True about Rotameter –
As the gas flows through the rotameter, bobbin rises and the upper end of bobbin determines the flow rate.
Rotameter works on variable area (variable orifice) and constant pressure principle (not variable pressure).
Causes of inaccurate reading in rotameter are :- Static electricity, Dirt inside the tube, Non-vertical tube, back pressure by ventilator, Defect in top sealing washer.
Rotameter reading may not get affected by dirt inside the tube
Rotameter reading may not get affected by static electricity
The height to which bobbin rises indicates the flow rate
A rotameter is a variable pressure flowmeter