Method for sensing a fluid in a compressor shell
First Claim
1. A method for sensing a fluid in a compressor, wherein the fluid exists in at least one of a plurality of states including at least one of a liquid state, a gaseous state, and a gas/liquid mixture, the method comprising:
- cyclically electrically heating and thermally cooling a thermistor that has a temperature that varies and is in heat transfer relationship with the fluid so that the thermistor experiences a plurality of temperatures during a plurality of heating and cooling cycles, the temperature of the thermistor decreases during the cooling cycle;
measuring the plurality of temperatures of the thermistor while the temperature of the thermistor decreases as a result of the temperature of the thermistor being greater than that of the fluid during the cooling cycle;
calculating via a microprocessor, a delta-temperature ratio involving the plurality of temperatures that the thermistor experienced during the plurality of heating and cooling cycles; and
determining, via the microprocessor, in which state the fluid exists based on magnitude of the delta-temperature ratio, wherein the magnitude of the delta-temperature ratio indicates in which of the liquid state, the gaseous state and the gas/liquid mixture that the fluid exists.
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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.
37 Citations
10 Claims
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1. A method for sensing a fluid in a compressor, wherein the fluid exists in at least one of 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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cyclically electrically heating and thermally cooling a thermistor that has a temperature that varies and is in heat transfer relationship with the fluid so that the thermistor experiences a plurality of temperatures during a plurality of heating and cooling cycles, the temperature of the thermistor decreases during the cooling cycle; measuring the plurality of temperatures of the thermistor while the temperature of the thermistor decreases as a result of the temperature of the thermistor being greater than that of the fluid during the cooling cycle; calculating via a microprocessor, a delta-temperature ratio involving the plurality of temperatures that the thermistor experienced during the plurality of heating and cooling cycles; and determining, via the microprocessor, in which state the fluid exists based on magnitude of the delta-temperature ratio, wherein the magnitude of the delta-temperature ratio indicates in which of the liquid state, the gaseous state and the gas/liquid mixture that the fluid exists. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification