A Venturi tube is primarily used for what purpose in instrumentation?

A Venturi tube is primarily utilized for flow measurement due to its design, which facilitates the determination of flow rates in a fluid system. The tube's shape includes a converging section that narrows down and then diverges, creating a difference in pressure inside the tube. According to Bernoulli's principle, as the fluid flows through the narrower section, its velocity increases, causing a drop in pressure. By measuring the pressure difference between the wider and narrower sections of the tube, you can apply the principles of fluid dynamics to calculate the flow rate of the fluid passing through. This makes the Venturi tube a key instrument in various applications where knowing the flow is vital for process control and monitoring.

The other options focus on different measurements that are not the primary function of a Venturi tube. Pressure indication relates to the measurement of pressure levels, while temperature control is about regulating heat within a system. Level indication measures the height of liquids in a container. None of these functions align with the primary use of a Venturi tube in flow measurement.