Step-by-Step Guide: Converting Electrical Diagrams into PLC Programs for Industrial Automation

  • Converting an electrical diagram into a Programmable Logic Controller (PLC) program is a critical process in industrial automation.
  • The purpose of this guide is to give a thorough overview of all the processes in this conversion procedure, covering understanding the electrical diagram, selecting the appropriate PLC and software, creating a program structure, mapping inputs and outputs, writing the PLC program, translating logic, testing and debugging, documenting the program, and finally, downloading, implementing, commissioning, and maintaining the system.
  • By following this comprehensive guide, engineers and technicians can successfully convert electrical diagrams into PLC programs for effective industrial automation.
Converting Electrical Diagrams into PLC Programs 1
  • The first step in converting an electrical diagram into a PLC program is to thoroughly understand the diagram. 
  • This involves identifying the various components, their connections, inputs, outputs, and the overall functionality of the system. 
  • Understanding the electrical diagram lays the groundwork for developing an accurate PLC program.
  • Once the electrical diagram is understood, the next step is to select the appropriate PLC model and programming software. 
  • Factors such as the system requirements, number of I/O points, processing power, communication capabilities, and supported programming languages play a crucial role in choosing the right PLC and software.
  • With the PLC and software selected, the next step is to create a program strucure. 
  • This involves breaking down the functionality of the system into manageable parts and planning how to organize the PLC program. 
  • Using a structured approach such as modular programming can help in dividing the program into logical sections for easier maintenance and troubleshooting.
  • Identifying the inputs and outputs of the system as per the electrical diagram is essential for accurately interfacing the PLC with the system. 
  • Inputs such as sensors, switches, etc., and outputs such as actuators, motors, solenoids, etc., need to be mapped to the corresponding inputs and outputs of the PLC.
  • Based on the identified inputs, outputs, and the functionality of the system, the PLC program is written using the selected programming software. 
  • Depending on the chosen PLC and programming language, this could involve ladder logic, structured text, function blocks, or a combination thereof.
  • The logic from the electrical diagram is translated into the PLC programming language in this step. Using appropriate instructions, conditions, timers, counters, etc., the desired functionality of the system is replicated in the PLC program. 
  • It’s crucial to ensure that the logic is accurately translated to achieve the intended operation.
  • Thorough testing of the PLC program is essential to ensure its correctness and functionality. 
  • Simulation tools provided by the programming software can be used to simulate inputs and verify outputs. 
  • Any errors or unexpected behaviors encountered during testing are debugged to ensure the smooth operation of the system.
  • Documenting the PLC program is crucial for future reference, maintenance, and troubleshooting. 
  • Before downloading the program, it’s essential to take a backup of the existing program (if any) in the PLC to avoid any loss of data.
  • The program should be thoroughly documented with comments, diagrams, and notes explaining the logic, input-output mappings, and other relevant information.
  • Using the programming software, download the developed PLC program to the PLC hardware. Follow the manufacturer’s instructions for the specific PLC model being used. 
  • Proper configuration and wiring of the PLC to the system components are ensured before implementing the program.
  • Check and configure any necessary settings within the PLC to ensure compatibility with the system components and requirements. This may include setting communication parameters, addressing, I/O configuration, etc.
  • Double-check the wiring connections between the PLC and the system components to ensure proper connectivity and adherence to the electrical diagram.
  • Power up the PLC hardware and ensure that it is functioning correctly.
  • Once the PLC program is downloaded and the system is powered up, conduct thorough testing to validate its functionality in the real-world environment. Test various scenarios such as starting, stopping, motor overload conditions, etc., to ensure proper operation.
  • After successful testing, commission the system by integrating it into the overall industrial automation setup. Verify its operation alongside other components and systems.
  • After successful implementation, the system is commissioned by verifying its operation in the actual environment. 
  • Regular monitoring and maintenance of the PLC program are performed to keep the system running optimally.

Let’s break down the process of converting the electrical diagram for a simple ON/OFF motor DOL (Direct-On-Line) starter circuit into a PLC program.

Converting Electrical Diagrams into PLC Programs 2

The electrical diagram consists of the following components:

  • Start Push Button
  • Stop Push Button
  • Motor Overload Trip Relay
  • Motor ON Command Relay
  • Motor ON Feedback Indication
  1. Input Mapping: Map the physical inputs (start push button, stop push button, motor overload trip relay) to PLC memory addresses.
  2. Output Mapping: Map the physical outputs (motor ON command relay, motor ON feedback indication) to PLC memory addresses.
  3. Control Logic: Develop the control logic using ladder logic to control the motor based on the status of inputs.
  4. Feedback Monitoring: Monitor the status of the motor ON command relay and provide feedback indication.

 Module Type
I/O Address
Rack SlotTerminal
Input000Start Push Button
001Stop Push Button
002Motor Overload Trip Relay
Output030Motor ON command relay 
031Motor ON Feedback Indication 
PLC Program (Ladder Logic): dol starter
  • I:0/0/0: Represents the start push button input.
  • I:0/0/1: Represents the stop push button input.
  • I:0/0/2: Represents the motor overload trip relay input.
  • O:0/3/0: Represents the motor ON command relay output.
  • O:0/3/1: Represents the motor ON feedback indication output.
PLC Program (Ladder Logic): dol starter 1
  • When the start push button is pressed, the corresponding input (I:0/0/0) receives a signal indicating the user’s intention to start the motor.
  • In response to this signal, the motor ON command relay (O:0/3/0) is energized through the ladder logic.
  • The energized motor ON command relay allows power to flow to the motor, initiating its operation and causing it to start.
PLC Program (Ladder Logic): dol starter 2
PLC Program (Ladder Logic): dol starter 3
  • If the stop push button is pressed (I:0/0/1) or the motor overload trip relay is activated (I:0/0/2), it indicates a condition where the motor needs to be stopped.
  • Upon detection of either of these conditions, the ladder logic program de-energizes the motor ON command relay (O:0/3/0).
  • De-energizing the motor ON command relay interrupts the power supply to the motor, causing it to stop.
  • The motor ON command relay (O:0/3/0) serves as the output that controls the operation of the motor.
  • When energized, the motor ON command relay allows power to flow to the motor, initiating its operation and causing it to start.
  • Conversely, when de-energized, the motor ON command relay interrupts the power supply to the motor, stopping its operation.
  • The motor ON feedback indication (O:0/3/1) is another output used to provide visual feedback regarding the status of the motor.
  • This feedback indication output is directly linked to the status of the motor ON command relay.
  • When the motor ON command relay (O:0/3/0) is energized, indicating that the motor is running, the motor ON feedback indication output (O:0/3/1) is also energized.
  • The energized feedback indication output typically activates a visual indicator such as a light or LED, providing a clear visual indication that the motor is currently in the ON state.
  • By observing the status of the motor ON feedback indication, operators or system users can easily determine whether the motor is running or not.
  • When the feedback indication is illuminated, it indicates that the motor ON command relay is energized and the motor is running.
  • Conversely, if the feedback indication is not illuminated, it suggests that the motor ON command relay is de-energized, and the motor is not running.

By following these steps, the process of downloading and implementing the PLC program for the simple ON/OFF DOL motor starter circuit can be completed effectively, leading to reliable and efficient industrial automation.

Click her for How to Create PLC Ladder Diagram

Click here for Getting Started with PLC Hardware and Software (PLC Basic to Troubleshooting)

Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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