JPH0380248B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a measuring tube for an electromagnetic flowmeter using ceramic material.

[Conventional technology]

Conventionally, in measuring tubes for electromagnetic flowmeters of this type, electrodes made of metal or conductive ceramic are inserted into electrode mounting holes in the ceramic tube.
A structure made by firing a ceramic tube and electrodes is used.

[Problem to be solved by the invention] However, in the former case, that is, one in which metal is used for the electrode, the metal has durability against the firing temperature of ceramic, and its coefficient of thermal expansion approximates that of ceramic. Therefore, there was a problem in that usable metals were limited to expensive metals such as platinum.

Therefore, in order to manufacture measurement tubes for electromagnetic flowmeters economically, it is possible to reduce the outer diameter of the electrodes, but in this case, the input impedance will be high when viewed from the converter side for electromagnetic flowmeters, and the This has the disadvantage that its performance is adversely affected during use.

On the other hand, the latter, that is, those in which conductive ceramic is used for the electrode, has a performance problem similar to the case described above because its conductivity is inferior to that of ordinary metals, although this differs somewhat depending on the composition.

[Means for solving problems]

The measurement tube for an electromagnetic flowmeter according to the present invention includes an unfired or semi-fired ceramic tube having an electrode attachment hole, and a metal tube inserted into the electrode attachment hole of the ceramic tube and provided on the inner peripheral surface and insertion end. It is made by firing an electrode formed of a ceramic cylinder having a conductive part.

Further, a measurement tube for an electromagnetic flowmeter according to another aspect of the present invention includes an unfired or semi-fired ceramic tube having an electrode attachment hole, and an inner peripheral surface of the ceramic tube that is fitted into the electrode attachment hole of the ceramic tube. It is made by firing an electrode formed of a ceramic tube having a metal conductive part at the insertion end, and a metal conductive member that is electrically connected to the conductive part is attached to the insertion side of the electrode.

The present invention was developed in view of the above circumstances, and it is possible to easily and reliably seal between an electrode and an electrode mounting hole, reduce costs, and improve performance when using a meter. To provide a measurement tube for an electromagnetic flowmeter that does not have an adverse effect on the flowmeter.

[Effect]

In the present invention, the ceramic tube is made by firing an unfired or semi-fired ceramic tube having an electrode attachment hole and an electrode formed of a ceramic tube that is fitted into the electrode attachment hole of the ceramic tube. The amount of shrinkage becomes larger than the amount of shrinkage of the electrode. Further, since the electrode is formed of a ceramic cylinder having a metal conductive portion on its inner circumferential surface and insertion end, the electrode diameter can be increased even if less metal is used.

Further, in another aspect of the present invention, since a metal conductive member electrically connected to the conductive portion is attached to the insertion end of the electrode, this conductive member is exposed inside the tube.

〔Example〕

FIG. 1 is a sectional view showing an embodiment of a measuring tube for an electromagnetic flowmeter according to the present invention. In the figure, the reference numeral 1 denotes a measurement tube for an electromagnetic flowmeter, which includes an unfired or semi-fired ceramic tube 3 having an electrode attachment hole 2 in the center in the axial direction, and
An electrode 6 formed of a fired ceramic cylinder 4 which is fitted into the electrode mounting hole 2 and has a metal conductive part 5 on its inner circumferential surface 4a and insertion end 4b is fired. The clamping pressure is maintained by piping (not shown). A signal lead wire 7 is connected to a terminal on a terminal board (not shown), and is soldered to the side of the conductive section 5 opposite to the fluid to be measured. The metal used for the conductive portion 5 is preferably a high melting point metal such as platinum or platinum-iridium alloy, which has a melting point higher than the ceramic firing temperature (1000 to 1600° C.) used in manufacturing the measuring tube.

The measurement tube for an electromagnetic flowmeter constructed in this manner includes an unfired or semi-fired ceramic tube 3 having an electrode attachment hole 2, and a fired ceramic tube fitted into the electrode attachment hole 2 of the ceramic tube 3. Since the formed electrode 6 is fired, the shrinkage margin of the ceramic tube 3 is larger than that of the electrode 6. Further, since the electrode 6 is formed of the ceramic cylinder 4 having a metal conductive portion 5 on its inner circumferential surface 4a and insertion end 4b, the electrode diameter can be increased even if less metal is used.

In this embodiment, an example is shown in which the fired ceramic tube 4 is used for the electrode 6, but the present invention may use a semi-fired ceramic tube as long as it has a relatively small shrinkage margin. That is, it is sufficient to use a combination of ceramic cylinders whose semi-firing temperature is higher than that of the ceramic tube 3.

Next, a method of manufacturing the electromagnetic flowmeter measuring tube 1 having the above-described configuration will be described.

