PURPOSE: To obtain an air flow rate measuring device which requires no bridge by connecting the series circuit of the 1st and 2nd temperature dependent resistance in parallel to an electric heater, and controlling a current supplied to the electric heater in accordance with variation in the temperature at the connection point of the resistances.
CONSTITUTION: The 1st and 2nd temperature dependent resistances 11 and 12 arranged before and behind an electric heater 10 are connected in series and the output from the connection point (a) of the resistances 11 and 12 is supplied to an error amplifying circuit 40, which inputs the output at the connection point (b) of the resistance and electric heater 10, through an amplifying circuit 30. The output of the circuit 40 is amplified by a power amplifier 50, whose output is supplied to the point (b) through a line 60. Consequently, the potential at the point (a) varies with an increase or decrease in air flow rate and the power amplifying circuit 50 varies a current supplied to the electric heater 10 through the error amplifying circuit 40, but the square of this current value is proportional to the air flow rate, so the value of the current supplied to the electric heater is measured to find the air flow rate.
KAWAI HISASHI
KOHAMA TOKIO
OOHAYASHI HIDEKI
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