Selmo in 10 minutes

This onboarding gives you in 10 minutes a resilient mental model of Selmo. Not complete – but correct.

If you read on after this, you'll know:

• what Selmo is

• how it thinks

• where you need to deepen

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Minute 1 – The basic problem

Classic machine logic is stuck in the code. The code works – but it explains nothing.

Questions like:

• Why is the machine stopped?

• What is currently being expected?

• What is allowed to happen here?

can often only be answered with experience.

Selmo exists to make machine behavior explainable.

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Minute 2 – Model before code

Selmo starts not with PLC code.

Selmo starts with a formal model, which describes:

• states

• expectations

• monitoring

• reactions

From this model arise:

• Code

• HMI

• Diagnosis

• documentation

The model is the truth. Code is only an implementation.

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Minute 3 – The central idea: states

A machine is at any time in exactly one state.

A state describes:

• a situation

• no action

• no instruction

Example:

• "Workpiece clamped"

• not: "Cylinder extend"

Selmo thinks in situations, not in commands.

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Minute 4 – Sequence: one task, one model

A Sequence is a deterministic state machine for a functional task.

Examples:

• Clamp

• Machine

• Inspect

• Release

A sequence:

• knows its current state

• knows what is expected next

• always reacts the same

One task → one sequence.

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Minute 5 – Zone: meaning for engineering

Signals alone mean nothing.

A Zone:

• gives signals meaning

• connects logic with engineering

• is uniquely diagnosable

Example:

• not: I0.3

• but: "Cylinder clamped"

Zones make engineering explainable.

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Minute 6 – Bit-Control: explicit behavior

Bit-Control determines what a zone may or must do in a state.

Three possibilities:

• 0 → doesn't matter

• S → behavior is expected

• i → condition must be fulfilled

This applies:

• in every state

• for every zone

No implicit behavior. Everything is explicit.

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Minute 7 – Operation: manual and automatic

Manual and automatic operation are not two logics.

Both operate:

• in the same state space

• with the same monitoring

• with the same rules

Difference:

• Automatic → system drives the sequence

• Manual → operator influences zones

Operation does not change the logic, only the source of influence.

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Minute 8 – CMZ: what must always be correct

Some things must be always correct:

• Doors

• Power

• basic releases

This is handled by the CMZ (Constantly Monitoring Zone).

A CMZ:

• is always active

• regardless of the state

• stops any movement on deviation

CMZ protects system integrity.

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Minute 9 – Diagnosis & HMI

Because behavior is modeled, diagnosis arises automatically.

A diagnosis knows:

• where in the sequence

• which zone

• which expectation is violated

The HMI:

• shows the model

• decides nothing

• interprets nothing

The HMI is a window into the model.

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Minute 10 – What Selmo really is

Selmo is:

• not a tool

• not a framework

• not a shortcut

Selmo is:

• a formal thinking model

• a common language

• a basis for responsibility

If you understand the model, you understand the machine.

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What happens next

If you want to dive deeper:

• Sequences → Sequence

• Engineering → Zone

• Monitoring → Bit-Control

• Operation → Manual & automatic operation

• Safety → CMZ

• Traceability → Diagnosis, HMI & Documentation

And if you're unsure: → Glossary

Do not read Selmo quickly. Read Selmo precisely.