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Detection of Water Level Using "Inter-digitized" Capacitative Plates and an Emitter Plate in the Washer/Laundry Machines.

IP.com Disclosure Number: IPCOM000031218D
Publication Date: 2004-Sep-17

Publishing Venue

The IP.com Prior Art Database

Abstract

The current washer uses a pressure switch to turn off the flow of water to the tub. Therefore, the volume of the fill is not known because the pressure switch is set by the consumer and only acts in a toggle on/off mode. The inter-digitized plates would give the microprocessor differing voltages that correspond to differing levels. Therefore, the microprocessor can "see" the level and predict how much hot and cold water to input in the tub for a "warm" temperature.

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SUBJECT: Detection of Water Level Using "Inter-digitized" Capacitative Plates and an Emitter Plate in the Washer/Laundry Machines.

Summary of Invention:

The current washer uses a pressure switch to turn off the flow of water to the tub. Therefore, the volume of the fill is not known because the pressure switch is set by the consumer and only acts in a toggle on/off mode. The inter-digitized plates would give the microprocessor differing voltages that correspond to differing levels. Therefore, the microprocessor can "see" the level and predict how much hot and cold water to input in the tub for a "warm" temperature.

Problem to be Solved and Detailed Description of Invention:

Level detection is the key to obtaining our tolerances for a warm temperature in the automatic temperature control as well as reducing the number times the solenoid has to be actuated. The fewer the number of actuations, the better the reliability of the water valves. Below are important figures and a set of equations that prove the initial concept.

Figure 1

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Figure 2

Figure 3

Once a schematic of the circuit is obtained, then H(s) = Vout/Vin was derived from figure #3.

Using a capacitance meter, Co was measured to be 110pF when full and 114pF when empty. Cl was measured at 54pF full and 14pF empty. Ignoring s because it is small compared to the ratio of (Co+Cl)/Cl, H(s) becomes a constant that does not change over frequency of interest.

Figures #4-#7 shown below display the output of the Spice circuit simulation of figure #3. The Vin of figure #3 was a square wave also shown as the "Input" in figures #4 and #6. Vout in figure #3 is the "Output" of the circuit, which is the voltage across Co. Figures #4 and #5 simulate the output of an empty tub while figures #6 and #7 show the output of a full tub of water.

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The results produced by the circuit simulation take into account a leakage resistance that changes the waveforms in Spice. The calculated H(s) is correct, but to get a workable Vout one must excite the H(s) with either a step function or sine wave and then convert trom Laplac...