Which instrument is typically used to measure flow rate in a pipe?

The magnetic flowmeter is specifically designed to measure the flow rate of liquids in a pipe. This instrument operates based on Faraday's law of electromagnetic induction, which states that a voltage is induced when a conductive fluid passes through a magnetic field. By measuring this induced voltage, the flowmeter can accurately determine the flow rate of the liquid.

Unlike other instruments listed, the magnetic flowmeter excels in applications involving conductive fluids and provides reliable measurements with minimal pressure drop. Its construction allows it to measure flow without any moving parts, which reduces wear and maintenance requirements, making it a popular choice in various industries.

Other options, such as RTDs, transmitters, and pressure gauges, serve different functions. RTDs (Resistance Temperature Detectors) are used for temperature measurement, transmitters can be used for a variety of measurements but they are not specific to flow, and pressure gauges measure the pressure of a fluid but do not directly provide flow rate information. Thus, the magnetic flowmeter is the correct choice for measuring flow rate in a pipe.