First, platinum paste is applied to the inner circumferential surface 4a and insertion end 4b of the fired ceramic cylinder 4, and the heating temperature is
The electrode 6 is formed by baking at 800 to 1600°C. At this time, the opening of the ceramic cylinder 4 on the electrode insertion side is closed with platinum. Next, after inserting this electrode 6 into the electrode mounting hole 2 of the unfired or semi-fired ceramic tube 3, the firing temperature is set at 1000 to 1600°C.
Fire it with

In this way, the electromagnetic flowmeter measurement tube 1 equipped with the electrode 6 can be manufactured reliably.

In the method of manufacturing the measuring tube 1 for an electromagnetic flowmeter according to this embodiment, the electrode 6 is first formed, and then the electrode 6 is inserted into the electrode mounting hole 2 of the unfired or semi-fired ceramic tube 3 and then fired. However, in the present invention, the fired ceramic cylinder 4 for the electrode is inserted into the electrode mounting hole 2.
After inserting them into the ceramic cylinder 4 and firing them,
The electrode 6 may be formed by applying platinum paste to the inner circumferential surface 4a and insertion end 4b of the electrode and baking it. In this case, a material having a melting point lower than that of platinum can be selected as the metal used for the conductive portion 5, and the material cost can be reduced.

In another aspect of the present invention, as shown in FIG. 2 or 3, a conductive chip 12 made of platinum-iridium alloy is electrically connected to the conductive parts 10 and 11 on the insertion side of the electrodes 8 and 9. Alternatively, since the conductive cap 13 is attached, the conductive chip 12 or the conductive cap 13 is exposed inside the pipe. In this case, the conductive chip 12 or conductive cap 13 is attached before firing the electrodes 8, 9 and the ceramic tube (not shown).

Further, in this embodiment, only the opening on the electrode insertion side of the ceramic cylinder 4 is closed with the conductive part 5 as the electrode 6, but the present invention is not limited to this. As shown in FIG. 5, platinum may be used as an electrode 16 that closes not only the opening of the ceramic cylinder 14 but also the inside thereof with a conductive part 15. In this case, as shown in FIG.
The connection is made directly during the formation of the conductive portion 15 or via a platinum terminal 18 shown in FIG.

Furthermore, since the ceramic cylinder 4 of the present invention can be easily subjected to various processes, in addition to the above-mentioned embodiments, for example, as shown in FIG. The electrode 19 is formed in a stepped manner, and the electrode 20 has a locking portion 20a inside to securely lock a lead wire (not shown in FIG. 8) as shown in FIG. The shape can be changed freely. Here the seventh
In the figure, 21 is a conductive chip attached to the insertion side of the electrode 19 by brazing or press-fitting.

〔Effect of the invention〕

As explained above, according to the present invention, an unfired or semi-fired ceramic tube having an electrode mounting hole and an electrode formed of a ceramic tube fitted into the electrode mounting hole of the ceramic tube are fired. Therefore, the shrinkage margin of the ceramic tube is larger than that of the electrode, making it possible to securely fix the electrode to the ceramic tube and easily and reliably seal between the electrode and the electrode mounting hole. Moreover, since the coefficient of thermal expansion of the electrode and the coefficient of thermal expansion of the ceramic tube are substantially the same, the sealing performance will not deteriorate even if there is a temperature change. Further, since the electrode is formed of a ceramic cylinder having a metal conductive portion on its inner circumferential surface and insertion end, the electrode diameter can be increased even if less metal is used. Therefore, the cost can be reduced, and the performance of the meter is not adversely affected when it is used, unlike the conventional method.

Another aspect of the present invention is that a metal conductive member that is electrically connected to the conductive part is attached to the insertion side of the electrode, so this conductive member is exposed inside the tube, which reduces the wear resistance of the electrode. can be increased.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of a measuring tube for an electromagnetic flowmeter according to the present invention, FIGS. 2, 3, and 4.
The figure is a sectional view showing an electrode in another embodiment.
6 and 6 are sectional views and front views for explaining the state of connection of lead wires to electrodes, and FIGS. 7 and 8 are sectional views showing electrodes in other embodiments. 1... Measuring tube for electromagnetic flowmeter, 2... Hole for electrode attachment, 3... Ceramic tube, 4... Ceramic tube,
4a...inner peripheral surface, 4b...insertion end, 5...conductive part, 6...electrode.

Claims (1)

[Scope of Claims] 1. An unfired or semi-fired ceramic tube having an electrode attachment hole in the central part in the axial direction, and a metal tube inserted into the electrode attachment hole of the ceramic tube on its inner peripheral surface and insertion end. A measuring tube for an electromagnetic flowmeter made by firing an electrode formed of a ceramic cylinder having a conductive part. 2. An unfired or semi-fired ceramic tube having an electrode attachment hole in the center in the axial direction, and a ceramic tube that is fitted into the electrode attachment hole of the ceramic tube and has a metal conductive part on its inner peripheral surface and insertion end. 1. A measuring tube for an electromagnetic flowmeter, characterized in that a metal conductive member electrically connected to the conductive portion is attached to the insertion side of the electrode.