TABLE OF CONTENTS In most PWR plants, the calibration of redundant sensors such as the primary coolant RTDs is verified periodically to ensure that any unacceptable drift or deviation is identified and corrected. For this purpose, the cross-calibration technique is used. This is a simple method that has received regulatory approval from the U.S. NRC, the British Nuclear Installation Inspectorate (NII), and others.
A more sophisticated and potentially more accurate technique also available for calibrating RTDs in-situ, is referred to as the "Johnson Noise" technique. [6] However, the Johnson Noise technique is still maturing and is, therefore, not currently used in nuclear power plants. ORNL and NIST in the United States and others in Australia, Germany, and elsewhere, have worked on the Johnson Noise technique for nearly three decades and continue to work to advance the technique for routine use in industrial applications. The Johnson Noise technique has application not only for calibrating RTDs in-situ, but also as the basis for developing a new and potentially very accurate sensor for high-temperature measurements.
A Johnson Noise thermometer is normally made out of an RTD that has sophisticated output electronics so it can measure a very small (in the nanovolt range) electrical signal that originates in the RTD element and varies with the temperature to which the RTD is exposed. The challenge posed by the Johnson Noise technique is in measuring the small signal in an industrial process at the end of long wires. This and other challenges posed by the Johnson Noise...
