A turbine flowmeter is a volumetric device that infers flow rate from the speed of a freely rotating turbine placed in the fluid stream. When liquid or gas enters the meter body, a flow straightener or stator removes swirl and guides the fluid into an axial path. The moving fluid strikes the angled blades of the rotor, creating a torque that spins it. The rotor speed depends on the average fluid velocity through the known cross-sectional area, so under designed conditions it is proportional to volumetric flow rate.

As each rotor blade passes a magnetic pickup mounted outside the flow path, the blade changes the magnetic circuit, causing a pulse in the pickup coil. These pulses are shaped by an amplifier into a clean square-wave frequency. Because every blade passage represents a small swept volume, the pulse frequency is directly proportional to flow. A transmitter converts this frequency into flow rate and totalized volume using the meter K-factor, usually expressed as pulses per liter or pulses per gallon. This pulse output supports flow control and batching.

The linear relationship holds best within a specified Reynolds number range. Viscosity, density, lubrication, bearing friction, and magnetic drag can affect accuracy at low flow. Proper upstream and downstream straight piping helps maintain a stable velocity profile. Turbine flowmeters offer fast response, high repeatability, and wide turndown, making them common in oil, gas, water, chemical, and custody-transfer applications.