Where are airflow pinwheel sensors installed?

• A. In a separate room
• B. At the air intake grill outside the building
• C. Mounted in the duct such that the pinwheel rotor (vanes) is in the center of the airstream
• D. Inside the control panel

Answer: (C)

Airflow pinwheel sensors measure velocity by a small turbine that spins as air moves. To get a reliable reading, mount the sensor inside the duct with the rotor positioned in the center of the airstream. Placing it at the center keeps the rotor in undisturbed air, away from the duct walls where the boundary layer slows flow and eddies can distort readings. Installing the sensor in a separate room, at an outside intake grill, or inside the control panel would expose it to non-representative air or electronic conditions, leading to inaccurate measurements.