Patent ID: 6813570
Filing Date: 2004-11-02
Classification: G01F

Abstract:
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 VRL 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 potentiometer, and an amplifier responsive to the difference between the signal voltage VRL and the reference voltage Vr for 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 VRL and the reference voltage Vr.