PROCESS TEMPERATURE TRANSMITTER WITH IMPROVED TEMPERATURE CALCULATION
First Claim
1. In a process temperature transmitter, a method for providing a process temperature output, the method comprising:
- providing a measurement current through a circuit including a reference resistor and a resistance temperature device (RTD);
measuring a first voltage across the reference resistor while the measurement current flows therethrough;
measuring a first voltage across the RTD while the measurement current flows therethrough;
calculating a first resistance of the RTD based on the measured voltage across the reference resistor and the measured first voltage;
providing a first process temperature output based on the first resistance of the RTD;
measuring a second voltage across the RTD while a measurement current flows therethrough, the second measurement occurring after measurement of the first voltage;
estimating a second voltage across the reference resistor based on the measured second voltage across the RTD and the measured first voltage across the reference resistor;
calculating a second resistance across the RTD based on the measured second voltage and the estimated second voltage; and
providing a second process temperature output based on the second resistance.
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Accused Products
Abstract
In a process temperature transmitter, a method for providing a process temperature output is described. The method includes providing a measurement current through a circuit including a reference resistor and a resistance temperature device (RTD). A first voltage across the reference resistor is measured while the measurement current flows through it. A first voltage across the RTD is also measured while the measurement current flows through it. A first resistance of the RTD is calculated based on the measured voltage across the reference resistor and the measured first voltage. A first process temperature output is provided based on the first resistance of the RTD. A second voltage is subsequently measured across the RTD while a measurement current flows through it. A second voltage across the reference resistor is then estimated based on the measured second voltage across the RTD and the measured first voltage across the reference resistor. A second resistance across the RTD is calculated based on the measured second voltage and the estimated second voltage. A second process temperature output is provided based on the second resistance.
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Citations
20 Claims
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1. In a process temperature transmitter, a method for providing a process temperature output, the method comprising:
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providing a measurement current through a circuit including a reference resistor and a resistance temperature device (RTD); measuring a first voltage across the reference resistor while the measurement current flows therethrough; measuring a first voltage across the RTD while the measurement current flows therethrough; calculating a first resistance of the RTD based on the measured voltage across the reference resistor and the measured first voltage; providing a first process temperature output based on the first resistance of the RTD; measuring a second voltage across the RTD while a measurement current flows therethrough, the second measurement occurring after measurement of the first voltage; estimating a second voltage across the reference resistor based on the measured second voltage across the RTD and the measured first voltage across the reference resistor; calculating a second resistance across the RTD based on the measured second voltage and the estimated second voltage; and providing a second process temperature output based on the second resistance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. In a process temperature transmitter, a method for providing a process temperature output, the method comprising:
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providing a measurement current through a circuit including a reference resistor and a resistance temperature device (RTD); measuring a voltage across the RTD while the measurement current passes therethrough; estimating a reference voltage based on a previous reference voltage and the voltage measured across the RTD; calculating a resistance of the RTD based on the estimated reference voltage and the measured voltage; and providing a process temperature output based on the resistance of the RTD. - View Dependent Claims (17, 18, 19)
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20. A process temperature transmitter comprising:
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a loop communicator configured to couple to a process communication loop and to communicate in accordance with a process protocol; measurement circuitry configured to couple to a resistance temperature device having a resistance that varies with temperature and operably coupled to a reference resistor; and a controller coupled to the measurement circuitry and the loop communicator, the controller being configured to provide at least one process temperature output based on a current resistance temperature device resistance and a previous reference resistor resistance.
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Specification