KR20200011371A - Electronic flow meter - Google Patents

Abstract

An object of the present invention is to accurately measure a flow rate and electrical conductivity of a fluid without making an electromagnetic flowmeter large. A signal generating circuit (11B) generates a square wave current of an alternating current having a constant amplitude [set current (Is)] at a preset signal frequency (fs) as a square wave signal (SG) and applies the square wave signal (SG) to electrodes (T1, T2) attached to a measuring pipe (2). An electrical conductivity detection circuit (11) detects the amplitude of a detection voltage (Vt) by sampling the detection voltage (Vt) detected from these T1 and T2.

Description

Electronic flow meter {ELECTRONIC FLOW METER}

The present invention relates to an electromagnetic flowmeter having a function of measuring the electrical conductivity of a fluid to be measured by the flow rate.

The electromagnetic flowmeter which measures the flow volume of the fluid which flows in a measurement tube calculates a flow volume based on the electromotive force detected from the fluid on the assumption that the fluid fills the inside of the measurement tube to some extent. Therefore, when the fluid does not fill the inside of the measuring tube, the calculated flow rate cannot be said to represent the correct value. For this reason, some electromagnetic flowmeters have a function of detecting (publicly detecting) a so-called empty state in which the fluid does not fill the inside of the measuring tube.

Conventionally, as a technique for detecting an empty state, Patent Literature 1 proposes a technique for public detection based on a relationship between an impedance of a fluid and an electrical conductivity. 14 is a circuit diagram showing a conventional blank finger. As shown in FIG. 14, the method of patent document 1 applies the direct current voltage to the electrodes Ta and Tb for flow measurement, and uses the obtained buffer voltages Vza and Vzb in buffer amplifiers U1a and U1b. After stabilization, comparators U2a and U2b are compared with reference voltages Vsa and Vsb, and based on the obtained comparison results Sa and Sb, it is determined whether or not the fluid is empty without filling the inside of the measuring tube. Judging.

However, the method of patent document 1 is a method of combining the electrode for flow measurement for a public detection, and cannot measure an electrical conductivity. In addition, even if a circuit for measuring the electrical conductivity is added, the flow rate and the electrical conductivity cannot be measured in parallel with the same electrode. For this reason, it is necessary to allocate a part of the flow measurement measurement period to the electric conductivity measurement period, and in order to allocate this electric conductivity measurement period, when the flow rate measurement period is shortened, the flow rate measurement accuracy is deteriorated, and the flow rate measurement If the period is extended, the flow rate measurement response is reduced.

On the other hand, as a technique for measuring the flow rate and the electrical conductivity in parallel, Patent Literature 2 proposes a technique for measuring the electrical conductivity using an electrode provided separately from the electrode for measuring the flow rate. Fig. 15 is a circuit diagram showing another conventional detection sheet. As shown in FIG. 15, the system of patent document 2 applies an alternating-current signal between the electrical conductivity detection electrodes T21 and T22 provided in the measuring tube 50, and the earth ring electrode 51, and between these electrodes. By detecting the electrical signal generated by the operational amplifier U2 different from the operational amplifier U1 for detecting the flow rate, the impedance of the fluid existing between the electrodes T21 and T22 is calculated to derive the electrical conductivity.

[Patent Document 1] Japanese Patent Application Laid-Open No. 8-210888 [Patent Document 2] Japanese Patent Application Laid-Open No. 7-5005

According to the method of patent document 2, since electrical conductivity can be measured using the electrodes T21 and T22 provided separately from the electrodes T11 and T12 for flow measurement, as shown in FIG. In the electromagnetic flowmeter, the flow rate of the fluid and the electrical conductivity can be measured in parallel. At this time, it becomes important that the applied signal for electric conductivity does not interfere with the applied signal for flow measurement.

On the other hand, when deriving the electrical conductivity of the fluid, it is possible to measure the electrical conductivity with a higher precision as the distance between the electrodes. However, since the length of the measuring tube is limited, when the electrode used for measuring the electrical conductivity and the electrode used for measuring the flow rate are close to each other, the applied signal for electric conductivity interferes with the applied signal for measuring the flow rate, and the measurement accuracy of the flow rate is measured. Causes a decrease. For this reason, in order to reduce such interference, it is necessary to extend the length of the measuring tube or to arrange an earth ring between the electrodes, and there is a problem that the electromagnetic flowmeter cannot be miniaturized.

An object of the present invention is to provide an electromagnetic flowmeter capable of accurately measuring the flow rate and the electrical conductivity of a fluid without increasing the size of the electromagnetic flowmeter.

In order to achieve this object, the electromagnetic flowmeter according to the present invention is an electromagnetic flowmeter which measures the flow rate of a fluid flowing in a measuring tube, and has a square wave signal of an alternating square wave current having a constant amplitude at a predetermined signal frequency. And a signal generating circuit to generate a signal, a first and a second electrode attached to the measuring tube to apply the square wave signal to the fluid, and a detection voltage detected from the first and second electrodes. The detection circuit which detects an amplitude, and the calculation processing circuit which calculate | requires the electrical conductivity with respect to the said fluid by a calculation process based on the said amplitude.

In addition, one configuration example of the electromagnetic flowmeter according to the present invention includes a buffer amplifier disposed at a position near the first and second electrodes and stabilizing the signal generation circuit and outputting the detected voltage to the detection circuit. And a printed circuit board on which at least one or both are mounted.

In addition, in one configuration example of the electromagnetic flowmeter according to the present invention, the first electrode is formed of a liquid contact electrode in contact with the fluid, and the second electrode is formed at an outer peripheral portion of the measurement tube. And a non-contact electrode which is not in contact with the fluid.

Moreover, one structural example of the said electromagnetic flowmeter which concerns on this invention is a thing in which the said 1st and 2nd electrode consist of a liquid contact electrode which contacts with the said fluid.

In addition, one configuration example of the electromagnetic flowmeter according to the present invention is such that the detection circuit samples the detection voltage at a central time position of a half cycle of the square wave signal.

