JPH1019637A - Capacitive level sensor - Google Patents

Abstract

(57) [Problem] To provide a structure of a capacitance type level sensor having a reliable sealing effect even without an inner seal ring. SOLUTION: A housing 1 having a housing chamber 11 for housing a circuit board 2 and a hole 12 communicating with the housing chamber 11.
An electrode rod 3 having a proximal end 31 and a distal end 32, the proximal end 31 being inserted into the hole 12 of the housing 1, and the distal end 32 projecting outward from the housing 1; The insulating film 4 tightly coated on the outer surface of the housing 1 and the housing 1
Between the hole 12 and the base end 31 of the electrode rod 3,
A capacitance type level sensor including a sealing member 5 for hermetically and liquid-tightly sealing the outside of the housing 1 and the accommodation chamber 11 of the housing 1 and a fixing member 6 for fixing the electrode rod 3; That you did.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type level sensor for detecting the level of a liquid or the like (remaining liquid amount) by utilizing a change in capacitance. It relates to a capacitance type level sensor to be used.

[0002]

2. Description of the Related Art Conventionally, as a level sensor for detecting the remaining capacity of a liquid or the like in a high-pressure vessel, Japanese Utility Model Laid-Open No. 57-1359 has been known.
No. 27, there is a thing as shown. About this one,
This will be described with reference to FIG.

In FIG. 2, reference numeral 21 denotes an electrode rod provided with an insulating film 22; 23, a nipple as a support for inserting and supporting the electrode rod 21; 24, an inner seal ring; 25, an outer seal ring; It is a holding screw for holding the ring 25 against the inner seal ring 24.

In the above-mentioned conventional level sensor, the outer seal ring 25 is fixed to the inner seal ring 2 by the set screw 26.
4, the sealing effect is improved by crushing the two rings 24 and 25, and the intrusion of a liquid or the like under high pressure can be prevented.

Further, even when the insulating film 22 is broken and liquid penetrates between the electrode rod 21 and the insulating film 22, the liquid is dammed by the inner seal ring 24 and the sealing effect can be maintained. .

[0006]

The conventional level sensor is configured as described above. By the way, in the conventional level sensor, the airtightness between the measurement unit and the outside is performed by the inside and outside seal rings. With such a sealing method, the setting of the clearance becomes very delicate, and it has a high precision when assembling them. In particular, the inner seal ring must be covered with an insulating film on the outside. If the dimensional accuracy of the insulating film and the sealing groove of the electrode are not compatible, a reliable sealing effect cannot be achieved.

SUMMARY OF THE INVENTION Therefore, the present invention has been made in view of the above-mentioned circumstances, and has as its technical object to provide a level sensor structure having a sealing effect with a simple configuration.

[0008]

According to a first aspect of the present invention, there is provided a housing for accommodating a circuit board, and a hole communicating with the housing. An electrode rod having a base end and a tip end, the base end being inserted into a hole of the housing, and the tip end projecting outward from the housing;
An insulating film tightly coated on the outer surface of the electrode rod, and disposed between the hole of the housing and the base end of the electrode rod, and hermetically seals the outside of the housing and the housing chamber of the housing. Further, the present invention provides a capacitance type level sensor including a sealing member for sealing in a liquid-tight manner and a fixing member for fixing the electrode bar.

In the above technical means, the most remarkable point is that the outer surface of the electrode rod is coated with an insulating film in close contact. By tightly coating the electrode bar with the insulating film, there is no gap between the electrode bar and the insulating film. Therefore, even if a part of the insulating film is broken, the liquid does not permeate between the electrode rod and the insulating film. Also, since a sealing member is interposed between the electrode rod and the housing,
Liquid does not penetrate from between the housing and the electrode rod.

[0010] Here, the term "adhesive coating" means to apply a coating with adhesive strength. For example, an electrode coated with an insulating coating material containing an adhesive, solidified, spray coating, electrostatic coating, baking coating, fluid immersion coating, etc. is there. These exhibit adhesion strength due to intermolecular attraction between the electrode and the insulating film, mechanical bonding force, and the like.

[0011]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a level sensor according to this embodiment. In the figure, reference numeral 1 denotes a housing.
The housing 1 has a housing chamber 11 formed therein, and the circuit board 2 is housed in the housing chamber 11. The housing 1 has a hole 12 communicating from the accommodation chamber 11 to the outside.
Are formed. The hole 12 includes a small-diameter portion 121 opened to the outside and a large-diameter portion 122 communicating the small-diameter portion 121 and the storage chamber 11. Reference numeral 3 denotes an electrode formed in an elongated frustoconical shape. The electrode 3 includes a proximal end 31 inserted into the hole 12 and a distal end 32 protruding from the hole 12 to the outside. The distal end portion 32 is mainly projected into the inside of the high-pressure container or the like, and functions as a detection unit for measuring the remaining capacity of the liquid in the high-pressure container. Flange 3 at base end 31
11 are formed. The outer surface of the electrode rod 3 is uniformly coated with an insulating film 4 by adhesion. 5 is an O-ring as an outer seal ring. The O-ring 5 is fitted in a groove formed on the wall surface of the small-diameter portion 121, and serves to seal invasion of liquid and gas from the outside. A lock nut 6 fixed to the housing is provided in the large-diameter portion 122, and a part of the base end 31 of the electrode 3 is inserted into a hole 61 formed in a substantially central portion of the lock nut 6. Have been. The electrode 3 is fixed by the lock nut 6. The base end face 311 of the base end portion 31 is in contact with the circuit board 2 housed in the housing chamber 11.

