Most rotameters are indicating devices only. They may be equipped to transmit flow information
electronically by adding sensors to detect the plummet’s position in the tube, but this is not common
practice.
Rotameters are very commonly used as purge flow indicators for pressure and level measurement
systems requiring a constant flow of purge fluid (see sections 19.6.6 and 20.3.2 for practical examples).
Such rotameters are usually equipped with hand-adjustable needle valves for manual regulation of
purge fluid flow rate