A flow sensor usually refers to a device for sensing the rate of fluid flow. Typically a flow sensor is the sensing element used in a flow meter, or flow logger, to record the flow of fluids.
While the objective is to measure the flow rate, the approach can vary and diverse. There are dozens of flow measuring methods available for industrial and commercial applications. Some that have a vane that is pushed by the fluid, some count the rotation of a rotary potentiometer driven by the flow, some measure the transfer of heat caused by the moving medium, some employ laser, ultrasound, or magnetic field to do the job.