JPH0312693B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a water level detection element that has high reliability and excellent responsiveness even under high temperature and high pressure conditions, and has high strength and long life when detecting the water level of various conductive aqueous solutions. Conventionally, water level detection elements have been widely known, which include an electrode and an insulating material that holds the electrode, and which detect the water level based on the presence or absence of conduction due to contact between the electrode and the water surface. There are known types that have a ferrite electrode or a stainless steel rod-shaped electrode covered with plastic. However, in such conventional elements, under high temperature and high pressure conditions, the strength of the insulating material and the insulation material decrease, and the adhesive strength between the insulating material and the electrode decreases, making it difficult to maintain sufficient airtightness between them. It was something that could not be maintained. The present invention was made to eliminate the drawbacks of such conventional elements, and makes it possible to detect water levels with good response and reliability over a long period of time even under high temperature and high pressure conditions. This is its purpose. In order to achieve such an object, the present invention provides a water level detection system that includes an electrode and an insulating material that holds the electrode, and detects the water level based on the presence or absence of electrical continuity caused by contact between the electrode and the water surface. In the element, the insulating material has a solid rod shape or a cylindrical shape having a hollow portion blocked by at least one airtight wall, and has a stepped portion in the circumferential direction at a predetermined portion of the outer surface. It is made of an electrically insulating ceramic body, and the electrode is composed of a film-like electrode formed on the surface of the electrically insulating ceramic body, and is further connected to a predetermined external circuit device. For electrical connection, a terminal portion formed on the surface of the electrically insulating ceramic body and an electrically connected terminal portion that penetrates through the electrically insulating ceramic body to electrically connect the terminal portion and the electrode. It is constructed to include a cermet conductor path formed by simultaneous integral firing with an electrically insulating ceramic body. By the way, as the material constituting the electrically insulating ceramic body in the present invention, a ceramic material that has excellent mechanical strength, airtightness, electrical insulation, water resistance, etc. as a holding material even under high temperature and high pressure conditions is used. For example, heat-resistant and water-resistant ceramic materials such as alumina porcelain, zirconia porcelain, silicon nitride porcelain, mullite porcelain, beryllia porcelain, and cordierite porcelain are preferably used. Electrically insulating ceramic bodies formed using such ceramic materials have high strength, high airtight reliability under high temperature and high pressure conditions, and
It has a solid rod shape or a cylindrical shape with a hollow part blocked by at least one airtight wall, and has a step part (offset part) in a predetermined part of its outer surface in the circumferential direction. More specifically, for example, in addition to a round bar shape with a rounded tip or a test tube shape, a hollow cylindrical shape with a middle section airtightly partitioned by a wall, a hollow body shape with both ends closed, etc. The outer surface thereof has a stepped portion projecting outward or recessing inward at a predetermined position in the circumferential direction. Note that this stepped portion serves as a sealing portion to airtightly seal between the water level detection surface of the electrically insulating ceramic body and other surfaces, and is also used in cases where the water level detection element is not placed in an airtight container with a high pressure inside. This is essential to prevent the element from falling off due to internal pressure when fixed to a wall. Further, in the present invention, an electrode formed on the surface of an electrically insulating ceramic body having a predetermined shape as an insulating material is an electrode that is exposed on the surface of the electrically insulating ceramic body and brought into contact with an aqueous solution whose water level is to be detected. It is a conductive part, and is a film-like electrode formed by applying a conductive paste on an electrically insulating ceramic body, baking it, electroless plating, vapor deposition, sputtering, etc. The thickness of such an electrode is generally preferably about 0.1 to 50 μm, and it is also desirable that it be in close contact with the electrically insulating ceramic body. In order to improve this adhesion, the film-like electrode is composed of a cermet formed integrally with the electrically insulating ceramic body by simultaneous firing with the conductor path passing through the electrically insulating ceramic body. It is desirable to do so. In addition, the electrode material for forming such an electrode should be one that maintains adhesion to the electrically insulating ceramic body for a long period of time and does not lose its conductivity even when a positive voltage is applied in a corrosive electrolyte aqueous solution. A material that is water resistant, oxidation resistant, or electrically conductive even when oxidized is preferable, and a corrosion resistant material whose main component is platinum, rhodium, palladium, ruthenium, gold, or an alloy containing at least one of these. It is preferable to use this material. Furthermore, in the present invention, in order to electrically connect the electrode formed on the surface of the electrically insulating ceramic body to a predetermined external circuit device, in other words, an electric circuit device for water level detection, It is necessary to provide a terminal section to which lead wires, etc. for extracting electrical signals to the outside are connected, on a surface that is airtightly isolated from the water level detection side (aqueous solution contact side) of the insulating ceramic body. The terminal portion and the electrode must be connected by a conductor path that passes through the electrically insulating ceramic body in an airtight manner. Moreover, this conductor path needs to be composed of cermet formed by co-firing with an electrically insulating ceramic body, which ensures the airtightness of the element for a long time even under severe high pressure and thermal cycle conditions. It can be held for a long time. It is preferable that such conductor paths and terminal parts are integrally formed of the same material as the electrode material, but the use of the