Patent ID: 7647843

Claim:
A flow switch that measures a flow velocity of a fluid flowing through a conduit, comprising: a first sensor in the conduit and immersed in the fluid, wherein: the first sensor has a first resistance that changes with temperature; the first sensor is heated by one of (1) a first current flowing through the first sensor and (2) the first current flowing through a heating element thermally coupled to the first sensor, the first sensor exchanging heat with the fluid; a second sensor in the conduit and immersed in the fluid, wherein: the second sensor has a second resistance that changes with temperature; and the second sensor is substantially at the temperature of the fluid; and a microcontroller containing firmware, wherein: the microcontroller calculates the first current; the microcontroller calculates the first and the second resistances; the microcontroller provides a control signal that sets the first current based on at least one of the first current, the first resistance, and the second resistance; and the microcontroller calculating the flow velocity based on at least one of the first current, the first resistance, and the second resistance; and the microcontroller provides an output signal related to the flow velocity.