Mitsubishi PLC Sequential Start and Stop Control Example

This program controls the sequential start and stop of conveyor motors using timers (T) for delay-based operations. It ensures a safe and efficient motor startup and shutdown process.

Component Description

• X0: Emergency stop button
• X1, X2, X3: Thermal relays for three motors
• X4: Start button
• X5: Stop button
• Y1, Y2, Y3: Motor contactors

Sequential Start Process

1. When the emergency stop and thermal relays are active, M0 auxiliary relay energizes.
2. Pressing X4 (start button) energizes Y1, activating the first motor. It also triggers T1 and T2 timers.
3. When T1 timer expires, Y2 energizes, starting the second motor.
4. When T2 timer expires, Y3 energizes, starting the third motor.
5. At this point, all three motors are running in sequence.

Sequential Stop Process

1. Pressing X5 (stop button) energizes M1 auxiliary relay, turning off Y3 and activating T3 and T4 timers.
2. When T3 timer expires, Y2 deactivates, stopping the second motor.
3. When T4 timer expires, Y1 deactivates, stopping the first motor.
4. At this stage, all three motors have stopped in sequence.

Emergency Stop Function

1. Pressing X0 (emergency stop button) or triggering any thermal relay (X1, X2, X3) immediately cuts power to all motors.
2. This ensures safety and prevents equipment damage.

Potential Issue in the Program

The program may contain a design flaw. Can you identify it? Review the logic carefully to find any inefficiencies or safety risks.