same material as the electrode material is not in any way limited. For example, it is possible to form conductor paths and terminal portions using materials such as tungsten, molybdenum, and copper for platinum electrodes. In order to form a conductor path that passes through the electrically insulating ceramic body in an airtight manner, at least one through hole is provided in the green molded or calcined body of the electrically insulating ceramic body, and a conductive paste is applied to the through hole. A method in which a conductive paste (cermet) is applied around the through hole, and then embedded with an electrically insulating ceramic paste or a molded body and fired; A method in which the electrically insulating ceramic body is filled with A method in which a part of the electrically insulating ceramic body is molded with cermet and fired to form a conductor path; or, a conductor path is screen printed on a piece of a divided electrically insulating ceramic body, and this part is connected to the interior. Among these methods, a method of integrally firing such a conductive path with an electrically insulating ceramic body is preferably employed. In forming such a conductor path, it is desirable to simultaneously form the intended terminal portion so that a portion of the conductor path becomes a terminal portion, but it is also desirable to separately form a terminal portion similar to the conductor path or electrode. Needless to say, it is possible to form the terminal portion even if using a similar material. The electrically insulating ceramic body of the present invention must be water repellent or have impurities in an aqueous solution to which it is difficult to adhere, in order to prevent malfunctions in water level detection due to electrical conduction through water adsorbed to impurities attached to the surface. It is preferable that the electrically insulating ceramic body has a smooth surface, and in order to improve the airtightness of the seal, it is preferable that the stepped portion of the electrically insulating ceramic body have a smooth surface. It is desirable to smooth the surface by coating it with glass or plastic.
Of course, such a coating with glass or plastic can damage the surface of such an electrically insulating ceramic body.
It is applied to at least a part of the outer surface other than the part where the electrode is formed, and generally, excluding the electrode part, the surface of the electrically insulating ceramic body from the electrode part to the stepped part is coated. It is desirable to do so. Some examples will be shown below together with drawings to further clarify the present invention, but it goes without saying that the present invention is not to be construed in any way limited by the description of these examples. It's a good place. Example 1 As shown in Fig. 1, an electrically insulating ceramic body 2 having a bottomed cylindrical shape (test tube shape) is formed from an alumina porcelain green molded body, and a 0.8 mm
A through hole 4 of φ is opened, the tip thereof is immersed in a platinum-alumina paste with a platinum:alumina volume ratio of 50:50, and the outer peripheral surface of the closed end side of the ceramic body 2 is spread over a predetermined range. Covering membrane electrode 6
, a terminal portion 8 that covers the inner circumferential surface of the closed end of the ceramic body 2 with a predetermined width, and a conductor path 10 that connects these electrodes 6 and the terminal portion 8 and covers the inner circumferential surface of the through hole 4.
were integrally formed at the same time. Next, after drying the ceramic body 2 on which the electrode 6, the terminal portion 8, and the conductor path 10 are formed, the through hole 4, which has been made finer due to the formation of the conductor path 10, is filled with
Alumina porcelain paste, which is an electrically insulating ceramic material, is embedded to form an airtight plug part 14, and after drying, it is placed in the atmosphere.
By integrally firing at 1500°C, a water level detection element according to the present invention was obtained. In addition, a flange portion 12 as a stepped portion is provided in the circumferential direction on the outer circumferential surface of the ceramic body 2 in the vicinity of the opening-side end thereof, and protrudes laterally. By attaching the ceramic body 2 to the holding member via the electrically insulating ceramic body 2, the outer circumferential surface and the inner circumferential surface of the electrically insulating ceramic body 2 are partitioned off. Next, using the water level detection element obtained in this way, it was connected as shown in Fig. 2, and 95
Water level detection was performed using tap water at ℃. In other words, the voltage of 12V of the DC power supply 16 is 50KΩ.
The voltage was divided by voltage dividing resistors 18 and 20 of 1 MΩ and applied to the terminal portion 8 of the water level detection element 24 via the lead wire 22. The potential of the terminal portion 8 is such that the electrode 6 is at the water surface 26.
When in contact, the voltage was 3.2V, and when not in contact, the voltage was 11.5V, and the response speed was less than 80msec. Further, the current flowing through the lead wire 22 at the time of contact with the water surface was 180 μA. In addition, in addition to the water level detection element according to the present invention shown in FIG. 1, a conventional water level detection element made of stainless steel as shown in FIG. Place the electrode in a sealed container and immerse it in tap water at 130℃ under a pressure of 2Kg/ ^cm2 .
Continuous energization was performed for 1000 hours. The applied voltage is +
A voltage of 12 V was applied to the terminal portion 8 of each detection element, and a stainless steel container was used as a counter electrode. 100 hours,
After continuous energization for 300 hours and 1000 hours, the insulation properties and airtightness of the insulating material of each water level detection element were evaluated, and the results are shown in Table 1 below. The insulation properties are evaluated by the ratio of the number of defective elements with insulation resistance of 10MΩ or less to the total number of elements, and the airtightness is evaluated by the ratio of the number of defective elements with insulation resistance of 10MΩ or ^less to the total number of elements.
Evaluation was made based on the ratio of the number of elements with poor airtightness of 2 m/min or more to the total number of elements. As is clear from the results in Table 1, the conventional water level detection element produced a large number of insulation failure elements after being energized for less than 300 hours, and all of them had poor airtightness, whereas the water level detection element according to the present invention The detection element is 1000
It was able to withstand electricity for hours, demonstrating its high reliability under high temperature and high pressure conditions.

