Battery electrolyte level sensor

• US 4,284,951 A
• Filed: 08/15/1979
• Issued: 08/18/1981
• Est. Priority Date: 08/15/1979
• Status: Expired due to Term

• Current Assignee: Ernest A. Dahl, George H. Barry
• Original Assignee: Ernest A. Dahl, George H. Barry
• Inventors: Dahl, Ernest A., Barry, George H.
• Primary Examiner(s): YASICH, DANIEL
• Application Number:
  US06/066,755
• Time in Patent Office: 734 Days
• Field of Search: 73/304 R, 324/344, 324/349, 324/430, 324/443, 324/436, 324/446, 324/449, 324/448, 324/432, 324/65 P, 340/636, 320/48
• US Class Current: 324/430
• CPC Class Codes: G01F 23/242 Mounting arrangements for electrodes

Abstract

Apparatus for indicating the level of the electrolyte in a battery cell. A three-electrode sensor probe having the electrodes partially embedded in an electrically insulating housing suspended in the electrolyte so that a portion of the probe is immersed in the electrolyte. The electrolyte provides the only conduction path between the electrodes so that the resistance between the electrodes varies according to the level of the electrolyte. An AC or pulsed DC sensing signal is applied between two of the electrodes and an output signal related to the level of the electrolyte is produced. A polarizing current is applied to the other electrode to prevent the buildup of surface contamination on the two sensing electrodes due to the sensing signal.

Claims

1. Apparatus for indicating the level of electrolyte in a battery cell comprising:

a. a probe including;

an elongated housing of an electrically insulating material which is chemically nonreactive with battery electrolyte;

six elongated metal bars embedded longitudinally in said housing in a substantially parallel arrangement around the perimeter of said housing, the outer surface of each said bar protruding from said housing to expose each said protruding surface to the ambient environment, said bars being electrically coupled in pairs to form first, second and third electrodes;

said first, second and third electrodes being spaced apart from each other and disposed vertically in a battery cell so that only a portion of the surface area of each electrode is in contact with battery electrolyte, the amount of the surface area of said second and third electrodes in contact with battery electrolyte varying as the level of electrolyte in the battery cell varies;

b. a source of electric potential coupled between said second and third electrodes;

c. a polarizing current source coupled to the first electrode;

said polarizing current source providing a current which operates to prevent the buildup of a contaminating layer on the surface of the second and third electrodes due to said second and third electrodes functioning as a battery whenever said source of electric potential has a direct current component that produces a net charge on said second and third electrodes; and

d. means for providing a signal proportional to the resistance between said second electrode and said third electrode through the electrolyte, said resistance varying inversely with the amount of surface area of said second and third electrodes which is in contact with the electrolyte.

3. Apparatus as recited in claim 1 wherein said six elongated metal bars are electrically coupled in pairs and adjacent bars are not electrically coupled.

4. Apparatus as recited in claim 3 wherein said means for providing a signal proportional to the resistance between said second and third electrodes through the electrolyte comprises:

a. differential amplifier means having a first input, a second input, and an output;

b. first resistance means coupled between the positive terminal of said source of electric potential and said second electrode;

c. second resistance means coupled between the third electrode and the first input of said differential amplifier means;

d. third resistance means coupled between the positive terminal of said source of electric potential and the first input to said differential amplifier; and

e. the second input of said differential amplifier being coupled between said first resistance means and said second electrode, the output of said differential amplifier proportional to the resistance between said second and third electrode and varying as the resistance between said electrodes varies.

5. The apparatus as recited in claim 1 or 2 wherein a D.C. blocking capacitor is coupled between the positive terminal of said source of electric potential and said first resistance means and said third resistance means.

6. The apparatus as recited in claims 1 or 2 wherein said source of electric potential provides pulses having substantially no D.C. component.

7. The apparatus as recited in claims 1 or 2 wherein said source of electric potential has substantially no D.C. component.

8. Apparatus as recited in claims 1 or 2 wherein said source of electric potential coupled between said second and third electrodes is a source of AC potential.

9. Apparatus is recited in claims 1 or 2 wherein said polarizing current source is a voltage source having its positive terminal coupled to the first electrode through a current limiting resistor and its negative terminal coupled to ground.

10. Apparatus as recited in claim 9 wherein said polarizing current source supplies a current of approximately 5 microamperes.

2. Apparatus for indicating the level of electrolyte in a battery cell, comprising:

a. an elongated probe including an elongated housing of an electrically insulating material which is chemically nonreactive with battery electrolyte, and at least three elongated metal bars embedded longitudinally in said housing in a substantially parallel arrangement around the perimeter of said housing, the outer surface of each said bar protruding from said housing to expose the protruding surface of said bar to the ambient environment, said at least three bars being electrically coupled to form a first electrode, a second electrode and a third electrode;

b. a source of electric potential coupled between said second and third electrodes;

c. a polarizing current source coupled to the first electrode;

said polarizing current source providing a current which operates to prevent the buildup of a contaminating layer on the surface of the second and third electrodes due to said second and third electrodes functioning as a battery whenever said source of electric potential has a direct current component which produces a net charge on said second and third electrodes; and

d. means for providing a signal proportional to the resistance between said second and third electrodes including;

a differential amplifier means having a first input, a second input, and an output;

a first resistance means coupled between the positive terminal of said source of electric potential and said second electrode;

a second resistance means coupled between the third electrode and the first input to said differential amplifier means;

a third resistance means coupled between the positive terminal of said source of electric potential and the first input to said differential amplifier; and

the second input of said differential amplifier being coupled between said first resistance means and said second electrode;

the output of said differential amplifier means being related to the resistance between said second and third electrodes;

e. said probe being disposed vertically in a battery cell so that only a portion of the surface area of each electrode which is exposed to the ambient environment is in contact with the electrolyte, the amount of the surface area in contact with the electrolyte varying as the level of the electrolyte in the cell varies.