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.

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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.

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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”

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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.

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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.

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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.

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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

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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.

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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.