JPH07306067A - Electrode of electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To stably measure a flow rate without flow rate noises by coating a part of surfaces of an electrode of an electromagnetic flowmeter in touch with a liquid which does not face a flow passage with an insulating film. CONSTITUTION:A surface of an electrode in touch with a liquid which is not seen from a flow passage is coated with a rigid insulating film. For instance, a side face part at a front end 9 of the electrode is coated with an insulating film 11 of 10-several hundreds mum thickness which adheres well to stainless steel, platinum or the like as a metal of the electrode. In order to apply the insulating film, a plastic or rubber insulating material is dissolved in an organic solvent and dried. Baking by heating is also carried out in some cases in order to enhance a strength of the coating film. Moreover, if a ceramic film or the like film is composed on the surface of the electrode through a vapor phase chemical reaction of a gas material, a further rigid coating is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an electromagnetic flow meter for measuring the flow rate of a conductive fluid in tap water, sewage or a chemical plant, and more particularly to the structure of an electrode for extracting a flow rate signal generated in the fluid. is there.

[0002]

2. Description of the Related Art As shown in FIG. 2, a conventional device insulates the inside of a pipe 1 through which a fluid is passed by a lining 2 made of an insulating material so that a conductive fluid flowing inside the lining is subjected to an AC rectangular wave at right angles to the flow direction. A magnetic field is applied by the excited coil 3 and a pair of electrodes 4 for detecting a flow rate signal generated in the fluid are attached in a direction perpendicular to both the flow direction and the magnetic field direction. Only half of the flowmeter detector is shown in this figure. The electrode is strongly pressed against the lining by the spring 5, and the sealing projection 6 of the electrode seals the fluid in the pipe so as not to leak to the outside. Further, since the electrode and the spring float from the pipe with high insulation, they are fixed by the cap nut 8 via the spacer 7 made of plastic.

Such a structure is also outlined in JIS B 7554. This type of structure has been used for a long time, but with the recent advancement of measurement technology, it has become possible to measure low flow velocities of 0.1 m / s or less, which was previously impossible to measure. . However, even if it becomes possible to electrically measure sufficiently, the electrical noise of the flow rate signal itself is large, and there is a signal change other than the flow rate fluctuation, which has been a problem from the past. At present, the magnitude of the flow rate signal generated in the electrode portion as a flow rate signal is 0.1 m / s and is about several microvolts to 10 microvolts. Further, since the accuracy of the electromagnetic flowmeter is about 0.5 to 1%, it is necessary to reduce the noise of the flow rate signal to 0.1 microvolt or less.

[0004]

DISCLOSURE OF THE INVENTION The present invention is to reduce the noise of the flow rate signal, and particularly pays attention to the noise generated from the portion where the fluid and the electrode are in contact with each other.

There is an electric double layer in the region where the electrode and the fluid are in contact with each other as shown in FIG. 2, and when the electrochemical phenomenon in this part is activated, the generation of noise also increases.

Further, there is a microscopic gap 10 between the electrode tip 9 and the lining, and the electrolytic solution as the measurement fluid is present in this part, and the following phenomenon occurs.

-Concentration and decomposition of electrolyte-Gross corrosion-Oxide film formation and damage-Bubble formation All of these phenomena cause instability of the electrode potential and cause noise.

[0008]

According to the present invention, an electrode of a liquid-contacting portion of the electrode, which is invisible to the flow channel, is divided into a portion which can be seen from the flow channel and a portion which is covered with the lining and is invisible. The surface was covered with a solid insulating coating.

[0009]

As a result, since the electrode and the fluid do not come into contact with each other in the gap portion, it is possible to eliminate major factors such as gap corrosion and generation of noise such as bubbles.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention.
The side surface of the tip of the electrode is in close contact with the electrode metal, such as stainless steel, platinum, and Hastelloy.
A 0 micron thick insulating coating 11 is applied. Alternatively, it is a method of applying an organic coating film such as applying rubber having good adhesiveness. Further, in order to apply a more robust insulating film, there is a method of applying a thin film of glass which is an inorganic insulator or a method of applying an oxide film such as SiO ₂ or Al ₂ O ₃ . The following methods are available for applying the above coating. (1) Application of Insulating Material (2) Vapor Deposition of Inorganic Material (3) Chemical Vapor Deposition Method (CVD) of Inorganic Material Hereinafter, a method for applying an insulating coating will be described in detail. The method (1) is generally performed, in which a plastic or rubber insulating material is dissolved in an organic solvent and dried. Baking by heating is also performed to increase the strength of the coating.
In (2), the inorganic insulator is heated and melted in a vacuum with a heater or an electron beam, and the inorganic insulator is vaporized and attached to the electrodes. In order to form an oxide film, the vapor-deposited film may be heated in the atmosphere to be oxidized to form an insulator.
For example, there are alumina (AlO ₃ ) and silica (SiO ₂ ). The method (3) is a method of synthesizing a coating film of ceramics or the like on the electrode surface by a gas phase chemical reaction of a gas raw material and is characterized in that a robust coating film can be obtained. In this method, since the coating film is attached to the entire surface of the electrode, it is necessary to remove the necessary portion and mechanically remove the coating film after growing the coating film.

[0011]

According to the present invention, by eliminating the gap between the electrodes which come into contact with a fluid and generate electrochemical noise,
Noise during flow rate measurement is reduced and stable flow rate measurement is possible.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional device.

[Explanation of Codes] 1 ... Piping, 2 ... Lining, 3 ... Coil, 4 ... Electrode, 5
... Spring, 6 ... Seal protrusion, 7 ... Spacer, 8 ... Cap nut, 9 ... Electrode tip, 10 ... Gap, 11 ... Insulating film.

Claims (1)

[Claims] 1. A conductive fluid flows and an alternating magnetic field is applied to a pipe having an insulating lining in a direction perpendicular to a pipe axis, and the pipe is arranged in a direction orthogonal to both the pipe axis and the magnetic field direction. An electrode of an electromagnetic flowmeter, characterized in that, in an electromagnetic flowmeter equipped with a pair of electrodes for detection, a portion of a liquid contact surface of the electrode which is not visible from a flow path is covered with an insulating coating.