Time domain measurement and control system for a hot wire air flow sensor

摘要

A time domain measurement and control system for a hot wire air flow sensor is disclosed in which the air flow sensor is of the type having a resistive heating element with an input end and an output end. The control system includes a fixed frequency variable width pulse generator which generates a pulse train through the heating element. This pulse train, furthermore, has a first predetermined voltage amplitude. The output voltage amplitude of the pulse train is determined at the outlet end of the heating element while a control circuit varies the duty cycle of the pulse train to maintain the output voltage amplitude at a second predetermined voltage level. The duty cycle of the pulse train is proportional to the air flow rate through the air flow sensor. In a modification of the invention, a fixed width variable frequency pulse train is generated through the resistive heating element and the frequency of the pulse train is varied to maintain the output voltage amplitude of the pulse train at the outlet end of the resistive heating element at a second predetermined voltage level. In this modification, the frequency of the pulse train is proportional to the air flow rate through the air flow sensor.