Measurement of AC and DC Insulation Leakage in Platinum Resistance Thermometers up to 960 °C

Abstract

It is well known that insulation leakage at high temperatures can be one of the major contributions to uncertainties in measured temperatures above 600 • C. On the one hand, this insulation leakage shunts the sensor resistor leading to systematic errors in the measured temperatures, which are, in principle, characteristics of each thermometer. On the other hand, at high temperatures, degradation of the insulation materials used in the furnaces enhances the decrease of the insulation impedance between the thermometer and the furnace which also causes a systematic temperature measurement error. Two high-temperature standard platinum resistance thermometers have been used to measure these effects in different heat-pipe and three-zone furnaces. One of them was open-circuited by cutting the sensing element end allowing the measurement of the resistance between the two pairs of current-potential leads. Two different setups were used to measure the AC and DC insulation resistances leadto-lead and thermometer-to-furnace. The first one was a teraohmeter with a high value standard resistor in parallel with the leakage resistance to be measured and the other one an LCR meter to perform the AC measurements at different frequencies. In this article, results for both methods are presented.

Correlation Between Insulation Resistance and Temperature Measurement Error in Type K and Type N Mineral Insulated, Metal Sheathed Thermocouples

“…2a. As expected [2,9], the resistance decreases approximately exponentially with temperature, and generally increases with increasing thermocouple cable thickness. This can be seen in Fig.…”

Desarrollo de la infraestructura y del sistema de medida para la calibración de termopares de metales nobles en puntos fijos hasta 13242C

“…La resistencia de las vainas cerámicas que actúan como aislante de cada termolemento y de los aislantes de los propios hornos de temperatura, decrecen con la temperatura, especialmente a temperaturas superiores a 600 ºC para los materiales de los hornos y a temperaturas superiores a 1500 ºC para vainas de alúmina de alta pureza. Esta falta de asilamiento hace que los electrones generados por efecto Seebeck migren por dichos materiales de aislamiento, en vez de por los propios hilos metálicos, generándose fuerzas electromotrices parásitas y, por tanto, un error en la medida de temperatura [31].…”