JPH0541375Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a ceramic electromagnetic flowmeter having a measuring tube made of ceramics.

More specifically, the present invention relates to an improvement in the electrode portion of a ceramic electromagnetic flowmeter having a measuring tube made of ceramics.

(Prior Art) FIG. 4 is a diagram illustrating the configuration of a conventional example that has been commonly used.

In the figure, 1 is a cylindrical measuring tube made of ceramics. Reference numerals 21 and 22 are columnar cermet electrodes arranged opposite to the measuring tube 1 and formed by mixing conductive powder and firing the mixture together with the measuring tube 1.

(Problems to be solved by the invention) In such an electrode, the material of the conductive powder must be one that has a melting point higher than the firing temperature of the ceramic measuring tube and has high corrosion resistance. For example, alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ )
A suitable combination is mixing platinum (Pt) or palladium (Pd) with oxide ceramics such as oxide ceramics.

Next, the ratio of the conductive powder to be mixed is preferably as small as possible within a range that provides conductivity in terms of reliability of sealing performance and cost.
From the viewpoint of the sealing performance at the boundary between 22 and the measuring tube 1,
The lower the content of the conductive fine powder, the better. This is because the higher the content, the smaller the shrinkage rate during firing, and the greater the difference in shrinkage rate with the surrounding ceramic substrate, which reduces the reliability of the sealing. For this reason, the content should be as low as possible while still providing electrical conductivity.

That is, as shown in FIG. 5, the shrinkage of the measurement tube 1 made of ceramic material that occurs when the two are fired together is in the radial X direction of the electrodes 21 and 22 and in the axial direction Y of the electrodes 21 and 22. . Electrodes 21, 2
When the volume content of the conductive fine powder 2 is high, it hardly shrinks compared to the measurement tube 1 made of ceramic material. , tensile stress in the circumferential direction is generated due to contraction X. Since the firing of the ceramic proceeds under such stress, cracks are likely to occur at the boundaries, and these cracks form leak holes, making it impossible to ensure sufficient airtightness.

In addition, even if the crack does not reach the point where a leak hole is formed immediately after firing, stress remains in the boundary area, and after that, repeated stress that occurs during use, such as thermal shock, etc. leakage holes may be formed due to thermal expansion differences due to

The present invention solves this problem.

An object of the present invention is to provide a ceramic electromagnetic flowmeter that can ensure high reliability in terms of sealing performance while ensuring good conductivity of the electrode portion.

(Means for solving the problem) In order to achieve this object, the present invention provides a ceramic electromagnetic flowmeter in which a conductive substance is embedded and fired in the electrode part of a ceramic measuring tube through which a measuring fluid flows. The electrode portion includes a columnar electrode body made of ceramics mixed with a conductive material having a required volume content, and a conductive material provided in a concentric closed curve shape on the electrode body and having a volume content smaller than that of the electrode body mixed therein. The present invention is a ceramic electromagnetic flowmeter characterized by comprising a cylindrical buffer body made of ceramics.

(Function) In the above configuration, since the electrode body is made of ceramics mixed with a conductive substance having a required volume content, reliable conductivity can be ensured. Then,
Since a buffer body made of ceramics containing a conductive substance with a volume content smaller than that of the electrode body is provided around the electrode body, the volume content of the conductive substance at each boundary between the electrode body, buffer body, and measurement tube is reduced. The difference in rate becomes smaller, and the difference in the amount of shrinkage during firing can be reduced.

Hereinafter, a detailed explanation will be given based on examples.

(Embodiment) FIG. 1 is an explanatory view of the main part of an embodiment of the present invention, in which A is a front view and B is a plan view.

In the figure, the same symbols as in FIG. 4 indicate the same functions.

Hereinafter, only the differences from FIG. 4 will be explained.

In the figure, 3 is an electrode section. The electrode 3 consists of a columnar electrode body 31 and a buffer body 32. The electrode body 31 is made of ceramics mixed with a conductive material having a required volume content. In this case, it is made of oxide ceramics such as alumina (Al ₂ O ₃ ) or zirconia (ZrO ₂ ) mixed with a conductive material of platinum or palladium with a volume content of 50%. The buffer body 32 is provided in a concentric closed curve shape on the electrode body 31, and is made of ceramic mixed with a conductive substance having a smaller volume content than the electrode body 31, and has a cylindrical shape. In this case, the volume content is 20
% of platinum or palladium conductive material mixed therein.

In the above configuration, the electrode body 31 is made of ceramics mixed with a conductive material of platinum or palladium with a volume content of 50%. In general, the larger the volume content of the conductive material mixed in ceramics, the more likely a continuous layer of conductive material will be formed, and if the volume content is 20% or more, reliable conduction can be obtained. . Therefore, a volume content of 50% is sufficient, and the impedance in contact with the measurement fluid can also be lowered. Batsuhua body 32
is made of oxide ceramics mixed with a conductive material of platinum or palladium with a volume content of 20%, so the difference in shrinkage rate during firing is small, and cracks etc. between the measuring tube 1, buffer body 32 and electrode Main body 31
There is no risk of this occurring at the boundary between the two, and a ceramic electromagnetic flowmeter with high reliability in sealing performance and high impact resistance can be obtained.

