JP7355613B2 - electromagnetic flow meter - Google Patents

Description

The present invention relates to an electromagnetic flowmeter that measures the flow rate of fluid flowing inside a measurement pipe.

In recent years, small capacitive electromagnetic flowmeters for the FA (Factory Automation) market, such as those described in Patent Document 1 and Patent Document 2, have been put into practical use. The electromagnetic flowmeter described in Patent Document 1 is configured as shown in FIGS. 19 and 20, and the electromagnetic flowmeter described in Patent Document 2 is configured as shown in FIG. 21. In FIGS. 19 to 21, reference numeral 1 indicates a box-shaped case body, 2 is a case top cover, 3 is a measurement tube, 4 and 5 are detection electrodes, 6 is an excitation coil, 7 is a preamplifier board, 8 is a main board, 9 indicates a shield case. The main board 8 of the electromagnetic flowmeter shown in Patent Document 1 is composed of a control board 8a and an excitation board 8b.

In a capacitive electromagnetic flowmeter, the impedance between the fluid to be detected and the detection electrodes 4, 5 is extremely high because it is configured so that the fluid to be detected and the detection electrodes 4, 5 are not in contact with each other. Become. For this reason, in the electromagnetic flowmeter shown in Patent Document 1 and Patent Document 2, noise countermeasures are taken near the measurement tube 3. A pair of detection electrodes 4 and 5 are provided in the measurement tube 3. A preamplifier circuit is connected to each of these detection electrodes 4 and 5. The preamplifier circuit is provided on a preamplifier board 7 provided for each of the detection electrodes 4 and 5. These preamplifier boards 7 are arranged in the immediate vicinity of the detection electrodes 4 and 5, and are covered together with the detection electrodes 4 and 5 by a shield case 9. By adopting such a configuration, it is possible to prevent external noise from being superimposed on the detection electrodes 4 and 5 and the preamplifier circuit.

The number of electrical connections between the preamplifier board 7 and the main board 8 (the latter stage of the signal amplification circuit, and the control board 8a in the electromagnetic flowmeter described in Patent Document 1) is at least 3 (power supply, signal, common) x Two sheets are required, which means a total of six electrical wirings are required.
Two (Patent Document 1) or one (Patent Document 2) excitation coils 6 are arranged at appropriate positions where the electromotive force generated between the detection electrodes 4 and 5 is maximized. This excitation coil 6 is fixed to the case body 1 via a yoke 10 and a bobbin 11. In this case, the number of electrical connections between the excitation coil 6 and the excitation circuit of the main board 8 (the excitation circuit of the excitation board 8b in the electromagnetic flowmeter described in Patent Document 1) is 4 (Patent Document 1) or 2 (Patent Document 1). Reference 2) is required.

JP2014-202662A Japanese Patent Application Publication No. 2016-188843

In the electromagnetic flowmeter shown in Patent Document 1 and Patent Document 2, the preamplifier board 7 and the excitation coil 6 are arranged at separate positions around the measurement tube 3 with the measurement tube 3 as the center, and each It is arranged so that it is oriented. Therefore, in order to electrically connect the preamplifier board 7 and the excitation coil 6 to the main board 8 (signal amplification circuit, excitation circuit, arithmetic circuit, power supply circuit, etc.), it was necessary to use lead wires. That is, it is impossible to directly connect the preamplifier board 7 and the excitation coil 6 to the main board 8 without using lead wires. Furthermore, since the preamplifier board 7 is entirely covered with the shield case 9, it is necessary to draw out the lead wires from the opening of the shield case 9. Furthermore, in order to prevent external noise from entering through the opening of the shielding case 9, it was necessary to close the opening of the shielding case 9 using a non-magnetic and conductive tape after the wiring work was completed.

The main board 8 is fixed to the case top lid 2 side, and in consideration of workability during assembly, it is necessary to provide an allowance for the length of the lead wire. By assembling the case top cover 2 to the case body 1, the excess lead wire is bent inside the case body 1 and placed at an unspecified position. For this reason, the lead wire on the excitation coil 6 side comes close to the lead wire on the preamplifier board 7 side and components on the main board 8, and the noise generated in the excitation coil 6 may be superimposed on the flow signal, or other parts on the main board 8 may be superimposed on the flow signal. This could have an adverse effect on the operation of the circuit. However, after the case top cover 2 is assembled to the case body 1, the condition of the lead wires inside the case body 1 cannot be visually checked. For this reason, these lead wires had to be made by combining shielded wires, twisted pair wires, etc. and connectors, and were made into dedicated wire harnesses in advance so that they would not have any effect even if they were brought close to each other. In the electromagnetic flowmeter shown in Patent Document 2, a wire harness 12 is used to connect the main board 8 and the preamplifier board 7 side. If the lead wire is formed into a wire harness in this way, the manufacturing cost will increase.

An object of the present invention is to provide an electromagnetic flowmeter that is not easily affected by noise generated in an excitation coil without using a wire harness in a conductive part that electrically connects a preamplifier board and a main board. .

In order to achieve this object, the electromagnetic flowmeter according to the present invention includes a measurement tube through which a fluid to be measured flows, an excitation coil that forms a magnetic circuit so as to pass through the measurement tube, and an excitation coil provided in the measurement tube. a pair of surface electrodes mounted on one surface of the preamplifier board close to the surface electrodes, a preamplifier board through which the measurement tube extends in a direction crossing the longitudinal direction of the measurement tube; a first connector provided on the preamplifier board and electrically connected to the preamplifier circuit; and a shield case covering the pair of surface electrodes and the preamplifier circuit. a main board having a first electric circuit electrically connected to the preamplifier circuit, extending in the longitudinal direction of the measurement tube and having one end positioned near the preamplifier board; a second connector provided at the one end and electrically connected to the first electric circuit and configured to be detachable from the first connector, the preamplifier circuit and the first electric circuit; and are electrically connected via the first connector and the second connector.

In the electromagnetic flowmeter according to the present invention, the main board has a second electric circuit electrically connected to the excitation coil, the excitation coil is wound and held around a coil bobbin, and the excitation coil is wound around and held by the coil bobbin. has a lead pin that protrudes in a direction crossing the longitudinal direction of the measurement tube and extends toward the main board, a base of the lead pin is electrically connected to the excitation coil, and a protruding side end of the lead pin is electrically connected to the excitation coil. The portion may be electrically connected to the second electric circuit across the main board in the thickness direction.

In the electromagnetic flowmeter according to the present invention, a portion of the main board across which the lead pin crosses in a thickness direction may be formed by an end face through hole opening in an end face of the main board.

The present invention provides the electromagnetic flowmeter further comprising a bottomed rectangular cylindrical case that accommodates the measurement tube, the excitation coil, and the preamplifier board, and the main board has an opening of the case. The lead pin may be disposed so as to close the case, and the lead pin may be formed to protrude from an opening edge of the case to the outside of the case.

