The Annubar primary element is an averaging

Pitot tube A pitot ( ) tube (pitot probe) measures fluid flow velocity. It was invented by a French engineer, Henri Pitot, in the early 18th century, and was modified to its modern form in the mid-19th century by a French scientist, Henry Darcy. It ...

manufactured by Rosemount Inc. used to measure the flow of fluid in a pipe. A Pitot tube measures the difference between the

static pressure In fluid mechanics the term static pressure has several uses: * In the design and operation of aircraft, ''static pressure'' is the air pressure in the aircraft's static pressure system. * In fluid dynamics, many authors use the term ''static pres ...

and the flowing

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

of the media in the pipe. The

volumetric flow In physics and engineering, in particular fluid dynamics, the volumetric flow rate (also known as volume flow rate, or volume velocity) is the volume of fluid which passes per unit time; usually it is represented by the symbol (sometimes ). ...

is calculated from that difference using

Bernoulli's principle In fluid dynamics, Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid's potential energy. The principle is named after the Swiss mathematici ...

, taking into account the pipe's inside diameter.Perry, Robert H., Don W. Green. "Perry's Chemical Engineer's Handbook, Seventh Edition". pages 10-8 to 10-9. McGraw Hill. 1997 An Annubar, as an averaging Pitot tube, takes multiple samples across a section of a pipe or duct, averaging the differential pressures encountered accounting for variations in flow across the section.

References

Measuring instruments {{engineering-stub