JPH0486523A - Electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To reduce the cost of a flowmeter by arranging the mutually opposed end surfaces of an inside electrode and an outside electrode in close vicinity to each other in a state holding the ceramics part constituting a pipe wall therebetween. CONSTITUTION:Coaxial bottomed holes having the same diameters are bored in the outer and inner peripheral surfaces of the wall of a measuring pipe 1 and the inner surfaces thereof are coated with metal film 4, 5 and outside and inside electrodes 2, 3 are inserted in the holes to be fixed thereto. Since the mutually opposed end surfaces of the electrodes 2, 3 are arranged in close vicinity to each other so as to hold the ceramics part being the insulating matter constituting the pipe wall therebetween, the electrodes 2, 3 function as one electrode electrically by electrostatic induction and, since the electrodes 2, 3 are inserted in the bottomed holes formed to the pipe wall and internally subjected to metal film treatment to be fixed thereto by soldering, a limit such that the electrode material withstands baking temp. and the coefficient of thermal expansion thereof is approximate to that of the ceramics becomes entirely unnecessary. Therefore, a material advantageous from the aspect of cost such as stainless steel can be used.

Description

[Detailed description of the invention] [Industrial application field]

This invention has excellent airtightness and high pressure resistance especially at the part where the electrode is inserted into the ceramic measuring tube, and the electrode is not limited to a platinum rod or the like! Regarding the magnetic current positioner.

[Conventional technology]

A conventional example will be explained with reference to FIG. 3, which is a cross-sectional view of the main part thereof. In addition, in FIG. 3, the illustration of the coil and core set as the magnetic field generating means is omitted, and only a pair of electrodes for extracting the electromotive force generated in response to the flow velocity of the fluid is shown. In FIG. 3, the measuring tube 8 is made of ceramics for corrosion resistance against fluids. Then, a pair of electrodes 9 made of a metal material are embedded and fired at opposing locations on the wall of the ceramic measuring tube 8, respectively.

[Problem to be solved by the invention]

As explained above, in the conventional technique, the pair of electrodes 9 are embedded and fired in opposing portions of the tube wall of the ceramic measuring tube 8, respectively. Therefore, if the coefficients of thermal expansion of the ceramic and the electrode material are not similar, the degree of thermal expansion between each member will differ due to the difference between the firing temperature and the operating temperature, resulting in a slight gap between the insertion parts. The airtightness there is impaired and the withstand pressure becomes low. Also, the electrode is approximately 1800°
The material must be able to withstand the firing temperature of C. Therefore, electrode materials are limited to platinum, tantalum, tungsten, and the like. By the way, the coefficient of linear expansion is ceramic nia, 6 Xl0-'/"C1 platinum: 8.9X 1
0-' C, tantalum: 6.6 Xl0-' C, tungsten: 6-7 Since the coefficient is 16.4 x 10-h/''C, which is different from that of ceramics, the dimensions must be determined by fully considering the interference from the degree of thermal expansion due to the difference between the firing temperature and the operating temperature. Even so, there is a risk that the airtightness at the insertion portion may be impaired due to variations in manufacturing conditions or usage conditions. The object of this invention is to solve the above-mentioned problems of the conventional technology, to provide excellent airtightness and high pressure resistance at the part where the electrode is inserted into the ceramic measuring tube, and to eliminate the need for electrodes to be limited to platinum rods. The object of the present invention is to provide an electromagnetic flowmeter that can reduce costs.

[Means to solve the problem]

In order to solve this problem, the electromagnetic flowmeter according to the present invention applies an electromotive force corresponding to the flow velocity of the fluid to be measured to the wall of the ceramic measurement tube through which the fluid to be measured flows, at opposing points on the diameter thereof. In a flowmeter in which a pair of electrodes are inserted for extraction, each of the electrodes includes an outer electrode of a metal rod inserted into the tube wall from the outer circumferential side thereof, and an outer electrode of a metal rod inserted into the tube wall from the inner circumferential side thereof. It consists of an inner electrode of a metal rod that is inserted and has the same axis and the same cross-sectional shape as the outer electrode, and the opposing end surfaces of the inner electrode and the outer electrode sandwich the ceramic part that constitutes the tube wall. placed in close proximity. Note that each electrode can be fitted into a bottomed hole formed in the tube wall and whose inner surface is treated with a metal coating, and fixed by brazing.

