# Chapter 8.10 – Why Selmo is a valuable tool even when conformity is lacking

#### **Introduction**

In practice we often encounter existing machines and systems that do not fully meet the requirements of the Selmo standard.\
There can be many reasons for this:\
Missing sensors, incomplete feedback, older control systems or simply economic limits in a retrofit project.

The central question then is:

> *"If a system is not fully Selmo-compliant – is it worth using the process model at all?"*

The answer is: **Yes – absolutely.**\
Because even under these conditions Selmo offers a decisive added value:\
It **makes the behavior of the system visible, explainable and documented** – and that is an essential component of the *state of the art* and the *legal responsibility* in mechanical engineering.

***

#### **1. The formal framework remains valid**

Selmo is based on the principle that every technical behavior of a system **can be described in a formal model** This model does not replace hardware – but it **orders it logically**.\
Even if feedback is missing or only partially available, the model remains a **structured mirror of the process**.

Therefore:

* Every state, every zone, every action is defined, **even if their monitoring is incomplete** is.
* The model clearly shows: *"An action takes place here – a reaction is missing here."*
* This gap becomes **visible, assessable and documented**.

That alone already represents progress compared to conventional programming,\
in which such gaps are mostly **implicitly hidden in the code** remain.

***

#### **2. Documentation creates responsibility and legal certainty**

The Machinery Regulation (EU) 2023/1230 explicitly requires\
that **safety according to the state of the art** is demonstrated by appropriate technical and **documented procedures** .

A Selmo model meets this requirement – even if it does not fully monitor all signals.\
Because:

* It documents **objectively**, which functions are fully monitored and which are not.
* It makes every deviation **conscious and comprehensible**.
* It enables the manufacturer or operator to assess and justify these deviations in the **risk assessment (according to ISO 12100)** .

> This turns uncertainty not into a hazard, but into a **conscious, documented decision**.\
> And that is the decisive difference legally and in terms of safety.

***

#### **3. The process model as a cognitive framework**

Even in incomplete systems Selmo provides a **formal thinking aid**:\
It forces you to think in **cause-effect relationships** rather than in signals and addresses.

This means:

* Every action must be assigned to a condition (cause).
* Every effect must – if present – be secured by feedback.
* Where this is not possible, a **fallback mechanism** (timer, plausibility, acknowledgement) is defined.

This creates a **complete representation of the behavior**,\
even if the physical monitoring is incomplete.

In teaching we call this a *reduced but complete model* –\
it does not perfectly map reality,\
but it is complete within the scope of the known information.

***

#### **4. Integration of special functions**

In industrial practice there are repeatedly situations\
in which certain functions do not fit into the standardized process model.\
This can be, for example, a very specific control, a communication module or a safety block.

Selmo offers three graded options for this:

1. **Function blocks within the model**\
   → special logic, but formally embedded in states and zones.
2. **Extended logic outside the model, but documented**\
   → manual programming with clear labelling *"outside Selmo structure"*.
3. **System extension at the engineering level**\
   → integration in E-Plan, CAD or PLCopen environment – with reference back to the Selmo model.

As a result the system remains **traceable and verifiable**,\
even if not every function is directly formulated in the Selmo syntax.

***

#### **5. Comparison with established design documents**

In engineering it is self-evident\
that a **P\&ID**, a **Circuit diagram** or a **CAD drawing** documents the technical structure.\
None of these plans directly creates safety –\
but they create **traceability and responsibility**.

Selmo takes on this role for the **behavior of the machine** .

One can say:

> **Selmo is to behavior what the circuit diagram is to the electrical system.**

Even if not every valve or every sensor is perfectly integrated,\
the model remains **the central document**, which shows\
how the machine should behave *and what actually* is present *.* is.

Thus Selmo forms a **bridge between engineering and reality**:

* formal thinking,
* structured representation,
* and a clear documentation of deviations.

***

#### **6. Conclusion: Awareness before completeness**

In engineering science a simple principle applies:

> *"What is described can be checked. What is not described remains chance."*

Selmo ensures that **everything is described** –\
including what is (still) not perfect.\
And that is precisely **state of the art** in terms of responsibility:

* Technical uncertainties become **visible**.
* Decisions are made **consciously and documented** .
* The entire process remains **formally comprehensible** –\
  regardless of whether every feedback signal exists.

Selmo is thus **not only a tool for ideal systems**,\
but a **tool for reality**:\
for existing plants, for retrofit projects,\
for step-by-step digitalization and safe further development.

> **In short:**\
> Even if Selmo conformity is (still) not fully achieved,\
> Selmo provides formal clarity, technical responsibility\
> and legally secure documentation –\
> and that is the basis of every modern, safe machine.
