TRANSIENT TEMPERATURE DISTRIBUTION WITHIN THERMAL SENSING ELEMENTS.

This report presents a criterion by which to judge the acceptability of the premise of instantaneous spatially uniform temperatures within a temperature sensing element during thermal transients, and subsequent use of a simplified analysis to determine the dynamic error in measurement. Errors inherent in temperature measuring elements immersed in fluid streams are discussed for both steady-state and transient temperature conditions. Errors in steady-state conditions are due to calibration error, irregularities in signal transmission, mechanical malfunction on instrumentation, and thermal effects owing to the exchange of heat between the measuring element and its environment. These may generally be reduced to an acceptable minimum by proper design and installation. An additional source of error which must be considered in transient temperature conditions is the thermal lag which results from the fact that any physical system immersed in a fluid of changing temperature does not respond with time nor amplitude as does the fluid itself. Author