Temperatures above 1000 °C are important in many industries and are generally measured by means of thermocouples. Thermocouples have the disadvantage, however, that they cannot be calibrated once irreversible ageing has taken place. Platinum resistance thermometers are commercially available for use up to 850 °C but their use at higher temperatures is limited due to the sensitivity of the platinum resistive wire to stress and their industrial application above 1000 °C is unlikely.

The aim of this project was to develop an accurate resistance thermometer, based upon MoSi2, which can be used at temperatures up to 1500 °C. A noise thermometer, initially tested with a PtRh sensor, would serve as a standard thermometer to evaluate the resistance temperature characteristic of the MoSi2 based resistance thermometer. The new MoSi2 thermometer would be used either alone, as a conventional resistance thermometer, or in conjunction with the noise thermometer. In the latter case, the device would be used either as a MoSi2 resistance thermometer that would be self-calibrating by noise thermometry, or, alternatively, as a noise thermometer equipped with a MoSi2 sensor.
The MoSi2 resistance thermometer was found to suffer from an initial anneal effect. In order to eliminate this effect, the thermometer needs to be stabilised before use. Longer term stabilisation experiments indicate that the thermometer stabilises to within what can be achieved with thermocouples that are presently available on the market. This resistance thermometer promises to be a good alternative for these thermocouples because it can be calibrated more readily. The sensitivity of the thermometer was found to compare well with platinum resistance thermometers. The thermometer was found to be quite linear over the entire range from 0°C to 1450°C.
A patent has been applied for on the developed resistance thermometer and it is planned to develop a commercial product. The industrial application is foreseen of relatively cheap MoSi2 resistance thermometers that are periodically calibrated in situ on the basis of their own thermal noise by means of a single noise thermometer.
The noise thermometer was constructed and measurements were made at a number of fixed points in order to verify its accuracy. Prototype MoSi2 resistance thermometers were designed and constructed and high temperature ageing tests carried out. Subsequently, the final MoSi2 thermometers were designed and constructed, and their anneal characteristics and their high temperature stability were evaluated up to 1600 °C. The resistance dependence of the MoSi2 thermometer was determined using the noise thermometer.