> 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/8-diagnosis-hmi-and-documentation/hmi-principles.md).

# HMI principles

### Operability through model clarity

This chapter describes the **basic principles of the HMI in Selmo**.

It is about **not** layout, styles or technologies,\
but about the **meaning of the displayed information**.

The HMI in Selmo is:

* not a control element
* not a carrier of logic
* not an interpretation tool

But:

> **A visible, consistent view of the model.**

***

### Basic principle: The HMI shows the model

The HMI:

* decides nothing
* judges nothing
* corrects nothing

It shows:

* active sequences
* current states
* relevant zones
* expectations and deviations

> **Everything that is visible in the HMI**\
> **must exist in the model.**

***

### Colors

Colors in the Selmo HMI have **a fixed, unambiguous meaning**.

They serve:

* quick orientation
* immediate assessment of the model state
* reduction of interpretation

#### Blue – state fulfilled

Blue indicates:

* the zone meets the expectation of the current state
* all associated conditions are fulfilled
* the state is correct from the perspective of this zone

Blue means **not**:

* “running”
* “active”
* “approximately correct”

***

#### Red – deviation

Red indicates:

* a deviation from the expected behavior
* a violated condition
* a state that cannot be continued

Red is:

* always justified
* always model-based
* always assigned to a zone

> **Red is not a malfunction,**\
> **but a precise piece of information.**

***

### Texts

Texts in the HMI originate **not from free-form wording**,\
but from the model.

Every text:

* belongs to a zone
* describes its meaning
* is context-dependent (state, sequence)

Texts answer:

* *What is expected?*
* *What is missing?*
* *Why does it not continue?*

They explain **not the solution**,\
but **the reason for the deviation**.

> **A good HMI text explains the state –**\
> **not the operating action.**

***

### Consistency

Consistency is the most important HMI principle in Selmo.

This means:

* same colors → same meaning
* same texts → same cause
* same reactions → same situation

This consistency applies:

* across projects
* regardless of machine or plant
* regardless of user interface or target system

The operator must:

* not relearn
* not interpret
* not guess

> **Consistency replaces training.**

***

### Distinction from classic HMI design

To clarify:

* HMI ≠ operating concept
* HMI ≠ workflow optimization
* HMI ≠ graphical preparation of code

The Selmo HMI:

* visualizes the model state
* follows the model, not the operator
* remains correct even with changes

***

### Benefits of the HMI principles

Through these principles the HMI becomes:

* immediately understandable
* unambiguously interpretable
* safe in operation
* consistent for diagnosis
* robust for audits

> **A good HMI is not created by design,**\
> **but by a good model.**

***

### Summary

The HMI principles in Selmo:

* are based on the model
* use fixed meanings for colors
* use model-based texts
* enforce consistency

> **The HMI does not show,**\
> **what to do –**\
> **but what the state is.**


---

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