CN112414480A - Electromagnetic flowmeter - Google Patents

Abstract

An electromagnetic flowmeter in which a joint is connected to a measurement tube that penetrates a printed circuit board without causing positional displacement of the measurement tube relative to the printed circuit board, the electromagnetic flowmeter comprising: the measuring tube, the exciting coil, the pair of surface electrodes, the case housing the measuring tube and the exciting coil, and the printed circuit board having a tube hole into which an end of the measuring tube is inserted and held by the case in a state in which the end of the measuring tube is inserted into the tube hole. The measuring device is provided with a connecting unit for electrically connecting the surface electrode with the printed substrate, a pair of joints fixed on the shell under the state that two end parts of the measuring tube are inserted, and an adhesive tape adhered on the measuring tube. The hole of the printed circuit board has a first hole for restricting the movement of the measuring tube relative to the printed circuit board in a direction perpendicular to the longitudinal direction of the measuring tube, and a second hole having a larger gap with the measuring tube than the first hole. The adhesive tape has a first movement restricting portion for restricting the movement of the end of the measurement tube in the direction of insertion into the tube hole, and a second movement restricting portion for restricting the rotation of the measurement tube with respect to the printed circuit board by being inserted between the measurement tube and the second hole portion.

Description

Electromagnetic flowmeter

Technical Field

The present invention relates to an electromagnetic flowmeter for measuring a flow rate of a fluid flowing in a measurement pipe.

Background

In the electromagnetic flow meter, in addition to a liquid-contact type (non-liquid-contact type) in which an electrode provided on an inner wall surface of a measurement tube is brought into direct contact with a fluid to be measured to detect an electromotive force of the fluid, a pair of surface electrodes are disposed on an outer surface of the measurement tube, and the electromotive force of the fluid is detected by a capacitance between the fluid and the surface electrodes without being brought into contact with the fluid to be measured.

Fig. 27 is a sectional view showing an example of the structure of the capacitive electromagnetic flowmeter. Fig. 28 is an explanatory diagram showing a measurement principle of the electromagnetic flowmeter. In general, a capacitance type electromagnetic flowmeter includes: excitation coils 91A and 91B that generate magnetic flux Φ in a magnetic flux direction Y orthogonal to the longitudinal direction X of the measurement tube 90 through which the fluid flows; and a pair of surface electrodes 92A and 92B arranged in an electrode direction Z orthogonal to the magnetic flux Φ generated by the excitation coils 91A and 91B, and configured to measure the flow rate of the fluid flowing through the measurement tube 90 by alternately switching the polarity of the excitation current flowing through the excitation coils 91A and 91B and detecting the electromotive force generated between the surface electrodes 92A and 92B (see patent document 1 and the like).

In such a capacitive electromagnetic flowmeter, an electromotive force generated between the surface electrodes is amplified by a signal amplification circuit (for example, a differential amplification circuit), and then converted into a digital signal by an a/D conversion circuit, and the digital signal is input to a program processing device such as a microcontroller to perform a predetermined arithmetic processing, thereby calculating a measured value of the flow rate. Such a capacitive electromagnetic flowmeter is particularly attracting attention in recent years because the detection electrodes are not easily deteriorated and are easily maintained.

However, since the capacitive electromagnetic flowmeter is configured such that the fluid does not contact the surface electrodes 92A and 92B, the capacitance between the fluid and the surface electrodes 92A and 92B is very small, on the order of several pF. Therefore, the impedance between the fluid and the surface electrodes 92A and 92B becomes very high, and is easily affected by noise. Further, the magnitude of the flow rate signal (electromotive force) detected from the fluid also changes depending on the position and the magnitude of the surface electrodes 92A and 92B.

Fig. 29 is an explanatory diagram showing the contribution rate of the fluid in the pipe to the flow rate signal with respect to the electrode position. As is clear from fig. 29, when the width of the surface electrodes 92A and 92B is an angle θ seen from both ends of the surface electrodes 92A and 92B toward the center, θ is preferably within 1.4rad (see patent document 2 and the like). Therefore, when the centers of the surface electrodes 92A and 92B are disposed at positions deviated from the axis P along which the flow rate signal is the maximum, the obtained flow rate signal becomes small, and as a result, the S/N ratio deteriorates.

A small-sized capacitive electromagnetic flowmeter for the FA market has been proposed (see patent document 3 and the like). In this conventional technique, as shown in fig. 30 and 31, surface electrodes 92A and 92B are disposed on the outer peripheral surface of a measurement tube 90, and two substrate holders 94A and 94B are attached to the measurement tube 90 from the top and bottom so as to cover the outer sides of the surface electrodes 92A and 92B and the preamplifier substrates 93A and 93B, thereby assembling a tube unit.

Then, the entire tube unit including the measurement tube 90 is mounted on the case 96 by inserting the projection 97A of the yoke 97 mounted on the bottom of the case 96 into the mounting hole of the substrate holder 94B formed in the lower portion. Thus, in the assembly work of the capacitive electromagnetic flowmeter, the surface electrodes 92A and 92B are attached so that the centers thereof coincide with the axis P.

Patent documents 4 and 5 propose a capacitive electromagnetic flowmeter having a significantly simplified structure. In patent document 4, as shown in fig. 32, a preamplifier circuit is integrated on 1 printed board 98 orthogonal to the measurement tube 90, and one surface of the printed board 98 is made to have a shielding function as a whole copper foil pattern 98a, thereby greatly simplifying the overall structure of the shield case and the detector unit.

In this structure, the wiring patterns 99A and 99B on the measuring tube 90 side and the wiring patterns 100A and 100B on the printed circuit board 98 side are electrically connected in advance by jumpers 101A and 101B, respectively, to form a unit, and then the assembly work to the housing is performed.

Patent document 5 discloses a support structure in which a measurement tube 90 is supported by a case 102 of an electromagnetic flowmeter via joints 103 and 104, as shown in fig. 33 and 34. Both ends of the measurement tube 90 shown in patent document 5 are inserted into pipe connection fittings 103 and 104. The joints 103 and 104 are fixed to the housing 102. Therefore, the measurement tube 90 is fixed to the case 102 via the joints 103 and 104.

[ Prior art documents ]

[ patent document ]

Patent document 1: japanese patent laid-open No. 2004-226394

Patent document 2: japanese patent laid-open No. Hei 7-120282

Patent document 3: japanese patent laid-open No. 2014-202662

Patent document 4: japanese patent laid-open publication No. 2018-077118

Patent document 5: japanese patent laid-open publication No. 2018-141667

Disclosure of Invention

Problems to be solved by the invention

As shown in patent document 4, when the measurement tube unit assembled by inserting the measurement tube 90 into the hole of the printed circuit board 98 is supported by the housing 102 by the support structure shown in patent document 5, there is a possibility that the measurement tube 90 moves relative to the printed circuit board 98 in the step of inserting the end of the measurement tube 90 into the joints 103 and 104. The reason why the measurement tube 90 moves in this manner is that the joints 103 and 104 are provided with sealing members for sealing the measurement tube 90 therebetween, and sliding resistance acts on the measurement tube 90.

If the positional relationship between the measurement tube 90 and the printed circuit board 98 is shifted during the operation of inserting the measurement tube 90 into the joints 103 and 104, stress is generated in the jumper wires 101A and 101B, the tips of the wiring patterns 99A and 99B on the measurement tube side, and the tips of the wiring patterns 100A and 100B on the printed circuit board 98 side. When the amount of movement of the measurement tube 90 increases, the conductive portion electrically connecting the measurement tube 90 and the printed circuit board 98 including the jumpers 101A and 101B is disconnected. Further, if the measurement tube 90 is twisted with respect to the printed circuit board 98, the positions of the surface electrodes 92A and 92B are changed, which causes a problem that the performance of the electromagnetic flowmeter is degraded.

