Thick film mass airflow meter with minimal thermal radiation loss

Abstract

A mass airflow meter having a first electrically heated resistive film and a temperature dependent resistive film sandwiched between plastic layers and positioned within an air duct. Symmetrically positioned around the first resistive film are a pair of electrically heated resistive films and associated temperature sensors, also encapsulated within plastic layers. Electronic circuitry applies electric power to the resistive films for maintaining each of them at a predetermined temperature above ambient air temperature regardless of airflow. Since the temperature and emissivity of each plastic layer is substantially equal, the thermal radiation of each is also substantially equal. The thermal radiation loss by the first resistive film is therefore balanced by a substantially equal thermal radiation gain. Accordingly, substantially all the heat transfer by the first resistive film is through convectional heat transfer to the airflow. An accurate measurement of airflow is thereby achieved.