Primary flow element

A primary flow element is the element of a flow meter that serves to indicate the quantity or velocity of flow.

For example, in the case of an orifice flow meter, the differential pressure across the orifice plate is the primary flow element. A turbine meter is equipped with a magnetic pickup that senses the proximity of the turbine blades as the fluid motion causes the turbine to spin; this pickup is the primary flow element for a turbine meter. Diaphragm meters and other positive displacement meters are equipped with a crank shaft, the rotation of which acts as the primary flow element.