THERMAL TYPE AIR FLOWMETER

摘要

PURPOSE:To correct the flow rate signal of a thermal type air flowmeter when a back flow occurs so as to improve the accuracy of measurement of the flowmeter by detecting the flow rate of air by means of an exothermic resistor and the flowing direction of the air from the difference between the signals of temperature sensors respectively provided on the upstream and downstream sides of the exothermic resistor. CONSTITUTION:A film type exothermic resistor 4 is formed on a substrate 3 composed of such an electrical insulator as a ceramic, silicon, etc., and two temperature detecting resistors 5 and 6 are respectively provided on the upstream and downstream sides of the resistor 4. In addition, an intake air temperature compensating resistor 7 is provided. The resistors 4 and 7 constitute a bridge together with resistors 10 and 11 and fetches a flow rate signal as the voltage Vi at the midpoint of the bridge by feeding back signals to a transistor 13 through a differential amplifier 12. The resistors 5 and 6 similarly constitute a bridge together with resistors 8 and 9 and the difference between both signals is fetched as an air flow signal through a comparator 14. A microcomputer 15 fetches the two signals and outputs an accurate flow rate signal by correcting the flow rate signal when the computer 15 discriminates that a back flow occurs.