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By using a simple model to relate the electromotive force drift rate of Pt–Rh thermoelements to dS/dc, i.e. the sensitivity of the Seebeck coefficient, S, to rhodium mass fraction, c, the composition of the optimal pair of Pt–Rh wires that minimizes thermoelectric drift can be determined. The model has been applied to four multi-wire thermocouples each comprising 5 or 7 Pt–Rh wires of different composition. Two thermocouples were exposed to a temperature of around 1324 °C, one thermocouple to around 1492 °C, i.e. the melting points of the Co–C and Pd–C high temperature fixed points, respectively, and one thermocouple to a series of temperatures between 1315 °C and 1450 °C. The duration of exposure at each temperature was several thousand hours. By performing repeated calibrations in situ with the appropriate fixed point during the high temperature exposure, the drift performance has been quantified with high accuracy, entirely free from errors associated with thermoelectric homogeneity. By combining these results it is concluded that the Pt-40%Rh versus Pt-6%Rh is the most stable at the temperatures investigated. A preliminary reference function was determined and is presented.

We present an imaging phosphor thermometry system using the time-domain intensity ratio technique and demonstrate surface temperature measurements that are traceable to ITS-90 with a calibration Standard uncertainty of 0.5 °C, over the range 20 °C to 450 °C. The thermographic phosphor used was Mg 4 FGeO 6 :Mn. Typically, imaging phosphor thermometry systems make use of the intensity ratio of the phosphor emission in two discrete wavelength bands, measured simultaneously using two cameras viewing the same surface. However, difficulties can arise with image registration (the requirement to spatially align the two images) due to lens distortion, non-normal viewing angles and camera alignment, and this can result in large temperature errors. The time-domain intensity ratio technique presented here avoids these difficulties by capturing two images at different times during the phosphorescence decay process using a single monochrome camera. Each pixel of the camera integrates the light collected over the exposure time. By careful selection of an appropriate exposure time, along with the timing of each exposure (image gating), it is possible to collect two specific time integrated portions of the phosphor decay curve. The phosphor decay time can then be calculated quickly and uniquely from the ratio of these two signals and related to the temperature through calibration. With this technique, there is no requirement for high framerates and satisfactory results can be obtained using a relatively inexpensive camera provided that suitable triggering and exposure control are available. Here, we provide a description of the technique, the instrumentation, calibration, and preliminary measurement made on a resistively heated steel coupon, where the standard uncertainty for a single imaged pixel (80 μm × 80 μm) was 7.7 °C, 6.6 °C and 3.8 °C at temperatures of 200 °C, 300 °C and 400 °C respectively. Additionally, a sensitivity analysis and an uncertainty budget are provided.

Intermediate level waste containers are used for the storage of an assortment of radioactive waste. This waste is heatgenerating and needs monitoring and so this work was undertaken to determine whether the mean internal container temperature can be inferred from the temperature of the vent. By using two independent thermometry techniquesphosphor thermometry and thermal imaging -the internal temperature was demonstrated to be proportional to the vent temperature as measured by both methods. The correlation is linear and given suitable characterisation could provide robust indication of the internal bulk temperature.