[Table] Example 2 In the water level detection element according to the present invention shown in FIG. By spraying CaO-BaO-SiO ₂ -Al ₂ O ₃ -ZrO ₂ glass paste to a thickness of approximately 60 μm on the entire circumferential surface of the ceramic body 2, and firing it at 1300°C in the atmosphere, A glass-coated water level detection element was obtained. Next, this glass-coated element and the uncoated element of Example 1 were immersed in 100°C engine cooling water.
After 300 hours, 1000 hours, and 3000 hours, the surface resistance of the alumina or glass of each element was measured. Elements with a surface resistance value of 10 MΩ/□ or less were defined as poor insulation elements, and the ratio of the poor insulation elements to the total number of elements is shown in Table 2. From the results in Table 2, the uncoated element is 3000
By this time, most of the elements had poor insulation due to surface contamination, but with glass-coated elements, even after 3000 hours, only a small number of elements had poor insulation, indicating that the elements are particularly resistant to surface contamination. be.

[Table] Example 3 As shown in Fig. 4, an electrically insulating ceramic body 2 made of a round bar-shaped alumina porcelain green molded body was calcined at 1250°C in the atmosphere, and then a hole was inserted into the through hole 4 at its center. , a tungsten-alumina paste having a tungsten:alumina capacity ratio of 55:45 is filled to form a conductor path 10, and a terminal portion 8 is formed at one end of the solid molded body (2) using tungsten paste; After drying, this was fired at 1500°C in a reducing atmosphere. Next, an electrode 6 made of various materials shown in the first column of Table 3 below is formed on one end of the electrically insulating ceramic body 2 opposite to the side on which the terminal portion 8 is provided by a sputtering method. As a result, the desired water level detection element was obtained. Note that this water level detection element is different from the previous example.
A groove 34 as a stepped portion is provided on the outer circumferential surface of the end where the terminal portion 8 is provided, and by being attached via this groove 34, the electrode of the electrically insulating ceramic body 2 The outer surface on the side where the terminal portion 6 is provided and the outer surface on the side where the terminal portion 8 is provided can be airtightly partitioned. The thus obtained water level detection elements according to the present invention were connected as shown in FIG. 2, and were continuously energized for 1000 hours in engine cooling water at 100°C. The applied voltage was +12 V, and the current density was 8 μA/mm ² . The second column of Table 3 shows the ratio of the number of elements that abnormally increased in electrode resistance and failed to conduct properly before the energization time reached 1000 hours, to the total number of elements.

