JPH0537208Y2 - - 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 an electromagnetic flowmeter.

(Prior Art) FIG. 2 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 11 and 12 denote columnar cermet electrodes 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 (Z _r O ₂ )
A suitable combination is mixing platinum (Pt) or palladium (Pd) with oxide ceramics such as oxide ceramics.

Next, the proportion of the conductive powder to be mixed is preferably as small as possible within the range that provides conductivity from the viewpoint of reliability of sealing performance and cost. electrode part 11,
From the sealing performance at the boundary between 12 and 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 larger the difference in shrinkage rate with the surrounding base ceramics, reducing the reliability of sealing performance. Therefore, the content should be as low as possible within the range that provides conductivity.

Furthermore, from the viewpoint of cost, the smaller the amount, the better, especially when using expensive metal powders such as platinum and palladium.

On the other hand, the resistance of the liquid-contacted part becomes smaller as the volume content of the conductive powder is higher. This is because the contact resistance becomes smaller as the contact area between the conductive fine powder and the measurement fluid increases.

When the wetted impedance increases, the following problems occur in terms of performance.

In FIG. 2, e _o is the external induced voltage, Z _s is the signal source impedance, and Z _o is the impedance between the induction source and the signal line. Here, the cermet electrode 1
The resistance within 1 and 12 is sufficiently small and can be ignored because conductivity is obtained by forming a continuous phase of a conductive substance. (Almost the same as the conductivity of conductive substances).

The output voltage e due to induction from the detector is e = Z _s / Z _s + Z _o e _o , and the larger the signal source impedance Z _s is,
This means that it is easily influenced by induction. The signal source impedance Z _s is the sum of the impedance of the measurement liquid and the wetted impedance. Therefore, as the wetted impedance increases, the signal source impedance _Zs increases.

As a result of the above, the content of conductive fine powder is kept as low as possible in the parts that do not come in contact with liquid to ensure high airtightness, and the part that comes into contact with liquid is made to have a high content to reduce the contact resistance and improve noise resistance. It is desirable to ensure that

The present invention focuses on this point.

An object of the present invention is to provide a ceramic electromagnetic flowmeter in which the impedance of electrode portions in contact with liquid is reduced, and which is low-cost and highly reliable.

(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 ceramic electromagnetic flowmeter is characterized in that a part of the electrode part in contact with the liquid is made of a highly concentrated conductive material, and another part of the electrode part is made of a low concentration conductive material. .

(Function) In the above configuration, since the liquid contact portion of the electrode portion has high conductivity, the liquid contact impedance to the measurement fluid can be lowered, and noise resistance can be improved. At the same time, since the other parts of the electrode part have a low concentration of conductive material and have the same shrinkage rate during firing as the measurement tube, sealability can also be ensured.

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

(Embodiment) FIG. 1 is an explanatory diagram of the main part configuration of an embodiment of the present invention.

In the figure, the same symbols as in FIG. 2 indicate the same functions.

Hereinafter, only the differences from FIG. 2 will be explained.

In the figure, 2 is an electrode. Reference numeral 21 denotes a main body portion of the electrode in which platinum or palladium powder is mixed with ceramic material to the extent necessary to provide electrical conductivity.
Here, the example has a 20% volume content of platinum. Reference numeral 22 denotes a part of the electrode part 2 in which the content of platinum or palladium metal powder is increased so as to lower the impedance in contact with the liquid to be measured. Here, for example, the volume content of platinum is 50%.

In the device configured in this way, the impedance of the liquid contacting portion 22 can be lowered and the noise resistance can be improved. On the other hand, the main body part 21
Since the metal volume content is low while ensuring electrical conductivity, the cost can be reduced and high reliability can be ensured in terms of sealing performance.

(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 measurement tube through which a measuring fluid flows, and the liquid contact part of the electrode part is A ceramic electromagnetic flowmeter is constructed in which the electrode part is made of a conductive material with a high concentration, and the other part of the electrode part is made with a conductive material with a low concentration. It is possible to improve the noise resistance, ensure conductivity in other parts of the electrode and function as a lead, and achieve high reliability in terms of sealing performance, as well as ensure low cost.

Therefore, according to the present invention, it is possible to realize a ceramic electromagnetic flowmeter in which the impedance of the electrode portion in contact with liquid can be lowered, and the sealing performance can be highly reliable and the cost can be reduced.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the main part configuration of an embodiment of the present invention,
FIG. 2 is an explanatory diagram of the configuration of a conventional example that has been generally used, and FIG. 3 is an explanatory diagram of FIG. 2. 1... Measuring tube, 2... Electrode, 21... Main body part, 22... Liquid contact part.

Claims (1)

[Scope of utility model registration request] In a ceramic electromagnetic flowmeter in which a conductive material is embedded and fired in the electrode part of a ceramic measuring tube through which the measuring fluid flows, the liquid contact part of the electrode part is made of a highly concentrated conductive material with a groove formed in the electrode part. A ceramic electromagnetic flowmeter characterized in that the other parts are made of a low concentration conductive material.