Temperature transmitter with on-line calibration using johnson noise

A transmitter in a process control system, comprising:

• a sensor input for coupling to a temperature sensor having a temperature dependant resistance;
• resistance measuring circuitry coupled to the sensor input having resistance output related to resistance of the temperature dependent resistance;
• an amplifier coupled to the sensor input providing an amplified output having an AC noise component and a Johnson noise component;
• analog to digital conversion circuitry coupled to the amplified output providing a digital output;
• digital signal processing circuitry coupled to the digital output for isolating the Johnson noise component and providing a digitized Johnson noise output;
• temperature measurement circuitry coupled to the resistance measurement circuitry and the digital signal processing circuitry providing a calibrated temperature output based upon the resistance output and the digitized Johnson noise output;
• and
• output circuitry for coupling to a process control loop and transmitting the calibrated temperature output over the loop.