Which statement best describes sensors?

• A. Devices that measure physical quantities such as temperature, light, pressure, speed, etc.
• B. Devices that store data
• C. Actuators that move loads
• D. Power supplies

Answer: (A)

Sensors are devices that detect and measure physical quantities and convert them into signals the control system can read. This input role is why they’re described as measuring things like temperature, light levels, pressure, or speed. That matches the statement because it highlights the sensing of physical quantities. Other components in a system serve different functions: storing data, producing motion or action (actuators), or providing electrical power (power supplies). So sensors are defined by their measurement and signal output, making them the input sources for monitoring and control in PLC and automation applications.