Moreover, one structural example of the said electromagnetic flowmeter which concerns on this invention is the current generation circuit which the said signal generation circuit detects the magnitude | size of the said square wave signal, the clock signal which shows the said signal frequency, and the detection result from the said current detection circuit. And an operational amplifier for maintaining the amplitude of the square wave signal at a set current.

According to the present invention, since the inclination of the detected voltage is linear, even if a frequency higher than the excitation frequency, for example, a frequency 100 times or more higher than the excitation frequency, is used, the amplitude of the detection voltage is stably maintained. Can be detected. Therefore, even if the applied signal for electric conductivity interferes with the applied signal for flow measurement, since the excitation frequency << signal frequency, the signal frequency can be easily removed by the low pass filter.

Thereby, in order to reduce the above interference, it is not necessary to enlarge the distance between the electrode for flow measurement and the electrode for electrical conductivity. For this reason, it is not necessary to extend the length of the measuring tube or arrange an earth ring between the electrodes. As a result, it becomes possible to accurately measure the flow rate and the electrical conductivity of the fluid without increasing the electromagnetic flowmeter. .

1 is a block diagram showing a circuit configuration of an electromagnetic flowmeter according to a first embodiment.
2 is a top view of the electromagnetic flowmeter according to the first embodiment.
3 is a cross-sectional side view of the electromagnetic flowmeter according to the first embodiment.
4 is an assembly view of the electromagnetic flowmeter according to the first embodiment.
5 is a side view of an essential part of the electromagnetic flowmeter according to the first embodiment.
It is a top view of the principal part of the electromagnetic flowmeter which concerns on 1st Embodiment.
7 is a signal waveform diagram showing the operation of the electromagnetic flowmeter according to the first embodiment.
8 is a configuration example of a square wave current source.
9 is an equivalent circuit on the electrode side according to the first embodiment.
10 is a signal waveform diagram showing an operation of an electromagnetic flowmeter using a square wave constant voltage signal.
11 is a characteristic diagram showing a correspondence relationship between amplitude data and electrical conductivity.
It is a side view of the principal part of the electromagnetic flowmeter which concerns on 2nd Embodiment.
It is a top view of the principal part of the electromagnetic flowmeter which concerns on 2nd Embodiment.
14 is a circuit diagram showing a conventional blank finger.
Fig. 15 is a circuit diagram showing another conventional detection sheet.

Next, embodiment of this invention is described with reference to drawings.

[First Embodiment]

First, with reference to FIG. 1, the electromagnetic flowmeter 10 which concerns on 1st Embodiment of this invention is demonstrated. 1 is a block diagram showing a circuit configuration of an electromagnetic flowmeter according to a first embodiment.

Hereinafter, an example of a capacitive electromagnetic flowmeter in which the pair of electrodes Ta and Tb for measuring the flow rate does not come into direct contact with the fluid flowing through the measurement tube will be described as an example, but the present invention is not limited thereto. Even if it is a contact type electromagnetic flowmeter, this invention is applicable similarly.

As shown in FIG. 1, the electromagnetic flowmeter 10 is a main circuit portion, and includes an electric conductivity detection circuit 11, a flow rate detection circuit 12, an arithmetic processing circuit (CPU) 13, and a setting / display circuit 14. ) And a transmission circuit 15.

The electrical conductivity detection circuit 11 applies, as a square wave signal, an alternating square wave current of an alternating current having a constant amplitude Is at a preset signal frequency fs to the electrodes T1 and T2 for electrical conductivity measurement. It has a function of sampling the detection voltage Vt generated between T2 and outputting amplitude data DA representing the amplitude.

The flow rate detection circuit 12 supplies an excitation current Iex of an alternating current having a preset excitation frequency to the excitation coils 3A and 3B, and according to the magnetic flux generated in the excitation coils 3A and 3B, the electrode for flow measurement The electromotive force Va and Vb generated between (Ta, Tb) is detected, and it has a function to output the flow volume data DF which shows the flow signal VF obtained from Va and Vb.

The arithmetic processing circuit 13 has a function of calculating the electrical conductivity of the fluid based on the amplitude data DA from the electrical conductivity detection circuit 11 and the fluid in the measurement tube 2 based on the obtained electrical conductivity. It has a function of determining the related empty state and a function of calculating the flow rate of the fluid based on the flow rate data DF from the flow rate detection circuit 12.

The setting and display circuit 14 is provided with display devices, such as an operation button, LED, and LCD, and detects and outputs the setting operation input of an operator to the arithmetic processing circuit 13, and the arithmetic processing circuit 13 It is equipped with the function to display various data from.

The transmission circuit 15 has a function of performing data transfer between a host device (not shown) such as a controller via the transmission line LT, and the electrical conductivity obtained from the arithmetic processing circuit 13 or the empty state determination result. And a function for transmitting to the host apparatus.

[Electric Conductivity Detection Circuit]

Next, with reference to FIG. 1, the structure of the electrical conductivity detection circuit 11 which concerns on this embodiment is demonstrated in detail.

As shown in Fig. 1, the electric conductivity detecting circuit 11 is a main circuit section, and includes a clock generating circuit 11A, a signal generating circuit 11B, a buffer amplifier 11C, a sample hold circuit 11D, and A. The / D conversion circuit 11E is provided.

The clock generation circuit 11A, based on the clock signal CLK0 from the arithmetic processing circuit 13, includes a clock signal CLKs for generating a square wave signal SG and clock signals CLKh and CLKl for sampling control. Has the function to generate

The signal generation circuit 11B has a function of generating, as a square wave signal SG, that is, a square wave constant current signal, an alternating square wave current having a constant amplitude (set current Is) at a predetermined signal frequency fs. Specifically, the signal generating circuit 11B is composed of a square wave current source IG operating on and off as a whole, and has a signal frequency fs equal to CLKs at the set current Is based on the CLKs. It has a function of generating a square wave signal SG.

