Measuring and testing – Liquid level or depth gauge – Immersible electrode type
Reexamination Certificate
1998-03-02
2001-06-05
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Immersible electrode type
C073S30400R, C324S664000, C324S689000, C324S690000, C324S694000, C324S696000, C324S697000
Reexamination Certificate
active
06240778
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to liquid level sensors, and more particularly to a capacitive liquid level sensor for sensing the level of a liquid within a reservoir, where the sensor is generally immune to changes in the dielectric constant of the fluid and the orientation of the sensor about the center of the plates.
2. Discussion
Liquid level sensors are used in a wide variety of applications to detect the levels of fluids within various forms of reservoirs. Frequently, such sensors are employed in the automotive industry to sense the level of oil in an oil pan or sump, or the level of transmission fluid, just to name a couple of applications.
In many applications, and particularly in applications where the reservoir or sump is located on a moving vehicle such as an automobile, tractor or earth moving equipment, the vehicle will be required to traverse uneven ground which will cause the liquid in one or more reservoirs of the vehicle to shift. For example, when the vehicle begins moving up an incline, the orientation of the upper level of oil in an oil reservoir of the vehicle may change significantly. This in turn may cause an oil level sensor disposed in the oil reservoir to erroneously indicate that the oil level has changed (for example, decreased) to an unacceptable degree. In other words, the change in orientation may cause the level sensor to provide inconsistent and erroneous indications as to the true level of the oil in the reservoir.
It would therefore be highly desirable to incorporate a liquid level sensing device which is capable of accurately indicating when the level of a liquid in a reservoir has reached a predetermined point regardless of changes in the orientation of the reservoir.
It would also be highly desirable to provide a liquid level sensor which is relatively inexpensive to construct, highly reliable, relatively compact and lightweight, and readily usable in a wide variety of liquid level sensing applications with little or no modifications.
SUMMARY OF THE INVENTION
The present invention is directed to a method and apparatus for sensing when a liquid in a reservoir has reached a predetermined point, regardless of changes in the dielectric strength of the liquid. The liquid level sensor comprises a substrate in the form of a circuit board which includes an electrically conductive first input plate and an electrically conductive second input plate mounted thereon. An electrically conductive receiver or output plate is positioned closely adjacent the input plates but out of physical contact therewith. The first input plate is of a shape such that when an imaginary line is drawn through a centroid (i.e., geometric center) thereof at any angle, the imaginary line divides the first input plate approximately in half. The second input plate is positioned and shaped to nearly or completely circumscribe the first input plate. The second input plate further has a shape such that when the imaginary line extends through the centroid of the first input plate and also completely through the second input plate, the second input plate will also be divided approximately in half. The first and second input plates are also approximately equal in area.
The liquid level sensor further includes a controller for providing electrical signals, one at a time, to the first and second input plates to electrically excite the input plates and cause electrical signals to be coupled onto the receiver plate. The controller circuitry also monitors the output signals coupled onto the receiver plate. The output varies as the fluid level in the reservoir changes. This is because the dielectric constant changes when the receiver plate and the input plates are separated by air as compared to when they are separated by some liquid. Since the area of the first input plate and the second input plate are approximately equal, when the fluid level reaches (i.e., either increases or decreases) to the point where it is at the centroid of the first input plate, the output signals coupled onto the receiver plate as the first and second input plates are electrically excited will be approximately equal. Thus, by detecting when the signal coupled onto the receiver plate when the first input plate is electrically excited equals in magnitude the signal coupled onto the output plate when the second input plate is electrically excited, and further when the substrate is positioned within the reservoir such that the centroid is at the critical level to be detected, it can readily be determined when the fluid has reached the critical point in the reservoir.
The method of the present invention involves orientating first and second input plates within a reservoir, where the second input plate circumscribes the first input plate. The input plates are each of a shape which permits an imaginary line drawn through the centroid of the first input plate at any angle to divide both the first input plate and the second input plate in half. The first and second input plates are alternately electrically excited and the output signals are coupled onto a receiver plate also disposed in the reservoir closely adjacent the input plates. When the fluid level has reached the centroid of the first input plate the output signals coupled onto the output plate produced by electrically exciting the first and second input plates will be approximately equal. At this point a signal is generated indicating that the fluid level has reached the centroid of the first input plate.
The apparatus and method of the present invention provides fluid level monitoring which is uninfluenced by changes in the dielectric constant of the fluid being sensed. In some applications, the present invention may even provide level sensing which is immune to minor changes in the orientation of the reservoir relative to the ground.
REFERENCES:
patent: 2648058 (1953-08-01), Breedlove
patent: 2651940 (1953-09-01), Kline
patent: 2751531 (1956-06-01), Barrett
patent: 2866337 (1958-12-01), Minneman et al.
patent: 2868015 (1959-01-01), Haropulos
patent: 3391547 (1968-07-01), Kingston
patent: 3620080 (1971-11-01), Ryder
patent: 4086528 (1978-04-01), Walton
patent: 4194395 (1980-03-01), Wood
patent: 4266144 (1981-05-01), Bristol
patent: 4417472 (1983-11-01), Tward
patent: 4470008 (1984-09-01), Kato
patent: 4499766 (1985-02-01), Fathauer et al.
patent: 4545020 (1985-10-01), Brasfield
patent: 4553434 (1985-11-01), Spaargaren
patent: 4589077 (1986-05-01), Pope
patent: 5012197 (1991-04-01), Seiffert et al.
patent: 5052223 (1991-10-01), Regnault et al.
patent: 5142909 (1992-09-01), Baughman
patent: 5406843 (1995-04-01), Hannan et al.
patent: 5437184 (1995-08-01), Shillady
Atkinson William E.
Hannan Alan R.
McQuitty Bryan H.
Nickolin Thomas M.
Noble J. Jacob
Harness Dickey & Pierce PLC
KDI Precision Products Inc.
Loo Dennis
Williams Hezron
LandOfFree
Liquid level point switch sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid level point switch sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid level point switch sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2456182