Method for sensing the liquid level in a compressor
First Claim
1. A method for sensing a fluid in a compressor, wherein the fluid can exist in a plurality of states including at least one of a liquid state, a gaseous state, and a gas/liquid mixture, the method comprising:
- positioning a thermistor in heat transfer relationship with the fluid, wherein the thermistor has a thermistor temperature that varies;
providing a feedback signal that varies with the thermistor temperature;
obtaining a ripple signal by a conventional method step wherein the ripple signal is indicative of voltage fluctuation;
adding the ripple signal to the feedback signal to create a dithered input;
calculating a dither-based temperature value based on the dithered input; and
based on the dither-based temperature value, determining at least one of the following;
a) a state of the fluid, and b) a temperature of the fluid.
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Accused Products
Abstract
Two vertically offset thermistors for sensing a fluid such as oil and refrigerant in a compressor shell are monitored by a method that takes into account rapidly changing conditions within the shell. The system can determine the fluid'"'"'s sump temperature, high/low liquid levels, and can determine whether the thermistors are sensing the fluid as a liquid, gas, or a mixture of the two, such as a foam or mist of liquid and gas. For greater accuracy, thermistor readings can be dithered and filtered to provide temperature or voltage values having more significant digits than the readings originally processed through a limited-bit A/D converter. For faster response, limited microprocessor time is conserved by sampling thermistor readings at strategic periods that enable the microprocessor to identify certain conditions and temperatures via simple delta-temperature ratios and undemanding equations rather than resorting to exponential functions or lookup tables to determine time constants.
39 Citations
8 Claims
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1. A method for sensing a fluid in a compressor, wherein the fluid can exist in a plurality of states including at least one of a liquid state, a gaseous state, and a gas/liquid mixture, the method comprising:
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positioning a thermistor in heat transfer relationship with the fluid, wherein the thermistor has a thermistor temperature that varies; providing a feedback signal that varies with the thermistor temperature; obtaining a ripple signal by a conventional method step wherein the ripple signal is indicative of voltage fluctuation; adding the ripple signal to the feedback signal to create a dithered input; calculating a dither-based temperature value based on the dithered input; and based on the dither-based temperature value, determining at least one of the following;
a) a state of the fluid, and b) a temperature of the fluid.- View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification