Abstract:
A temperature transmitter (10) and a process control system includes a sensor input (1, 2, 3, 4) for coupling to a temperature sensor (16) having a temperature dependent resistance. Resistance measuring circuitry (20, 26, 50) couples to the sensor input (1, 2, 3, 4) and provides a resistance output related to resistance of the temperature dependent resistance. Analog to digital conversion circuitry (78, 88) couples to the sensor input (1, 2, 3, 4) and provides a digital output related to AC signals across the sensor input. Digital signal processing circuitry (64) isolates a Johnson noise component of the AC signals and provides a digitized Johnson output. Temperature measurement circuitry provides a calibrated temperature output based upon the resistance output and the digitized Johnson noise output. Output circuitry (24) transmits the calibrated temperature output over the process control loop (11).
Abstract:
A transmitter (100) in a process control system includes a resistance sensor (110) sensing a process variable and providing a sensor output. Sensor monitoring circuitry (116) coupled to the sensor (110) provides a secondary signal related to the sensor (110). Analog-to-digital conversion circuitry (114) coupled to the sensor output and the sensor monitoring circuitry (116) provides a digitized sensor output and a digitized secondary signal. Output circuitry (124) coupled to a process control loop (102, 104) transmits a residual life estimate related to residual life of the sensor. A memory stores a set of expected results (120) related to the secondary signal and to the sensor (110). Diagnostic circuitry (118) provides the residual life estimate as a function of the expected results (120) stored in the memory, the digitized sensor output and the digitized secondary signal.
Abstract:
A transmitter (100) in a process control system includes a resistance sensor (110) sensing a process variable and providing a sensor output. Sensor monitoring circuitry (116) coupled to the sensor (110) provides a secondary signal related to the sensor (110). Analog-to-digital conversion circuitry (114) coupled to the sensor output and the sensor monitoring circuitry (116) provides a digitized sensor output and a digitized secondary signal. Output circuitry (124) coupled to a process control loop (102, 104) transmits a residual life estimate related to residual life of the sensor. A memory stores a set of expected results (120) related to the secondary signal and to the sensor (110). Diagnostic circuitry (118) provides the residual life estimate as a function of the expected results (120) stored in the memory, the digitized sensor output and the digitized secondary signal.
Abstract:
A temperature transmitter (10) and a process control system includes a sensor input (1, 2, 3, 4) for coupling to a temperature sensor (16) having a temperature dependent resistance. Resistance measuring circuitry (20, 26, 50) couples to the sensor input (1, 2, 3, 4) and provides a resistance output related to resistance of the temperature dependent resistance. Analog to digital conversion circuitry (78, 88) couples to the sensor input (1, 2, 3, 4) and provides a digital output related to AC signals across the sensor input. Digital signal processing circuitry (64) isolates a Johnson noise component of the AC signals and provides a digitized Johnson output. Temperature measurement circuitry provides a calibrated temperature output based upon the resistance output and the digitized Johnson noise output. Output circuitry (24) transmits the calibrated temperature output over the process control loop (11).