Plant

This chapter describes the Plant as the top structural level in the Selmo system. The goal is to understand the entire plant as a unit – independent of individual processes or stations.

The Plant forms the global frameworkin which all other elements exist.

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Role of the Plant

The Plant represents the entire machine or plant.

It is:

• the top level in the Selmo model

• holder of global states

• place for plant-wide monitoring

• not responsible for processes

The Plant:

• describes no sequences

• contains no state machines

• makes no process decisions

The Plant defines the framework – not the behavior in detail.

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Global states

At the plant level, states are described that:

• apply to the entire plant

• are independent of individual hardware zones

• are not tied to a specific process

Typical global states are:

• plant ready / not ready

• plant released / locked

• overall fault

• global safety state

These states:

• are visible to all subordinate levels

• influence their behavior indirectly

• are not controlled by sequences

Global states describe the plant context, not the process state.

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Plant-wide CMZ

Certain conditions must be valid for the entire plant at all times be.

These are modeled as plant-wide CMZ (Constantly Monitoring Zones) .

Examples:

• main power supply

• central protective devices

• overarching safety releases

• plant-wide emergency stop states

Characteristics of Plant CMZ:

• permanently active

• state-independent

• override all subordinate levels

In case of a deviation:

• automation is locked plant-wide

• all hardware zones react deterministically

• there are no movements possible anymore

Plant CMZ protect the integrity of the entire plant.

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Distinction from hardware zones

For clear classification:

• Plant

  • describes the entire plant

  • manages global states

  • contains plant-wide monitoring

• hardware zone

  • describes a part of the plant

  • manages operating modes

  • starts and stops sequences

The Plant knows no processes. Hardware zones know no entire plant.

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Placement in the overall model

The hierarchical structure is:

Plant └─ Hardware Zone └─ Sequence └─ Zone

The Plant:

• is above all hardware zones

• forms the stable upper closure of the model

• enables clear hierarchy and escalation

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Summary

The Plant is:

• the structural representation of the entire plant

• holder of global states

• place for plant-wide CMZ

• deliberately free of process and detail knowledge

The Plant creates order at plant level – so that what is modeled below can be clear.