New Approach for Airflow Measurement Using Thermal Resistance Simulation

Abstract

This paper presents a new model-based approach to detect and compensate errors of positive temperature coefficient (PTC) sensors used for airflow measurement.  From modeling and simulation, it can be shown that the thermal resistance of the sensor at self-heating mode was influenced by air flow magnitude. The sensor of type EPCOS-AG B59010 in a steel case, length 20 mm, diameter 2 mm was characterised over the flow rate range between 0 and 6 m/s and modeled to determine coupling thermal resistance interaction R th between the medium surrounding and sensor’s structure.  Soiling caused by dust transported with the air on the sensor surface changing in the thermal resistance has observed and simulated in an experiment using a cylindrical sheath of PTFE – Polytetrafluorethylen with known heat conductivity λ S = 0.24 W/Km and diameter D.  Parameters of model were then calibrated by evaluating current-voltage I(U)-characteristic at air velocity of v = 0m/s, and recalibration is then also used to correct the model parameters for v ¹ 0m/s. Result shows the soiling has exceeded critical thickness at D/d = 9 wherein the thermal resistance tends to be constant meaning cleaning sensor surface or replacing are needed.