JPH10253411A - Low-conductivity electromagnetic flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the flow of a low-conductivity fluid to be measured by applying electric charge to the measurement fluid with a charge generating device, then measuring the flow velocity of the fluid under measurement with an electromagnetic flow meter main body. SOLUTION: The electromagnetic flow meter main body 11 measures the flow of a fluid to be measured. A charge generating device 12 is provided on a pipe on the upstream side from the electromagnetic flow meter main body 11. The charge generating device 12 is made of a metal lattice-shaped body split with the pipe into multiple passages parallel with the axial direction of the pipe. After the fluid under measurement is applied with negative charges by the charge generating device 12, the flow velocity of the fluid under measurement is measured by the electromagnetic flow meter main body 11. When the fluid under measurement is an insulating fluid, no ionic dissociation normally occurs, only polarized charges exist, and charges are applied to the low- conductivity measurement fluid. When the charge generating device 12 with a simple structure is added, the flow velocity of the low-conductivity fluid, unmeasurable in the past, can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-conductivity electromagnetic flowmeter capable of measuring a flow rate of a low-conductivity measurement fluid.

[0002]

2. Description of the Related Art FIG. 9 is an explanatory view of the configuration of a conventional example generally used in the past, for example, the title: Industrial Measurement Handbook (transistor type meter), date of issue: June 1967
On March 10, the editor is shown; Yokogawa Electric Corporation, publishing office; Tokyo Denki University Press.

In FIG. 1, reference numeral 1 denotes a measurement pipe through which a measurement fluid flows. Reference numerals 2 and 3 denote electrodes provided in the measurement pipeline 1. Reference numeral 4 denotes an iron core provided across the measurement pipe 1. 5
Is an exciting coil wound around the iron core 4. 6 is an electrode 2,
This is a converter that converts three outputs.

In the above configuration, when a magnetic field B is applied to a measurement fluid flowing at a flow velocity V, a potential U represented by the following equation is generated in the measurement fluid. Δ ² U = ((σ + jω (ε−ε ₀ )) / (σ + jωε))
div (V × B) σ: electric conductivity, ε: dielectric constant, ε ₀ : dielectric constant in vacuum

Here, if σ >> ωε, Δ ² U = div (V × B) The magnetic field B and the flow velocity V are orthogonal to each other, and the electrode 2
3, the potential difference E between the electrodes 2 and 3 is assumed.
Is E∝V · B · DD: distance between electrodes 2 and 3

Therefore, V can be measured by measuring E. The current flowing through the measurement fluid between the electrodes 2 and 3 is due to the movement of positive and negative ions that are dissociated in the measurement fluid. The above is the basic principle of the electromagnetic flow meter.

[0007]

However, the above description assumes that the conductivity σ of the measurement fluid is σ >> ωε. Therefore, a conduction current according to Ohm's law flows in the measurement fluid. In order to measure E with high accuracy, the input impedance of the converter 6 needs to be sufficiently larger than the internal impedance (∝1 / σd) of the voltage source E. Here, d: diameter of electrodes 2 and 3

In reality, it is impossible to make the input impedance of the converter 6 infinite, so that in the wetted electrode type electromagnetic flow meter, 10 ⁻⁵ to 10 ⁻⁶ S · cm ⁻¹ , and In the case of a capacitance type electromagnetic flow meter, the lowest value of the measurable conductivity is about ^10-8 S · cm ^-1 . That is, the measurement fluid to be measured by the electromagnetic flowmeter is an ionic fluid, and cannot measure alcohols or petroleums showing almost no ionicity.

The present invention solves this problem. An object of the present invention is to provide a low-conductivity electromagnetic flowmeter that can measure the flow rate of a low-conductivity measurement fluid.

[0010]

In order to achieve this object, the present invention provides: (1) a low-conductivity electromagnetic flowmeter for measuring the flow rate of a low-conductivity measurement fluid; A low-conductivity electromagnetic flowmeter, comprising: an electromagnetic flowmeter main body; and a charge generation device provided in a conduit on an upstream side of the electromagnetic flowmeter main body to apply electric charge to the measurement fluid. (2) The low-conductivity electromagnetic flowmeter according to claim 1, further comprising a charge generation device including an aggregate that divides the conduit into a plurality of flow passages parallel to the axial direction of the conduit. . (3) The low-conductivity electromagnetic flow rate according to claim 1, further comprising a charge generation device including a lattice-shaped body that divides the conduit into a plurality of flow passages parallel to the axial direction of the conduit. Total. (4) The low-conductivity electromagnetic flowmeter according to (1), further comprising a charge generation device comprising a collection of a plurality of small-diameter circular pipes which are parallel to the conduit in the axial direction of the conduit. . It is what constituted.