The operation of the capacitance type level sensor having the above configuration will be described below. First, when the level sensor is hermetically fixed to the inner peripheral wall or the like of the high-pressure container, high pressure is applied from the distal end portion 32 side to the proximal end portion 31 side of the electrode 3. Then, this pressure is transmitted from the flange portion 311 to the lock nut 6, and the electrode 3 is supported by the lock nut 6 against high pressure. At this time, O
The airtightness between the high-pressure container and the storage chamber 11 is maintained by the ring 5, and no high pressure is applied to the storage chamber 11.

The electrode 3 is mainly made of brass. The capacitance of the electrode 3 differs between the case where the outside is air and the case where the outside is liquid. This change in capacitance is electrically transmitted to the circuit board, and based on the information, determines whether or not the liquid has reached the level sensor.

In the capacitance type level sensor having the above structure, the outer surface of the electrode 3 is coated with an insulating film 4 in close contact. Since the electrode 3 and the insulating film 4 are in close contact with each other, even if a part of the insulating film 4 is torn, the other portions are in close contact with the electrode 3. Therefore, the liquid does not permeate between the insulating film 4 and the electrode 3 from the torn portion. In this case,
The thickness of the insulating film is preferably about 0.2 to 0.4 mm. With such a thickness, the adhesion strength is further enhanced, and the insulating film itself is not broken. 0.4 thickness
mm or more, the film is too thick, causing dimensional changes,
This has an adverse effect on sealing. Conversely, if it is 0.2 mm or less, it is too thin and easily broken.

In this embodiment, PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer) was used as the material of the insulating film. Also,
The method of adhering the insulating film to the electrode was achieved by spraying PFA powder on the electrode heated to 200 to 300 ° C. and welding the PFA powder on the electrode. Thereby, a strong adhesion between the electrode and the insulating film can be secured, and even if the insulating film is broken during use as a level sensor, liquid does not permeate therefrom.

The capacitance type level sensor described above is
For example, in a Stirling engine, it is attached to a high-pressure oil chamber or the like that stores oil to be supplied to a high-pressure oil sealing chamber provided on the outer periphery of a piston rod to separate an operating space from an external space. FIG. 2 shows an example in which the capacitance type level sensor of this embodiment is attached to this type of high-pressure oil chamber. In the figure, the piston reciprocates according to a known Stirling cycle. Therefore, the piston rod connected to the piston also reciprocates in the direction shown by the arrow in the figure. Various components such as a high-pressure gas chamber, an oil scraper, a high-pressure oil sealing chamber, a main seal, a low-pressure oil sealing chamber, and a bearing are attached to the piston rod. The high pressure oil chamber is connected to the high pressure oil chamber. The high-pressure oil chamber stores oil to be supplied to the high-pressure oil sealing chamber, and is maintained at the same high-pressure state as the high-pressure oil sealing chamber. In addition, the high-pressure oil chamber communicates with the high-pressure gas chamber via an oil mist filter,
The pressures in the high-pressure gas chamber and the high-pressure oil chamber are also set to the same pressure. The capacitance type level sensor described in the present embodiment is attached to this high-pressure oil chamber, and monitors the upper limit amount of oil inside. When an increase in the amount of oil in the high-pressure oil chamber is detected based on the change in the capacitance, the normally closed solenoid valve is opened, and the oil in the high-pressure oil chamber is discharged to the outside. As described above, by using the capacitance level sensor described in the present embodiment in the high-pressure oil chamber that stores the oil to be supplied to the high-pressure oil sealing chamber disposed on the piston rod of the Stirling engine, Oil management is stable. If the oil management in the high-pressure oil sealed chamber is unstable, the oil in the high-pressure oil chamber flows through the oil mist filter to the high-pressure gas chamber, and contaminates the working gas. In this regard, if the capacitance type level sensor described in the present embodiment is used, oil management is stabilized, and the above-described problem does not occur. In the above description, the upper limit of the oil amount is monitored, but two capacitance level sensors according to the present embodiment are attached to the high-pressure oil chamber so that both the upper limit and the lower limit can be monitored. You can also.

[0018]

The invention of claim 1 has the following effects.

Since the insulating film is coated on the electrode rod in close contact, the sealing property can be maintained without the inner seal ring. This makes it possible to provide a level sensor having a simple configuration and a reliable sealing effect.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a capacitance type level sensor according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an example in which a capacitance type level sensor according to an embodiment of the present invention is attached to a high-pressure oil chamber attached to a Stirling engine.

FIG. 3 is a cross-sectional view of a capacitance type level sensor according to the related art.

[Explanation of symbols]

1 housing, 11 accommodation room, 12 holes, 1
21 Large brother 121 Small diameter part, 122 Large diameter part 2 Circuit board 3 Electrode rod, 31 Base end part, 311 Flange part,
312 Base end surface 32 Tip 4 Insulation coating 5 O-ring (sealing member) 6 Lock nut (fixing member)

Claims (1)

[Claims] 1. A housing having a housing for housing a circuit board, a hole communicating with the housing, a base end and a distal end, wherein the base end is a hole in the housing. An electrode rod, the tip of which protrudes outward from the housing; an insulating film coated in close contact with the outer surface of the electrode rod; and a hole in the housing and a base end of the electrode rod. A capacitance member disposed between the sealing member and a sealing member for hermetically and liquid-tightly sealing the outside of the housing and the housing chamber of the housing; and a fixing member for fixing the electrode rod. Level sensor.