NALMCO Certified Apprentice Lighting Technician (CALT) Practice Exam

What type of occupancy sensor uses sound waves to detect motion?

1. PIR sensor

2. Ultrasonic sensor

3. Photoelectric sensor

4. Thermal sensor

The correct answer is: Ultrasonic sensor

Ultrasonic sensors utilize sound waves to detect motion, which makes them particularly effective in various environments. They emit high-frequency sound waves that are inaudible to the human ear. When these sound waves travel and bounce off an object, such as a person moving within the sensor's coverage area, the sensor picks up the changes in the returning sound waves. This allows the ultrasonic sensor to detect motion even in areas where line-of-sight may be obstructed, making them versatile for a wide range of applications. In contrast, passive infrared (PIR) sensors detect motion based on changes in infrared radiation, primarily from human body heat. Photoelectric sensors rely on changes in light levels to operate and can be affected by environmental light conditions. Thermal sensors, similarly, respond to changes in temperature rather than motion detection through sound waves. Each of these other types has distinct operating principles that differentiate them from ultrasonic sensors, highlighting why the ultrasonic sensor is the correct choice for detecting motion via sound waves.