Johnson noise thermometry for harsh environments

The technology of temperature measurement appears to some to be a mature field. However, to many, requirements for improved performance and reliability are a driver for continual scientific and technology advancement. Although Johnson noise has been proposed as a thermometry method for several decades, it is only recently that digital and analog electronics have made it possible to economically fabricate measurement systems based on Johnson noise. Johnson noise, which is a result of fundamental physics, is caused by the random thermal motions of electrons in all conductors. Its fundamental nature allows us to construct temperature measurement systems that do not require periodic calibration. Thus long, unattended operating intervals are feasible. Several unique implementations of Johnson noise thermometry (JNT) are possible. One permits temperature measurement without contacting the measured surface - inductive JNT. Another implementation measures the Johnson noise of a resistance element in contact with the measured surface - conductive JNT. The resistive element in conductive JNT can be an RTD. Apparatus have been recently fabricated demonstrating the practicality of both JNT implementations. A demonstration of conductive JNT is planned at a nuclear facility within two years. We will present new hardware implementations that allow real-time calibration of the signals that have the potential of allowing a fully-integrated, physically small and robust system to be achieved.