PLC from Draft to Software - 01

How to develop PLC software from scratch. 

In this new series of videos, articles, and programming challenges, we will learn from the idea's draft to the software's conception. We will understand what processes and tools are needed to develop software based on software engineering principles. To follow this series, you should know algorithms and data structures.

Other desirable knowledge: electrical commands, basic computer skills, basic instrumentation.

Fundamental item: Willingness to learn!

Someone asked me to develop software—where do I start?

So, someone asked you to develop software for a specific industrial machine—something you’d never even thought about before, or maybe it was a big dream that just came true. Congratulations! You’ve just been promoted to industrial programmer, but what are your responsibilities?

• Develop COHERENT software that others, not just you, can maintain.

• Develop software that GUARANTEES the equipment functions as required.

• Develop software that prioritizes the SAFETY of the people operating it and the equipment itself.

  
  

Now we know the essential responsibilities—and trust me, they’ll grow as you gain experience. Why?

Because the industrial programmer (or PLC programmer, who usually also handles the HMI—Human-Machine Interface) is always the link in direct contact with project management, operators, mechanical design teams, simulation teams, and even electricians, they check for assembly errors that could interfere with the machine’s proper functioning. In short, they’re the "do-it-all" person during startup, especially when experienced and part of the company’s operational structure.

Knowing the responsibilities, what’s the first step? Where do I begin?

We start by gathering as much information as possible about the process we’ll be programming. This could be a robotic cell, a concrete block-making machine, or even a pressure control system for a large biomass boiler. The work spans multiple industries and equipment types. It’s common for some professionals to specialize in just one industry or process, aiming to become experts not only in PLC programming but also in that specific process.

How do we gather information?

The first step is to talk to the person who requested the software— Project Manager, Project Supervisor, Maintenance Manager, company owner, etc.

Start by asking these 10 essential questions:

1. What is the process?

2. What are the basic premises?

3. What are the project requirements?

4. Do you already have the electrical schematic?

5. Do you have a functional diagram/flowchart / any other documentation about how it works?

6. What critical points were identified by the team that developed the line/equipment?

7. How will the interfaces be designed?

8. What standards need to be followed according to the company’s guidelines?

9. What platform will be used?

10. Is there a programming standard? If so, is it documented?

    
    

These 10 questions help draft the software we’ll develop. But getting clear answers early on is tough— requirements often change and evolve as the project progresses, which ties into project management and strategic goals.

Can you see how software development touches multiple areas?

We interact with project management, application, workplace safety, and company executives. We’re the spearhead of the project, connected to management, electrical, instrumentation, and mechanical teams. We work with everyone to ensure the software fits the final product!

Information gathering can be done in many ways.

Request all project documents from the electrical and mechanical design teams. Another key document (if it exists) is the project charter, which contains basic information like desired production output, some premises, etc.

The most important thing is that when we discuss information gathering, we discuss something fundamental in software engineering. Yes, folks—don’t run from it, you can’t! Software only works with software engineering.

So now we’re talking about requirements gathering, a crucial step in developing our software.

See you in the next article!

Bibliography:

• Catho - PLC Programmer

• Freelancermap - What does a PLC Programmer do?

• Clean Code, originally published August 1, 2008, Author: Robert Cecil Martin