The invention aims to provide an electromagnetic flowmeter which does not cause the position deviation of a measuring pipe relative to a printed substrate when a joint is connected with the measuring pipe penetrating the printed substrate.

Means for solving the problems

In order to achieve the above object, an 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; a pair of face electrodes provided on an outer surface of the measurement tube; a case that houses the measurement tube and the excitation coil; a printed substrate having a hole into which an end of the measurement tube is inserted, the printed substrate being held in the housing in a state in which the end of the measurement tube is inserted into the hole; a connection unit electrically connecting the surface electrode and the printed circuit board; a pair of joints fixed to the housing in a state where both end portions of the measurement tube are inserted; and an adhesive tape attached to the measurement tube, wherein the hole of the printed circuit board has a first hole portion that restricts movement of the measurement tube relative to the printed circuit board in a direction orthogonal to a longitudinal direction of the measurement tube, and a second hole portion that has a wider gap with the measurement tube than a gap between the first hole portion and the measurement tube, the adhesive tape including: a first movement restricting portion that restricts movement of the end portion of the measurement tube in a direction of insertion into the hole, and a second movement restricting portion that: and a second hole portion that is inserted between the measurement tube and the second hole portion, engages with the printed circuit board, and restricts rotation of the measurement tube with respect to the printed circuit board.

In the electromagnetic flowmeter according to the present invention, the adhesive tape may be configured by a first adhesive tape body that is attached to the measurement tube and extends along an outer surface of the measurement tube in a direction orthogonal to a longitudinal direction of the measurement tube, and a second adhesive tape body that is inserted between the measurement tube and the second hole portion with a portion thereof overlapping the outer surface of the first adhesive tape body.

In the electromagnetic flowmeter according to the present invention, the first adhesive tape main body may have an insulating property and cover the surface electrode.

In the electromagnetic flowmeter according to the present invention, the printed boards may be provided at both ends of the measurement tube, and the adhesive tape may restrict rotation of the measurement tube with respect to one of the printed boards and movement of the measurement tube in a direction in which the measurement tube is inserted into the hole of one of the printed boards, and may restrict rotation of the measurement tube with respect to the other printed board and movement of the measurement tube in a direction in which the measurement tube is inserted into the hole of the other printed board.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, the adhesive tape attached to the measurement tube is brought into contact with the printed circuit board, thereby restricting the movement and rotation of the measurement tube in one longitudinal direction with respect to the printed circuit board. Therefore, by setting the connection direction in which the joint is connected to the measurement pipe as the direction in which the movement is restricted, it is possible to provide an electromagnetic flowmeter in which the measurement pipe does not shift with respect to the printed circuit board.

Drawings

Fig. 1 is a plan view showing an electromagnetic flowmeter according to a first embodiment.

Fig. 2 is a block diagram showing a circuit configuration of the electromagnetic flow meter according to the first embodiment.

Fig. 3 is a side view of the electromagnetic flow meter of the first embodiment.

Fig. 4 is a sectional perspective view of the electromagnetic flow meter of the first embodiment.

Fig. 5 is an assembly diagram of the electromagnetic flow meter of the first embodiment.

Fig. 6 is a plan view showing the detector according to the first embodiment.

Fig. 7 is a side view showing the detector of the first embodiment.

Fig. 8 is a front view showing the detector of the first embodiment.

Fig. 9 is a diagram illustrating an example of the configuration of a differential amplifier circuit using a preamplifier.

Fig. 10 is a plan view of a main portion of the first embodiment.

Fig. 11 is a front view of a main part of the first embodiment.

Fig. 12 is a diagram showing components of the detector unit of the first embodiment.

Fig. 13 is a side view of the measuring tube to which the adhesive tape is attached according to the first embodiment.

Fig. 14 is a sectional view taken along line a-a of fig. 11.

Fig. 15 is a sectional view taken along line B-B of fig. 11.

Fig. 16 is a diagram showing a detector unit.

Fig. 17 is an explanatory view showing the insertion of the measurement tube according to the first embodiment.

Fig. 18 is an explanatory view showing the joint connection according to the first embodiment.

Fig. 19 is a plan view showing an electromagnetic flow meter according to a second embodiment.

Fig. 20 is a side view of the electromagnetic flow meter of the second embodiment.

Fig. 21 is a diagram illustrating an example of the configuration of the conductivity (electric conductivity) measuring circuit.

Fig. 22 is a view showing a modification of the tube hole.

Fig. 23 is a view showing a modification of the tube hole.

Fig. 24 is a diagram showing a modification of the connection unit.

Fig. 25 is a diagram showing a modification of the measurement tube.

Fig. 26 is a view showing a modification of the adhesive tape.

Fig. 27 is a sectional view showing an example of the structure of the capacitive electromagnetic flowmeter.

Fig. 28 is an explanatory diagram showing a measurement principle of the electromagnetic flowmeter.

Fig. 29 is an explanatory diagram showing the contribution rate of the fluid in the pipe to the flow rate signal with respect to the electrode position.

Fig. 30 is a sectional view showing the structure of a conventional capacitive electromagnetic flowmeter.

Fig. 31 is another sectional view showing the structure of the conventional capacitive electromagnetic flowmeter.

Fig. 32 is a plan view schematically showing a structure around a detection unit of the electromagnetic flowmeter.

Fig. 33 is a perspective view of the electromagnetic flow meter.

Fig. 34 is a perspective sectional view showing the inside of the housing.

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings.

[ first embodiment ]

First, an electromagnetic flow meter 200 according to a first embodiment of the present invention will be described with reference to fig. 1. Fig. 1 is a plan view showing an electromagnetic flowmeter 200 according to a first embodiment. Fig. 2 is a block diagram showing a circuit configuration of an electromagnetic flow meter 200 according to a first embodiment. Hereinafter, a capacitance type electromagnetic flowmeter in which a pair of detection electrodes are not in direct contact with a fluid to be measured flowing in a measurement tube will be described as an example, but the present invention is not limited to this, and can be similarly applied to a liquid-contact type electromagnetic flowmeter in which the detection electrodes are in direct contact with the fluid.

As shown in fig. 2, the capacitive electromagnetic flowmeter 200 includes, as main circuit units, a detection unit 20, a signal amplification circuit 21, a signal detection circuit 22, an excitation circuit 23, a conductivity measurement circuit 24, a transmission circuit 25, a setting and display circuit 26, and an arithmetic processing Circuit (CPU) 27.

The detection unit 20 includes a measurement tube 2, excitation coils 3A and 3B forming a magnetic circuit so as to pass through the measurement tube 2, surface electrodes 10A and 10B, and a preamplifier 5U as main components, and has a function of detecting electromotive forces Va and Vb corresponding to the flow velocity of the fluid flowing through the flow path 1 in the measurement tube 2 by the surface electrodes 10A and 10B, and outputting an alternating-current detection signal Vin corresponding to the electromotive forces Va and Vb.

The excitation control unit 27A of the arithmetic processing circuit 27 outputs an excitation control signal Vex for switching the polarity of the excitation current Iex in accordance with a predetermined excitation cycle. The exciting circuit 23 supplies an alternating-current exciting current Iex to the exciting coils 3A and 3B based on an excitation control signal Vex from the excitation control unit 27A of the arithmetic processing circuit 27.

The signal amplifier circuit 21 filters a noise component included in the detection signal Vin output from the detection unit 20, and outputs an ac flow rate signal VF obtained by amplification. The signal detection circuit 22 samples and holds the flow rate signal VF from the signal amplification circuit 21, converts the obtained dc voltage a/D into a flow rate amplitude value DF, and outputs the flow rate amplitude value DF to the arithmetic processing circuit 27.