The buffer amplifier 11C is formed of, for example, an operational amplifier or a buffer circuit, and has a function of stabilizing the detection voltage Vt detected from the electrodes T1 and T2 and outputting the output voltage Vt '.

The sample hold circuit 11D samples and holds the output voltage Vt 'from the buffer amplifier 11C on the basis of the clock signals CLKh and CLKl from the clock generation circuit 11A, thereby obtaining the detected voltage VH. , VL) is output to the A / D conversion circuit 11E.

The A / D conversion circuit 11E performs A / D conversion on the difference voltages of VH and VL from the sample hold circuit 11D, that is, the amplitude voltage of Vt, and converts the obtained amplitude data DA into the arithmetic processing circuit 13. It has a function to output to.

In this embodiment, the case where the non-contact electrode which does not directly contact with the fluid which flows in the measurement tube 2 as an electrode T2 for electrical conductivity measurement is demonstrated as an example, but it is not limited to this, T2 As a liquid contact electrode, it may be used.

[Flow detection circuit]

Next, with reference to FIG. 1, the structure of the flow volume detection circuit 12 which concerns on this embodiment is demonstrated in detail.

As shown in FIG. 1, the flow rate detection circuit 12 includes an excitation circuit 12A, a signal amplification circuit 12B, and a signal detection circuit 12C as main circuit parts.

The excitation circuit 12A has a function of outputting an excitation control signal Vex for switching the polarity of the excitation current Iex based on a preset excitation period. Specifically, the excitation circuit 12A applies the excitation current Iex of the alternating current to the excitation coils 3A and 3B based on the excitation control signal Vex from the excitation control unit 13C of the arithmetic processing circuit 13. To feed.

The signal amplifying circuit 12B filters the noise components included in the electromotive force Va and Vb detected by the electrodes Ta and Tb with a low pass filter and a high pass filter, and then amplifies the flow rate signal of the alternating current obtained by amplification. VF) is output.

The signal detection circuit 12C samples and holds the flow rate signal VF from the signal amplifying circuit 12B, A / D converts the obtained DC voltage into the flow rate data DF, and outputs it to the arithmetic processing circuit 13. Has the ability to

[Computation Processing Circuit]

Next, with reference to FIG. 1, the structure of the arithmetic processing circuit 13 which concerns on this embodiment is demonstrated in detail.

The arithmetic processing circuit 13 is provided with a CPU and its peripheral circuits, and executes a predetermined program by a CPU, and cooperates with hardware and software, and implement | achieves the various processing part which performs the process regarding a flow measurement. Have

As the main processing unit realized by the arithmetic processing circuit 13, there are an electric conductivity calculating unit 13A, an empty state determining unit 13B, an excitation control unit 13C, and a flow rate calculating unit 13D.

The electrical conductivity calculation unit 13A has a function of calculating the electrical conductivity of the fluid based on the amplitude data DA from the electrical conductivity detection circuit 11. Specifically, although the electrical conductivity corresponding to the amplitude data DA may be calculated using the electrical conductivity calculation formula set in advance, the correspondence between the amplitude data DA and the electrical conductivity is measured in advance, and the characteristics obtained are obtained. It is set as a lookup table in advance, and the electrical conductivity with respect to the fluid may be derived by referring to the lookup table based on the amplitude data DA from the electrical conductivity detection circuit 11.

The empty state determination unit 13B has a function of determining the presence or absence of the fluid in the measurement tube 2 based on the electrical conductivity of the fluid calculated by the electrical conductivity calculation unit 13A.

Usually, the electrical conductivity of the fluid is larger than that of air. For this reason, the empty state determination part 13B determines the presence or absence of the fluid by processing the electrical conductivity of the fluid computed by the electrical conductivity calculation part 13A by the threshold value.

The excitation control unit 13C has a function of outputting an excitation control signal Vex for switching the polarity of the excitation current Iex based on the preset excitation period.

The flow rate calculation unit 13D has a function of calculating the flow rate of the fluid based on the flow rate data DF from the flow rate detection circuit 12, and the flow rate measurement result is set / displayed by the circuit 14 or the transfer circuit 15. It has a function to output to.

[Structure of Electronic Flowmeter]

Next, with reference to FIGS. 2-4, the structure of the structure of the electromagnetic flowmeter 10 is demonstrated in detail. 2 is a top view of the electromagnetic flowmeter according to the first embodiment. 3 is a cross-sectional side view of the electromagnetic flowmeter according to the first embodiment. 4 is an assembly view of the electromagnetic flowmeter according to the first embodiment.

As shown in FIG. 2 to FIG. 4, the measuring tube 2 is made of a material having excellent insulation and dielectric properties such as a ceramic or resin forming a cylindrical shape, and the measuring tube 2 is located outside the measuring tube 2. Yoke (for example, the same shape as the yoke 4 in FIG. 4) of substantially C-shape so that the magnetic flux direction (second direction) Y is perpendicular to the longitudinal direction (first direction) X of the A pair of excitation coils 3A and 3B are disposed to face each other with the measuring tube 2 interposed therebetween. In addition, below, only the opposite yoke end surface, ie, the yoke surfaces 4A and 4B, is shown in order to make drawing easy to see.

On the other hand, on the outer circumferential surface 2P of the measurement tube 2, the electrode for flow measurement in the electrode direction (third direction) Z perpendicular to the longitudinal direction X and the magnetic flux direction (second direction) Y (Ta, Tb) are arrange | positioned opposingly. Ta and Tb are formed by a pair of surface electrodes made of a thin film conductor.

Thereby, when AC excitation current Iex is supplied to excitation coil 3A, 3B, a magnetic flux will generate | occur | produce between the yoke surfaces 4A, 4B located in the center of excitation coil 3A, 3B, and a measuring tube (2) In the fluid flowing inside, an electromotive force of an alternating current having an amplitude corresponding to the flow velocity of the fluid is generated along the electrode direction Z, and the electromotive force is generated by the electrostatic capacitance between the fluid and the electrodes Ta and Tb. It is detected at (Ta, Tb).

