Capacitance-Based Fluid Level Sensor

Abstract

A fluid level sensor comprises a parallel plate capacitor coupled to an integrated circuit located in the bottom of an oil pan or other receptacle in which fluid level is being sensed. The sensor is preferably mounted on a drain plug for the receptacle. It includes an integrated circuit board encapsulated in a potting material disposed within the drain plug and a probe extending upwardly from the integrated circuit with its lower end also encapsulated with a resin such that its leads are protected by the resin encapsulating the integrated circuit. The probe may include one or more slotted plates in which capacitance bridges are formed within the slots or a plurality of parallel plates in which capacitance bridges are formed between adjacent plates. The sensor can be used to control operation of a gauge and/or an ignition control circuit for the machine's engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred exemplary embodiments of the invention are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which:

FIGS. 1 and 2 are front and side elevation views, respectively, of a rammer incorporating an oil level sensor constructed in accordance with a first preferred embodiment of the present invention;

FIG. 3 is a perspective view of a crankcase of the rammer of FIGS. 1 and 2, shown open so as to reveal the oil level sensor disposed therein;

FIG. 4 is a side sectional view of a crankcase of FIG. 3;

FIGS. 5 and 6 are perspective and top plan views, respectively, of the oil level sensor of FIGS. 3 and 4;

FIG. 7 is a partially cutaway side elevation view of the oil level sensor of FIGS. 5 and 6;

FIG. 8 is a sectional view of the oil level sensor of FIGS. 5-7, shown along the lines 8-8 in FIG. 6;

FIG. 9 is an enlarged fragmentary view of a portion of the oil level sensor of FIGS. 5-8;

FIG. 10 is a perspective view of an oil level sensor usable on the rammer of FIGS. 1-4 and constructed in accordance with a second preferred embodiment of the present invention;

FIGS. 11, 12, and 13 are top elevation, bottom elevation, and side elevation views, respectively of the oil level sensor of FIG. 10; and

FIG. 14 is a sectional side elevation view of a portion of the oil level sensor of FIGS. 10-13, taken along the lines of 14-14 in FIG. 10.

Claims

1. A fluid level sensor comprising: (A) a parallel plate capacitor-based probe located in a bottom portion of a fluid receptacle; and(B) a controller that receives signals from the probe and that generates capacitance-dependent signals indicative of a fluid level in the receptacle.

2. The sensor of claim 1, wherein the capacitor is formed from at least one slotted plate.

3. The sensor of claim 1, wherein the capacitor is formed from a plurality of parallel plates.

4. The sensor of claim 1, wherein the controller includes an integrated circuit board connected to the probe to form a single unit, and wherein the unit is mounted in the receptacle.

5. The sensor of claim 4, wherein the integrated circuit board and the probe are mounted on a drain plug.

6. The sensor of claim 4, wherein the integrated circuit board is encapsulated in a potting material into which is embedded a base of the probe.

7. The sensor of claim 1, wherein a frequency of a capacitance field of the probe varies with fluid levels in the receptacle, and the controller generates a low fluid level warning signal in response to sensed variations of capacitance field frequency.

8. The sensor of claim 8, wherein the controller generates a low fluid warning level only if the fluid level in the receptacle drops below a bottom of parallel plates of the probe.

9. A low fluid level detection system comprising: (A) a fluid level sensor comprising i. a parallel plate capacitor-based probe located in a bottom portion of a fluid receptacle, andii. a controller that receives signals from the probe and that generates capacitance-dependent signals indicative of a fluid level in the receptacle; and(B) a gauge that receives signals from the controller.

10. The system of claim 9, wherein the capacitor of the probe is formed from at least one slotted plate.

11. The system of claim 9, wherein the capacitor of the probe is formed from a plurality of parallel plates.

12. The system of claim 9, wherein the controller includes an integrated circuit board connected to the probe to form a single unit, and wherein the unit is mounted in the receptacle.

13. The system of claim 9, wherein the integrated circuit board is encapsulated in a potting material into which is embedded a base of the probe.

14. The system of claim 9, wherein a frequency of a capacitance field of the probe varies with fluid levels in the receptacle and the controller generates a low fluid level warning signal in response to sensed variations of capacitance field frequency.

15. The system of claim 14, wherein the controller generates a low fluid warning level only if the fluid level in the receptacle drops below a bottom of parallel plates of the probe.

16. The system of claim 9, wherein the gauge includes a second controller that is connected to an ignition system of an engine.

17. The system of claim 16, wherein the second controller prevents the engine from running upon detection of a low fluid level condition by the controller of the sensor.

18. The system of claim 16, wherein the second controller is non-responsive to signals from the sensor after a designated period of time following engine startup.

19. A machine including the system of claim 9.

20. A rammer including the system of claim 9.

21. A method comprising: sensing fluid levels in a receptacle using a parallel plate-type probe located in the receptacle.

22. The method of claim 21, wherein a frequency of a capacitance field of the probe varies with fluid levels in the receptacle, and further comprising generating the controller a low fluid level warning signal in response to sensed variations of capacitance field frequency.

23. The method of claim 21, further comprising generating a low fluid warning level only if the fluid level in the receptacle drops below a bottom of parallel plates of the probe

24. The method of claim 21, further comprising controlling operation of at least one of a gauge and an ignition system for an engine based on the sensing step.

25. The method of claim 24, further comprising preventing the engine from running upon detection of a low fluid level condition.

26. The method of claim 24, wherein the sensing step is performed by a sensor including a parallel plate capacitor further comprising disregarding or disabling signals from the sensor after a designated period of time following engine startup.

27. A method comprising: (A) connecting a parallel plate capacitor probe to a printed circuit board, the capacitor having a capacitance field having a frequency which varies with fluid levels thereacross;(B) encapsulating the printed circuit board in a potting material to form a unit;(C) mounting the unit in a receptacle.