An apparatus for measuring the quantity of airflow passing through an intake passage of an engine.

摘要

Disposed in a intake pipe (13) of an engine is a temperature-sensitive element (17) formed of a resistance element whose resistance value varies with temperature. A heating current is supplied to the temperature-sensitive element (17) through a transistor (37). The voltage of the heating current is set by a constant-voltage circuit (38, 49). The temperature of the temperature-sensitive element (17) is compared with a reference temperature of an auxiliary temperature-sensitive element (30). When the temperature of the temperature-sensitive element (17) is increased to a predetermined level, an output signal is delivered from a comparator (33). A flip-flop circuit (34) is reset by the output signal from the comparator (33), and is set by a start pulse signal. When the flip-flop circuit (34) is set, the transistor (37) is turned on, allowing the heating current to be supplied to the temperature-sensitive element (17). A burning-off instruction signal is supplied to a monostable multivibrator (42), and a signal with a) duration suited for the burning-off operation is delivered' from an AND circuit (43). In response to the output signal from the AND circuit (43), the flip-flop circuit (34) is held set, and a reference voltage supplied to the differential amplifier (39) is changed to a low level.