What are the two primary types of flow measurement devices?

The two primary types of flow measurement devices are classified as positive displacement flow meters and velocity flow meters.

Positive displacement flow meters operate by trapping a fixed volume of fluid and then releasing it, allowing for accurate measurement of the flow rate based on the number of times the volume is filled and emptied. These devices are particularly useful for applications where high accuracy is required, and they can measure flows of varying viscosity without significant adjustments.

On the other hand, velocity flow meters measure the velocity of the fluid passing through a pipe and calculate the flow rate based on the cross-sectional area of the pipe. These devices, such as turbine and electromagnetic flow meters, are widely used in various industrial applications due to their broad range of measurement capabilities and cost-effectiveness.

Together, these two categories encompass the majority of flow measurement technologies available, covering different operational needs and fluid types. While the other answer choices contain specific types of flow meters, they do not encompass the broad classifications that define primary measurement principles.