Switch assembly, electric machine having the switch assembly, and method of controlling the same

• US 7,427,844 B2
• Filed: 01/24/2007
• Issued: 09/23/2008
• Est. Priority Date: 07/09/2003
• Status: Active Grant

• Current Assignee: Regal Beloit America, Inc.
• Original Assignee: A. O. Smith Corporation
• Inventors: Mehlhorn, William L.
• Primary Examiner(s): Ip; Paul
• Application Number:
  US11/626,755
• Publication Number:
  US 20070113647A1
• Time in Patent Office: 608 Days
• Field of Search: 318481-483, 318/806, 733/04.C, 733/350.4, 361/286
• US Class Current: 318/483
• CPC Class Codes: F04D 15/0218 the condition being a liquid level or a lack of liquid supply
• CPC Class Codes: G01F 23/266 measuring circuits therefor
• CPC Class Codes: H02P 1/42 for starting an individual single-phase induction motor H02P27/04 takes precedence
• CPC Class Codes: H02P 1/44 by phase-splitting with a capacitor
• CPC Class Codes: H03K 17/08 Modifications for protecting switching circuit against overcurrent or overvoltage
• CPC Class Codes: H03K 17/292 in thyristor, unijunction transistor or programmable unijunction transistor switches
• CPC Class Codes: H03K 17/305 in thyristor switches
• CPC Class Codes: H03K 17/725 for ac voltages or currents H03K17/722, H03K17/735 take precedence

Abstract

A pump assembly for pumping a liquid and a method of controlling the pump assembly. The pump assembly includes a motor coupled to a pump, and an electronic switch assembly electrically connected to the motor to control the current through the motor. The electronic switch assembly includes an electronic switch, a generator that provides a substantially periodic pulsing signal, a circuit control configured to provide a second signal, and decision logic connected to the generator, the circuit control, and the electronic switch. The decision logic receives the periodic pulsing and second signals and generates a control signal that selectively controls the electronic switch based on the periodic pulsing and second signals.

Claims

1. A liquid-level sensor to sense a liquid having a level with respect to an axis, the liquid level sensor comprising

a circuit board having a first length and a first height, the first height being along the axis, the circuit board comprising

a first capacitive plate having a second length and a second height, the second height being along the axis,

a second capacitive plate having a third length and a third height, the third height being along the axis, the third height being disposed above the second height, and

a notch disposed in the circuit board between the second height and the third height with respect to the axis, the notch reducing leakage between the first capacitive plate and the second capacitive plate, and

a charge-transfer sensor coupled to the first and second capacitive plates to measure the capacitance between the first capacitive plate and the second capacitive plate.

2. A liquid level sensor as set forth in claim 1 wherein the first, second, and third lengths are orthogonal to the first, second, and third heights, respectively, and wherein the notch includes a fourth length greater than at least one of the second length and the third length.

3. A liquid level sensor as set forth in claim 2 wherein the fourth length is greater than both of the second length and the third length.

4. A liquid level sensor as set forth in claim 1 wherein the sensor further comprises a second circuit board having a fourth length and a fourth height, the fourth height being along the axis and being disposed above the first height, the second circuit board comprising a third capacitive plate having a fifth length and a fifth height, the fifth height being along the axis, and wherein the charge-transfer sensor couples to the third capacitive plate to measure the capacitance between the first capacitive plate and the third capacitive plate.

5. A liquid level sensor as set forth in claim 4 wherein the charge-transfer sensor is configured to generate a first signal related to the capacitance between the first capacitive plate and the second capacitive plate, wherein the charge-transfer sensor is further configured to generate a second signal related to the capacitance between the first capacitive plate and the third capacitive plate, and wherein the charge-transfer sensor is further configured to compare the first signal to the second signal.

6. A liquid level sensor as set forth in claim 1 wherein the circuit board includes a first layer and a second layer, and wherein at least one of the first capacitive plate and the second capacitive plate is disposed between the first layer and the second layer.

7. A liquid-level sense circuit comprising:

a substrate having a first length along a first axis and a second length along a second axis, the first axis being orthogonal to the second axis, the substrate defining an indentation having a third length along the first axis;

a first capacitive element supported by the substrate, the first capacitive element having a fourth length along the first axis and a fifth length along the second axis;

a second capacitive element above the first capacitive element and supported by the substrate, the second capacitive element having a sixth length along the first axis and a seventh length along the second axis;

a sensor configured to compare the capacitance between the first capacitive element and the second capacitive element to a first value,

wherein the third length is greater than at least one of the fourth length and the sixth length; and

wherein the indentation is disposed between the first capacitive element and the second capacitive element along the second axis and reduces leakage between the first capacitive element and the second capacitive element.

8. The sense circuit of claim 7, wherein the third length is greater than both of the fourth length and the sixth length.

9. The sense circuit of claim 7, wherein the substrate includes a circuit board.

10. The sense circuit of claim 7, wherein the first capacitive element includes a first conductive plate, and wherein the second capacitive element includes a second conductive plate.

11. The sense circuit of claim 10, wherein the substrate includes a circuit board having a first layer and a second layer, and wherein the first conductive plate includes a first metal foil disposed between the first layer and the second layer, and wherein the second conductive plate includes a second metal foil disposed between the first layer and the second layer.

12. The sense circuit of claim 7, further comprising a third capacitive element supported by the substrate above the second capacitive element, the third capacitive element having an eighth length along the first axis and a ninth length along the second axis, and wherein the sensor is configured to compare the capacitance between the first capacitive element and the third capacitive element to a second value.

13. The sense circuit of claim 12, wherein the substrate includes a first substrate supporting the first capacitive element and the second capacitive element, and wherein the substrate further includes a second substrate supporting the third capacitive element.

14. The sense circuit of claim 13, wherein the second substrate is disposed a distance from the first substrate along the second axis.

15. The sense circuit of claim 12, wherein the second capacitive element is disposed between the first capacitive element and the third capacitive element along the second axis.

16. The sense circuit of claim 12, further comprising an alarm configured to generate a signal based on the comparison of capacitance between the first capacitive element and the third capacitive element to the second value.

17. A method for operating a motor with a liquid-level sensor assembly including

a first substrate having a first plate with a first length and a first height, a second plate with a second length and a second height, the first height and the second height being along an axis, and an indentation with a third length, the indentation being disposed between the first plate and the second plate along the axis, and the third length being greater than at least one of the first length and the second length,

a second substrate having a third plate, the second substrate placed at a distance from the first substrate along the axis, and

a sensor electrically coupled to the first plate, the second plate, and the third plate, the method comprising:

detecting a first capacitance between the first plate and the second plate;

detecting a second capacitance between the first plate and the third plate;

comparing the first capacitance to a first threshold value;

comparing the second capacitance to a second threshold value;

generating a signal in response to comparing the first capacitance to the first threshold value and comparing the second capacitance to the second threshold value; and

operating the motor in response to generating the at least one signal.

18. The method of claim 17, wherein the generating the signal includes

generating a first signal in response to comparing the first capacitance to the first threshold value, and

generating a second signal in response to comparing the second capacitance to the second threshold value.