In the electromagnetic flowmeter, the present invention further provides a surface electrode for conductivity measurement provided in the measurement tube on the opposite side of the preamplifier board from the pair of surface electrodes, and the measurement tube penetrates. a conductivity measurement substrate extending in a direction crossing the longitudinal direction of the measurement tube and positioned on the opposite side of the conductivity measurement surface electrode from the preamplifier substrate; a conductivity measuring circuit mounted on one surface close to a surface electrode for measuring conductivity and electrically connected to the surface electrode for measuring conductivity; a third connector electrically connected to the conductivity measurement circuit; a third electrical circuit provided on the main board and electrically connected to the conductivity measurement circuit; and a third connector electrically connected to the conductivity measurement circuit; a fourth connector provided and electrically connected to the third electric circuit and configured to be detachable from the third connector, the conductivity measurement circuit and the third electric circuit being connected to each other; The third connector and the fourth connector may be electrically connected to each other.

In the electromagnetic flowmeter of the present invention, the connection portion that electrically connects the preamplifier circuit and the first connector includes a wiring pattern extending along the one surface of the preamplifier board, and the wiring pattern may extend from the inside of the shield case to the outside through a notch formed at an end of the shield case on the side of the preamplifier board.

In the electromagnetic flowmeter according to the present invention, the connection portion that electrically connects the preamplifier circuit and the first connector is a first connector that extends along the one surface of the preamplifier board inside the shield case. a wiring pattern portion, a via hole portion connected to the tip of the first wiring pattern portion and penetrating the preamplifier board inside the shield case, and one end extending along the other surface of the preamplifier board. may have a second wiring pattern part connected to the via hole part and the other end connected to the first connector.

According to the present invention, lead wires are not required for electrically connecting the preamplifier circuit and the first electric circuit of the main board. Therefore, the conductive portion that electrically connects the preamplifier circuit and the main board can be easily separated from the conductive portion of the excitation coil. Therefore, it is possible to provide an electromagnetic flowmeter that is less susceptible to the effects of noise generated by the excitation coil without using a wire harness for the conductive portion that connects the preamplifier board and the main board.

FIG. 1 is a cross-sectional view showing the configuration of an electromagnetic flowmeter according to a first embodiment. FIG. 2 is a top view of a case portion of the electromagnetic flowmeter according to the first embodiment. FIG. 1 is a block diagram showing a circuit configuration of an electromagnetic flowmeter according to a first embodiment. FIG. 1 is a cross-sectional perspective view of an electromagnetic flowmeter according to a first embodiment. 1 is an assembly diagram of an electromagnetic flowmeter according to a first embodiment; FIG. FIG. 2 is a top view showing the detector according to the first embodiment. FIG. 1 is a side view showing a detector according to a first embodiment. FIG. 1 is a front view showing a detector according to a first embodiment. FIG. 2 is a diagram illustrating a configuration example of a differential amplifier circuit using a preamplifier. 9 is a sectional view taken along line XX of the preamplifier board in FIG. 8. FIG. FIG. 3 is a top view of the main board. FIG. 7 is a front view showing a detector according to a second embodiment. 13 is a sectional view taken along the line XIII-XIII of the preamplifier board and shield case in FIG. 12. FIG. FIG. 7 is a top view of the main board according to the third embodiment. FIG. 7 is a partially cutaway perspective view of a main board and lead pins according to a third embodiment; It is a sectional view showing the composition of the electromagnetic flow meter concerning a 4th embodiment. FIG. 2 is a diagram illustrating the configuration of an electric circuit for measuring conductivity. It is a sectional view showing the composition of the electromagnetic flow meter concerning a 5th embodiment. FIG. 2 is a sectional view seen from the side for explaining the configuration of a conventional electromagnetic flowmeter. FIG. 2 is a sectional view seen from the front for explaining the configuration of a conventional electromagnetic flowmeter. FIG. 2 is a sectional view seen from the front for explaining the configuration of a conventional electromagnetic flowmeter.

Next, embodiments of the present invention will be described with reference to the drawings.
[First embodiment]
First, an electromagnetic flowmeter 21 according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. This electromagnetic flowmeter 21 is constructed by attaching various parts described later to a case 22 in the shape of a rectangular cylinder with a bottom. The opening 22a of the case 22 is closed by a lid 23. The parts provided in the case 22 include a measurement tube 24 extending from one end of the case 22 to the other end, and a pair of excitation coils 25 and 26 arranged on both sides of the measurement tube 24, which will be described in detail later. , a preamplifier board 27 through which the measurement tube 24 passes, and a main board 28 attached to the opening 22a of the case 22.

The upstream end (the left end in FIG. 1) of the measurement tube 24 is supported by the case 22 via a first joint 29. A downstream end of the measurement tube 24 is supported by the case 22 via a second joint 30. A fluid to be measured flows into the measurement tube 24 from the upstream end to the downstream end. The preamplifier board 27 and the main board 28 are electrically connected via first and second connectors 31 and 32, which will be described later. Further, the preamplifier board 27 and the main board 28 are provided with an electric circuit as shown in FIG.

FIG. 3 is a block diagram showing the circuit configuration of the electromagnetic flowmeter 21 according to the first embodiment. In the following, a capacitive electromagnetic flowmeter in which a pair of detection electrodes do not come into direct contact with the fluid to be measured flowing inside the measurement tube 24 will be described as an example, but the present invention is not limited to this. The present invention can be similarly applied to a liquid-contact type electromagnetic flowmeter that comes into direct contact with the liquid.
As shown in FIG. 3, the capacitive electromagnetic flowmeter 21 includes a detection section 41, a signal amplification circuit 42, a signal detection circuit 43, an excitation circuit 44, and an electric It includes a circuit 45, a transmission circuit 46, a setting/display circuit 47, and an arithmetic processing circuit (CPU) 48.

The detection unit 41 mainly includes a measurement tube 24 , excitation coils 25 and 26 that form a magnetic circuit passing through the measurement tube 24 , a pair of surface electrodes 51 and 61 , and a preamplifier 71 . The surface electrodes 51 and 61 detect electromotive forces Va and Vb corresponding to the flow velocity of the fluid flowing through the flow path 24a, and output an alternating current detection signal Vin corresponding to these electromotive forces Va and Vb. .

The excitation control unit 48A of the arithmetic processing circuit 48 outputs an excitation control signal Vex for switching the polarity of the excitation current Iex based on a preset excitation period. The excitation circuit 44 supplies an alternating current excitation current Iex to the excitation coils 25 and 26 based on the excitation control signal Vex from the excitation control section 48A of the arithmetic processing circuit 48.
The signal amplification circuit 42 filters the noise component included in the detection signal Vin output from the detection unit 41, and then outputs the amplified AC flow rate signal VF. The signal detection circuit 43 samples and holds the flow rate signal VF from the signal amplification circuit 42, A/D converts the obtained DC voltage into a flow rate amplitude value DF, and outputs it to the arithmetic processing circuit 48.