[Effect]

Since the opposing end surfaces of the inner and outer electrodes are placed close to each other with the ceramic part that makes up the tube wall in between, the inner and outer electrodes are electrically connected as one electrode due to electrostatic induction. Moreover, the insertion part has excellent airtightness and high pressure resistance. In addition, each electrode can be inserted into a bottomed hole formed in the tube wall and whose inner surface is treated with a metal coating, and fixed by brazing, so that the electrode material can withstand the firing temperature and have a low coefficient of thermal expansion. Restrictions such as approximation to those of ceramics become unnecessary.

【Example】

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of the main parts of this embodiment. In the figure, reference numeral 1 denotes a ceramic measurement tube that has corrosion resistance against the fluid to be measured flowing through it. Reference numeral 2 denotes an outer electrode, and 3 an inner electrode, each of which is a cylindrical member made of stainless steel and inserted into the tube wall, and a set of these constitutes one electrode. This pair of electrodes is inserted into the measurement tube 1 at diametrically opposed locations, and the electromotive force generated according to the flow velocity is extracted. Note that the illustration of a coil and core set as a magnetic field generating means is omitted. FIG. 2 is a sectional view of the electrode insertion portion of this embodiment. In the figure, holes with coaxial and same diameter bottoms are drilled in the wall of the measuring tube 1 from the outer circumferential side and the inner circumferential side, and the inner surfaces of each are coated with metal coatings 4 and 5. outer electrode 2.
After inserting the inner electrode 3, it is fixed by brazing. Here, usually the outer electrode 2. The common diameter of the inner electrode 3 is 1 to 5
m, the facing distance between the bottoms of the bottomed holes on the outer peripheral surface side and the inner peripheral surface side is designed to be 10 to 100 μm. Outer electrode 2. Since the opposing end surfaces of the inner electrodes 3 are arranged close to each other with the ceramic part as an insulator constituting the tube wall sandwiched between them, the outer electrodes 2 and the inner electrodes 3 are
Electrically functions as an electrode due to electrostatic induction,
Moreover, the insertion part has excellent airtightness and high pressure resistance. In addition, the outer electrode 2. The inner electrodes 3 are fitted into bottomed holes formed in each tube wall and whose inner surfaces are treated with a metal coating, and are fixed by brazing, so that the electrode material can withstand the firing temperature and has a thermal expansion coefficient similar to that of ceramics. Restrictions such as approximation are completely unnecessary. Therefore, instead of noble metals such as platinum, tantalum, and tungsten used in the conventional example, cost-effective materials such as stainless steel can be used as in this embodiment.

【Effect of the invention】

According to this invention, there are the following superior effects compared to the conventional technology. (1) Since the insertion holes for the inner and outer electrodes are completely separated via the ceramic portion of the tube wall, the electrode insertion portion has excellent airtightness and high pressure resistance. (2) Since the inner electrode and the outer electrode electrically function as one electrode due to electrostatic induction, measurement accuracy is high and stable. (3) According to the embodiment, each electrode is inserted into a bottomed hole formed in the tube wall and whose inner surface is treated with a metal coating, and can be fixed by brazing, so that the electrode material can withstand the firing temperature and There is no need to limit the expansion coefficient to be similar to that of ceramics, and low-cost materials such as stainless steel can be used, reducing the cost of the flowmeter.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part of an embodiment according to the present invention, FIG. 2 is a sectional view of an electrode insertion part of this embodiment, and FIG. 3 is a sectional view of a main part of a conventional example. Symbol explanation 1: Measuring tube, 2: Outer electrode, 3: Inner electrode, 9F side 1ya Figure 2

Claims (1)

[Claims] 1) A pair of electrodes for extracting an electromotive force corresponding to the flow velocity of the fluid to be measured are inserted into the wall of the ceramic measuring tube through which the fluid to be measured flows, at opposing points on the diameter thereof. In the flowmeter, each of the electrodes includes an outer electrode of a metal rod that is inserted into the tube wall from the outer circumference side thereof, and an outer electrode that is inserted into the tube wall from the inner circumference side. It consists of an inner electrode of a metal rod having the same axis and the same cross-sectional shape, and the opposing end surfaces of the inner electrode and the outer electrode are arranged close to each other so as to sandwich the ceramic portion constituting the tube wall. Electromagnetic flow meter. 2) In the flowmeter according to claim 1, each electrode is fitted into a bottomed hole formed in the tube wall and whose inner surface is treated with a metal coating, and is fixed by brazing. Electromagnetic flowmeter.