The case 8 is comprised from the bottom-shaped box-shaped resin or metal case which has the opening 8B at the upper side and accommodates the measurement tube 2 inside. The pair of inner wall portions 8A parallel to the longitudinal direction X among the inner wall portions of the case 8 are guide portions 81A and 81B at positions opposing each other, and guide portions 83A, at positions opposing to each other. 83B) is formed.

The guide parts 81A and 81B consist of two protrusion parts formed in parallel with the electrode direction Z, and the printed circuit board 5 in which the fitting parts 82A and 82B between these protrusion parts were inserted from the opening part 8B. Is fitted with the side ends 5I, 5J of the. The guide parts 83A and 83B consist of two protrusions formed in parallel with the electrode direction Z, and the printed circuit board 6 in which the fitting parts 84A and 84B between these protrusions were inserted from the opening part 8B. Is fitted with the side ends 6I and 6J.

On the other hand, the protrusions of the guide portions 81A, 81B, 83A, and 83B need not be continuously formed in the electrode direction Z, and the intervals at which the side ends 5I, 5J, 6I, 6J are smoothly inserted. You may separate and form in multiple numbers. The guide portions 81A, 81B, 83A, and 83B may be grooves formed in the inner wall portion 8A, not the protrusions, and into which the side end portions 5I, 5J, 6I, 6J are inserted.

Of the side surfaces of the case 8, a pair of side surfaces 8C parallel to the magnetic flux direction Y can connect a pipe (not shown) and the measurement tube 2 provided outside the electromagnetic flowmeter 10 to each other. The tubular joints 1A and 1B made of a metal material (for example, SUS) are disposed. At this time, the measurement tube 2 is accommodated in the case 8 along the longitudinal direction X, and a joint 1A is provided at both ends of the measurement tube 2 with a pair of O-rings 87 interposed therebetween. ) And the joint 1B are respectively connected.

Here, at least one of the joints 1A and 1B functions as the electrode T1 (common electrode). For example, the joint 1A is connected to the common potential (ground voltage GND), thereby not only connecting the external pipe and the measurement tube 2 but also functioning as the electrode T1.

Thus, by realizing the electrode T1 by the joint 1A made of metal, the area in contact with the fluid of T1 is widened. As a result, even if adhesion or corrosion of foreign matter occurs in T1, the area of the portion where adhesion or corrosion of foreign matter occurs is relatively small relative to the entire area of T1. Therefore, it is necessary to suppress measurement errors due to changes in polarization capacity. It becomes possible.

The shield 9 which consists of a cross-section U-shaped metal plate is affixed to the side surface 8E of the both sides of the inner wall part 8A of the case 8, and the outer surface of the bottom part 8D of the case 8. Thereby, the noise radiated externally from the electromagnetic flowmeter 10 can be reduced.

[Printed board]

The printed circuit board 5 is a general printed circuit board (for example, glass cloth base epoxy resin copper clad laminated board of 1.6 mm of plate | board thickness) for mounting an electronic component, As shown in FIG. In the position, a pipe hole 5H for penetrating the measurement tube 2 is formed. Therefore, the printed board 5 is attached along the direction which intersects the measuring tube 2. The size of this tube hole 5H is set equal to or slightly smaller than the size of the outer peripheral part of the measuring tube 2. The measuring tube 2 is pressed into the tube hole 5H and caught by the printed board 5.

In addition, you may fix the outer peripheral surface 2P of the measuring pipe 2 and the edge part of the pipe hole 5H with an adhesive agent. In the example of FIG. 4, the tube hole 5H is not opened toward the side end portion of the printed circuit board 5, but a part of the circumferential portion of the tube hole 5H is cut off to form the side end portion of the printed circuit board 5. It may be opened directly to form a notch, or may be indirectly opened through a slit. In this case, the notch formed in the printed circuit board 5 forms the tube hole 5H into which the measurement tube 2 is press-fitted.

Therefore, when assembling the measurement tube 2 in the case 8, first, in the state which screwed the yoke 4 with excitation coil 3A, 3B to the bottom part 8D of the case 8, The printed circuit board 5 in which the measuring tube 2 is press-fitted into the tube hole 5H, and the side ends 5I, 5J are fitted with fitting portions 82A, 82B of the guide portions 81A, 81B of the case 8. The fitting is inserted into the case 8 from the opening 8B of the case 8. Thereafter, the joints 1A and 1B are connected to both ends of the measuring tube 2 from the outside of the case 8 with a pair of O-rings 87 interposed therebetween, and the joints 1A and 1B are connected to the case 8. Screw it in.

Thereby, the printed circuit board 5 is affixed inside the case 8 in the state which the measurement pipe 2 was press-fitted into the pipe hole 5H, As a result, a measurement pipe ( 2) is attached to the inside of the case (8). At this time, it is not necessary to fix the printed circuit board 5 with the guide parts 81A and 81B, and, on the contrary, when the screw is fixed by the joints 1A and 1B which have a slight margin, the measuring tube 2 or the printed circuit board ( 5) No mechanical stress is applied.

The printed board 6 is a general printed board (for example, a glass cloth base epoxy resin copper clad laminate having a plate thickness of 1.6 mm) for mounting electronic components, similarly to the printed board 5, and is almost at the center of the printed board 6. In the position, a pipe hole 6H for penetrating the measurement tube 2 is formed. Therefore, the printed board 6 is attached along the direction which intersects the measuring tube 2. The size of this tube hole 6H is set equal to or slightly smaller than the size of the outer peripheral part of the measuring tube 2.

In addition, in the example of FIG. 4, although the hole 6H does not open toward the side end part of the printed circuit board 6, a part of the periphery of the pipe hole 6H is cut off, and the side of the printed board 6 is not shown. It may be opened directly toward the end to form a notch, or may be indirectly opened through the slit. In this case, the notch formed in the printed circuit board 6 forms the tube hole 6H into which the measuring tube 2 is press-fitted. In addition, similarly to the printed board 5, the convex part may be provided in the hole wall surface of the tube hole 6H, and this convex part may be made to contact the outer peripheral surface 2P.