The flow rate calculation unit 48B of the arithmetic processing circuit 48 calculates the flow rate of the fluid based on the flow rate amplitude value DF from the signal detection circuit 43, and outputs the flow rate measurement result to the transmission circuit 46. The transmission circuit 46 transmits the flow rate measurement result and empty state determination result obtained by the arithmetic processing circuit 48 to the host device by transmitting data with the host device via the transmission path L.

The electric circuit 45 for measuring conductivity is configured to apply an alternating current to a surface electrode 72 for measuring conductivity through a resistive element, with the fluid flowing in the measuring tube 24 via the first joint 29 set to a common potential Vcom, for example. A signal is applied, the amplitude of the AC detection signal generated at the surface electrode 72 for conductivity measurement at that time is sampled, and the AC amplitude value data DP obtained by A/D conversion is output to the arithmetic processing circuit 48. It is a circuit.

The electrical conductivity calculation unit 48C of the arithmetic processing circuit 48 has a function of calculating the electrical conductivity of the fluid based on the AC amplitude value data DP from the electrical circuit 45 for measuring electrical conductivity.
The empty state determination unit 48D of the arithmetic processing circuit 48 has a function of determining whether or not fluid is present in the measurement tube 24 based on the electrical conductivity of the fluid calculated by the conductivity calculation unit 48C.
Typically, the electrical conductivity of a fluid is greater than that of air. For this reason, the empty state determining unit 48D determines whether or not the fluid is present by subjecting the electrical conductivity of the fluid calculated by the electrical conductivity calculating unit 48C to threshold processing.

The setting/display circuit 47 detects, for example, an operator's operation input, and outputs various operations such as flow rate measurement, conductivity measurement, and empty state determination to the arithmetic processing circuit 48, and outputs the information output from the arithmetic processing circuit 48. The flow rate measurement results and empty status determination results are displayed on display circuits such as LEDs and LCDs.

The arithmetic processing circuit 48 includes a CPU and its peripheral circuits, and executes a preset program on the CPU to cooperate with hardware and software to control the excitation control section 48A, the flow rate calculation section 48B, and the conduction control section 48A. Various processing units such as a rate calculation unit 48C and a vacant state determination unit 48D are implemented.

Among the circuits shown in FIG. 3, the preamplifier 71 of the detection section 41 is mounted on a preamplifier board 27, which will be described later. The signal amplification circuit 42, the signal detection circuit 43, the excitation circuit 44, the electric conductivity measurement circuit 45, the transmission circuit 46, the setting/display circuit 47, and the arithmetic processing circuit 48 are connected to the main board 28, which will be described later. has been implemented. Electrical connection between the preamplifier 71 and the signal amplification circuit 42 is made using a first connector 31 provided on the preamplifier board 27 and a second connector 32 provided on the main board 28. Further, the electrical connection between the excitation circuit 44 and the excitation coils 25 and 26 is made using a plurality of lead pins 73, which will be described later.

[Measurement tube mounting structure]
Next, the mounting structure of the measurement tube 24 will be described in detail with reference to FIGS. 1, 2, and 4. FIG. 2 is a top view of the electromagnetic flowmeter 21 according to the first embodiment. FIG. 4 is a cross-sectional perspective view of the electromagnetic flowmeter 21 according to the first embodiment.

In this embodiment, the measurement tube 24 is inserted into a tube hole 27a provided in a preamplifier board 27, and the side ends 27b, 27c of the preamplifier board 27 are connected to guide parts 74, 75 formed on the inner wall part 22b of the case 22. By inserting the preamplifier board 27 through the opening 22a of the case 22 so as to fit into the case 22, the preamplifier board 27 is held in the case 22, and the measurement tube 24 is attached to the case 22.

The measurement tube 24 is cylindrical and made of a material with excellent insulation and dielectric properties, such as ceramic or resin. As shown in FIG. 2, a yoke 76 and a pair of excitation coils 25 and 26 are provided on the outside of the measurement tube 24. The yoke 76 has a substantially C-shaped cross section that opens toward the opening of the case 22 so that the magnetic flux direction (second direction) Y is orthogonal to the longitudinal direction (first direction) X of the measurement tube 24. It is formed. The pair of excitation coils 25 and 26 are each wound and held by a coil bobbin 77, and are attached to a yoke 76 so as to face each other with the measurement tube 24 in between. Note that, in the following description, only the end faces of the opposing yokes 76, that is, only the yoke surfaces 76A and 76B are shown in order to make the drawings easier to read.

On the other hand, on the outer peripheral surface 24b of the measuring tube 24, a pair of surface electrodes (first A surface electrode) 51 and a surface electrode (second surface electrode) 61 are arranged to face each other.
As a result, when the AC excitation current Iex is supplied to the excitation coils 25 and 26, a magnetic flux Φ is generated between the yoke surfaces 76A and 76B located at the center of the excitation coils 25 and 26, and the fluid flowing through the flow path 24a is An alternating current electromotive force is generated along the electrode direction Z with an amplitude corresponding to the flow velocity of the fluid, and this electromotive force is applied to the surface electrodes 51, 61 via the capacitance between the fluid and the surface electrodes 51, 61. Detected in

The case 22 has an opening 22a at the top, and is made of a bottomed rectangular cylindrical (box-like) resin or metal housing that houses the measurement tube 24, excitation coils 25, 26, preamplifier board 27, etc. inside. has been done. As shown in FIG. 2, guide portions 74 and 75 are formed in a pair of inner wall portions 22b of the inner wall portions of the case 22 that are parallel to the longitudinal direction X at positions facing each other. The guide parts 74 and 75 are each composed of two protrusions 74a, 74b, 75a, and 75b formed parallel to the electrode direction Z, and the fitting parts 78 and 79 between these protrusions extend from the opening 22a. The side ends 27b and 27c of the inserted preamplifier board 27 fit together.

Note that the protrusions 74a, 74b, 75a, 75b of the guide portions 74, 75 do not need to be formed continuously in the electrode direction Z, and are formed in plural at intervals such that the side end portions 27b, 27c are smoothly inserted. It may be formed separately. Further, the guide portions 74 and 75 may be grooves formed in the inner wall portion 22b and into which the side end portions 27b and 27c of the preamplifier board 27 are inserted, instead of the protrusions.

A pair of side surfaces 22c that are parallel to the magnetic flux direction Y among the side surfaces of the case 22 are made of a metal material (for example, Tubular first and second joints 29 and 30 made of stainless steel (SUS) are provided. At this time, the measurement tube 24 is housed inside the case 22 along the longitudinal direction Each is connected.

Here, at least one of the first and second joints 29 and 30 functions as a common electrode 82 (see FIG. 3). For example, by being connected to the common potential Vcom, the first joint 29 not only connects the external piping and the measurement tube 24, but also functions as the common electrode 82.
In this way, by realizing the common electrode 82 by the first joint 29 made of metal, the area of the common electrode 82 in contact with the fluid becomes larger. As a result, even if foreign matter adheres or corrodes to the common electrode 82, the area of the part where the foreign matter adheres or corrodes occurs is relatively small with respect to the total area of the common electrode 82, so polarization It is possible to suppress measurement errors due to changes in capacitance.

