A flowmeter suitable for flow measurement of extremely-low temperature fluids and high temperature fluids includes a flow path pipe having a flow path for fluid to flow through; an impeller supported in the interior of the flow path pipe in a rotatable manner; and a sensor that measures the flow of the fluid flowing in the flow path through the rotation of the impeller. The sensor has a metal-based wiring substrate inside a sensor housing provided outside the flow path pipe. The wiring substrate is equipped with a magnetic sensor package that detects the magnetic force of the impeller; a heater that heats the wiring substrate; and a temperature control circuit that controls the heater to power on/off based on the temperature of the wiring substrate.

A method of fabricating a paddlewheel for a flow meter is provided. The method can include providing an inner part of the paddlewheel. The method can also include inserting a plurality of magnets in the inner part of the paddlewheel. The method can also include overmolding an outer part of the paddlewheel over the inner part of the paddlewheel.