[Table] As shown in Table 3, it is clear that the water level detection elements of the present invention using various film-like electrode materials all have excellent water resistance and corrosion resistance. Example 4 As shown in FIG. 5, alumina powder and a mixed powder having a tungsten:alumina volume ratio of 50:50 were used to form a bottomed cylinder with the latter localized at the tip. An electrically insulating ceramic body 2 consisting of a shaped alumina porcelain green molded body was formed, and this was fired at 1500° C. in a reducing atmosphere. By this firing, the conductor path 10 is formed of tungsten localized at the tip of the electrically insulating ceramic body 2. Then, on the outer surface of the electrically insulating ceramic body 2 on which the conductor path 10 is formed, an electrode 6 is formed by electroless plating of gold, and on the inside thereof, a terminal portion 8 is formed by electroless plating of nickel. was formed and used as the desired water level detection element. Although the present invention has been specifically described above based on several embodiments, the present invention may include various changes, modifications, improvements, etc. based on the knowledge of those skilled in the art without departing from the spirit thereof. It goes without saying that the present invention includes such embodiments. Further, the water level detection element according to the present invention as described above is used, for example, in an embodiment as shown in FIG. That is, the water level detection element 24 according to the present invention has a housing 4 as a holding member.
0, and is attached to the mounting wall 42 by screwing or the like. The housing 40 includes a cylindrical element cover part 44, and a water level detection element 2 is mounted inside the element cover part 44.
4 on the electrode 6 side is inserted and arranged,
The electrode 6 is brought into contact with the aqueous solution that enters through the water hole 46 provided in the element cover 44. Further, the water level detection element 24 housed in the housing 40 has a disc spring 4 attached to its opening end.
8. By arranging the crimping ring 50 and crimping the end of the housing 40, the disc spring 48 is biased, and this biasing action causes the water level detection element 24 to move toward the element cover portion 44 side. Due to this pressing action, the flange portion 12 as a stepped portion of the water level detection element 24 is sealed against the stopper portion 52 provided protruding from the inner peripheral surface of the housing 40. By abutting through the ring 54, both sides of the flange portion 12 are airtightly sealed. That is, the electrode 6 provided on the outer surface of the closed end side of the water level detection element 24 and the terminal portion 8 (not shown) provided on the inner surface of the water level detection element 24 are airtightly partitioned. . An appropriate lead portion is connected to the terminal portion 8 provided on the inner surface of the water level detection element 24 for electrical connection to an external circuit device, such as a lead wire. A method such as connecting the terminal to the terminal portion 8 will be adopted. As is clear from the above description, the water level detection element of the present invention uses an electrically insulating ceramic body and a film-like electrode formed on the electrically insulating ceramic body, The electrode is electrically connected to a predetermined terminal portion through a conductor path made of an integral cermet co-fired with the electrically insulating ceramic body, which passes through the electrically insulating ceramic body in an airtight manner. It is possible to detect the water level of various conductive aqueous solutions with good responsiveness and reliability over a long period of time even under high temperature and high pressure conditions. It is useful for detecting water levels, etc., and therein lies the great industrial significance of the water level detection element according to the present invention.

[Brief explanation of the drawing]

1, 4, and 5 are cutaway front views of main parts showing one specific example of the water level detection element according to the present invention, and FIG. 2 is a water level detection circuit using the water level detection element of the present invention. FIG. 3 is an explanatory diagram showing an example, and FIG. 3 is an external view of a specific example of a conventional water level detection element, and FIG. It is a front view. 2... Electrically insulating ceramic body, 4... Through hole, 6... Electrode, 8... Terminal section, 10... Conductor path, 12... Flange section, 14... Airtight plug section, 18... Partial pressure Resistor (50KΩ), 20...Divider resistance (1MΩ), 24...Water level detection element, 32...
Glass covering part, 34... Concave groove part, 40... Housing, 42... Mounting wall, 44... Element cover part,
46...Water hole, 48...Disc spring, 50...Crimping ring, 52...Stopper portion, 54...Sealing ring.

Claims (1)

[Scope of Claims] 1. A water level detection element that has an electrode and an insulating material that holds the electrode, and detects the water level based on the presence or absence of electrical continuity due to contact between the electrode and the water surface, wherein the insulating material is solid. An electrically insulating ceramic body having a rod shape or a cylindrical shape with a hollow portion blocked by at least one airtight wall, and having a stepped portion in the circumferential direction at a predetermined portion of the outer surface thereof; The electrode is a film-like electrode formed on the surface of the electrically insulating ceramic body, and a terminal portion is formed on the surface of the electrically insulating ceramic body for electrically connecting to a predetermined external circuit device. and a cermet conductor path formed by co-firing with the electrically insulating ceramic body and electrically connecting the terminal portion and the electrode by airtightly penetrating the electrically insulating ceramic body. A water level detection element characterized by: 2 The electrode is made of platinum, rhodium, palladium,
The water level detection element according to claim 1, which is formed of a corrosion-resistant material whose main component is ruthenium, gold, or an alloy containing at least one of these. 3. At least a portion of the outer surface of the electrically insulating ceramic body other than the portion where the electrode is formed is coated with glass or resin to smooth the surface. The water level detection element according to item 1 or 2. 4. Claim 1, wherein the film-like electrode is composed of a cermet formed integrally with the electrically insulating ceramic body by co-firing together with the conductor path passing through the electrically insulating ceramic body. The water level detection element according to any one of items 1 to 3.