Ladder Logic for: Entrance–Exit Door and Elevator Control System

PLC ladder programming provides:

  • Automation Efficiency – Doors open/close automatically when a person approaches.

  • Safety Control – Emergency stop and interlocks prevent accidents.

  • Flexibility – Manual override for security guards or authorized staff.

  • Scalability – Easy to extend for more floors or doors.

This application is common in offices, malls, hospitals, and industrial facilities.

PLC Inputs and Outputs

Inputs (I)

  • I0.0 → Entrance Sensor

  • I0.1 → Exit Sensor

  • I0.2 → Emergency Stop (NC)

  • I0.3 → Manual Override Switch

  • I1.0 – I1.2 → Elevator Call Buttons (Floors 1–3)

  • I1.3 – I1.5 → Elevator Floor Position Sensors

  • I1.6 → Elevator Door Closed Sensor

Outputs (Q)

  • Q0.0 → Entrance Door Motor

  • Q0.1 → Exit Door Motor

  • Q1.0 → Elevator Up Motor

  • Q1.1 → Elevator Down Motor

  • Q1.2 → Elevator Door Motor

  • Q1.3 – Q1.5 → Floor Indicator Lamps

Internal Memory (M)

  • M0.0 → Elevator Moving Status

  • M0.1 – M0.3 → Floor Requests

Timers (T)

  • T0 → Entrance Door Timer (5 sec)

  • T1 → Exit Door Timer (5 sec)

  • T2 → Elevator Door Timer (7 sec)

Ladder Logic Program Rung Analysis

1. Entrance and Exit Door Control

  • Automatic Opening: When a person is detected (I0.0 or I0.1), the respective door motor (Q0.0 or Q0.1) runs.

  • Timer Function: Doors stay open for 5 seconds using timers (T0, T1).

  • Manual Override: Security guard can force open the entrance door via I0.3.

  • Safety Interlock: Doors will not open if the elevator is moving (M0.0).

2. Elevator Control Logic

  • Call Buttons: Requests stored in memory bits (M0.1 – M0.3).

  • Movement: Elevator moves up or down (Q1.0, Q1.1) until it reaches the requested floor.

  • Door Logic: When at the correct floor, the door opens (Q1.2) for 7 seconds (T2).

  • Priority: Floor 1 → Floor 2 → Floor 3 (based on rung evaluation).

3. Safety Features

  • Emergency Stop (I0.2):

    • Immediately closes entrance/exit doors.

    • Stops elevator at its current floor.

    • Keeps elevator door open for passenger safety.

  • Interlocks:

    • Elevator won’t move unless the door is closed (I1.6).

    • Entrance/Exit doors won’t open while the elevator is moving (M0.0).

System Operation Sequence

  1. Person Approaches: Door sensor detects presence → Door opens → Timer runs → Door closes.

  2. Call Elevator: Passenger presses a call button → Elevator moves to requested floor.

  3. Elevator Arrival: Door opens for 7 seconds → Door closes automatically.

  4. Emergency Stop: All movements stop instantly, elevator remains safe.