An anemometer is a device used to measure wind speed, air velocity, or gas flow in both atmospheric (weather) and confined (HVAC/duct) environments. The most common types include cup (three-four cups), vane (impeller), and hot-wire models, often used for meteorology, drone piloting, and HVAC diagnostics. 

Key Types and Working Principles

• Ultrasonic Anemometer: Measures speed based on the time-of-flight of sonic pulses between pairs of transducers. 

• Cup Anemometer: Features three or four cups on horizontal arms that spin as wind blows; the rotation speed corresponds to wind speed.
• Vane/Impeller Anemometer: Uses a propeller-like fan that rotates in the wind, commonly used for quick air speed measurements, particularly in HVAC.
• Hot-Wire Anemometer

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   Employs a thin, electrically heated wire; the speed of the air cools the wire, allowing the device to calculate velocity based on the electrical energy required to keep it hot.