These types of instruments are ideal for saturated steam or super heated steam applications. The principle itself is simple, there is a bluff body within the center of the instrument. This creates vortexes after shedding has occurred, when a fluid such as water flows past the bluff body (as opposed to streamlined) body. The frequency that the vortexes are shed depend on the size and shape of the body. It is ideal for applications where low maintenance costs are important. However, there will be a set amount of flow required for a reading to be registered.