PLC Programming & Implementation: An Introduction to PLC Programming Methods and Applications

About the Author

Bolakale Aremu is a Control Systems Engineer. He has worked with hundreds of clients across the Programmable Logic Controllers (PLC) automation industry. He has written many books and articles, and created courses for higher education institutions. With his 15 years of experience in the Control Systems Engineering, he has helped some world class organizations like Post Holdings, Kraft Heinz and Procter & Gamble.

He has used several PLC-based systems like the Allen-Bradley’s RSLogix 5, 500, 5000, Studio 5000 and PACs. He is also a master of other great technologies like Cognex In-Sight Vision Systems to mention a few.

How this Book can Help You

This short book is a valuable introduction to Programmable Logic Controllers, and also a reference guide for beginners. It provides an overview of how relay logic can be converted into PLC logic. I included lots of examples, tables, and ladder diagrams to help simplify the topics I covered for beginners.

You will find this book very helpful if you are an electrician, an instrumentation technician, an automation professional or engineer that wants to improve their knowledge of PLC programming.

Getting Started

Simple Key Terms to Understand Relay Logic to PLC Logic Conversion

Control strategy: This is the sequence of steps that take place in a PLC program, which produces our desired output control.

Control task: It is our desired results of a control program.

Flowcharting: This is a method used to pictorially represent the operation of a process in a sequential manner.

Program coding: This is the process of translating a logic or relay diagram into the PLC ladder program form.

The implementation of a control program requires complex organizational and analytical skills, which change depending on the application. Because they are so varied, we cannot explain how to solve every specific control task.

Nevertheless, we can provide you with techniques and guidelines for completing this problem-solving process. In this handbook, we will introduce a strategy for implementing a control program, which includes program organization, system configuration, and I/O programming.

These strategies also apply to PLCs with the IEC 1131-3 programming standard. Additionally, we will present both simple and complex PLC programming examples. After you finish, you will be ready to learn how to document the PLC system—the last step in implementing the control program.

1. Define the Control Task

The control task should be defined by the user to begin the problem-solving process. This is basically defining what must be done. This information is the foundation of the control program. The control task should only be used by people who are familiar with the operation and processes of the machine. The success or failure of the control program directly affects the proper definition of the task.

There are many levels involved in the control task definition process. Each department must collaborate to identify the inputs required so everyone is clear about the project's purpose and scope. If a project involves automation of a manufacturing facility, in which materials are to be retrieved from the warehouse, and then sent to the automated packaging area, both warehouse personnel and those working in packaging areas must work together with the engineering group during system definition.

If the project involves data reporting, management should be involved. The user should look at the steps used to control the task, whether it is done manually or via relay logic. This will help determine if there are any improvements that can be made. Relay logic can be implemented directly in a PLC. However, it is important to redesign the process to meet current project requirements and take advantage of the capabilities of programmable controllers.

2. Determine a Control Strategy

Once the control task is defined, it's time to plan its solution. This involves the creation of a control strategy. This is the sequence of actions that must be taken within the program in order to achieve the desired output control. This is the process of developing an algorithm. It may seem strange or new to some, but algorithm is not. Everybody uses algorithms to complete certain tasks in their daily lives.

An algorithm is a process that allows a person to move from their home to school or work. The person leaves the house, gets in the car and starts the engine. He or she will reach the destination in the final of a finite number steps.

Implementing a PLC strategy for a control task closely matches the development of an algorithm. The control task must be implemented using a set of basic instructions. It should also be completed in a limited number of steps. If the task of creating an algorithm to solve the problem proves difficult, the user may need to go back to the control task definition in order to redefine the problem.

If we don't know where we are and what Bullfrog County are, then we can't explain how we get there. We need to determine if a specific method of transportation is necessary as part of the problem definition. We need to be aware of any time constraints. Without all the problem definition information, we cannot create a control strategy.

For program strategy definition, the fundamental rule is to think first and program later. You should consider other ways to solve the problem. Before you