Whenever a flow passes an obstacle in a pipe, it causes a drag to push the obstacle in the direction of the flow. If the obstacle is constrained by a force that is equal and opposite to the drag, the magnitude of that force is used to determine the flow rate. This is the operating principle of the target flowmeter.

Drag force consists of two parts. One is the friction drag caused by the viscosity of the fluid as it slides by the obstacle. The other is the pressure drag caused by the pressure difference between the pressures immediately before and immediately after of the obstacle.

Governing equation:

All the factors in the equations are known except for Ft and Q. However, Ft can usually be measured through a series of strain gauges. And that leaves Q to be calculated to give the flow rate in volume/s. Target is one of the most versatile flowmeters in the market. They are used to measure liquids, gases, vapors, dirty fluids, light slurries, and high viscosity fluids- particularly where fluid characteristics preclude the use of flowmeters with pressure taps or moving parts.