The flow rate calculation unit 27B of the arithmetic processing circuit 27 calculates the flow rate of the fluid based on the flow rate amplitude value DF from the signal detection circuit 22, and outputs the flow rate measurement result to the transmission circuit 25. The transmission circuit 25 transmits data to and from the host device through the transmission path L, and transmits the flow rate measurement result and the empty state determination result obtained by the arithmetic processing circuit 27 to the host device.

The conductivity measurement circuit 24 is a circuit including: for example, in a state where the fluid flowing through the measurement tube 2 is set to the common potential Vcom through the joint 85, an ac signal is applied to the conductivity measurement electrode 10C through the resistance element, the amplitude of the ac detection signal generated in the conductivity measurement electrode 10C at that time is sampled, and ac amplitude value data DP obtained by a/D conversion is output to the arithmetic processing circuit 27.

The conductivity calculation unit 27C of the arithmetic processing circuit 27 has a function of calculating the conductivity of the fluid from the ac amplitude value data DP from the conductivity measurement circuit 24.

The empty state determination unit 27D of the arithmetic processing circuit 27 has a function of determining the presence or absence of the fluid in the measurement tube 2 based on the conductivity of the fluid calculated by the conductivity calculation unit 27C.

Typically, the electrical conductivity of the fluid is greater than the electrical conductivity of air. Therefore, the empty state determination unit 27D determines the presence or absence of the fluid by performing threshold processing on the conductivity of the fluid calculated by the conductivity calculation unit 27C.

The setting and display circuit 26 detects an operation input by an operator, for example, and outputs various operations such as flow rate measurement, conductivity measurement, and empty state determination to the arithmetic processing circuit 27, and displays the flow rate measurement result and the empty state determination result output from the arithmetic processing circuit 27 by a display circuit such as an LED or an LCD.

The arithmetic processing circuit 27 includes a CPU and peripheral circuits thereof, and realizes various processing units such as the excitation control unit 27A, the flow rate calculation unit 27B, the conductivity calculation unit 27C, and the empty state determination unit 27D by causing hardware and software to cooperate with each other by executing a predetermined program by the CPU.

[ mounting Structure of measuring tube ]

Next, the structure of the mounting structure of the measurement tube 2 will be described in detail with reference to fig. 1, 3, and 4. Fig. 3 is a side view of the electromagnetic flow meter of the first embodiment. Fig. 4 is a sectional perspective view of the electromagnetic flow meter of the first embodiment.

In the present embodiment, the measurement tube 2 is attached to the case 8 by inserting the measurement tube 2 into the tube hole 5H provided in the printed circuit board 5, inserting the side end portions 5I and 5J of the printed circuit board 5 from the opening 8B of the case 8, and fitting the side end portions into the guide portions 81A and 81B formed in the inner wall portion 8A of the case 8, thereby holding the printed circuit board 5 on the case 8. An adhesive tape 202 constituting a part of a coupling structure 201 described later is attached to the outer peripheral surface of the measurement tube 2. The coupling structure 201 and the adhesive tape 202 will be described in detail later.

As shown in fig. 1, the measurement tube 2 is made of a material having excellent insulating properties and dielectric properties, such as ceramic or resin, in a cylindrical shape, and a substantially C-shaped yoke (for example, the same shape as the yoke 4 in fig. 5) and a pair of excitation coils 3A and 3B are arranged on the outside of the measurement tube 2 so as to face each other with the measurement tube 2 interposed therebetween, such that the magnetic flux direction (second direction) Y is orthogonal to the longitudinal direction (first direction) X of the measurement tube 2. Hereinafter, for the sake of easy observation, only the yoke end faces, i.e., the yoke faces 4A and 4B, are shown.

On the other hand, on the outer peripheral surface 2A of the measuring tube 2, a pair of surface electrodes (first surface electrodes) 10A and surface electrodes (second surface electrodes) 10B made of thin-film conductors are arranged facing each other in an electrode direction (third direction) Z orthogonal to the longitudinal direction X and the magnetic flux direction (second direction) Y.

Thus, when an alternating excitation current Iex is supplied to the exciting coils 3A, 3B, a magnetic flux Φ is generated between the yoke surfaces 4A, 4B positioned at the centers of the exciting coils 3A, 3B, an alternating electromotive force having an amplitude corresponding to the flow velocity of the fluid is generated in the fluid flowing through the flow path 1 along the electrode direction Z, and the electromotive force is detected by the surface electrodes 10A, 10B via the electrostatic capacitance between the fluid and the surface electrodes 10A, 10B.

The case 8 has an opening 8B at the top, and is formed of a bottomed box-shaped resin or metal frame body that accommodates the measurement tube 2 therein. Guide portions 81A and 81B are formed at positions facing each other on a pair of inner wall portions 8A parallel to the longitudinal direction X among the inner wall portions of the housing 8. The guide portions 81A and 81B are formed of two protruding strips formed parallel to the electrode direction Z, and fitting portions 82A and 82B between these protruding strips are fitted to the side end portions 5I and 5J of the printed circuit board 5 inserted from the opening 8B.

The projections of the guide portions 81A and 81B need not be formed continuously in the electrode direction Z, but may be formed separately in a plurality at intervals at which the side end portions 5I and 5J are smoothly inserted. The guide portions 81A and 81B may be grooves into which the side end portions 5I and 5J of the printed circuit board 5 are inserted, instead of the protrusions, in the inner wall portion 8A.

Of the side surfaces of the case 8, a pair of side surfaces 8C parallel to the magnetic flux direction Y are provided with tubular fittings 85 and 86 made of a metal material (e.g., SUS) and capable of connecting a pipe (not shown) provided outside the electromagnetic flowmeter 200 to the measurement pipe 2. At this time, the measurement tube 2 is housed in the case 8 along the longitudinal direction X, and the joint 85 and the joint 86 are respectively connected to both end portions of the measurement tube 2 via O-rings 87.

Here, at least one of the tabs 85 and 86 functions as the common electrode 10D. For example, the joint 85 is connected to the common potential Vcom, thereby not only connecting an external conduit and the measurement tube 2, but also functioning as the common electrode 10D.

In this way, the common electrode 10D is realized by the joint 85 made of metal, and thus the area of the common electrode 10D in contact with the fluid is increased. Thus, even when foreign matter adheres to or corrodes on the common electrode 10D, the area of the portion where the foreign matter adheres or corrodes is relatively small with respect to the entire area of the common electrode 10D, and therefore, a measurement error caused by a change in polarization capacitance can be suppressed.

Fig. 5 is an assembly diagram of the electromagnetic flow meter of the first embodiment.

The printed board 5 is a general printed board (for example, a glass cloth-based epoxy resin copper-clad laminate having a thickness of 1.6 mm) for mounting electronic components, and as shown in fig. 5, a tube hole 5H for passing the measurement tube 2 therethrough is formed in a substantially central position of the printed board 5. Therefore, the printed board 5 is attached in a direction intersecting the measurement tube 2. The tube hole 5H constitutes a connection structure 201 together with an adhesive tape 202 described later. The description of the pipe hole 5H will be described later.

Fig. 6 is a plan view showing the detector according to the first embodiment. Fig. 7 is a side view showing the detector of the first embodiment. Fig. 8 is a front view showing the detector of the first embodiment.

The capacitance between the fluid and the surface electrodes 10A and 10B is very small, of the order of several pF, and the impedance between the fluid and the surface electrodes 10A and 10B is high, and thus is easily affected by noise. Therefore, the electromotive forces Va and Vb obtained by the surface electrodes 10A and 10B are reduced in impedance by the preamplifier 5U using the operational amplifier IC or the like.

