> 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/7-safety-and-monitoring.md).

# 7 Safety & monitoring

## 7. Security Architecture

This chapter describes, **how security is conceived, modeled and made effective in Selmo**.

Security in Selmo is:

* **not an addition**
* **not a special case**
* **not an exception to the logic**

Security is **an integral part of the model**.

***

### 7.1 Security as a Property of the Model

In classical control systems, security is often:

* considered outside the process
* implemented in separate programs or layers
* added as a reaction to risks

Selmo pursues a different approach:

> **Security arises where**\
> **behavior is described explicitly.**

This means:

* Security relevance is modeled
* monitoring is unambiguously defined
* reactions are determined deterministically

Therefore, security is **not a reactive element**,\
but a **the consistent consequence of clear models**.

***

### 7.2 Separation of Types of Security

Selmo consciously distinguishes different levels of security:

* **Process safety**\
  → protection against inadmissible state combinations\
  → implemented via Interlock (`i`)
* **system integrity**\
  → protection of people, machines and plants\
  → implemented via CMZ
* **Operator safety in manual operation**\
  → protection against incorrect manual actions\
  → implemented via MXIC

These mechanisms:

* complement each other
* are clearly delineated
* are not mixed

> **Each safety function has a unique task.**

***

### 7.3 Security Always Applies

A central principle in Selmo is:

> **Security is independent of the operating mode.**

This means:

* Security applies in automatic operation
* Security applies in manual operation
* Security applies during commissioning
* Security does not know a "service mode"

Monitoring is:

* permanently active
* state-dependent or state-independent
* hierarchically effective

***

### 7.4 Hierarchical Security Effect

Safety mechanisms act in a clear hierarchy:

Plant\
└─ Hardware Zone\
└─ Sequence

A deviation:

* at a higher level
* overrides all underlying levels

Examples:

* Plant-CMZ stops the entire plant
* HW-Zone-CMZ stops all contained sequences
* Interlock stops a single sequence

> **The higher the level,**\
> **the greater the effect.**

***

### 7.5 Distinction from Hardware Safety

Selmo does not replace **no**:

* emergency stop chain
* safe shutdown
* safety PLC
* mechanical protective measures

Selmo complements these with:

* formal description
* deterministic monitoring
* traceable reactions

> **Hardware safety protects physically.**\
> **Selmo security protects logically and systemically.**

***

### 7.6 Structure of This Chapter

Chapter 7 is divided into the following parts:

#### 7.1 Interlock (`i`)

→ state-dependent process safety

#### 7.2 CMZ – Constantly Monitoring Zone

→ state-independent system integrity\
→ Sequence / Hardware Zone / Plant

#### 7.3 Further Monitoring

→ Pair check\
→ Bear check\
→ Plausibility checks

***

### Transition to the details

The following sections describe:

* how individual safety mechanisms work
* when they are used
* how they complement each other

> **Security in Selmo is not a separate chapter –**\
> **it is a structural principle.**


---

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