Error correction for temperature measurement in insulating material: Application to the aluminum electrolysis cell

Temperature measurements using thermocouples are an essential input for many industrial processes. It allows the control of their heat balance, the calibration of numerical simulations, and the optimization of process operation and control. Even though it is a very common and straightforward practice, significant errors may occur when the temperature measurements are performed inside an insulating material such as sand, alumina, or other powder materials. For instance, contact resistance, fin effect, and macro-constriction are factors that affect the temperature measured by the thermocouple. Experimental work along with numerical studies were performed to find ways to identify and correct these inaccuracies. The result is a set of recommendations and the development of a new strategy for "a posteriori" error correction which depends on two parameters beta = Ep/HACM and theta = Timp/Tamb. Ep, HACM, Timp and Tamb are respectively the probe penetration depth, the total insulating material thickness, the temperature at the bottom boundary and the ambient air temperature. The new correction strategy has been validated with an experimental laboratory setup and tested using industrial measurements. Results of temperature measurements performed inside insulating material at high temperature show that the error in temperature measurements range from 40 degrees C up to 100 degrees C and can be reduced by up to 80% with this new strategy.