In the present embodiment, the printed board 5 is attached to the measurement tube 2 at a position outside the magnetic flux region F, which is a region where the magnetic flux Φ is generated between the yoke surfaces 4A and 4B of the excitation coils 3A and 3B in the direction intersecting the measurement tube 2, and the preamplifier 5U is attached, and the surface electrodes 10A and 10B are electrically connected to the preamplifier 5U via the connection wirings 11A and 11B.

In the example of fig. 7 and 8, the mounting position of the printed circuit board 5 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). As described above, the mounting direction of the printed circuit board 5 is a direction in which the substrate surface intersects the measurement tube 2, and here, is a direction along a two-dimensional plane formed by the magnetic flux direction Y and the electrode direction Z. The mounting position of the printed circuit board 5 may be a position outside the magnetic flux region F, or may be a position separated from the magnetic flux region F in the upstream direction opposite to the downstream direction. The mounting direction of the printed circuit board 5 is not limited to a direction along the two-dimensional plane, and may be inclined to the two-dimensional plane.

The surface electrodes 10A and 10B, the connection wirings 11A and 11B, and the preamplifier 5U are electrically shielded by a shield case 7, and the shield case 7 is formed of a metal plate connected to a ground potential. The shield case 7 has a substantially rectangular shape extending in the longitudinal direction X, and openings through which the measurement tube 2 passes are provided in the upstream and downstream directions of the magnetic flux region F.

This shields the entire circuit portion having high impedance by the shield case 7, thereby suppressing the influence of external noise. At this time, the shield pattern 5G composed of a ground pattern (overall pattern) connected to the ground potential may be formed on the solder surface of the printed board 5 on the side opposite to the mounting surface of the preamplifier 5U. Accordingly, of the planes constituting the shield case 7, the planes in contact with the printed circuit board 5 may be all opened, and the structure of the shield case 7 can be simplified.

The connection wirings 11A and 11B are wirings connecting the surface electrodes 10A and 10B and the preamplifier 5U, and as described above, the whole is shielded by the shield case 7, so that a pair of general wiring cables may be used. In this case, both ends of the wiring cable may be soldered to the surface electrode 10A and the lands formed on the printed circuit board 5.

In the present embodiment, as shown in fig. 7 and 8, as the connection wirings 11A and 11B, tube- side wiring patterns 12A and 12B formed on the outer peripheral surface 2A of the measurement tube 2 are used.

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

The connection wiring 11B is composed of a tube-side wiring pattern 12B, a substrate-side wiring pattern 5B, and a jumper wire 15B, the tube-side wiring pattern 12B is formed on the outer peripheral surface 2A, one end of the tube-side wiring pattern 12B is connected to the surface electrode 10B, the other end of the tube-side wiring pattern is connected to a pad 16B for connection of the jumper wire 15B disposed near the printed substrate 5, the substrate-side wiring pattern 5B is formed on the printed substrate 5, one end of the substrate-side wiring pattern 5B is connected to the preamplifier 5U, and the jumper wire 15B connects the tube-side wiring pattern 12B and the substrate. The jumper wire 15B is soldered on a land 16B formed on the other end of the tube-side wiring pattern 12B and a land 5D formed on the other end of the substrate-side wiring pattern 5B. In this embodiment, the jumpers 15A and 15B correspond to "connecting means" in the present invention.

Thus, the tube- side wiring patterns 12A and 12B formed on the outer peripheral surface 2A are used in the sections from the surface electrodes 10A and 10B to the positions near the printed circuit board 5 in the connection wirings 11A and 11B. Therefore, as in the case of using the pair of wiring cables, the installation work such as the handling and fixing of the wiring cables can be simplified, and the cost of connecting the wirings and the burden of the wiring work can be reduced.

Further, since the surface electrodes 10A, 10B and the tube- side wiring patterns 12A, 12B are formed of a thin film of a nonmagnetic metal such as copper and integrally formed on the outer peripheral surface 2A of the measurement tube 2 by metallization, the manufacturing process can be simplified, which also leads to reduction in product cost. The metallization treatment may be plating treatment, vapor deposition treatment, or the like, and a previously formed nonmagnetic metal thin film body may be attached. When the nonmagnetic metal thin film body is bonded, the leading end portions of the nonmagnetic metal thin film body (the other end sides of the tube- side wiring patterns 12A, 13A) can be directly connected to the pads 5C, 5D, respectively, without using the jumpers 15A, 15B. The details will be described later. (reference paragraph 0092)

As shown in fig. 7 and 8, the tube-side wiring pattern 12A includes a longitudinal wiring pattern 13A formed linearly in the longitudinal direction X on the outer peripheral surface 2A of the measurement tube 2, and the tube-side wiring pattern 12B includes a longitudinal wiring pattern 13B formed linearly in the longitudinal direction X on the outer peripheral surface 2A of the measurement tube 2.

Since the connecting wirings 11A and 11B are partially disposed inside or in the vicinity of the magnetic flux region F, when a pair of wiring cables are used as the connecting wirings 11A and 11B, a signal loop is formed due to a positional deviation between the two wirings as viewed from the magnetic flux direction Y, which causes a magnetic flux differential noise. As shown in the present embodiment, if the wiring pattern formed on the outer peripheral surface 2A of the measurement tube 2 is used, the positions of the connection wirings 11A and 11B can be accurately fixed. Therefore, a positional shift between the two wirings as viewed in the magnetic flux direction Y can be avoided, and the generation of magnetic flux differential noise can be easily suppressed.

As shown in fig. 7 and 8, the tube-side wiring pattern 12A includes a circumferential wiring pattern 14A, and the circumferential wiring pattern 14A is formed on the outer circumferential surface 2A of the measurement tube 2 along the circumferential direction W of the measurement tube 2 from the first end 17A of the surface electrode 10A along the longitudinal direction X to one end of the longitudinal wiring pattern 13A.

The tube-side wiring pattern 12B includes a circumferential wiring pattern 14B, and the circumferential wiring pattern 14B is formed on the outer circumferential surface 2A of the measurement tube 2 along the circumferential direction W of the measurement tube 2 from the second end 17B of the surface electrode 10B along the longitudinal direction X to one end of the longitudinal wiring pattern 13B.

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

In the example of fig. 7 and 8, the longitudinal wiring patterns 13A and 13B are formed on intersecting lines JA and JB intersecting the outer peripheral surface 2A on a plane passing through the tube axis J of the measurement tube 2 along the magnetic flux direction Y, respectively. One end of the circumferential wiring pattern 14A is connected to the center position of the surface electrode 10A in the longitudinal direction X in the first end 17A of the surface electrode 10A. Similarly, one end of the circumferential wiring pattern 14B is connected to the center position of the surface electrode 10B in the longitudinal direction X in the second end 17B of the surface electrode 10B.

Thus, since the longitudinal wiring patterns 13A and 13B are formed at positions overlapping each other when viewed in the magnetic flux direction Y, the formation of signal loops can be accurately avoided, and the generation of magnetic flux differential noise can be easily suppressed.

The connection points between the circumferential wiring patterns 14A and 14B and the surface electrodes 10A and 10B may not be located at the center of the surface electrodes 10A and 10B, as long as they are connected at symmetrical positions with respect to the tube axis J, that is, at the same positions as each other in the longitudinal direction X of the surface electrodes 10A and 10B.

Further, by forming the longitudinal wiring patterns 13A and 13B on the intersecting lines JA and JB, the lengths of the circumferential wiring patterns 14A and 14B become equal, and the lengths of the entire pipe- side wiring patterns 12A and 12B become equal, so that imbalance in phase difference, amplitude, and the like of the electromotive forces Va and Vb from the surface electrodes 10A and 10B, which occurs due to the difference in the lengths of the pipe- side wiring patterns 12A and 12B, can be suppressed. In addition, if the degree of the imbalance is negligible in terms of measurement accuracy, the longitudinal wiring patterns 13A and 13B may be formed at positions overlapping each other as viewed from the magnetic flux direction Y, instead of the intersecting lines JA and JB.

