A flow meter is a device that measures the rate or quantity (volume/mass) of a liquid, gas, or steam moving through a pipe or channel, providing crucial data for process control, efficiency, and cost management across industries. Also known as flow sensors, gauges, or indicators, these instruments work mechanically or electronically, with types varying from simple visual displays to complex digital readouts, using principles like ultrasound, pressure, or fluid interaction with internal components. 

What they measure:

• Volumetric Flow Rate: Volume of fluid per unit time (e.g., gallons per minute, cubic feet per second).
• Mass Flow Rate: Mass of fluid per unit time (e.g., pounds per hour). 

Key functions:

• Monitoring: Provide visibility into fluid movement in pipelines, HVAC, and drainage systems.
• Control: When paired with valves (forming a flow controller), they can regulate flow rates.
• Accuracy: Help ensure systems are balanced, identify leaks, and optimize processes. 

Common types & principles:

• Volumetric Meters: Measure volume directly (e.g., variable area, turbine).
• Mass Meters: Measure mass, often using Coriolis or thermal principles.
• Ultrasonic Meters: Use sound waves to measure fluid speed (clamp-on or in-line).
• Electromagnetic Meters: Measure flow by sensing voltage induced by conductive fluids.