Abstract

A sensor for measuring the flow rate of a fluid through a conduit. The fluid flow rate in the vicinity of a heated temperature sensor is made to cyclically vary from a minimum to a maximum to produce a cyclic signal indicative of the heat removed from the sensor by the fluid flow. The magnitude of the cyclic signal is representative of the mass flow rate of the fluid. A detection circuit responsive to the cyclic signal extrapolates therefrom the mass flow rate and provides an output signal related thereto. Mechanically and electrically balanced configurations enable high speed and high precision measurements to be obtained. Bypass and sampling embodiments are presented. In alternative preferred embodiments circuits are disclosed for determining and maintaining a constant average temperature difference between the sensors and the fluid being sensed, to thereby replace heat loss by the sensors as a result of contact with the fluid being sensed.