Abstract: A thermal type flow meter for measuring the mass flow rate of a fluid medium especially that of a gas in a duct, said meter comprising a plurality of thermistors operated electrically in the "self-heated" mode located on the trailing edge of rigid, rectangular members oriented with the long axis perpendicular to the primary direction of flow. The thermistors are located strategically throughout transverse plan of the duct. Each sensor (thermistor) is located substantially at the center of the downstream end of a right circular cylinder. The voltage drops through all of the thermistors located in a two-dimensional array oriented normal to the flow direction are summed electrically using an operational amplifier. Due to both the geometrical location of the sensors and the characteristics of thermistors in the self-heated mode, the voltage drop across each sensor is linearly proportional to the local mass flow velocity.

Abstract: Improved structure for measuring the air flow in large conduits, such as those used to supply air conditioning and heating ducts, by sampling substantially all of the cross sectional area of the conduit in a given transverse plane to obtain an average electrical signal which is compared with a reference signal to obtain a measured voltage corresponding to average flow.