Dual-Element, Solid-State Fluid Flow Sensor

The theory, design and operation of a solid-state fluid-flow sensor are presented together with some results of laboratory evaluations. Two silicon sensing elements, mounted inside a cylindrical tube and connected through a resistance bridge, are maintained at a constant temperature differential with one element at the temperature of the fluid, providing a reference. The magnitude of flow can be determined from the heat transfer rate off the hotter of the two elements. Flow rates between about 2 and 40 liters/hr may be resolved with the present sensor arrangement. Dynamic range and resolution can be adjusted for particular applications by varying the values of the fixed bridge resistors, thus varying the temperature differential between sensors, or by varying the tube diameter. The measurement of fuel flow is a potential application.