FIG. 5 is an assembly diagram of the electromagnetic flowmeter 21 according to the first embodiment.
The preamplifier board 27 is a general printed circuit board (for example, a 1.6 mm thick glass cloth-based epoxy resin copper-clad laminate) for mounting circuit components, and as shown in FIG. A tube hole 27a for passing the measurement tube 24 therethrough is formed. Therefore, the preamplifier board 27 is penetrated by the measurement tube 24 and extends in a direction intersecting the longitudinal direction of the measurement tube 24 .
The main board 28 is a printed circuit board equivalent to the preamplifier board 27, and as shown in FIG. 22a. The main board 28 according to this embodiment is arranged to cover the opening 22a of the case 22. The main board 28 is fixed to mounting seats 83 provided at four corners of the case 22 with fixing bolts 84.

FIG. 6 is a top view of a detector which is a part of the electromagnetic flowmeter 21 that measures 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.
The capacitance between the fluid and the surface electrodes 51, 61 is very small, about several pF, and the impedance between the fluid and the surface electrodes 51, 61 becomes high, making it susceptible to noise. For this reason, the electromotive forces Va and Vb obtained by the surface electrodes 51 and 61 are made to have low impedance by a preamplifier 71 using an operational amplifier IC or the like. The preamplifier 71 is mounted on one surface of the preamplifier board 27 adjacent to the surface electrodes 51 and 61.

In this embodiment, the preamplifier board 27 is measured in a direction intersecting the measurement tube 24 in a region where magnetic flux Φ is generated between the yoke surfaces 76A and 76B of the excitation coils 25 and 26, that is, at a position outside the magnetic flux region F. A preamplifier 71 is mounted on the tube 24, and the surface electrodes 51, 61 and the preamplifier 71 are electrically connected via connection wirings 52, 62.

In the examples shown in FIGS. 6 to 8, the mounting position of the preamplifier board 27 is a position spaced apart 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 preamplifier board 27 is the direction in which the board surface intersects the measurement tube 24, in this case, the direction along the two-dimensional plane consisting of the magnetic flux direction Y and the electrode direction Z. Note that the mounting position of the preamplifier board 27 may be any position outside the magnetic flux region F, and may be a position spaced apart from the magnetic flux region F in the upstream direction opposite to the downstream direction. Further, the mounting direction of the preamplifier board 27 is not strictly limited to the direction along the two-dimensional plane, but may be inclined with respect to the two-dimensional plane.

Further, the surface electrodes 51 and 61, the connection wirings 52 and 62, and the preamplifier 71 are electrically shielded by a shield case 85 made of a metal plate connected to a ground potential. The shield case 85 has a substantially rectangular cross section extending along the longitudinal direction X, and as shown in FIG. It is set in. One end of the shield case 85 close to the preamplifier board 27 is fixed in contact with the preamplifier board 27.

As a result, the entire high impedance circuit portion is shielded by the shield case 85, thereby suppressing the influence of external noise. In this embodiment, a shield pattern 86 consisting of a ground pattern (solid pattern) connected to the ground potential is formed on the other surface of the preamplifier board 27 (the surface opposite to the mounting surface). has been done. As a result, among the planes constituting the shield case 85, all planes that come into contact with the preamplifier board 27 may be open, and the structure of the shield case 85 can be simplified.

The connection wirings 52, 62 are wirings that connect the surface electrodes 51, 61 and the preamplifier 71, and as mentioned above, the entirety is shielded by the shield case 85, so even if a pair of general wiring cables are used. good. At this time, both ends of the wiring cable may be soldered to the pads formed on the surface electrodes 51 and 61 and the preamplifier board 27, respectively.
In this embodiment, as shown in FIGS. 6 to 8, tube-side wiring patterns 53 and 63 formed on the outer peripheral surface 24b of the measurement tube 24 are used as the connection wirings 52 and 62.

That is, the connection wiring 52 includes a tube-side wiring pattern 53 formed on the outer circumferential surface 24b and having one end connected to the surface electrode 51, and a board-side wiring pattern 54 formed on the preamplifier board 27 and having one end connected to the preamplifier 71. and a jumper wire 55 connecting the tube-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 tube-side wiring pattern 53 and a pad 54a formed at the other end of the board-side wiring pattern 54.

Further, the connection wiring 62 includes a tube-side wiring pattern 63 formed on the outer circumferential surface 24b and having one end connected to the surface electrode 61, and a board-side wiring pattern 64 formed on the preamplifier board 27 and having one end connected to the preamplifier 71. and a jumper wire 65 connecting the tube-side wiring pattern 63 and the board-side wiring pattern 64. The jumper wire 65 is soldered to a pad 63a formed at the other end of the tube-side wiring pattern 63 and a pad 64a formed at the other end of the board-side wiring pattern 64.

As a result, the tube side wiring patterns 53, 63 formed on the outer circumferential surface 24b are used in the section of the connection wirings 52, 62 from the surface electrodes 51, 61 to a position near the preamplifier board 27. Therefore, as in the case of using the above-mentioned pair of wiring cables, installation work such as routing and fixing the wiring cables can be simplified, and the cost of connection wiring and the burden of wiring work can be reduced.

Furthermore, the surface electrodes 51, 61 and the tube-side wiring patterns 53, 63 are made of a non-magnetic metal thin film such as copper, and are integrally formed on the outer circumferential surface 24b of the measurement tube 24 by metallization, which simplifies the manufacturing process. This can lead to a reduction in manufacturing costs. Note that the metallization process described above may be a plating process, a vapor deposition process, or the like, and furthermore, a nonmagnetic metal thin film formed in advance may be attached. When pasting a non-magnetic metal thin film, the jumper wires 55 and 65 are not used, and the tips of the non-magnetic metal thin film (the other ends of the tube-side wiring patterns 53 and 63) are directly connected to the pads 54a and 64a, respectively. can do.

Further, as shown in FIGS. 6 and 7, the tube side wiring pattern 53 includes a longitudinal wiring pattern 56 formed linearly along the longitudinal direction X on the outer circumferential surface 24b of the measurement tube 24, The pattern 63 includes a longitudinal wiring pattern 66 formed linearly along the longitudinal direction X on the outer peripheral surface 24b of the measurement tube 24.

A part of the connection wirings 52, 62 is arranged inside or near the magnetic flux region F, so when a pair of wiring cables is used as the connection wirings 52, 62, the distance between the two wirings as seen from the magnetic flux direction Y is A signal loop is formed due to the positional deviation, which causes magnetic flux differential noise. By using the wiring pattern formed on the outer circumferential surface 24b of the measurement tube 24 as in this embodiment, the positions of the connection wirings 52 and 62 can be accurately fixed. Therefore, it is possible to avoid positional deviation between both wirings as seen from the magnetic flux direction Y, and it is possible to easily suppress the occurrence of magnetic flux differential noise.

