Parameter layer

Flexibility without breaking the logic

The Parameter layer supplements the Selmo model with variable values, without changing the logical flow or the behavior.

The purpose of the parameter layer is to enable flexibility, without:

• complicating logic

• blurring states

• losing determinism

Parameters change values – not the behavior.

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Basic principle of the parameter layer

In the Selmo model there is a clear separation:

• Logic layer defines when something happens

• System layer defines what is expected or monitored

• Parameter layer defines with which values is worked

The parameter layer:

• contains no logic

• contains no states

• makes no decisions

It provides exclusively data.

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times

meaning

Time parameters describe process-relevant time values, e.g.:

• hold times

• wait times

• delays

• time limits

These times:

• are used in the logic layer (e.g. in timer states)

• influence the flow quantitatively, not qualitatively

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When it makes sense to parameterize times

• when time is part of the process

• when values vary depending on project or product

• when adjustment should be possible without changing the model

When times should not be parameterized

• to compensate for unstable technology

• as a substitute for missing feedback

• to “fix” an incorrect model

Time parameters must not mask logic.

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Positions

meaning

Position parameters describe:

• target positions of axes

• reference points

• mechanical end positions

• setpoints for movements

These values:

• are used by zones and the system layer

• do not change, that a movement takes place

• only change where to or how far

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Purpose of position parameters

• adaptation to different products

• fine adjustment without changing the model

• reusability of sequences

The movement remains the same – only the target value changes.

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Repetitions

meaning

Repetition parameters define:

• number of loop iterations

• maximum retry attempts

• test cycles

They are typically used in:

• repeater elements in the logic layer

• controlled iterations

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Rules for repetitions

• Repetitions must be limited

• the meaning of the repetition must be explainable from a domain perspective

• the parameter does not change the flow, but its scope

Not allowed are:

• infinite repetitions

• parameter-driven flow changes

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Displays & inputs

meaning

The parameter layer can contain values that:

• are displayed in the HMI

• are entered by the operator

• serve process monitoring

These parameters:

• are not control elements for logic

• do not change state transitions

• do not influence safety decisions

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Distinction from operator logic

Inputs in the parameter layer:

• are values, not commands

• are validated, not interpreted

• only take effect within defined limits

The operator changes parameters – not the model.

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Determinism and parameters

Despite parameterizable values, the system remains:

• deterministic

• reproducible

• explainable

Because:

• logic is fixed

• behavior is fixed

• only numerical values change

Same parameters + same states always lead to the same behavior.

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Typical mistakes in dealing with parameters

Common mistakes are:

• parameters replace logic

• parameters control flow decisions

• safety-relevant values are parameterizable

• parameters are not limited or validated

Rule of thumb:

If a parameter changes the flow, it is used incorrectly.

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Summary

The parameter layer:

• enables flexibility

• protects the logic

• prevents model breakage

• increases reusability

It is:

• not a shortcut

• not a replacement for configuration

• not a decision-making mechanism

Parameters make models adaptable – not unclear.