In PLC-controlled systems, the end-of-travel signal for a moving carriage is typically provided by a ______.

In PLC-controlled systems, the end-of-travel signal for a moving carriage is typically provided by a ______.

• A. Proximity sensor
• B. Photoelectric sensor
• C. Thermal switch
• D. Limit switch

Answer: (D)

The end-of-travel signal is provided by a limit switch. When the moving carriage reaches its end, a mechanical actuator on the carriage presses the switch, causing its contacts to change state and send a clean, binary signal to the PLC. This direct, rugged contact is ideal for position sensing at a physical limit, delivering a reliable, fast, and simple input that’s easy to wire and immune to many optical issues like dust or misalignment. Other sensors like proximity or photoelectric devices detect presence or distance without contact and can be more sensitive to target shape, reflectivity, or ambient conditions; a thermal switch detects temperature, not position. Thus, a limit switch is the typical choice for reliable end-of-travel signaling.

The end-of-travel signal is provided by a limit switch. When the moving carriage reaches its end, a mechanical actuator on the carriage presses the switch, causing its contacts to change state and send a clean, binary signal to the PLC. This direct, rugged contact is ideal for position sensing at a physical limit, delivering a reliable, fast, and simple input that’s easy to wire and immune to many optical issues like dust or misalignment. Other sensors like proximity or photoelectric devices detect presence or distance without contact and can be more sensitive to target shape, reflectivity, or ambient conditions; a thermal switch detects temperature, not position. Thus, a limit switch is the typical choice for reliable end-of-travel signaling.