Furthermore, as shown in FIGS. 6 and 7, the tube side wiring pattern 53 extends from the first end 51a of the surface electrode 51 along the longitudinal direction X to one end of the longitudinal direction wiring pattern 56, It includes a circumferential wiring pattern 57 formed along the circumferential direction W of the measuring tube 24 on the outer circumferential surface 24b of the measuring tube 24 .
In addition, the tube-side wiring pattern 63 extends from the second end 61a of the surface electrode 61 along the longitudinal direction It includes a circumferential wiring pattern 67 formed along the direction W.

At this time, the longitudinal wiring pattern 66 is formed on the outer peripheral surface 24b on the opposite side of the longitudinal wiring pattern 56 with the measurement tube 24 in between, at a position that overlaps with the longitudinal wiring pattern 56 when viewed from the magnetic flux direction Y. There is. That is, the longitudinal wiring patterns 56 and 66 are formed on the outer circumferential surface 24b at positions that are symmetrical with respect to a plane along the electrode direction Z passing through the tube axis J.

In the examples shown in FIGS. 6 and 7, longitudinal wiring patterns 56 and 66 are placed on intersection lines JA and JB where a plane passing through the tube axis J of the measurement tube 24 along the magnetic flux direction Y intersects the outer circumferential surface 24b, respectively. It is formed. Further, one end of the circumferential wiring pattern 57 is connected to the center position of the surface electrode 51 in the longitudinal direction X among the first ends 51a of the surface electrodes 51. Similarly, one end of the circumferential wiring pattern 67 is connected to the center of the second end 61a of the surface electrode 61 in the longitudinal direction X.

As a result, since the longitudinal wiring patterns 56 and 66 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. I can do it.
Note that the connection points between the circumferential wiring patterns 57, 67 and the surface electrodes 51, 61 are connected at symmetrical positions across the tube axis J, that is, at the same position in the longitudinal direction X of the surface electrodes 51, 61. If it is, it does not need to be at the center position of the surface electrodes 51, 61.

Furthermore, by forming the longitudinal wiring patterns 56 and 66 on the intersecting lines JA and JB, the lengths of the circumferential wiring patterns 57 and 67 are made equal, and the entire length of the tube side wiring patterns 53 and 63 is made equal. Therefore, it is possible to suppress unbalance in the phase difference and amplitude of the electromotive forces Va and Vb from the surface electrodes 51 and 61, which are caused by the difference in length between the tube-side wiring patterns 53 and 63. In addition, as long as these unbalances are negligible in terms of measurement accuracy, the longitudinal wiring patterns 56 and 66 do not have to be on the intersecting lines JA and JB, but can be formed in overlapping positions when viewed from the magnetic flux direction Y. That's fine.

FIG. 9 shows a configuration example of a differential amplifier circuit 91 using a preamplifier 71. In this embodiment, this differential amplifier circuit 91 corresponds to the "preamplifier circuit" in the present invention. As shown in FIG. 9, the preamplifier 71 includes two operational amplifiers UA and UB that individually reduce the impedance of the electromotive forces Va and Vb from the surface electrodes 51 and 61 and output them. These operational amplifiers UA and UB are sealed within the same IC package (dual operational amplifier). Moreover, these differentially amplify the inputted Va and Vb, and output the obtained differential output as the detection signal Vin.

Specifically, Va is input to the non-inverting input terminal (+) of UA, and Vb is input to the non-inverting input terminal (+) of UB. Further, the inverting input terminal (-) of UA is connected to the output terminal of UA via resistor element R1, and the inverting input terminal (-) of UB is connected to the output terminal of UB via resistor element R2. has been done. The inverting input terminal (-) of UA is connected to the inverting input terminal (-) of UB via a resistive element R3. At this time, by making the values of R1 and R2 equal, the amplification factors of UA and UB are matched. 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 51 and 61 are signals that have opposite phases to each other, by configuring such a differential amplifier circuit 91 on the preamplifier board 27 using UA and UB, excitation can be achieved. Even if a temperature drift occurs in Va and Vb due to the influence of heat from the coils 25 and 26 and the measuring tube 24, 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 together, making it possible to obtain a good S/N ratio.

As shown in FIG. 9, the preamplifier 71 has four wires such as power supply, signal 1, signal 2, and common (circuit GND) in addition to the board side wiring patterns 54 and 64 that serve as inputs from the surface electrodes 51 and 61. wiring is connected. These four wires are connected to a first connector 31 provided on the preamplifier board 27. Among the four wires, the common wire is connected to the first connector 31 via the shield pattern 86 of the preamplifier board 27. As shown in FIG. 8, the other three wires are formed as an output wiring pattern 92 extending along one surface of the preamplifier board 27 (the surface on which the preamplifier 71 is mounted), and are connected to the first connector 31. It is connected.
That is, the connection portion that electrically connects the differential amplifier circuit 91 (preamplifier circuit) and the first connector 31, which is the output destination of the preamplifier 71, is an output wiring pattern that extends along one surface of the preamplifier board 27. 92 and a shield pattern 86 formed on the other surface of the preamplifier board 27.

The first connector 31 is a so-called female connector, and although not shown in detail, it opens toward the opening direction of the case 22 (upward in FIG. 8), and has a plurality of female contacts inside. It has a terminal. A second connector 32 (see FIG. 1) of the main board 28 is connected to the first connector 31. The second connector 32 is a so-called male connector, and although not shown in detail, the second connector 32 is a male contact that fits into the female contact terminal of the first connector 31 and is electrically connected. It has a terminal.

The second connector 32 is electrically connected to the signal amplification circuit 42 on the main board 28. In this embodiment, the signal amplification circuit 42 corresponds to the "first electric circuit" in the present invention. Therefore, by connecting the second connector 32 to the first connector 31, the differential amplification circuit 91 (preamplifier circuit) of the preamplifier 71 is electrically connected to the signal amplification circuit 42. The second connector 32 is connected to the first connector 31 of the preamplifier board 27 by attaching the main board 28 to the case 22 to which the preamplifier board 27 is attached.

The output wiring pattern 92 extending from the preamplifier 71 to the first connector 31 on the preamplifier board 27 extends from the preamplifier 71 toward the opening of the case 22, and further toward the side of the preamplifier board 27, as shown in FIG. It extends. In order to prevent the output wiring pattern 92 from coming into contact with the shield case 85, the portion of the output wiring pattern 92 extending toward the opening of the case 22 is inserted into a notch 93 formed in the shield case 85, as shown in FIG. It extends from the inside of the shield case 85 to the outside. The notch 93 is formed at the end of the shield case 85 on the preamplifier board side. Since the thickness t of the output wiring pattern 92 is approximately several tens of μm and the width W is approximately 0.3 mm, it is sufficient that the size of the notch is approximately 0.5 mm×3 mm. With a gap of this size, only noise of tens of GHz or higher, which does not affect flow measurement by the electromagnetic flowmeter 21, will enter the shield case 85 from the outside, so there will be no problem with external noise. This means that there is no need to cover the cutout 93 of the shield case 85 with conductive tape.