[0011]

In the above configuration, in the charge generation device,
After applying a charge to the measurement fluid, the flow rate of the measurement fluid is measured in the main body of the electromagnetic flow meter. Hereinafter, a detailed description will be given based on embodiments.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of a main part of an embodiment of the present invention, FIG. 2 is a detailed explanatory view of a charge generating device of FIG. 1, and FIG. 3 is a side view of FIG. In the figure, the configuration of the same symbol as in FIG. 9 represents the same function. Hereinafter, only differences from FIG. 9 will be described.

Reference numeral 11 denotes an electromagnetic flowmeter main body for measuring the flow rate of the measurement fluid. Reference numeral 12 denotes a charge generation device provided in a pipe on the upstream side of the electromagnetic flowmeter main body 11. in this case,
The charge generation device 12 is formed of a lattice-shaped body made of a metal obtained by subdividing a pipe into a plurality of flow paths parallel to the axial direction of the pipe.

In the above configuration, as will be described later, after the measurement fluid is negatively charged in the charge generation device 12, the flow rate of the measurement fluid is measured in the main body 11 of the electromagnetic flow meter.

Here, when the measurement fluid is an insulating fluid (dielectric fluid), there is usually no dissociation of ions and only a polarization charge. Therefore, no current flows continuously even when an electric field is applied.

By the way, as shown in FIG. 4, an electric double layer B is formed in the vicinity where the measurement fluid contacts the solid wall A.
At this time, the solid wall A has a positive charge, and the measurement fluid near the solid wall A has an excessive negative charge.

A diffusion layer C is formed inside the measurement fluid,
The density of the negative charge decreases as the distance from the solid wall A increases. Here, assuming that the measurement fluid has a flow and the solid wall A is grounded, a positive charge flows to the ground, and a negative charge near the solid wall A is carried into the measurement fluid.

As a result, negative charges increase in the measurement fluid. This is called a flow electrification phenomenon. If the conductivity of the measuring fluid is high, these excess charges will conduct in the measuring fluid and eventually flow into the solid wall A and disappear.

That is, when the conductivity is high, since the time from generation to disappearance of charge (relaxation time) is short, the negative charging of the measurement fluid does not appear as a significant phenomenon. However, in the case of an insulating fluid, the relaxation time is long, and the measurement fluid is in a negatively charged state for a long time. The relaxation time τ is represented by τ = ε / σ.

FIGS. 5A and 5B show the state of the current between the electrodes 13 and 14 of the electromagnetic flowmeter main body 11 when the magnetic field B is applied to the electromagnetic flowmeter main body 11.
In the case of an ionic fluid, dissociated negative ions and positive ions move to the respective electrodes 13 and 14, and current flows. In the present invention, however, the carriers that carry charges are excessively charged, and FIG. Moves from the electrode 14 to the electrode 13.

Since the conductivity of the measurement fluid is represented by the product of the concentration of the charge serving as a carrier and the moving speed, the conductivity increases as the number of excess charges increases. Note that it is unnatural that the charge moves in the measurement fluid as it is, and it is considered that the charge eventually moves as a molecular ion or a part thereof dissociates and moves as an ion.

That is, the internal impedance Z _i (∝1 / σd) of the induced voltage source E is small. Here, d: electrode 1
3,14 diameter

By the way, as shown in FIG. 1, the charge generation device 12 has a grid shape over the entire flow path, and the measurement fluid flows along a narrow flow path divided by the grid. Electricity 2
Since the layer B is generated at a portion in contact with the solid wall A, the larger the liquid contact area of the solid wall A, the better the charge generation efficiency. Further, the reason why the lattice-like body 12 is provided over the entire cross section of the flow path is that it is preferable that the excess charge flowing away is uniformly present in the entire flow path.

Regarding the type of the electrode, it can be applied to either the liquid contact type or the capacity type, in principle. As a wetted type electrode material, an electrode with platinum black having an effective diameter several thousand times is preferable. However, as shown in FIG. 6, the inflow of charges into the electrodes 13 and 14 is caused by the induced voltage E
It is conceivable that not only the electric charge that moves based on the flow rate but also the collision with the flow of the measurement fluid directly collides with and flows into the electrodes 13 and 14.

Also on the surfaces of the electrodes 13 and 14,
Formation of the electric double layer B and separation of electric charges due to the flow of the measurement fluid occur. From the above, as shown in FIG.
The surfaces of 3 and 14 are made to be concave portions 15 from the flow path,
It is considered that the flow of the measurement fluid is preferably stagnant.

