PLC Sequential Motor Control

A Siemens S7-300 PLC project for sequential control of three motors using Ladder Logic (LAD).

Project Overview

This project implements a sequential motor control system with independent stop functionality and timed protection against excessive simultaneous operation of motors M1 and M3.

The control logic is developed using SIMATIC Manager (STEP 7 V5.7) for a Siemens S7-300 PLC and tested in a simulation environment.

Operating Sequence

1. When the Start command is activated, motor M1 starts.
2. After 6 seconds, motor M2 starts.
3. After another 10 seconds, motor M3 starts.
4. Each motor can be stopped independently without intentionally affecting the operation of the other motors.
5. If M1 and M3 remain ON simultaneously for 10 seconds, both motors are switched OFF and an alarm is activated.

Hardware & Software

• PLC: Siemens S7-300
• CPU: CPU 314C-2 DP
• Programming Software: SIMATIC Manager / STEP 7 V5.7
• Programming Language: Ladder Logic (LAD)
• Testing: PLC Simulation

I/O Assignment

Address	Description
I0.0	Start command
I0.1	Stop M1
I0.2	Stop M2
I0.3	Stop M3
Q4.0	Motor M1
Q4.1	Motor M2
Q4.2	Motor M3
Q4.3	Alarm signal

Timer Configuration

Timer	Preset Time	Function
T0	6 seconds	Delayed start of M2
T1	10 seconds	Delayed start of M3
T2	10 seconds	Monitoring simultaneous operation of M1 and M3

Project Files

• PLC_Program.pdf – Exported PLC program and LAD networks.
• Screenshots/ – Program and simulation screenshots.

Ladder Logic (LAD) Networks

The PLC program is organized into four networks:

Network 1 – Motor M1 Control

Network 2 – Motor M2 Delayed Start

Network 3 – Motor M3 Delayed Start

Network 4 – Simultaneous Operation Monitoring

Simulation Demo

The following animation demonstrates the PLC program execution, including sequential motor startup, independent motor stop functionality, and timed protection logic.

Simulation Test Cases

The following test cases were performed to verify the PLC control logic in the simulation environment.

Test ID	Test Scenario	Expected Result
TC-01	Activate the Start command	Motor M1 turns ON.
TC-02	Wait 6 seconds after M1 starts	Motor M2 turns ON.
TC-03	Wait another 10 seconds	Motor M3 turns ON.
TC-04	Press Stop M1	Only M1 turns OFF.
TC-05	Press Stop M2	Only M2 turns OFF.
TC-06	Press Stop M3	Only M3 turns OFF.
TC-07	Keep M1 and M3 ON simultaneously for 10 seconds	Both M1 and M3 turn OFF and the alarm activates.

Test Environment: Siemens S7-300 / SIMATIC Manager STEP 7 V5.7

Test Method: PLC simulation

Test Status: All listed scenarios were tested successfully.

Learning Objectives

• Sequential motor control using PLC.
• Timer-based control with S5 timers.
• Independent motor start/stop logic.
• Monitoring simultaneous motor operation.
• Alarm and protection logic.
• Siemens S7-300 programming using LAD.

Project Status

Implemented and tested in a simulation environment.

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This project is an educational simulation. Practical implementation with real motors requires appropriate electrical protections, safety circuits, and engineering validation.