Measuring and testing – Liquid level or depth gauge – Immersible electrode type
Patent
1994-01-24
1995-12-26
Cuchlinski, Jr., William A.
Measuring and testing
Liquid level or depth gauge
Immersible electrode type
361284, G01F 2326, H01G 500
Patent
active
054777275
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a capacitive level sensor which is suitable for use with a tank for a nonconductive liquid or a tank for a conductive liquid (of low electrical resistance) such as water.
As shown in FIG. 1, a conventional capacitive level sensor of this kind is composed of a pair of opposed electrodes, that is, an outer tube 1 made of metal (referred to also as a common electrode) and an inner tube 2 made of metal and disposed concentrically therewith, and the inner tube 2 is made up to a main sensor electrode part 3 and a reference sensor electrode part 4. The main sensor electrode part 3 and the reference sensor electrode part 4 have the same radius and are mechanically secured to the outer tube 1 by support members 5 made of an insulating material. Cables 6 and 7 are connected to the main sensor electrode part 3 and the reference sensor electrode part 4, respectively.
Such a level sensor is disposed with the reference sensor electrode part 4 positioned at the bottom of a tank on the inside thereof, whereby the height of the liquid level H or liquid level h in the range from the lower and to the upper end of the main sensor electrode part 3 can be detected. When oil or similar liquid enters the space defined between the outer tube or common electrode 1 and the inner tube 2, the electrostatic capacitance between the main sensor electrode part 3 and the common electrode 1 changes in proportion to the liquid level h. Letting the length of the main sensor electrode part 3 in its axial direction (in the vertical direction) be represented by L, the electrostatic capacitance between the main sensor electrode part 3 and the common electrode 1 when the liquid level is h (which electrostatic capacitance will be referred to simply as the electrostatic capacitance of the main sensor electrode part) by Csh, the electrostatic capacitance when the space between the main sensor electrode part 3 and the common electrode 1 is filled with air (that is, when h=0) by Cso and the specific inductivity of the liquid by .epsilon., the following equation holds true: Cra is the electrostatic capacitance when the space between the reference sensor electrode part 4 and the common electrode 1 is filled with air and Cr is the electrostatic capacitance when the space between the reference sensor electrode part 4 and the common electrode 1 is filled with the liquid. Cso and Cra are both constants that depend on the sizes and constructions of the main sensor electrode part 3 and the reference sensor electrode part 4. The specific inductivity e can be preobtained by premeasuring the electrostatic capacitance Cra of the reference sensor electrode part 4 in the state of no liquid being filled in the tank and the electrostatic capacitance Cr in the state of the reference sensor electrode part 4 being submerged in the liquid. The height h of the liquid level H can be obtained by measuring the electrostatic capacitance Csh of the main sensor electrode part 3 by means of an instrument not shown.
Since such a capacitive level sensor requires, as the tubular electrode 2, the two electrically insulated sensor electrode parts 3 and 4, it is necessary in the prior art to fix these sensor electrode parts 3 and 4 to the outer tube 1 through the support members 5; thus, the conventional level sensor has disadvantages of requiring many support members 5 and involving work of securing the sensor electrode parts to the outer tube through the support members. Another problem is the use of the cables 6 and 7 that are connected to the sensor electrode parts 3 and 4, respectively.
An object of the present invention is to provide a capacitive level sensor which overcomes these problems and, though simple-structured, ensures the same performance as is obtainable with the prior art.
DISCLOSURE OF THE INVENTION
To solve the above-mentioned problems, according to the present invention, in a capacitive level sensor of type that has first and second electrode means disposed opposite each other with a space defined therebetween wh
REFERENCES:
patent: Re24082 (1955-11-01), Smith
patent: 4924702 (1990-05-01), Park
patent: 5103368 (1992-04-01), Hart
patent: 5144835 (1992-09-01), McDonald
Cuchlinski Jr. William A.
Japan Aviation Electronics Industry Limited
Worth Willie Morris
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