Digital liquid level sensing apparatus

• US 6,125,696 A
• Filed: 03/19/1998
• Issued: 10/03/2000
• Est. Priority Date: 10/27/1993
• Status: Expired due to Term

• Current Assignee: Hannan - Nickolin Intellectual Properties, LLC
• Original Assignee: KDI Precision Products Inc (L3Harris Technologies, Inc.)
• Inventors: Lewis, Ted W., Nickolin, Thomas M., Hannan, Alan R.
• Primary Examiner(s): HIRSHFELD, ANDREW HOWARD
• Application Number:
  US09/044,419
• Time in Patent Office: 929 Days
• Field of Search: 73/304 C, 324/658, 324/665, 340/618, 340/620, 702/52, 702/55
• US Class Current: 73/304.00C
• CPC Class Codes: G01F 23/265 for discrete levels
• CPC Class Codes: G01F 23/266 measuring circuits therefor
• CPC Class Codes: G01F 23/268 mounting arrangements of probes

Abstract

A digital liquid level sensing apparatus for detecting variations in the dielectric of a substance being sensed, to thereby provide a signal indicative of the level of the liquid being sensed in relation to a known full level. The apparatus includes a reservoir having an output plate and an input plate assembly associated therewith. The input plate assembly includes a plurality of independently electrically excitable input plates which transmit a signal through the liquid being sensed to the output plate. The signals from the output plate are processed and a determination is made as to the level of liquid in the reservoir relative to a known full level. If the input plate assembly is located against the exterior surface of one wall of the reservoir, then both of the interior and exterior portions of that particular wall should be devoid of any metallic surface. In an alternative embodiment, a discardable interior reservoir is provided which fits nestably within the reservoir of the sensor. The interior reservoir is particularly useful for measuring water-based bodily fluids such as urine, where it may be desirable to discard just the reservoir after use.

Claims

1. An apparatus for detecting a level of a liquid-based fluid, comprising:

a capacitive element array including a plurality of independent input plates spaced longitudinally along an axis of measurement;

a reservoir for supporting said capacitive element array thereon and a quantity of said fluid therein, said reservoir having an interior wall and an exterior wall and having a metallized surface forming an output plate which substantially conforms to the cross-sectional shape of the reservoir, the output plate being spaced apart from said input plates and having a length sufficient to span all of said input plates;

a controller for sequentially applying an input signal to each one of said input plates sequentially, one at a time, to thereby electrically excite each said input plate;

a current-to-voltage amplifier responsive to said output plate for generating a voltage output signal representative of the current coupled onto said output plate each time one of said input plates is electrically excited by said controller;

a peak detector responsive to said current-to-voltage amplifier for generating a peak voltage signal representative of the peak magnitude of the voltage signal from said current to voltage amplifier each time one of said input plates is electrically excited by said controller;

memory for storing each one of said peak voltage signals associated with the current coupled onto said output plate for each input plate excited by said controller;

said controller including a comparator for comparing said peak voltage signals generated from the excitation of said input plates, one of said input plates at a time in sequential fashion against a reference value, and for determining the difference in each of said peak voltage signals from said reference value, to thereby detect a change in a dielectric of said fluid adjacent any one of said input plates relative to said reference value, to thereby detect a liquid/air interface within said fluid reservoir from which a level of said fluid can be determined; and

said controller further operating to determine the percentage of each said input plate that is disposed below said liquid/air interface such that a precise level of said fluid can be determined.

2. The apparatus of claim 1, further comprising an integrator for integrating an output signal generated by said controller representative of said peak voltage signals for providing an analog indication of a level of said fluid within said reservoir.

3. The apparatus of claim 1, further including an interface in communication with said controller for coupling an output representative of said liquid level to an external device.

4. The apparatus of claim 1, wherein said controller includes a low level signal generator for generating an output signal when said fluid level within said reservoir is determined to be below a predetermined lower level limit.

5. The apparatus of claim 1, further comprising an electrically erasable, programmable, read-only memory for storing information for each one of said input plates relating to outputs generated when each said input plate is completely disposed in air and completely submerged in said fluid.

6. The apparatus of claim 1, further comprising a temperature sensor for sensing a temperature of said fluid and providing a signal representative of said sensed temperature to said controller.

7. The apparatus of claim 1, wherein said reservoir includes an electrically insulated, metallic ground plate.

8. The apparatus of claim 1, wherein said metallized surface is formed on said interior wall of said reservoir.

9. The apparatus of claim 1, wherein said reservoir comprises a molded plastic structure, and wherein said metallized surface is embedded in one wall of said reservoir so as not to be exposed to contact with said fluid within said reservoir.

10. The apparatus of claim 1, wherein said metallized surface is formed on said interior wall;

and

said reservoir further comprising a metallized ground plate secured to said exterior wall adjacent said metallized surface.

11. A liquid level sensing apparatus comprising:

a reservoir having an interior wall and an exterior wall, said interior wall including a metallized portion forming an output plate shaped generally in accordance with a cross-sectional overall shape of said reservoir and said exterior wall including a metallized portion forming a ground plate, said reservoir being adapted to hold a quantity of liquid therein;

an input plate assembly including a plurality of spaced apart metallized input plates, said input plate assembly being disposed so as to be positioned generally vertically within said reservoir, said input plate assembly being approximately equal to or less in length than said output plate; and

an electrical circuit assembly for independently electrically exciting each of said input plates, sequentially, one after another and being electrically coupled to said output plate to read a plurality of signals coupled onto said output plate;

said electrical circuit assembly further operating to determine the approximate percentage coverage of each one of said input plates, and from said approximate percentage coverage of said input plates a precise level of said liquid within said reservoir.

12. A method for detecting a level of a liquid within a liquid reservoir, the method comprising:

disposing at least a portion of a probe in said reservoir, wherein said probe includes a plurality of individually excitable input plates and a common output plate, said probe being positioned relative to said reservoir such that at least a portion of one of said output plate or said at least one of said plurality of input plates are disposed in said reservoir;

applying an electrical signal to each one of said input plates, sequentially, one at a time, to electrically excite each said input plate;

reading an output signal generated on said output plate each time one of said input plates is electrically excited;

determining whether each one of said input plates is disposed below a level of said liquid in said reservoir;

extrapolating from which ones of said input plates are disposed below said level of liquid in said reservoir what an actual upper level of said liquid is within said reservoir relative to a known full level;

further comprising the step of determining what percentage of each said input plate is disposed below said upper level of said liquid; and

from said percentage of each said input plate which is determined to be below said upper level of said liquid, further extrapolating a precise level of said liquid within said liquid reservoir.