What is a rotameter used for?

A rotameter is an instrument specifically designed for measuring the flow rate of gases or liquids in a closed tube. It operates based on the principle of variable area flow measurement, where the flow of fluid lifts a float within a tapered tube. As the flow rate increases, the float rises in the tube, opening a larger area for the fluid to flow through, which allows the measurement of the flow rate based on the position of the float.

In this context, the use of a rotameter is particularly effective for monitoring gas flow from a cylinder, such as in gas distribution systems, laboratory settings, or various industrial applications. The calibration of the rotameter is generally done in such a way that the height of the float corresponds directly to a specific flow rate, making it a reliable tool for flow measurement.

The other options mentioned do not align with the primary function of a rotameter. Measuring temperature and pH involves entirely different instruments, while filling a line with water is typically managed through valves and pumps instead of a measuring device like a rotameter.