The electrodes Ta and Tb are connected to the printed board 5 via the observation wiring patterns 2A and 2B formed on the outer circumferential surface 2P of the measuring tube 2 and jumper lines (not shown). The printed circuit board 5 is connected to the flow rate detection circuit 12 of the main board (all not shown) in the upper case attached to the upper side of the case 8, for example through connection wiring (not shown).

The electrodes Ta and Tb are electrically shielded with the shield case 7 made of a metal plate connected to the common potential (ground voltage GND) together with the observation wiring patterns 2A and 2B and the jumper wires. The shield case 7 has a substantially rectangular shape extending along the longitudinal direction X, and an opening for allowing the measurement tube 2 to penetrate the inside thereof has an upstream direction from the magnetic flux regions of the excitation coils 3A and 3B. It is formed in the downstream direction. As a result, the entire circuit portion having a high impedance is shielded by the shield case 7, whereby the influence of external noise is suppressed.

On the other hand, the preamplifier for low-impedance the electromotive force Va and Vb obtained by Ta and Tb may be mounted on the printed circuit board 5, and a preamplifier may also be shielded by the shield case 7. As shown in FIG. At this time, the shield pattern which consists of a ground pattern (solid pattern) connected to the ground potential may be formed in the solder surface of the printed circuit board 5 on the opposite side to the mounting surface of the preamplifier. Thereby, all the planes which contact the printed circuit board 5 may be opened among the planes which comprise the shield case 7, and the structure of the shield case 7 can be simplified.

Further, the electrodes Ta and Tb, the observation wiring patterns 2A and 2B, and further, the electrode T2 are made of a nonmagnetic metal thin film such as copper, and metallized on the outer circumferential surface 2P of the measurement tube 2. Since it is integrally formed by the treatment, the manufacturing process can be simplified, and the product cost can be reduced. In addition, the metallization process mentioned above may be plating process, vapor deposition process, etc. Furthermore, you may attach the non-magnetic metal thin film body shape | molded previously.

[Electrode for electric conductivity]

Next, with reference to FIGS. 5 and 6, the electrodes T1 and T2 for electrical conductivity according to the present embodiment will be described. 5 is a side view of an essential part of the electromagnetic flowmeter according to the first embodiment. It is a top view of the principal part of the electromagnetic flowmeter which concerns on 1st Embodiment.

At least one of the joints 1A, 1B functions as an electrode (first electrode) T1. For example, as shown in FIGS. 5 and 6, the joint 1A is connected to a common potential (ground voltage GND), thereby not only connecting the external pipe and the measurement tube 2, but also the electrode T1. It also functions as. T1 is connected to the pad (electrode connection terminal) P1 formed in the printed circuit board 6 through the jumper wire J1. J1 is soldered to the outer surfaces of P1 and T1.

Meanwhile, as shown in FIGS. 5 and 6, of the outer circumferential surface 2P of the measurement tube 2, the electrode Ta is opposite to the electrode T1 formed of the joint 1A with the printed board 6 interposed therebetween. , Tb, are pattern-formed as a non-contact electrode with an electrode (second electrode) T2 made of a thin film conductor over the entire circumference of the measuring tube 2. Pad P3 protrudes toward the printed circuit board 6, and the pattern is formed in the side end part of the printed circuit board 6 side in T2. T2 is connected to the pad (electrode connection terminal) P2 formed in the printed circuit board 6 through the jumper wire J2 from P3. J2 is soldered to P2 and P3.

Thereby, the length of J1 and J2 which connects the printed circuit board 6 and the electrodes T1 and T2 can be made very short, and the impedance of J1 and J2 can be suppressed very low.

In addition, the printed circuit board 6 is connected to the electrical conductivity detection circuit 11 of the main board (all of which is not shown) in the upper case attached to the upper side of the case 8, for example through connection wiring (not shown). It is. Therefore, if the signal generation circuit 11B or the buffer amplifier 11C is mounted on the printed board 6, the impedance of a connection wiring can also be suppressed low. For this reason, in the measurement of electric conductivity, the impedance regarding the electrode wiring for connecting T1 and T2 can be ignored.

[Operation of First Embodiment]

Next, with reference to FIG. 7, the operation | movement of the electromagnetic flowmeter 10 which concerns on this embodiment is demonstrated. 7 is a signal waveform diagram showing the operation of the electromagnetic flowmeter according to the first embodiment.

Here, the case where the electrode T2 is a non-contact electrode and the square wave signal SG is a square wave constant voltage signal is demonstrated as an example.

The clock generation circuit 11A, based on the clock signal CLK0 from the arithmetic processing circuit 13, includes a clock signal CLKs for generating a square wave signal SG and clock signals CLKh and CLKl for sampling control. Create Here, the case where the frequency of CLKs, ie, the signal frequency fs of the square wave signal SG, is 150 Hz is shown.

The signal generation circuit 11B controls the square wave current source IG on and off based on the CLKs. As a result, as shown in FIG. 7, the applied current Ig is switched between the preset setting current Is and zero at every half cycle of the signal frequency fs to be applied to the electrode T2. . Therefore, due to the applied current Ig supplied from the signal generation circuit 11B, the voltage generated by the fluid resistance of the fluid between the electrodes T1 and T2 is the voltage between the electrodes T1 and T2, that is, the detection voltage. (Vt).

The sample hold circuit 11D has a high output of which Is is supplied among the output voltages Vt 'obtained by stabilizing (impedance conversion) Vt in the buffer amplifier 11C based on the CLKh from the clock generation circuit 11A. The detection voltage VH in the level period TH (half cycle of SG) is sampled. Further, the sample hold circuit 11D is based on the CLKl from the clock generation circuit 11A, and the detection voltage VL in the low level period TL (half period of SG) to which zero is supplied during Vt '. Sampling).

The A / D conversion circuit 11E performs A / D conversion on the difference voltage ΔVt between VH and VL obtained by the sample hold circuit 11D into amplitude data DA and outputs the result.

