> For the complete documentation index, see [llms.txt](https://infosys.selmotech.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://infosys.selmotech.com/selmo-solution/selmo-solution-en/selmo-documentation/1-why-selmo/engineering-in-transition.md).

# Engineering in transition

## 1.1 Engineering in transition

This chapter describes, **why the engineering of machines has fundamentally changed**\
— and why proven practices are increasingly reaching their limits.

It's about **not yet about Selmo**,\
but about the context in which Selmo has become necessary.

***

### Increasing complexity of modern machines

Machines today are:

* modular in design
* highly automated
* flexibly configurable
* relevant to safety and liability
* software-driven

What used to be manageable is now a **complex system of states, dependencies and constraints**.

Typical drivers of this complexity are:

* variety of variants
* increasing safety requirements
* shorter product life cycles
* growing integration of software, sensors and communication
* increasing demands on diagnosis and documentation

This complexity arises **not from poor engineering**,\
but from real technical and regulatory requirements.

***

### Limits of classic PLC programming

Classic PLC programming is historically designed to:

* link signals
* switch sequences
* represent states implicitly in code

This approach works reliably —\
**as long as complexity is limited**.

However, with increasing complexity systemic limits become apparent:

* Sequence, safety and operation mix together in the code
* States are not explicitly defined but arise implicitly
* Behavior can only be understood through code analysis
* Diagnosis is created afterwards and manually
* Documentation no longer reflects the actual code state

The code says:

> *What is happening right now.*

However it does not say:

* why it is happening
* what is actually expected
* what is allowed or forbidden in this state

***

### Consequences for engineering and responsibility

This development has direct consequences:

* Machines become hard to explain
* Commissioning becomes more elaborate
* Troubleshooting becomes slower and dependent on individuals
* Changes increase the risk of unintended side effects
* Responsibility and liability are hard to justify

The problem is **not the PLC technology**,\
but the lack of a **formal, explicit model for machine behavior**.

***

### Transition to the next question

The central question therefore is no longer:

> *How do I program a machine?*

But:

> **How do I describe machine behavior so that**\
> **it is explainable, verifiable and accountable?**

This question is the starting point for the Selmo attitude.


---

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