Insulation Degradation in Long, Mineral Insulated Metal Sheathed Thermocouples

摘要

As the lead temperature of a mineral insulated thermocouple is raised, the resistance of the insulator decreases and acts as a resistive shunt on any thermoelectric emf which is generated, thereby leading to errors in temperature measurement. Furnace tests are described in which such errors are demonstrated and a computer code has been used to predict the magnitudes of the errors. A method of predicting the performance of a thermocouple under high lead temperature conditions is proposed, which could be used as a selection process by a thermocouple manufacturer. The work has applications in the field of nuclear reactor in-core temperature instrumentation, in high temperature test rigs and in fire test facilities, where long thermocouple leads pass through high temperature environments. (Atomindex citation 14:747054)