A plurality of lead pins 73 that electrically connect the excitation circuit 44 of the main board 28 and the excitation coils 25 and 26 are located adjacent to the inner wall portion 22b of the case 22 in the coil bobbin 77, as shown in FIGS. Two of them are erected on each of the matching side parts 77a and 77b. The lead pin 73 is a linearly extending conductor pin that protrudes from the coil bobbin 77 in a direction intersecting the longitudinal direction of the measurement tube 24 and extends toward the main board 28 . The bases of the two lead pins 73 attached to one side 77a of the coil bobbin 77 are electrically connected to both ends of the excitation coil 25. The bases of the other two lead pins 73 are electrically connected to both ends of the excitation coil 26.

The protruding ends of these lead pins 73 are inserted into through holes 94 (see FIG. 11) of the main board 28, and cross the main board 28 in the thickness direction. A land 95 for soldering is provided around the through hole 94. Although not shown, this land 95 is electrically connected to the excitation circuit 44 via a wiring pattern formed on the main board 28. Therefore, by passing the lead pin 73 through the through hole 94 and soldering it to the land 95, the excitation coils 25 and 26 are connected to the excitation circuit 44 through the lead pin 73, the land 95, and the wiring pattern on the main board 28. electrically connected to. In this embodiment, the excitation circuit 44 corresponds to the "second electric circuit" in the present invention. Note that in connecting the lead pins 73 to the main board 28, a so-called press-fitting method can be adopted. In this case, the hole wall surface of the through hole 94 is covered with a film made of a conductor connected to the land 95, and the hole diameter of the through hole 94 is formed to be slightly smaller than the outer diameter of the lead pin 73. By press-fitting the lead pin 73 into the through hole 94, the lead pin 73 is electrically connected to the land 95. Adopting this press-fit connection structure eliminates the need for soldering work.

As shown in FIG. 1, the lead pin 73 is formed such that its leading end protrudes outside the case 22 from the opening edge 22d of the case 22 when it is attached to the coil bobbin 77. By adopting this configuration, it is possible to easily pass the lead pin 73 through the through hole 94 of the main board 28. That is, with the main board 28 close to the opening edge 22d of the case 22, a tool such as tweezers is inserted between the main board 28 and the case 22, and the tip of the lead pin 73 is pinched and penetrated with this tool. It can be guided through the hole 94.

[Effects of the first embodiment]
In the electromagnetic flowmeter 21 configured in this way, when electrically connecting the differential amplification circuit 91 (preamplifier circuit) of the preamplifier 71 and the signal amplification circuit 42 (first electric circuit) of the main board 28, a lead is used. Lines are no longer needed. Therefore, the conductive portion that electrically connects the differential amplifier circuit 91 and the main board 28 can be easily separated from the conductive portion of the excitation coils 25 and 26, and the conductive portion on the differential amplifier circuit side is connected to the excitation coil. It becomes less susceptible to the effects of noise generated at 25 and 26. As a result, a dedicated wire harness is not required to connect the output side of the preamplifier 71 and the signal amplification circuit 42.

The excitation coils 25 and 26 according to this embodiment are electrically connected to the excitation circuit 44 of the main board 28 via lead pins 73. The lead pin 73 extends from the coil bobbin 77 toward the main board 28 , is passed through a through hole 94 in the main board 28 , and is soldered to a land 95 . Therefore, lead wires are not required when connecting the excitation coils 25, 26 and the excitation circuit 44, and there is no influence on the differential amplifier circuit 91 (preamplifier circuit) or other circuits. As a result, a dedicated wire harness is not required to connect the excitation coils 25, 26 and the excitation circuit 44. In this embodiment, since lead wires are not required on both the preamplifier 71 side and the excitation coils 25 and 26, an electromagnetic flowmeter that is not affected by noise generated in the excitation coils 25 and 26 can be obtained.

The lead pin 73 and the first and second connectors 31 and 32 are provided at separate positions in the longitudinal direction of the measurement tube 24. Therefore, the signal amplification circuit 42 is not affected by noise on the excitation circuit 44 side.

The lead pin 73 according to this embodiment is formed to protrude from the opening edge 22d of the case 22 to the outside of the case 22. Therefore, the leading end of the lead pin 73 can be guided into the through hole 94 of the main board 28 while being visually observed. Therefore, the work of connecting the lead pins 73 to the main board 28 can be easily performed.

By connecting the tip of the lead pin 73 to the main board 28, the central part of the main board 28 is fixed to the case 22 via the lead pin 73, the coil bobbin 77, and the yoke 76. Since the coil bobbin 77 is arranged in the center of the case 22, a mounting seat for fixing the main board 28 cannot be provided. Therefore, the main board 28 can only be fixed to the case 22 with the fixing bolts 84 at the four corners of the main board 28. However, in this embodiment, the central portion of the main board 28 can be supported by the lead pins 73. Therefore, the main board 28 can be firmly supported, and the main board 28 can be prevented from vibrating relative to the case 22. As a result, contact failure between the first and second connectors 31 and 32 does not occur when vibrations are transmitted to the case 22 from the outside.

The output wiring pattern 92 according to this embodiment passes through the notch 93 of the shield case 85 and extends from the inside of the shield case 85 to the outside. The cutout 93 through which the output wiring pattern 92 can pass passes only noise of tens of GHz or more that does not affect flow measurement, so there is no need to paste a conductive tape to the cutout 93 to shield it. Therefore, according to this embodiment, the number of assembly steps is reduced compared to the case where a conductive tape is used, so it is possible to provide an electromagnetic flowmeter that is easy to assemble.

[Second embodiment]
A connection portion that electrically connects the differential amplifier circuit 91 (preamplifier circuit) and the first connector 31, which is the output destination of the preamplifier 71, can be configured as shown in FIGS. 12 and 13. In FIGS. 12 and 13, members that are the same or equivalent to those described with reference to FIGS. 1 to 11 are given the same reference numerals, and detailed explanations are omitted as appropriate. In this embodiment, the three signal lines connected to the preamplifier 71, signal 1, signal 2, and power supply, are configured as an output wiring pattern 101 consisting of three wiring sections, which will be described later.

As shown in FIG. 12, the first wiring section is a first wiring pattern section 101a that extends along one surface of the preamplifier board 27 (the surface on which the preamplifier 71 is mounted) inside the shield case 85. . The second wiring section is a via hole section 101b connected to the tip of the first wiring pattern section 101a and penetrating the preamplifier board 27 inside the shield case 85, as shown in FIG. The third wiring section extends along the other surface of the preamplifier board 27 (the surface on which the shield pattern 86 is formed), and has one end connected to the via hole section 101b and the other end connected to the first connector. 31 is the second wiring pattern section 101c. An insulating gap 86a is formed in the shield pattern 86 and extends along the second wiring pattern portion 101c.
By adopting the configuration in which the second wiring pattern section 101c extends along the other surface of the preamplifier board 27, the wiring pattern does not cross the shield case 85, and the notch 93 as shown in FIG. It is no longer necessary to form this on the shield case 85.