Fig. 9 shows an example of the configuration of a differential amplifier circuit using a preamplifier. As shown in fig. 9, the preamplifier 5U includes two operational amplifiers UA and UB that independently reduce the impedances Va and Vb of the electromotive forces from the surface electrodes 10A and 10B and output the impedances. These operational amplifiers UA, UB are sealed within the same IC package (dual operational amplifier). These differentially amplify the input Va and Vb and output the obtained differential output as a detection signal Vin to the signal amplification circuit 21 in fig. 2.

Specifically, Va is input to a non-inverting input terminal (+) of UA, and Vb is input to a non-inverting input terminal (+) of UB. The inverting input terminal (-) of UA is connected to the output terminal of UA via the resistance element R1, and the inverting input terminal (-) of UB is connected to the output terminal of UB via the resistance element R2. The inverting input terminal (-) of UA is connected to the inverting input terminal (-) of UB via the resistance element R3. At this time, by making the values of R1 and R2 equal, the magnifications of UA and UB coincide. The values of R1, R2, and R3 determine the amplification factor.

Since the electromotive forces Va and Vb from the surface electrodes 10A and 10B are signals having opposite phases to each other, when such a differential amplifier circuit is configured on the printed circuit board 5 using UA and UB, Va and Vb are differentially amplified even if temperature drift occurs in Va and Vb due to the influence of heat from the exciting coils 3A and 3B and the measuring tube 2. In this way, in the detection signal Vin, the temperature drifts in the same phase are canceled, and Va and Vb are added to obtain a good S/N ratio.

Next, a connection structure 201 for connecting the measurement tube 2 and the printed circuit board 5 will be described with reference to fig. 10 to 18. As shown in fig. 10 and 11, the coupling structure 201 is configured using an adhesive tape 202 that is stuck to the measurement tube 2 and the tube hole 5H of the printed circuit board 5 into which the measurement tube 2 is inserted. The tube hole 5H corresponds to a "hole of the printed circuit board" in the present invention. In the present embodiment, the adhesive tape 202 is formed by combining two adhesive tapes. The adhesive tape 202 of the present embodiment is composed of a relatively large first adhesive tape main body 203 formed so as to cover the conductor portion on the measurement tube 2, and a relatively small second adhesive tape main body 204 located near the printed circuit board 5. As shown in fig. 12 (a), the conductor portions on the measurement tube 2 are the surface electrodes 10A, 10B, the conductivity measurement electrode 10C, and the tube- side wiring patterns 12A, 12B.

The first adhesive tape main body 203 and the second adhesive tape main body 204 are not shown in detail, but both are so-called tapes having an adhesive on one side, which are composed of a tape base material made of an insulating material and an adhesive covering the back surface of the tape base material. Further, an adhesive tape having no insulation property may be used as the second adhesive tape main body 204. The first adhesive tape main body 203 and the second adhesive tape main body 204 of the present embodiment are formed using the same tape having an adhesive on one side. Therefore, the thickness of the first adhesive tape main body 203 is equal to the thickness of the second adhesive tape main body 204.

As shown in fig. 12 (B), the first adhesive tape main body 203 is formed in a quadrangular sheet shape. A cutout 205 is formed in one side portion 203a of the first adhesive tape main body 203, and the cutout 205 is used to expose the pads 16A, 16B of the pipe- side wiring patterns 12A, 12B. As shown in fig. 13a, the first adhesive tape main body 203 is attached to the measurement tube 2 with the notch 205 facing the pads 16A and 16B (the pad 16B is not shown), and extends (wraps) along the outer peripheral surface of the measurement tube 2 in a direction orthogonal to the longitudinal direction of the measurement tube 2.

As shown in fig. 12C, the second adhesive tape main body 204 is formed in a sheet shape having a band-shaped portion 206 and a plurality of protruding pieces 207, the band-shaped portion 206 extending in the up-down direction in fig. 12C, and the protruding pieces 207 protruding to one side from the band-shaped portion 206. The entire length of the band-shaped portion 206 is equal to the circumference of the outer peripheral surface of the first adhesive tape main body 203 wound around the measurement tube 2. The plurality of protruding pieces 207 are arranged at predetermined intervals in the longitudinal direction of the band-shaped portion 206. As shown in fig. 13 (B), the second adhesive tape main body 204 is wound around the outer peripheral surface of the first adhesive tape main body 203 in a state where the band-shaped portion 206 and a part of the protruding piece 207 overlap the first adhesive tape main body 203.

As shown in fig. 13 (B), the base portion 207a of the tab 207 on the band-shaped portion 206 side is stuck to the first adhesive tape main body 203. The protruding end 207b of the protruding piece 107 is deformed so as to be offset from the first adhesive tape main body 203 toward the inside in the radial direction of the measurement tube 2, and is stuck to the measurement tube 2. The projecting end 207b of the projecting piece 207 is inserted between the measurement tube 2 and the printed circuit board 5 as described later (see fig. 15).

As shown in fig. 11 and 12 (D), the opening shape of the tube hole 5H of the printed circuit board 5 is formed in a so-called rounded square shape. Therefore, the tube hole 5H is formed by the 4-position first hole portion 211 composed of the 4 sides of the square and the 4-position second hole portion 212 composed of the 4 rounded portions. The 4-position first hole 211 is formed with a gap of a pitch degree from the outer peripheral surface of the measurement tube 2. Therefore, in a state where the measurement tube 2 is inserted into the tube hole 5H, the first hole portion 211 restricts the movement of the measurement tube 2 relative to the printed circuit board 5 in a direction orthogonal to the longitudinal direction of the measurement tube 2.

As shown in fig. 14, the distance a between the two first hole portions 211 facing each other is larger than the outer diameter Φ of the measurement tube 2. When the thickness of the first adhesive tape main body 203 is denoted by t, the interval a between the two first holes 211 is smaller than the outer diameter (Φ +2t) of the first adhesive tape main body 203 wound around the measurement tube 2. Therefore, the relationship between the outer diameter Φ of the measurement pipe 2, the interval a between the first hole portions 211, and the outer diameter (Φ +2t) of the first adhesive tape main body 203 is Φ < a < Φ +2 t.

As shown in fig. 12 (D), second hole 212 of pipe hole 5H is formed in an arc shape. The center of the arc constituting the second hole portion 212 coincides with the center of the pipe hole 5. The diameter d of an imaginary circle passing through the second hole portion 212 at 4 is larger than the interval a between the 2 first hole portions 211 opposite to each other. Therefore, the gap between the second hole 212 and the measurement tube 2 is wider than the gap between the first hole 211 and the measurement tube 2. The protruding piece 207 of the second adhesive tape main body 204 is inserted into the gap between the second hole 212 and the measurement tube 2 (see fig. 15). As shown in fig. 15, the diameter d of the imaginary circle passing through the second hole portion 212 is larger than the outer diameter (Φ +2t) of the tab 207 bonded to the measurement tube 2. The diameter d of the imaginary circle is smaller than the outer diameter (Φ +4t) of the band-shaped portion 206 of the second adhesive tape main body 204. Therefore, the relationship among the diameter d of the imaginary circle, the outer diameter (φ +2t) of the tab 207, and the outer diameter (φ +4t) of the band 206 is φ +2t < d < φ +4 t.

When the measurement tube 2 to which the first adhesive tape main body 203 and the second adhesive tape main body 204 are attached is inserted into the tube hole 5H that is opened to be square with rounded corners, the projecting piece 207 is inserted into the second hole portion 212. When the measurement tube 2 is inserted into the tube hole 5H in this way, as shown in fig. 14 and 15, the first adhesive tape main body 203 and the second adhesive tape main body 204 regulate the movement of the measurement tube 2 in the insertion direction (the right direction in fig. 14 and 15). At this time, as shown in fig. 14, the one end 203b of the first adhesive tape main body 203 faces the portion of the printed circuit board 5 corresponding to the first hole 211.

