Introduction
They are four occasions when it's a bad idea to do a retrofit and that's what we'll discuss now. We will discuss today a little bit about machine automation. We are back to the hardware world today, I want to take one example to give you an idea about the risks that sometimes we take by accepting or trying to do a retrofit. Sometimes it can go very bad and this is why. We are going to take one example, a machine that our company had to retrofit in 2022. If we go on that link 2022 retrofit counter-example you can view a little summary of the machine that's I'm talking about. I take this example because it's a pretty good example to show you why we can sometimes take a lot of risks when we are accepting to do a retrofit. So, why it is a risk sometimes to make a retrofit ? Let see the differents risks.
Risk 1 - The Platform Gap
The fact of Switching brands (Schneider to Siemens) is a major risk compared to sticking with the same manufacturer. Moving a program from one brand (e.g., Schneider) to another (e.g., Siemens) is not a simple "copy-paste" and involves fundamental architectural changes .
The best practice is to stay on the same platform to minimize conversion errors.
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Risk 2 - The 50/50 Debugging Rule
Debugging time is almost always underestimated. It should be budgeted as equal to the total programming time (1:1 ratio).
Debugging time should equal programming time. You must allocate as much time for debugging as you do for actual programming . Underestimating this leads to "infinite" project timelines.
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Risk 3 - Programming "Frankenstein"
Retrofitting code that mixes multiple languages (like Graphset and Ladder) without a clean structure often makes a rewrite from scratch more efficient than a conversion.
Avoid retrofitting code that lacks a clean methodology or mixes too many languages, as it’s often faster to rewrite it from scratch.
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Risk 4 - The Documentation "Hard No"
Without electrical diagrams and a functional description of the machine's behavior, a retrofit should be rejected as it will inevitably spiral into a new, undocumented project.
Without these two factors, a retrofit is essentially a "blind" project and should be rejected .
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