Platinum Resistance Thermometry in the Range 630–900 °C

The performance of commercially produced, standard platinum resistance thermometers has been investigated in the region 630 - 900 °C. Particular attention was paid to resistance stability, quenching effects, and electrical insulation leakage. The limit of 900 °C was dictated by the use of mica insulation in these instruments. The most serious problem encountered was that of insulation leakage at both high and low temperatures. The low temperature leakage was due to water that had been released from mica insulation when the thermometers were used at high temperatures, and this problem is studied in some detail here. A relationship between the magnitude of the galvanometer `wet kick' and the insulation resistance has been established. The useful lifetime of the dry air filling in a thermometer has been estimated for various conditions of use. Based on these studies, procedures have been recommended for stabilizing platinum resistance thermometers, annealing-out quenching effects, and reducing insulation leakage over this temperature range.