Measuring transient temperature of the medium in power engineering machines and installations

Under steady-state conditions when fluid temperature is constant, there is no damping and time lag and temperature measurement can be made with high accuracy. But when fluid temperature is varying rapidly as during start-up, quite appreciable differences occur between the true temperature and the measured temperature because of the time required for the transfer of heat to the thermocouple placed inside a heavy thermometer pocket. In this paper, two different techniques for determining transient fluid temperature based on the first and second order thermometer model are presented. The fluid temperature was determined using measured thermometer temperature, which is suddenly immersed into boiling water. To demonstrate the applicability of the presented method to actual data, the air temperature which changes in time, was calculated based on the temperature readings from the sheathed thermocouple.