At this time, as shown in fig. 15, the projecting piece 207 comes into contact with a portion of the printed board 5 corresponding to the second hole portion 212. The portion of the tab 207 that contacts the printed circuit board 5 is a boundary portion between the base portion 207a and the end portion 207b on the protruding side. Therefore, the one end 203b of the first adhesive tape main body 203 and the protruding piece 207 serve as a first movement restricting portion 213 that restricts the movement of the measurement tube 2 in the insertion direction.

When the measurement tube 2 inserted into the tube hole 5H is rotated with respect to the printed circuit board 5, the protruding end 207b of the protruding piece 207 engages with the printed circuit board 5 (the hole wall surface of the tube hole 5H). Therefore, in this embodiment, the protruding end 207b of the protruding piece 207 serves as a second movement restricting portion 214 that restricts the rotation of the measurement tube 2 with respect to the printed circuit board 5.

Here, the procedure for assembling the measurement tube 2 into the case 8 will be described with reference to fig. 16 to 18. To assemble the measurement tube 2 into the case 8, first, as shown in fig. 16, the one end portion 2a of the measurement tube 2 to which the first adhesive tape main body 203 and the second adhesive tape main body 204 are attached is inserted into the tube hole 5H of the printed circuit board 5. Fig. 16 (a) is a plan view of the measurement tube 2 and the printed board 5, and fig. 16 (B) is a side view of the measurement tube 2 and the printed board 5. At this time, as shown in fig. 11, the projecting piece 207 of the second adhesive tape main body 204 is inserted between the second hole 212 and the measurement tube 2. In the state where the printed circuit board 5 and the measurement tube 2 are connected in this way, the pads 16A, 16B and the pads 5C, 5D are electrically connected by the jumpers 15A, 15B, as shown in fig. 6. Then, the shield cover 7 is mounted on the printed substrate 5. By mounting the shield case 7 on the printed circuit board 5 in this manner, the detector unit 221 including the measurement tube 2 and the printed circuit board 5 is formed.

Next, as shown in fig. 17, the detector unit 221 is inserted into the housing 8. Although not shown, the yoke 4 to which the excitation coils 3A and 3B are screwed is fixed to the bottom 8D of the case 8 in advance before the insertion operation. The insertion operation of the detector unit 221 is to insert the printed circuit board 5 into the housing 8 from the opening 8B of the housing 8 so that the side end portions 5I, 5J are fitted into the fitting portions 82A, 82B of the guide portions 81A, 81B of the housing 8.

Then, one of the pair of contacts 85 and 86 located on the opposite side of the printed circuit board 5 is attached to the housing 8 (see fig. 18). This mounting operation is performed by pressing the joint 85 toward the printed circuit board 5 side in a state where the other end 2b of the measurement tube 2 is inserted into the joint 85 and the O-ring 87 is sandwiched between the measurement tube 2 and the joint 85. At this time, the other end 2b of the measurement tube 2 is pressed to the one end 2a side by the sliding resistance, but the first adhesive tape main body 203 and the second adhesive tape main body 204 regulate the movement of the measurement tube 2 with respect to the printed substrate 5. In addition, even if the joint 85 is twisted with respect to the case 8 during this mounting operation, the projecting piece 207 of the second adhesive tape main body 204 engages with the printed circuit board 5, so that the measurement tube 2 does not rotate with respect to the printed circuit board 5.

Next, the other joint 86 is attached to the housing 8. This mounting operation is performed by pressing the joint 86 toward the printed circuit board 5 with the one end 2a of the measurement tube 2 inserted into the joint 86 and the O-ring 87 interposed between the measurement tube 2 and the joint 86. At this time, the one end 2a of the measurement tube 2 is pressed toward the other end 2b by the sliding resistance, but the other end of the measurement tube 2 is restricted from moving by contacting one of the joints 85, so that the measurement tube 2 does not move relative to the printed circuit board 5. In addition, even if the joint 86 is twisted with respect to the case 8 during this mounting operation, the projecting piece 207 of the second adhesive tape main body 204 engages with the printed circuit board 5, so that the measurement tube 2 does not rotate with respect to the printed circuit board 5.

By attaching the connectors 85 and 86 to the case 8 in this manner, the printed circuit board 5 is attached to the inside of the case 8 with the measurement tube 2 inserted into the tube hole 5H, and as a result, the measurement tube 2 is attached to the inside of the case 8 via the printed circuit board 5. At this time, there is no need to fix the printed circuit board 5 by the guide portions 81A and 81B, and on the contrary, if there is a slight play, there is no mechanical stress applied to the measurement tube 2 or the printed circuit board 5 when the joints 85 and 86 are screwed to the case 8.

[ Effect of the first embodiment ]

According to this embodiment, the adhesive tape 202 attached to the measurement tube 2 is brought into contact with the printed circuit board 5, thereby restricting the movement and rotation of the measurement tube 2 in one longitudinal direction with respect to the printed circuit board 5. Therefore, as in the case of connecting the joint 85 to the measurement tube 2, the operation is performed so as to press the measurement tube 2 in the direction in which the movement of the measurement tube 2 is restricted, thereby preventing the measurement tube 2 from being positionally displaced with respect to the printed circuit board 5. Since the movement and rotation of the measurement tube 2 can be restricted by the adhesive tape 202 in this way, it is not necessary to form a projection, a groove, or the like that engages with the printed circuit board 5 on the measurement tube 2 when restricting the movement and rotation. Therefore, the measuring tube 2 can be easily formed even with a ceramic material or the like having high hardness, which is difficult to be specially processed.

The adhesive tape 202 of the present embodiment is composed of a first adhesive tape main body 203 which is stuck to the measurement tube 2 and extends in a direction orthogonal to the longitudinal direction of the measurement tube 2 along the outer surface of the measurement tube 2, and a second adhesive tape main body 204 which is inserted between the measurement tube 2 and the second hole portion 212 in a state where a part of the second adhesive tape main body 204 overlaps the outer surface of the first adhesive tape main body 203. The second adhesive tape main body 204 extends from the portion overlapping the first adhesive tape main body 203 to between the measurement tube 2 and the second hole 212, and is in contact with the printed circuit board 5, thereby pressing the first adhesive tape main body 203 against the measurement tube 2. Therefore, it is possible to provide an electromagnetic flowmeter in which the adhesive tape 202 is less likely to peel off when a pressing force is applied to the adhesive tape 202 from the printed circuit board 5.

The first adhesive tape main body 203 of the present embodiment has insulation properties, and covers the surface electrodes 10A and 10B and the conductivity measurement electrode 10C. Therefore, it is possible to prevent the insulation between the pair of electrodes and between the electrodes-common from deteriorating due to the influence of humidity. Further, since the entire surface of the measurement tube 2 is covered with the first adhesive tape main body 203, the surface of the measurement tube 2 is not affected by the thermoelectric effect, the electrification due to the piezoelectric effect, the flow electrification, and the like.

[ second embodiment ]

Next, an electromagnetic flow meter 200 according to a second embodiment will be described with reference to fig. 19 to 21. In fig. 19 to 21, the same or equivalent members as those described with reference to fig. 1 to 18 are denoted by the same reference numerals, and detailed description thereof is omitted as appropriate.

Fig. 19 is a plan view showing an electromagnetic flowmeter 300 according to a second embodiment. Fig. 20 is a side view showing a casing 8 of an electromagnetic flowmeter 300 according to a second embodiment in a partially cut-away state.