Next, in the conventional electromagnetic flow meter shown in FIG. 9, when the conductivity of the measurement fluid decreases, a noise voltage called flow noise is generated as the flow rate of the measurement fluid increases. This is presumed to be due to the inflow of positive charges at the electrode surface described above.

In this case, since the internal impedance Z _i of the measurement fluid is large, the noise voltage (V _N = _IN · Z _i ) at the input stage of the converter becomes large even if the noise current _IN is small. In the present invention, since the internal impedance Z _i is small, noise current I _N is the noise voltage V _N even if, rather than the conventional example, can be reduced.

Next, regarding the determination of the zero point, when the flow rate of the measurement fluid is zero, there is no generated charge, and thus the conductivity becomes low. On the other hand, the operable conductivity is determined from the relationship between the conductivity and the input impedance of the conversion circuit 6. Since the minimum flow rate that can be measured is determined by the electric conductivity, a flow rate lower than this is a dead zone. Therefore, a zero cut function is added to the converter 6 as shown in FIG.

As a result, the flow rate of the low-conductivity measurement fluid, which could not be measured conventionally, can be measured by adding the charge generation device 12 having a simple structure for applying a charge to the low-conductivity measurement fluid. A possible low conductivity electromagnetic flowmeter is obtained.

In the above-described embodiment, the charge generation device 12 is described as being formed of a lattice-shaped body. However, the present invention is not limited to this. For example, a small-diameter circular tube may be bundled. In short, any assembly that divides the pipeline into a plurality of flow paths parallel to the axial direction of the pipeline may be used.

In the above-described embodiment, the charge generation device 12 has been described as a device using an electric double layer. However, the present invention is not limited to this. For example, charging by electron irradiation or ion-exchange resin Injection is also acceptable. In short, any device may be used as long as it can apply a charge to the low-conductivity measurement fluid.

[0032]

As described in detail above, the present invention provides
According to the first aspect of the present invention, the flow rate of the low-conductivity measurement fluid, which cannot be measured conventionally, is measured by adding a charge generating device having a simple structure that applies a charge to the low-conductivity measurement fluid. A low-conductivity electromagnetic flowmeter that can be obtained.

According to the second aspect of the present invention, since the area of the fixed wall in contact with the measurement fluid can be increased, the charge generation efficiency is high. For this reason, a low-conductivity electromagnetic flowmeter capable of performing a stable flow rate measurement even in a low flow rate range is obtained.

According to the third aspect of the present invention, it is possible to obtain a low-conductivity electromagnetic flowmeter capable of increasing the area of the fixed wall without disturbing the flow velocity distribution and performing stable flow measurement up to a low flow rate region.

According to the invention of claim 4 of the present invention, the area of the fixed wall can be increased without disturbing the flow velocity distribution, and a simple bundle of thin tubes can be used. A conductivity electromagnetic flowmeter is obtained.

Therefore, according to the present invention, a low-conductivity electromagnetic flowmeter capable of measuring the flow rate of a low-conductivity measurement fluid can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a main part configuration of an embodiment of the present invention.

FIG. 2 is a detailed explanatory diagram of the charge generation device of FIG.

FIG. 3 is a side view of FIG. 2;

FIG. 4 is an operation explanatory diagram of FIG. 1;

FIG. 5 is an operation explanatory diagram of FIG. 1;

FIG. 6 is an operation explanatory diagram of FIG. 1;

FIG. 7 is an explanatory view of a main part configuration of another embodiment of the present invention.

FIG. 8 is an operation explanatory diagram of FIG. 1;

FIG. 9 is an explanatory diagram of a configuration of a conventional example generally used in the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measurement pipeline 4 Iron core 5 Excitation coil 6 Converter 11 Electromagnetic flowmeter main body 12 Charge generator 13 Electrode 14 Electrode A Solid wall B Electric double layer C Diffusion layer

Claims (4)

[Claims] 1. A low-conductivity electromagnetic flowmeter for measuring a flow rate of a low-conductivity measurement fluid, comprising: an electromagnetic flowmeter main body for measuring a flow rate of a measurement fluid; And a charge generator for applying a charge to the measurement fluid. 2. A low-conductivity electromagnetic device according to claim 1, further comprising a charge generating device comprising an aggregate that divides the conduit into a plurality of flow passages parallel to the axial direction of the conduit. Flowmeter. 3. The low-conductivity device according to claim 1, further comprising a charge generating device comprising a lattice-shaped body that divides the conduit into a plurality of flow passages parallel to the axial direction of the conduit. Electromagnetic flow meter. 4. The low-conductivity electromagnetic device according to claim 1, further comprising a charge generating device comprising a collection of a plurality of small-diameter circular pipes parallel to an axial direction of the conduit. Flowmeter.