of the present invention is exhibited.
That is, even if there is a gap of, for example, about 1 mm or less between the main board 19 and the sub board, and between each board and the case 12, the performance of the product, the thermal effect of the temperature range of the circuit component, and the heat effect. The effect of the present invention is exhibited because the thermal convection is limited to some extent if the thermal effect is within an acceptable range in the life of the component.

11,201,301 ... Electromagnetic flowmeter, 12 ... Case 12, 12a ... Opening, 13 ... Lid, 14 ... Measuring tube 14, 15, 16 ... Exciting coil, 17 ... First sub-board, 18 ... Second Sub-board, 19 ... Main board 19, 21 ... First joint, 22 ... Second joint, 23 ... First side wall, 24 ... Second side wall, 91, 113, 114 ... Circuit parts, 92 ... Yes Life parts, 93 ... Shield case, 112 ... Lid side board, 202 ... Bracket, 202a ... Hole, 207 ... Convex part, S ... Sealed space, S1 ... Closed space, S1a ... First space, S1b ... Second Space, S1c ... third space, S2a ... fourth space, S2b ... fifth space, S3 ... inner space, S4 ... outer space.

Claims (5)

A measuring tube formed of a material with low thermal conductivity and through which the fluid to be measured flows,
An exciting coil that forms a magnetic circuit so that it passes through the measuring tube,
A pair of sub-boards that penetrate the measuring tube and extend in a direction that intersects the longitudinal direction of the measuring tube.
A pair of joints connected to both ends of the measuring tube,
A box-shaped case having first and second side walls through which the pair of joints are fixed and accommodating the measuring tube, the exciting coil, and the sub-board.
A main substrate that closes the opening of the case and forms a closed space inside the case is provided.
The closed space is
A first space partitioned by the pair of sub-boards and accommodating the exciting coil and a second and third spaces formed outside the first space and accommodating the pair of joints are provided. Including
An electromagnetic flowmeter characterized in that the first space is formed so as to regulate the flow of air with the second and third spaces. In the electromagnetic flowmeter according to claim 1,
further,
A shield case that surrounds the measuring tube in cooperation with the pair of sub-boards is provided.
The shield case is an electromagnetic flowmeter characterized in that the inside of the first space is divided into an inner space in which the measuring tube is housed and an outer space around the inner space. In the electromagnetic flowmeter according to claim 1 or 2.
An electromagnetic flowmeter characterized in that circuit components having relatively low heat resistance are mounted at positions on the main board other than the second and third spaces. In the electromagnetic flowmeter according to any one of claims 1 to 3.
further,
A lid that is attached to the open end of the case and cooperates with the case to form a sealed space.
A lid-side substrate that partitions the sealed space inside the lid into a fourth space on the main substrate side and a fifth space on the opposite side is provided.
A circuit component having a relatively low heat resistance as compared with a circuit component having a relatively low heat resistance mounted on the main board is mounted on a portion of the lid-side substrate included in the fifth space. An electromagnetic flowmeter characterized by being. In the electromagnetic flowmeter according to any one of claims 1 to 4.
further,
A plate-shaped bracket located between the main board and the pair of sub boards is provided.
The bracket supports the main board and closes the opening of the case to form the closed space inside the case, and cooperates with the pair of sub-boards to form the first to third parts. An electromagnetic flowmeter characterized by forming a space.

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