In the present embodiment, a case where two sets of the printed circuit board and the guide portion are provided will be described.

The printed board 6 is a general printed board (for example, a glass cloth-based epoxy resin copper-clad laminate having a thickness of 1.6 mm) for mounting electronic components, as with the printed board 5, and a tube hole 6H for passing the measurement tube 2 therethrough is formed at a substantially central position of the printed board 6. Therefore, the printed board 6 is attached in a direction intersecting the measurement tube 2. The opening of the pipe hole 6H is formed in a rounded square shape, similarly to the pipe hole 5H of the printed circuit board 5.

As shown in fig. 19 and 20, guide portions 83A and 83B are formed at positions facing each other in addition to the guide portions 81A and 81B in a pair of inner wall portions 8A parallel to the longitudinal direction X among the inner wall portions of the housing 8. The guide portions 83A and 83B are formed of two projecting strips formed parallel to the electrode direction Z, and fitting portions 84A and 84B between these projecting strips are fitted to the side end portions 6I and 6J of the printed circuit board 6 inserted from the opening 8B.

The projections of the guide portions 83A and 83B need not be formed continuously in the electrode direction Z, and may be formed separately in a plurality at intervals at which the side end portions 6I and 6J are smoothly inserted. The guide portions 83A and 83B may be grooves into which the side end portions 6I and 6J of the printed circuit board 6 are inserted, instead of the protrusions, in the inner wall portion 8A.

In this embodiment, the first adhesive tape main body 203 of the adhesive tape 202 attached to the measurement tube 2 extends from a position adjacent to one printed circuit board 5 to a position adjacent to the other printed circuit board 6. The second adhesive tape bodies 204A and 204B of the adhesive tape 202 of the present embodiment are provided in the vicinity of the printed circuit board 5 and the printed circuit board 6, respectively. That is, one second adhesive tape main body 204A is attached to a position adjacent to one printed circuit board 5 in the first adhesive tape main body 203, and the projecting piece 207 of the second adhesive tape main body 204A is inserted between the second hole 212 of the printed circuit board 5 and the measurement tube 2. The other second adhesive tape main body 204B is bonded to the first adhesive tape main body 203 at a position adjacent to the other printed circuit board 6, and the projecting piece 207 of the second adhesive tape main body 204 is inserted between the second hole 212 of the printed circuit board 6 and the measurement tube 2.

The end portion of the first adhesive tape main body 203 adjacent to the one printed circuit board 5 and the one second adhesive tape main body 204A located near the one printed circuit board 5 restrict rotation of the measurement tube 2 with respect to the one printed circuit board 5 and movement of the measurement tube 2 in a direction (rightward direction in fig. 19 and 20) in which the measurement tube 2 is inserted into the tube hole 5H of the one printed circuit board 5.

The end portion of the first adhesive tape main body 203 adjacent to the other printed circuit board 6 and the other second adhesive tape main body 204B located near the other printed circuit board 6 restrict rotation of the measurement tube 2 with respect to the other printed circuit board 6 and movement of the measurement tube 2 in a direction (left direction in fig. 19 and 20) in which the measurement tube 2 is inserted into the tube hole 6H of the other printed circuit board 6.

By adopting the configuration in which the measurement tube 2 is inserted into the two printed boards 5 and 6 in this way, the order of connection when connecting the two joints 85 and 86 to the measurement tube 2 is not limited. That is, in the case of the first embodiment, it is necessary to assemble the joint 85 away from the printed board 5 first, but according to this embodiment, there is no problem in assembling either the joint 85 or the joint 86 first.

By connecting the joints 85 and 86 to the measurement tube 2, the printed boards 5 and 6 are mounted inside the case 8 with the measurement tube 2 inserted into the tube holes 5H and 6H, and as a result, the measurement tube 2 is mounted inside the case 8 via the printed boards 5 and 6. In this case, there is no need to fix the printed boards 5 and 6 by the guides 81A, 81B, 83A, and 83B, and on the contrary, if there is a slight play, there is no mechanical stress applied to the measurement tube 2 or the printed boards 5 and 6 when the joints 85 and 86 are screwed to the housing 8.

In order to measure the conductivity (electric conductivity) of the fluid, it is necessary to provide the electric conductivity measuring electrode 10C separately from the surface electrodes 10A and 10B, and the electric conductivity measuring electrode 10C is disposed at a position apart from the magnetic flux region F on the outer peripheral surface 2A of the measuring tube 2. Therefore, as shown in fig. 19 and 20, if the printed board 6 is disposed in the vicinity of the conductivity measuring electrode 10C, a part of the circuit and the connection wiring for connecting the conductivity measuring electrode 10C can be provided on the printed board 6.

Fig. 21 shows an example of the configuration of the conductivity measurement circuit. The conductivity measurement circuit 24 includes a clock signal generation circuit 24A, A/D converter 24B and a measurement I/F circuit 24C as main circuit units.

The clock signal generation circuit 24A generates 3 clock signals CLK1, CLKp, and CLKn from the clock signal CLK0 output from the conductivity calculation unit 27C of the arithmetic processing circuit 27.

The measurement I/F circuit 24C generates an ac signal having the amplitude of the voltage VP by switching the switch SWv based on CLK1, and applies the ac signal to the conductivity measurement electrode 10C via the resistance element RP.

The detection signal Vp generated at the conductivity measurement electrode 10C at this time is amplified by the amplifier AMP of the measurement I/F circuit 24C, and then the switches SWp and SWn are controlled based on CLKp and CLKn, whereby the high level and the low level of Vp are sampled, a/D conversion is performed in the a/D converter 24B, and the obtained detection data Dp is output to the arithmetic processing circuit 27. The conductivity calculating unit 27C calculates the conductivity of the fluid based on the amplitude voltage of Vp indicated by the detection data Dp from the conductivity measuring circuit 24.

In this case, since the impedance of the conductivity measuring electrode 10C is very high and is easily affected by noise, it is preferable to dispose the measuring I/F circuit 24C as close as possible to the conductivity measuring electrode 10C. In the present embodiment, from such a viewpoint, the measurement I/F circuit 24C is mounted on the printed circuit board 6.

The printed board 6 may be connected to the conductivity measurement electrode 10C by a jumper 15C. This can significantly shorten the length of the connection wiring between the conductivity measuring electrode 10C and the measurement I/F circuit 24C, and reduce the influence of noise by making the detection signal Vp low impedance by the amplifier AMP.

In the present embodiment, the measurement I/F circuit 24C may be mounted on the printed circuit board 6, mounted in the vicinity of the conductivity measurement electrode 10C, and electrically connected to the conductivity measurement electrode 10C. This allows the printed circuit board 6 to be used not only for mounting the measurement tube 2 but also for connecting the measurement I/F circuit 24C and the conductivity measurement electrode 10C. Therefore, the entire configuration can be greatly simplified, and the capacitance type electromagnetic flowmeter can be downsized in accordance with the FA market demand.

[ modification of tube holes ]

The tube holes 5H and 6H of the printed boards 5 and 6 used in the first and second embodiments may be formed as shown in fig. 22 and 23. In fig. 22 and 23, the same or equivalent members as those described with reference to fig. 1 to 21 are given the same reference numerals, and detailed description thereof is omitted as appropriate. Fig. 22 and 23 illustrate modifications of the tube hole 5H of the printed circuit board 5 for convenience. The pipe hole 6H of the printed circuit board 6 may be configured in the same manner as the pipe hole 5H of the printed circuit board 5.

The tube hole 5H shown in fig. 22 is directly opened toward the side end of the printed circuit board 5, and is formed as a notch 5K. In this case, the first hole portion 211 is formed at three places and the second hole portion 212 is formed at two places.

