What type of measuring level system has to compensate for the air temperature because the speed of sound in air varies with temperature?

• A. Float gauge
• B. Ultrasonic system
• C. Radar level sensor
• D. Pressure transducer

Answer: (B)

Ultrasonic level measurement relies on the travel time of sound waves through air. Since the speed of sound in air changes with temperature, the system must adjust the conversion from time to distance using the current air temperature. When air is warmer, sound travels faster, so the measured time corresponds to a shorter distance unless compensated. Conversely, cooler air slows sound down, making the same time correspond to a longer distance. By incorporating temperature compensation, the ultrasonic sensor accurately determines the liquid level.

Other methods don’t depend on the speed of sound in air in the same way: a float gauge is purely mechanical, radar uses electromagnetic waves whose speed in air is effectively constant for typical conditions, and a pressure transducer measures hydrostatic pressure to infer level.