What is the function of a presence sensing device, such as a light curtain?

• A. To stop a machine when a hazard is detected
• B. To monitor lubricant levels
• C. To count production cycles
• D. To record temperature

Answer: (A)

Presence sensing devices like a light curtain are safety sensors that stop a machine when someone or something enters the hazard area. They project a grid of beams across an opening; if a beam is interrupted, the control system triggers an immediate stop or safe state to prevent contact with moving parts. This protects workers from injury in automated environments. They aren’t used for monitoring lubricant levels, counting production cycles, or recording temperature, which are forms of process monitoring or data logging rather than operator protection.