In general, a method of full-wave rectifying the detection voltage Vt of alternating current, for example, a method of adding the detection voltage Vt in TL back to the intermediate level of Vt and adding it to the Vt of TH. However, in such a method, if the Vt of TL and TH is not the same, a ripple remains even after full-wave rectification and since it does not become a stable DC voltage, it becomes a cause of a measurement error.

According to this embodiment, the differential voltage of VH and VL obtained by sampling separately from TL and TH is acquired as amplitude data DA, without full-wave rectifying AC detection voltage Vt. For this reason, the influence on the amplitude data DA can be avoided even when the vibration is contained in the Vt due to a change in the flow velocity of the fluid or when the common mode noise is mixed into the Vt through the fluid from the outside. It is possible to realize stable measurement of electrical conductivity.

The electrical conductivity calculation unit 13A calculates the electrical conductivity of the fluid based on the DA from the A / D conversion circuit 11E.

In addition, the empty state determination unit 13B determines whether or not the measuring tube 2 is empty by comparing the electrical conductivity obtained by the electrical conductivity calculation unit 13A with the threshold conductivity.

8 is a configuration example of a square wave current source. As shown in FIG. 8, the square wave current source IG includes a switch SWi, an operational amplifier Ug, and a current detection circuit DET. SWi is an analog switch that switches between Vs and GND based on CLKs. DET is a circuit for detecting the current value of the applied current Ig output from IG. Ug has a function of holding and controlling the current value of Ig at the set current Is based on the current detection output from the DET, and controlling the output of Ig on and off based on the output of SWi.

9 is an equivalent circuit on the electrode side according to the first embodiment. As described above, in the present embodiment, the square wave constant current signal is used as the square wave signal SG. For this reason, as shown in FIG. 9, the equivalent circuit of the electrode side seen from the printed board 6 has the impedance between electrodes T1 and T2 with respect to the square wave current source IG of the signal generation circuit 11B. The equivalent circuit Zt on the side shown is connected.

At this time, in Zt, the polarization capacity Cp and the polarization resistance Rp are generated between the electrode and the fluid when the electrodes T1 and T2 are in contact with the fluid, and since T2 is a non-contact electrode, the fluid and the electrode ( The electrode capacitance Ct is generated between T2). Therefore, if the fluid resistance with respect to the fluid between electrodes T1 and T2 is Rl, Zt is a parallel circuit of polarization capacitance Cp and polarization resistance Rp, fluid resistance Rl, and electrode capacitance Ct. ) Appears as an equivalent circuit connected in series. Here, when the signal frequency of the square wave signal SG is set to fs = 150 Hz, the impedance of Cp is relatively small, but the impedance of Ct increases to a certain extent, so that the voltage Vct between both ends of Ct, and Vt changes transiently. Done.

10 is a signal waveform diagram showing an operation of an electromagnetic flowmeter using a square wave constant voltage signal. In the same manner as in Fig. 7, when fs = 150 kHz, the impedance of Cp is relatively small, but the impedance of Ct is somewhat large. For this reason, when a square wave voltage of AC having a constant amplitude (reference voltage Vs) is used as a square wave signal SG, that is, a square wave constant voltage signal, Vct or Vrl, and moreover, Vt is exponentially in each time constant. As a result, VH and VL cannot be stably detected.

In this way, when the waveform of Vt is deformed, an error is likely to be included in the detection of the amplitude data DA, and as a result, it becomes a factor of the decrease in the measurement accuracy regarding the electrical conductivity. For this reason, as fs, it is necessary to use the high frequency which can ignore the impedance of Cp and Ct. On the other hand, when fs is made high, the influence by the line capacitance Cw of an electrode wiring will become large, and signal leakage will arise in an electrode wiring, and it will become a cause of the waveform of Vt being deformed.

In contrast, in the present embodiment, since the square wave constant current signal is used as the square wave signal SG, the slopes of Vct and Vt become linear even when fs = 150 Hz, so that VH and VL can be stably detected. Can be.

If the detected voltage Vt detected in the high level period TH in which the applied current Ig is the set current Is is VH, and Vrl and Vct at that time are VrlH and VctH, then VH = VrlH + VctH. . If the detected voltage Vt detected in the low level period TL at Ig = 0 is VL, and Vrl and Vct at that time are VrlL and VctL, then VL = VrlL + VctL.

At this time, Vct is included in the detected VH and VL, but since CLKh and CLKl represent the center positions of TH and TL (semi-period of SG), the VctH and VctL included in the sampled VH and VL become the same. As a result, by adopting the difference voltage ΔVt between VH and VL, VctH and VctL are canceled to obtain amplitude data DA without Vct.

That is, ΔVt = VH-VL = VrlH-VrlL. Thereby, since Ig is constant, Rl is calculated | required by following formula (1).

[Equation (1)]

In Equation (1), Ig is known, and the differential voltages VH-VL are detected by the sample hold circuit 11D, converted into amplitude data DA by the A / D conversion circuit 11E, and the arithmetic processing circuit. It is input to (13). Therefore, the electric conductivity calculation unit 13A can easily calculate Rl based on these data.

11 is a characteristic diagram showing a correspondence relationship between amplitude data and electrical conductivity, and the vertical axis represents amplitude data DA, and the horizontal axis represents electrical conductivity. By performing a calibration operation using a plurality of standard fluids of known electrical conductivity, the correspondence between the amplitude data DA and the electrical conductivity as shown in FIG. 11 is measured in advance, and the obtained characteristics are used as a lookup table, for example, a semiconductor. It is set in a memory (not shown), and based on the amplitude data DA from the electrical conductivity detection circuit 11, the electrical conductivity calculation unit 13A refers to the look-up table and the fluid in the measurement tube 2 The electrical conductivity with respect to may be derived.

[Effect of 1st Embodiment]

Thus, in this embodiment, the signal generation circuit 11B produces | generates the square wave current of alternating current having a constant amplitude as a square wave signal SG at the preset signal frequency fs, and is attached to the measurement tube 2, It applies to the electrodes T1 and T2, and the electric conductivity detection circuit 11 detects the amplitude of the detection voltage Vt by sampling the detection voltage Vt detected from these T1 and T2.