When adopting this configuration, the shield pattern 86 is removed only in the portion where the second wiring pattern portion 101c and the gap 86a are formed, but as shown in FIG. The length of the second wiring pattern portion 101c is several mm or less. Furthermore, the second wiring pattern section 101c is located at a position sufficiently apart from the substrate side wiring patterns 54 and 64 which are the input side of the differential amplifier circuit 91. Therefore, even if a sealing function cannot be obtained in the part where the second wiring pattern portion 101c is formed, only noise of several tens of GHz or more that does not affect the flow measurement of the electromagnetic flowmeter 21 is transmitted from the outside into the shield case 85. No problems will arise because of the intrusion.

[Third embodiment]
The portion where the lead pin 73 crosses the main board 28 in the thickness direction can be configured as shown in FIGS. 14 and 15. In FIGS. 14 and 15, members that are the same as or equivalent to those described with reference to FIGS. 1 to 11 are designated by the same reference numerals, and detailed description thereof will be omitted as appropriate.
An end surface through hole 111 is formed at the end of the main board 28 shown in FIG. As shown in FIG. 15, the end surface through hole 111 is formed in a shape in which a portion of the end surface 28a of the main board 28 is partially recessed to have a U-shaped cross section.

The recessed portion of the end surface through hole 111 is formed in a size that allows the lead pin 73 to be inserted therein. Further, a film 112 made of a conductor is formed on the wall surface 111a of the concave portion of the end face through hole 111 and the opening edge 111b located on the main surface 28b side of the main board 28. In FIG. 15, the area where the film 112 is formed is hatched. The lead pin 73 is electrically connected to the end surface through hole 111 by being inserted into the end surface through hole 111 and soldered to the membrane 112 .
By adopting this configuration, there is no need to insert the lead pins 73 into the through holes 94 of the main board 28, so the positioning of the lead pins 73 when attaching the main board 28 to the case 22 becomes easier, and the assembly work becomes easier. will improve.

[Fourth embodiment]
The electromagnetic flowmeter according to the present invention can be configured as shown in FIGS. 16 and 17. In FIGS. 16 and 17, members that are the same as or equivalent to those described with reference to FIGS. 1 to 11 are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate. The electromagnetic flowmeter 121 shown in FIG. 16 includes a conductivity measurement circuit board 122 that is penetrated by the upstream end of the measurement tube 24. In this embodiment, this conductivity measurement circuit board 122 corresponds to the "conductivity measurement board" in the present invention.

The conductivity measurement circuit board 122 has the same structure as the preamplifier board 27, and has a tube hole 122a for passing the measurement tube 24 formed therein approximately in the center. This conductivity measurement circuit board 122 is positioned on the opposite side of the conductivity measurement surface electrode 72 from the preamplifier board 27, and is held in the case 22 by the same holding structure as the preamplifier board 27. That is, guide portions 74 and 75 are provided on the inner wall portion 22b of the case 22 according to this embodiment at positions corresponding to the conductivity measurement circuit board 122. Note that the guide portion 74 is not shown in FIG. 16. Therefore, this conductivity measurement circuit board 122 also extends in a direction intersecting the longitudinal direction of the measurement tube 24, with the measurement tube 24 passing through it.

The surface electrode 72 for measuring conductivity is provided on the opposite side (upstream side) of the preamplifier board 27 from the pair of surface electrodes 51 and 61 for measuring flow rate in the measurement tube 24 .
A part of the electrical circuit 45 for conductivity measurement is provided on one surface of the conductivity measurement circuit board 122 that is close to the surface electrode 72 for conductivity measurement.
As shown in FIG. 17, the electrical circuit 45 for measuring conductivity according to this embodiment includes, as main circuit parts, a clock signal generation circuit 131 and an A/D converter 132 mounted on the main board 28, and a conductivity measurement circuit 45, as shown in FIG. The conductivity measurement circuit 133 is mounted on the conductivity measurement circuit board 122.
Of these circuits, the circuit on the main board 28 side and the conductivity measurement circuit 133 on the conductivity measurement circuit board 122 are connected to the third connector 134 provided on the conductivity measurement circuit board 122 and the main board 28 It is electrically connected via a fourth connector 135 provided in the. In this embodiment, the clock signal generation circuit 131 and the A/D converter 132 provided on the main board 28 side are connected to the "third electrical circuit electrically connected to the conductivity measuring circuit" in the present invention. corresponds to "circuit".

The third connector 134 and the fourth connector 135 are equivalent to the first and second connectors 31 and 32 described above. The third connector 134 is provided at the end of the conductivity measurement circuit board 122 on the opening side of the case 22 and is electrically connected to the conductivity measurement circuit 133. The fourth connector 135 is provided at the other end of the main board 28 (the end opposite to the preamplifier board 27), and is configured to be detachable from the third connector 134. This fourth connector 135 is connected to the third connector 134 by attaching the main board 28 to the case 22.

In the electrical circuit 45 for measuring conductivity, the clock signal generation circuit 131 generates three clock signals CLK1, CLKp, and CLKn based on the clock signal CLK0 output from the conductivity calculation unit 48C of the arithmetic processing circuit 48. be done.
The conductivity measurement circuit 133 generates an AC signal having an amplitude of the voltage VP by switching the switch SWv based on CLK1, and applies it to the conductivity measurement surface electrode 72 via the resistance element RP.

The detection signal Vp generated at the surface electrode 72 for conductivity measurement at that time is amplified by the amplifier AMP of the conductivity measurement circuit 133, and then the switches SWp and SWn are controlled based on CLKp and CLKn to increase the voltage of Vp. The high level and low level are sampled and A/D converted by the A/D converter 132, and the obtained detection data DP is output to the arithmetic processing circuit 48. The electrical conductivity calculation unit 48C calculates the electrical conductivity of the fluid based on the amplitude voltage of Vp indicated by the detection data DP from the electrical circuit 45 for measuring electrical conductivity.

At this time, since the impedance of the surface electrode 72 for conductivity measurement is very high and susceptible to noise, it is desirable to arrange the conductivity measurement circuit 133 as close to the surface electrode 72 for conductivity measurement as possible. From this point of view, in this embodiment, a conductivity measurement circuit 133 is mounted on the conductivity measurement circuit board 122.

As shown in FIG. 17, the conductivity measurement circuit 133 is connected to a power source and four wires such as signal 3, signal 4, and common (circuit GND). These four wires are connected to a third connector 134. Of these four wires, the power supply, signal 3, and signal 4 wires are formed as a conductivity measurement wiring pattern 136 (see FIG. 16) extending along one surface of the conductivity measurement circuit board 122. has been done. The common wiring is connected to the third connector 134 via a shield pattern 137 made of a solid pattern formed on the other surface of the conductivity measurement circuit board 122.

The conductivity measurement circuit 133 and the surface electrode 72 for conductivity measurement may be connected via a jumper wire 138, or a wiring pattern connected to the surface electrode 72 for conductivity measurement may be connected, although not shown. This can also be done by soldering the conductivity measurement circuit 133 along the conductivity measurement circuit board 122. As a result, the length of the connection wiring between the conductivity measurement surface electrode 72 and the conductivity measurement circuit 133 can be significantly shortened, and the impedance of the detection signal Vp can be made low by the amplifier AMP, thereby reducing the influence of noise. be able to.

