US Patent 7647843 Universal sensor controller for a thermal anemometer

A flow switch uses an analog-to-digital converter combined with a multiplexer to measure voltages at one or more points of a measurement circuit and an algorithm within a microcontroller to calculate flow velocity. The measurement circuit has at least one sensor in the fluid stream. The sensor is heated by passing an electric current through the sensor. A second optional upstream sensor is not heated and is at the fluid temperature. The microcontroller then uses the voltage measurements with calibration information and equations based on the desired mode of operation to calculate the flow velocity.