Optimized convection based mass airflow sensor circuit

Abstract

A method and apparatus for measuring the amount of flow of a flowing medium. The method and apparatus include a bridge circuit configured to develop a bridge voltage Vb such that the magnitude of the bridge voltage Vb is indicative of the amount of flow. The bridge circuit is configured without having an ambient temperature sensor, thus the bridge voltage is uncompensated with respect to ambient temperature. A thermistor circuit is configured to generate a temperature reference voltage indicative of ambient temperature. A conditioning circuit is configured to receive the uncompensated bridge voltage and the temperature reference voltage to process the same and generate a compensated bridge voltage with respect to ambient temperature. The compensated bridge voltage is indicative of fluid flow

1 . An apparatus for measuring the amount of flow of a flowing medium comprising: 
 a bridge circuit across which a bridge voltage Vb is developed such that the magnitude of the bridge voltage Vb is indicative of the amount of flow,    the bridge circuit including a signal side for deriving a signal voltage V RL  which is a voltage divided function of the bridge voltage Vb as determined at least in part by the resistance RH of a self-heated resistor in ratio to the resistance RL of a power resistor where the resistance RH is related to the temperature of the heated resistor as determined at least in part by the difference between the heat generated within the heated resistor as a function of the voltage applied across the heated resistor and the heat transferred away from the heated resistor as a function of the amount of fluid flow,    the bridge circuit also including a reference side for defining a reference voltage Vr which is a voltage divided function of the bridge voltage Vb as determined at least in part by a resistance Rp of a digital programmable potentiometer,    a thermistor circuit configured to generate a temperature reference voltage to correct the bridge voltage Vb with respect to ambient air changes,    and an amplifier responsive to the difference between the signal voltage V RL  and the reference voltage Vr for further altering the bridge voltage Vb to maintain the heat generated within the self-heated resistor thereby maintaining its temperature and related resistance RH so as to equalize the signal voltage V RL  and the reference voltage Vr.    
   
   
       2 . (canceled)  
   
   
       3 . (canceled)