FIG. 2 is an explanatory diagram of the configuration of another embodiment of the present invention.

In this embodiment, centering around the electrode body 31,
A first buffer layer 331 made of oxide ceramics such as alumina or zirconia mixed with a conductive material of platinum or palladium with a volume content of 40% in the outer diameter direction in a concentric manner, and on the outside thereof,
A second buffer layer 332 with a volume content of 30%, a third buffer layer 333 with a volume content of 20% on the outside thereof,
On the outside, a fourth buffer layer 3 with a volume content of 10%
The buffer body 33 is made up of 24 parts.

The buffer body 33 has first, second, third, and fourth buffer layers 331, 332, 333, and 334 whose volume content gradually decreases by 10%, and the electrode body 33 has a volume content that gradually decreases by 10%.
The difference in volume content between 1 and the first buffer layer 331 is 10
%, and the volume content of the fourth buffer layer 334 and the measuring tube 1 is 10%, so the difference in shrinkage rate during firing is small, and the electrode body 31 and the first buffer layer 33
1 and the boundary between the fourth buffer layer 334 and the measuring tube 1, there is no risk of cracks or the like occurring, and a ceramic electromagnetic flowmeter with high sealing performance and thermal shock resistance can be obtained.

Note that each buffer layer 331, 332, 333,
Of course, the volume content of 334 is not limited to 10%.

FIG. 3 is an explanatory diagram of another embodiment of the present invention.

In this embodiment, the ceramic concentration is gradually and continuously increased from the ceramic concentration of the electrode body 31 to the ceramic concentration of the measuring tube 1 in the direction from the inner diameter to the outer diameter of the buffer body 34.

In this way, there is no need to construct the buffer layer in stages as in the embodiment of FIG. 2, and the cost can be reduced, and differences in the volume content of the conductive material can be smoothly absorbed.

Although it has been explained that the electrode body 31 is made of ceramic mixed with a conductive substance having a volume content of 50%, the electrode body 31 is not limited to this, and may be any material that has conductivity and can ensure a low wetted impedance. Bye.

(Effects of the Invention) As explained above, the present invention provides a ceramic electromagnetic flowmeter in which a conductive material is embedded and fired in the electrode part of a ceramic measuring tube through which a measuring fluid flows, and in which the electrode part has a required volume. A columnar electrode body made of ceramics mixed with a conductive material having a volume content of 100%, and a cylindrical electrode body made of ceramics mixed with a conductive material with a volume content smaller than that of the electrode body provided in a concentric closed curve shape on the electrode body. Since the ceramic electromagnetic flowmeter is characterized in that it is equipped with a buffer body, the electrode body can have reliable conductivity and a low wetted impedance. On the other hand, the buffer body reduces the difference in the volume content of the conductive material at each boundary between the electrode body, the buffer body, and the measuring tube, and the difference in the volume content of the conductive material at each boundary between the electrode body, the buffer body, and the measuring tube is reduced, and the difference in the volume content of the conductive material at the boundary surface due to the difference in the amount of shrinkage during firing and the difference in the coefficient of thermal expansion when applying a heat shock is The occurrence of cracks can be prevented, and reliable sealing performance can be obtained.

As explained above, according to the present invention, it is possible to realize a ceramic electromagnetic flowmeter that can ensure high reliability in terms of sealing performance while ensuring good conductivity of the electrode portion.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of one embodiment of the present invention.
is a front view, B is a plan view, FIG. 2 is an explanatory diagram of the configuration of another embodiment of the present invention, A is a front view, B is a plan view,
FIG. 3 is an explanatory diagram of the configuration of another embodiment of the present invention;
The figure is an explanatory diagram of the configuration of a conventional example that has been generally used, and FIG. 5 is an explanatory diagram of the operation of FIG. 4. DESCRIPTION OF SYMBOLS 1... Measuring tube, 3... Electrode part, 31... Electrode body, 32, 33, 34... Buffer body, 331...
...first buffer layer, 332...second buffer layer,
333...Third buffer layer, 334...Fourth buffer layer.

Claims (1)

[Scope of utility model registration request] In a ceramic electromagnetic flowmeter in which a conductive substance is embedded and fired in an electrode part in a ceramic measurement tube through which a measuring fluid flows, the electrode part is a columnar structure made of ceramics mixed with a conductive substance with a required volume content. A ceramic electromagnetic flow rate comprising an electrode body and a cylindrical buffer body made of ceramics, which is provided in the shape of a concentric closed curve on the electrode body and mixed with a conductive substance having a volume content smaller than that of the electrode body. Total.