How are flowmeter accuracy rates stated?
The accuracy of flowmeters, and other instruments, is usually stated as either a % of full scale (FS) or a % of reading. It is important to understand the meaning of each as they represent very different numbers. A flowmeter with a velocity accuracy of 1% FS and a range of 20 ft. per second (fps) would have an error of ± 0.2 fps throughout the operating range. At 1 fps this flowmeter has an error of 0.2 fps or 20% of reading. It is only at 20 fps that this flowmeter actually performs to an accuracy of 1%.A flowmeter with its velocity accuracy expressed as 1% percent of reading with the same 20 fps operating range will have an accuracy of 1% regardless of the actual velocity.
