Your attention to elevator safety details is commendable; understanding these details certainly makes riding elevators safer. The limit switch in a passenger elevator is the last line of defense at the terminal station. When the elevator operates outside its normal range, it forcibly cuts off the main power supply to prevent overshooting or bottoming out accidents.
Its working principle is as follows:
Triggering Condition: When the elevator car reaches the top or bottom landing position and fails to be effectively slowed or stopped by the previous two levels of protection (forced deceleration device, limit switch), and continues to overtravel upwards or downwards, the limit switch will be activated.
Action Mechanism: The limit switch is a non-automatic reset safety device. Once triggered, it directly cuts off the elevator's power supply and control circuit, causing the elevator to stop completely. Operation can only be restored after on-site inspection and manual reset by professional maintenance personnel.
Installation Location: It is usually installed near the terminal station of the shaft, after the forced deceleration switch and limit switch, ensuring its continued operation even if those fail. According to regulations, the actuation point is set before the car or counterweight contact buffer to achieve step-by-step protection.
Structural form: Early elevators were mostly mechanical (such as wire rope linked iron-shell switches), while modern elevators generally use electrical limit switches, which are directly triggered by the impact of the door panel on the car, resulting in a more sensitive and reliable response.
Simply put, the limit switch is like an elevator's "emergency brake," only activating when all preceding protections fail, but ensuring that the elevator does not suffer a serious accident involving a collision with the floor or pit.