In the case of this embodiment, the same adhesive tape as in the case of the first and second embodiments can be used for the first adhesive tape main body 203 of the adhesive tape 202. The second adhesive tape main body 204 may be formed to have the protruding pieces 207 at positions corresponding to the two second hole portions 212, respectively.

The pipe hole 5H shown in fig. 23 is formed in an oblong shape. Therefore, the printed circuit board 5 is provided with two first hole portions 211 and two second hole portions 212. In this case, the second adhesive tape main body 204 of the adhesive tape 202 includes two projecting pieces 207 so as to be inserted into two second hole portions 212.

Even if the tube hole 5H is formed as shown in fig. 22 and 23, the movement and rotation of the measurement tube 2 in one longitudinal direction with respect to the printed circuit board 5 can be restricted by the adhesive tape 202. Therefore, as in the first and second embodiments, it is possible to provide an electromagnetic flowmeter in which the measurement pipe 2 does not shift with respect to the printed circuit board 5.

[ modification of measuring the electric connection part between the tube and the printed substrate ]

As shown in fig. 24, the surface electrodes 10A and 10B and the tube- side wiring patterns 12A and 12B of the measurement tube 2 may be formed of a nonmagnetic metal thin film 232 provided on a film 231 made of an insulating material. In this case, by raising the distal end 231a of the film 231 from the measurement tube 2 and along the printed board 5, the tube- side wiring patterns 12A and 12B can be directly connected to the substrate- side wiring patterns 5A and 5B of the printed board 5 by soldering or the like without using a jumper wire. In this embodiment, the film 232 provided on the distal end 231a of the film 231 corresponds to the "connecting means" in the present invention.

[ modification of measuring tube and printed substrate ]

The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. The configuration and details of the present invention may be variously modified within the scope of the present invention as understood by those skilled in the art. In addition, the embodiments can be arbitrarily combined and implemented within a range not to be contradicted.

For example, although the case where the measurement tube 2 has a cylindrical shape has been described in the above embodiment, a square tube portion formed in a square tube shape may be provided in a part thereof. Fig. 25 shows another configuration example of the measuring tube 2. In FIG. 25, (a) is a plan view of the measuring tube 2', (b) is a side view, (c) is a front view, and (d) is a cross-sectional view of AA shown in (b).

The measuring tube 2' is made of a synthetic resin mixed with high dielectric constant ceramics such as alumina or high dielectric constant ceramic powder, and as shown in fig. 25, has: cylindrical portions 2L and 2R provided at both ends, formed in a cylindrical shape, and connected to a pipe not shown; and a square tube portion 2C provided between the cylindrical portions 2L and 2R and formed in a square tube shape. As shown in fig. 25 (d), in the square tubular portion 2C of the measurement tube 2', both the tube wall and the tube path have a substantially square cross section. The measuring tube 2 ' is inserted into a substantially square tube hole 5H ' formed in the printed substrate 5 '. The pipe hole 5H' is formed in a rounded square shape into which the square tube portion 2C is inserted in a loosely fitted state. The first hole portion 211 and the second hole portion 212 are formed in portions of four sides of the printed substrate 5' that become rounded squares. The protruding piece 207 of the second adhesive tape main body 204 is inserted into the second hole 212.

Surface electrodes 10B 'and 10A' are formed on the mutually parallel wall surfaces of the square tubular portion 2C of the measurement tube 2 '(in fig. 25, the upper surface and the lower surface of the square tubular portion 2C), respectively, and these surface electrodes 10B' and 10A 'are connected to a circuit (not shown) formed on the printed board 5' via tube-side wiring patterns 13B ', 14B', 13A ', 14A' and jumpers 15B ', 15A', respectively.

The measuring tube 2 ' has the square tube portion 2C, and the two surface electrodes 10A ' and 10B ' can be arranged in parallel to each other, and therefore, improvement of the S/N ratio can be expected. In addition, since the coil and other components are easily housed in the housing, the device can be further miniaturized.

When the measurement tube 2 is formed in a square tube shape as described above, the movement of the measurement tube 2 in one longitudinal direction is restricted by the adhesive tape 202.

[ modification of adhesive tape ]

The adhesive tape may be formed as shown in fig. 26. In fig. 26, the same or equivalent members as those described in fig. 12 are designated by the same reference numerals and detailed description thereof is omitted as appropriate, fig. 26 (a) is a plan view of the adhesive tape, and fig. 26 (B) is a side view of the measuring tube to which the adhesive tape is attached.

The adhesive tape 241 shown in fig. 26 is formed in a shape covering the electrode forming portion of the measuring tube 2, and a plurality of protruding pieces 242 are integrally formed at one end portion. That is, the adhesive tape 241 realizes the first adhesive tape main body 203 and the second adhesive tape main body 204 in the above embodiment by one adhesive tape. In this adhesive tape 241, the tip 41a of the protruding piece 242 corresponds to the first movement restricting portion 213, and the protruding piece 242 corresponds to the second movement restricting portion 214.

Even when the adhesive tape 241 is formed in this manner, the movement and rotation of the measurement tube 2 in one longitudinal direction with respect to the printed boards 5 and 6 can be restricted.

Description of the symbols

200. 300 … electromagnetic flowmeter, 2 … measuring tube, 3A, 3B … exciting coil, 5, 6 … printed circuit board, 5H, 6H … tube hole (hole), 8 … case, 10A, 10B … surface electrode, 15A, 15B … jumper (connecting unit), 85, 86 … joint, 202, 241 … adhesive tape, 203 … first adhesive tape body, 204 … second adhesive tape body, 211 … first hole, 212 … second hole, 213 … first movement limiting part, 214 … second movement limiting part, 231a … top end part (connecting unit).

Claims (4)

1. An electromagnetic flowmeter, comprising:

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 case that houses the measurement tube and the excitation coil;

a printed substrate having a hole into which an end of the measurement tube is inserted, the printed substrate being held in the housing in a state in which the end of the measurement tube is inserted into the hole;

a connection unit electrically connecting the surface electrode and the printed circuit board;

a pair of joints fixed to the housing in a state where both end portions of the measurement tube are inserted; and

an adhesive tape which is adhered to the measurement tube and restricts rotation of the measurement tube with respect to the printed circuit board and movement of the measurement tube in a direction of insertion into the hole,

the hole of the printed circuit board has a first hole portion that restricts movement of the measurement tube relative to the printed circuit board in a direction orthogonal to a longitudinal direction of the measurement tube, and a second hole portion that has a wider gap with the measurement tube than a gap between the first hole portion and the measurement tube,

the adhesive tape has:

a first movement restricting portion that restricts movement of the end portion of the measurement tube in a direction of insertion into the hole; and

and a second movement restricting unit inserted between the measurement tube and the second hole and engaged with the printed circuit board.

2. An electromagnetic flowmeter according to claim 1,

the adhesive tape is composed of a first adhesive tape main body and a second adhesive tape main body,

the first adhesive tape main body is adhered to the measurement tube and extends along an outer surface of the measurement tube in a direction orthogonal to a longitudinal direction of the measurement tube,

the second adhesive tape main body is inserted between the measurement tube and the second hole portion in a state where a part of the second adhesive tape main body overlaps with an outer surface of the first adhesive tape main body.

3. An electromagnetic flowmeter according to claim 2,

the first adhesive tape main body has an insulating property and covers the surface electrode.

4. An electromagnetic flowmeter according to any one of claims 1 to 3,

the printed circuit boards are respectively arranged at two ends of the measuring tube,

the adhesive tape restricts rotation of the measurement tube with respect to one of the printed circuit boards and movement of the measurement tube in a direction in which the measurement tube is inserted into the hole of one of the printed circuit boards, and restricts rotation of the measurement tube with respect to the other printed circuit board and movement of the measurement tube in a direction in which the measurement tube is inserted into the hole of the other printed circuit board.

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