When the measuring tube 24 is provided with the surface electrode 72 for measuring conductivity, the overall length of the measuring tube 24 becomes relatively long, and the case 22 and the main board 28 become larger in the longitudinal direction of the measuring tube 24. Fixing bolts 84 for fixing the main board 28 to the case 22 can only be provided at the four corners of the main board 28. Therefore, when the main board 28 becomes larger in the longitudinal direction of the measuring tube 24, the main board 28 becomes more likely to vibrate relative to the case 22. However, according to this embodiment, since the central portion of the main board 28 is supported by the case 22 via the lead pins 73, the coil bobbin 77, and the yoke 76, the vibration of the main board 28 relative to the case 22 is suppressed. Therefore, even if the case 22 vibrates due to external vibrations, the first to fourth connectors 135 will not cause contact failure.

[Fifth embodiment]
In each of the embodiments described above, an example is shown in which the electric circuit for flow rate measurement and the excitation circuit 44 are provided on one main board 28. However, the main board 28 can be configured as shown in FIG. In FIG. 18, the same or equivalent members as those explained with reference to FIGS. 1 to 11 are given the same reference numerals, and detailed explanations will be omitted as appropriate.
The main board 141 shown in FIG. 18 includes a first board 142 attached to the case 22 so as to close the opening 22a of the case 22, and a main board 142 located at a predetermined distance between the first board 142 and the first board 142 inside the lid body 23. The second substrate 143 may be arranged to face each other.

The first board 142 is provided with an excitation circuit 44 and the second connector 32, and the second board 143 is provided with an electric circuit 144 for measuring flow rate. The electric circuit 144 for flow rate measurement here refers to the signal amplification circuit 42, signal detection circuit 43, electric conductivity measurement electric circuit 45, transmission circuit 46, setting/display circuit 47, and arithmetic processing circuit 48 shown in FIG. etc.
Excitation circuit 44 is electrically connected to lead pins 73 that cross first substrate 142 . An electric circuit 144 for flow rate measurement is electrically connected to the second connector 32 via a lead wire 145.
By adopting this embodiment, the electric circuit 144 for flow rate measurement is separated from the excitation circuit 44 in the longitudinal direction It can be made even more difficult to accept.

22... Case, 24... Measurement tube, 25, 26... Excitation coil, 27... Preamplifier board, 28... Main board, 31... First connector, 32... Second connector, 42... Signal amplification circuit (first electric circuit), 44... Excitation circuit (second electric circuit), 51, 61... Surface electrode, 71... Preamplifier, 72... Surface electrode for conductivity measurement, 73... Lead pin, 77... Coil bobbin, 85... Shield case, 92 ...Output wiring pattern, 93...Notch, 101a...First wiring pattern section, 101b...Via hole section, 101c...Second wiring pattern section, 111...End face through hole, 122...Conductivity measurement circuit board (conductivity rate measurement board), 131... Clock signal generation circuit (third electric circuit), 132... A/D converter (third electric circuit), 133... Conductivity measurement circuit, 134... Third connector, 135 ...Fourth connector.

Claims (6)

A measurement tube through which a fluid to be measured flows;
an excitation coil that forms a magnetic circuit so as to pass through the measurement tube;
a pair of surface electrodes provided on the measurement tube;
a preamplifier board through which the measurement tube extends in a direction crossing the longitudinal direction of the measurement tube;
a preamplifier circuit mounted on one surface of the preamplifier board close to the surface electrodes and electrically connected to the pair of surface electrodes;
a first connector provided on the preamplifier board and electrically connected to the preamplifier circuit;
a shield case that covers the pair of surface electrodes and the preamplifier circuit;
a main board having a first electrical circuit electrically connected to the preamplifier circuit, extending in the longitudinal direction of the measurement tube, and having one end positioned near the preamplifier board;
a second connector provided at the one end of the main board, electrically connected to the first electric circuit, and configured to be detachable from the first connector;
the preamplifier circuit and the first electric circuit are electrically connected via the first connector and the second connector ,
The main board has a second electric circuit electrically connected to the excitation coil,
The excitation coil is wound and held on a coil bobbin,
The coil bobbin has a lead pin that protrudes in a direction crossing the longitudinal direction of the measurement tube and extends toward the main board,
The base of the lead pin is electrically connected to the excitation coil,
The electromagnetic flowmeter is characterized in that a protruding end of the lead pin is electrically connected to the second electric circuit across the main board in the thickness direction. The electromagnetic flowmeter according to claim 1 ,
An electromagnetic flowmeter characterized in that a portion of the main board that the lead pin crosses in a thickness direction is constituted by an end face through hole that opens in an end face of the main board. The electromagnetic flowmeter according to claim 1 or 2 ,
Further, it includes a bottomed rectangular cylindrical case that accommodates the measurement tube, the excitation coil, and the preamplifier board,
The main board is arranged to close an opening of the case,
The electromagnetic flowmeter is characterized in that the lead pin is formed to protrude from an opening edge of the case to the outside of the case. In the electromagnetic flowmeter according to any one of claims 1 to 3 ,
moreover,
a surface electrode for conductivity measurement provided on the opposite side of the preamplifier board from the pair of surface electrodes in the measurement tube;
a conductivity measurement substrate through which the measurement tube extends in a direction crossing the longitudinal direction of the measurement tube, and positioned on the opposite side of the conductivity measurement surface electrode from the preamplifier substrate;
a conductivity measurement circuit mounted on one surface of the conductivity measurement substrate close to the conductivity measurement surface electrode and electrically connected to the conductivity measurement surface electrode;
a third connector provided on the conductivity measurement board and electrically connected to the conductivity measurement circuit;
a third electric circuit provided on the main board and electrically connected to the conductivity measurement circuit;
a fourth connector provided at the other end of the main board, electrically connected to the third electric circuit, and configured to be detachable from the third connector;
An electromagnetic flowmeter characterized in that the conductivity measuring circuit and the third electric circuit are electrically connected via the third connector and the fourth connector. In the electromagnetic flowmeter according to any one of claims 1 to 4 ,
A connection part that electrically connects the preamplifier circuit and the first connector,
including a wiring pattern extending along the one surface of the preamplifier board,
The electromagnetic flowmeter is characterized in that the wiring pattern extends from the inside of the shield case to the outside through a notch formed at an end of the shield case on the side of the preamplifier board. In the electromagnetic flowmeter according to any one of claims 1 to 4 ,
A connection part that electrically connects the preamplifier circuit and the first connector,
a first wiring pattern portion extending along the one surface of the preamplifier board inside the shield case;
a via hole portion connected to the tip of the first wiring pattern portion and penetrating the preamplifier board inside the shield case;
and a second wiring pattern section extending along the other surface of the preamplifier board, one end of which is connected to the via hole section, and the other end of which is connected to the first connector. Features of electromagnetic flowmeter.

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