Generally, as an excitation frequency fex for flow measurement, frequencies of several tens of Hz-about several hundreds of Hz are used. In particular, when the non-contact surface electrode is used as the flow rate measuring electrodes Ta and Tb, the excitation frequency is slightly higher than that in which the contact electrode is used in order to make the capacitance component generated between Ta and Tb and the fluid as small as possible. (fex) tends to be used.

According to this embodiment, since the inclination of Vt becomes linear, a frequency higher than fex, for example, a frequency of several kHz to several tens of kHz, which is higher than fex, for example, 100 times higher than fex, is used as the signal frequency fs for electric conductivity measurement. Also, the amplitude of the detection voltage Vt can be detected stably.

Therefore, even if the applied signal for electric conductivity interferes with the applied signal for flow measurement, fex << fs, it is possible to easily remove fs with the low pass filter of the signal amplifying circuit 12B.

Thus, in order to reduce the interference as described above, it is not necessary to increase the distance between the electrodes Ta and Tb for flow measurement and the electrodes T1 and T2 for electrical conductivity. For this reason, it is not necessary to extend the length of the measuring tube 2 or arrange | position an earth ring between mutual electrodes, and as a result, it does not have to enlarge the electromagnetic flowmeter 10, and as a result, the flow volume and electrical conductivity of a fluid are corrected. It becomes possible to measure well.

Further, according to the present embodiment, as described above, since the inclination of the detection voltage Vt becomes linear and the amplitude of the detection voltage Vt can be stably detected, the electrode wiring connecting T1 and T2 as fs. It is possible to use a frequency that can suppress the influence of the line capacitance of, and to measure the electrical conductivity with high accuracy.

In addition, in this embodiment, the contact liquid electrode which contacts with a fluid as T1 may be used, and the noncontact liquid electrode which is formed in the outer peripheral part of the measurement tube 2 as T2 and does not contact with a fluid may be used.

Thereby, generation | occurrence | production of the measurement error resulting from adhesion of dirt to an electrode surface, or corrosion of an electrode can be suppressed. In addition, it is not necessary to use an expensive liquid contact electrode such as platinum black, so that a significant cost reduction can be achieved. In the case where a non-contacting electrode is used, the electrode capacitance Ct is generated between the electrode and the fluid, but since the square wave constant current signal is used as the square wave signal SG, the amplitude of the detection voltage Vt can be stably detected. Can be.

In addition, in this embodiment, the electrical conductivity detection circuit 11 may sample the detection voltage Vt at the center time position of the half period of the square wave signal SG.

As a result, even when a non-contact electrode is used as T2, the voltage VctH at both ends of the electrode capacitance Ct of T2 included in the VH sampled in the high level period TH is sampled in the low level period TL. The voltage VctL of both ends of Ct contained in VL becomes the same. Therefore, by adopting the difference voltage ΔVt between VH and VL, VctH and VctL are canceled to obtain amplitude data DA without Vct. For this reason, it becomes possible to measure electrical conductivity with high precision.

In the present embodiment, the square wave current source IG of the signal generating circuit 11B includes the current detection circuit DET for detecting the magnitude of the applied current Ig, which is the square wave signal SG, and the signal frequency fs. May be constituted by an operational amplifier Ug that maintains the amplitude of Ig at the set current Is, based on the clock signal CLKs indicating?) And the detection result from the current detection circuit DET. Thereby, stable Ig with high precision can be produced with a comparatively simple structure.

In addition, in this embodiment, the signal generation circuit 11B which arrange | positions the printed circuit board 6 in the vicinity of the electrodes T1 and T2 attached to the measurement tube 2, and produces | generates the square wave signal SG. And at least one or both of the buffer amplifiers 11C for stabilizing and outputting the detected voltage Vt detected from the electrodes T1 and T2 may be mounted on the printed board 6.

As a result, the lengths of the electrode wirings that connect the signal generating circuit 11B, the buffer amplifier 11C, and the electrodes T1 and T2, that is, the jumper lines J1 and J2, can be significantly shortened, and the lines between the electrode wirings can be shortened. The capacity can be made small. Therefore, even when a relatively high signal frequency is used, the electrical conductivity can be measured with high accuracy.

In addition, in this embodiment, the tube holes 5H and 6H into which the measurement tube 2 is inserted are formed in the printed boards 5 and 6, and the outer peripheral surfaces of the tube holes 5H and 6H and the measurement tube 2 are formed. By contacting 2P, you may make it adhere to the outer peripheral surface 2P.

Thereby, the printed circuit board 6 can be fixed to the measuring tube 2 with a very simple structure, without using fixing members, such as a mounting screw.

Moreover, with this structure, the printed circuit board 6 can be arrange | positioned orthogonally to the longitudinal direction of the measurement tube 2 between the electrode T1 and the electrode T2. For this reason, the electrode wiring from the printed circuit board 6 to the electrodes T1 and T2, that is, the jumper wires J1 and J2 can be arranged and connected at different positions and directions, and the line capacitance between the electrode wirings is very small. can do. In addition, when a metal pipe is connected to the joint 1A which is the electrode T1, a current applied to the fluid may return to the metal pipe and measurement errors may occur. However, the above configuration provides a certain distance from T1. And T2 can be easily disposed. Therefore, the return of the applied current to the metal pipe can be suppressed, and the electrical conductivity can be measured with high accuracy.

In this embodiment, pads (electrode connection terminals) P1 and P2 for connecting the electrode wirings to the electrodes T1 and T2 to the pattern surface of the printed board 6 and the signal generating circuit 11B. And a wiring pattern for connecting the pads P1 and P2 to at least one or both of the buffer amplifiers 11C.

This makes it very easy to use the jumper wires J1 and J2 to connect the signal generating circuit 11B, the buffer amplifier 11C, and the electrodes T1 and T2 mounted on the printed board 6 without using a connector. Can be connected.

