Calibration of process control temperature transmitter
First Claim
1. A temperature transmitter in a process control loop, comprising:
- a terminal block for receiving a temperature calibration input resistance from a temperature sensor thermally coupled to the terminal block for cold junction compensation calibration;
a cold junction compensation temperature sensor coupled to the terminal block for providing an output related to cold junction temperature of the terminal block;
A/D conversion circuitry for converting the temperature calibration input resistance and the output related to cold junction temperature into digital values;
I/O circuitry coupling to the process control loop and sending and receiving information over the loop; and
microprocessor circuitry coupled to the A/D converter for calculating a calibration value for the cold junction compensation temperature sensor based upon the temperature calibration input resistance and the cold junction temperature measured by the cold junction compensation temperature sensor.
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Accused Products
Abstract
A transmitter in a process control loop measures temperature. A calibrator includes a known calibration element which is connected to the transmitter. Software in the transmitter compares a measured value of the calibration element with the actual value of the calibration element and responsively calibrates the transmitter. The calibrator includes a temperature calibration sensor for coupling to a terminal block of the transmitter. The temperature calibration sensor provides an actual temperature input to the transmitter. The transmitter measures actual temperature of the terminal block and compares actual temperature with a temperature measured by an internal terminal block temperature sensor, and responsively calibrates the internal temperature sensor.
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Citations
14 Claims
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1. A temperature transmitter in a process control loop, comprising:
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a terminal block for receiving a temperature calibration input resistance from a temperature sensor thermally coupled to the terminal block for cold junction compensation calibration; a cold junction compensation temperature sensor coupled to the terminal block for providing an output related to cold junction temperature of the terminal block; A/D conversion circuitry for converting the temperature calibration input resistance and the output related to cold junction temperature into digital values; I/O circuitry coupling to the process control loop and sending and receiving information over the loop; and microprocessor circuitry coupled to the A/D converter for calculating a calibration value for the cold junction compensation temperature sensor based upon the temperature calibration input resistance and the cold junction temperature measured by the cold junction compensation temperature sensor. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A temperature transmitter in a process control loop, comprising:
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a terminal block for coupling to a sensor resistance; a current source providing a current through the sensor resistance and through a reference resistance coupled in series with the sensor resistance; an A/D converter which converts voltage differences across the sensor resistance and the reference resistance into digital values; I/O circuitry for sending and receiving information; memory containing a value of the reference resistance RREF and a resistance calibration value RCAL3 ; and a microprocessor receiving an actual value of the sensor resistance from the I/O circuitry, receiving the digital values of the voltage differences across the sensor resistance and the reference resistance from the A/D converter, and receiving the value of the reference resistance RREF from memory and responsively calculating a new calibration value RCAL3(NEW), wherein RCAL3(NEW) is stored in the memory as RCAL3 for subsequent use during temperature measurements. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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Specification