Second Embodiment

Next, with reference to FIG. 12 and FIG. 13, the electromagnetic flowmeter 10 which concerns on 2nd Embodiment of this invention is demonstrated. 12 is a side view of an electromagnetic flowmeter according to a second embodiment. It is a top view of the electromagnetic flowmeter which concerns on 2nd Embodiment.

In 1st Embodiment, the case where the non-contacting electrode which does not contact with a fluid as the electrode T2 was used as an example. In this embodiment, the case where the liquid-contacting electrode which contacts with a fluid as electrode T2 is demonstrated.

As shown in FIG. 12 and FIG. 13, of the outer circumferential surface 2P of the measurement tube 2, the wall 1 of the measurement tube 2 penetrates on the opposite side to the joint 1A with the printed board 6 interposed therebetween. The contact electrode which consists of a metal rod, ie, electrode T2, is attached so that it may protrude into the measuring tube 2. The part which protrudes in the measurement tube 2 comes into contact with the fluid in the measurement tube 2.

At this time, T2 is connected to the pad P2 formed in the printed circuit board 6 through the jumper wire J2. J2 is soldered to P2 and T2.

[Operation of Second Embodiment]

Next, operation | movement of the electromagnetic flowmeter 10 which concerns on this embodiment is demonstrated.

When the electrode T2 is changed from the non-contact electrode to the contact electrode, the electrode capacitance Ct between T2 and the fluid in the case of the non-contact electrode is lost. For this reason, the equivalent circuit Zt shown in FIG. 9 is shown by the parallel circuit of polarization capacitance Cp and polarization resistance Rp, and the equivalent circuit with fluid resistance Rl connected in series. The other electrical conductivity measurement operation | movement which concerns on this embodiment is the same as that of 1st Embodiment, and detailed description here is abbreviate | omitted.

[Effect of 2nd Embodiment]

As described above, in the present embodiment, the electrodes T1 and T2 are made of a liquid contact electrode that comes into contact with the fluid. Thereby, the influence of the capacitance Ct generated between the fluid and the electrode T2, which is unique when the non-contacting electrode is used as T2, can be eliminated, and the signal frequency of the square wave signal SG is relatively low. Can be used. For this reason, the influence by the line capacitance of electrode wiring, ie, jumper wires J1 and J2 can be made very small, and electrical conductivity can be measured with a very high precision.

Extension of Embodiments

As mentioned above, although this invention was demonstrated with reference to embodiment, this invention is not limited to the said embodiment. Various changes which can be understood by those skilled in the art can be made to the structure and details of the present invention within the scope of the present invention. In addition, about each embodiment, it can implement combining arbitrarily in the range which does not contradict.

10: electromagnetic flow meter 1A, 1B: joint
2: measuring tube 2A, 2B: observation wiring pattern
2P: outer peripheral surface 3A, 3B: excitation coil
4: York 4A, 4B: York Side
5, 6: Printed board 5H, 6H: tube hole
5I, 5J, 6I, 6J: side end 7: shield case
8: Case 8A: Interior Wall
8B: opening 8C, 8E: side
8D: Bottom portion 81A, 81B, 83A, 83B: Guide portion
82A, 82B, 84A, 84B: Fitting Part 9: Shield
11: electrical conductivity detection circuit 11A: clock generation circuit
11B: Signal Generation Circuit 11C: Buffer Amplifier
11D: Sample Hold Circuit 11E: A / D Conversion Circuit
12: flow detection circuit 12A: excitation circuit
12B: Signal Amplification Circuit 12C: Signal Detection Circuit
13: Operation Processing Circuit 13A: Electric Conductivity Calculator
13B: Empty state determination unit 13C: Excitation control unit
13D: Flow rate calculator 14: Setting and display circuit
15: transmission circuit IG: square wave current source
Ta, Tb: electrode T1, T2: electrode
P1, P2, P3: Pads J1, J2: Jumper Wires
SWi: Switches CLK0, CLKs, CLKh, CLKl: Clock Signal
Vs: reference voltage GND: ground voltage
SG: square wave signal Ig: applied current
Vt, VH, VL: Detection voltage Vt ': Output voltage
DA: amplitude data Vex: excitation control signal
Iex: excitation current Va, Vb: electromotive force
VF: Flow Signal DF: Flow Data

Claims (6)

An electromagnetic flowmeter which measures the flow rate of the fluid flowing in a measurement tube,
A signal generating circuit for generating an AC square wave current having a constant amplitude at a predetermined signal frequency as a square wave signal;
A first electrode and a second electrode attached to the measuring tube to apply the square wave signal to the fluid;
A detection circuit for detecting an amplitude of the detection voltage by sampling a detection voltage detected from the first electrode and the second electrode;
An arithmetic processing circuit for calculating an electrical conductivity with respect to the fluid by arithmetic processing based on the amplitude
Electromagnetic flow meter comprising a. The method of claim 1,
A printed circuit board disposed in the vicinity of the first electrode and the second electrode, the printed circuit board further including at least one or both of the signal generation circuit and a buffer amplifier for stabilizing the detection voltage and outputting the detected voltage to the detection circuit; Electronic flow meter, characterized in that. The method according to claim 1 or 2,
The first electrode is made of a liquid contacting electrode that is in contact with the fluid, and the second electrode is formed of an outer circumferential portion of the measuring tube, and is made of a non-contacting electrode which is not in contact with the fluid. Electronic flow meter. The method according to claim 1 or 2,
The first electrode and the second electrode are electromagnetic flowmeters, characterized in that the liquid contact electrode in contact with the fluid. The method according to claim 1 or 2,
And the detection circuit samples the detection voltage at a central time position of a half cycle of the square wave signal. The method according to claim 1 or 2,
The signal generation circuit,
A current detection circuit for detecting a magnitude of the square wave signal;
An operational amplifier which maintains the amplitude of the square wave signal at a set current based on a clock signal indicating the signal frequency and a detection result from the current detection circuit;
Electromagnetic flow meter comprising a.

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