Selmo standard overview

1.2 The Selmo Standard

The Selmo Standard describes machines in a fixed structure:

PLANT(PLC)
└── Hardware zones (HWZ)
    └── Sequences (SEQ)
        └── Zones (Input, Output, In-Out, Mem)

Each logical process unit (e.g., stations, robot control, conveyor, etc.) is modeled as its own SEQ – with defined states and linked signals in zones.

Each zone contains:

• Signal name

• IO definition

• HMI text

• Behavior per state (via bit control defined)

🔧 The Selmo Standard – Overview and core functions

The Selmo Standard defines a consistent structure for modeling, control, and diagnostics of machines. It is modular and based on three central principles:

1. Model instead of program code

2. State-based behavior instead of signal sequences

3. Automated diagnostics through fixed system behavior

Each machine is represented in a clear hierarchy :

Plant → Hardware Zone → Sequence → Zone

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🔹 Structural elements of the Selmo Standard

Level	Description
Plant	The entire machine or system in one PLC
Hardware Zone	A controllable machine part (e.g., station with multiple SEQs, areas) with its own operating mode
Sequence	A logical process flow with defined states in a station (e.g., clamping, drilling)
Zone	A technical functional unit (e.g., cylinder, pushbutton, sensor)

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🧩 Core functions of the Selmo Standard

Below are the most important integrated functions that every Sequence and Zone supports according to the Selmo Standard:

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⚙️ 1. Bit Control (System Layer)

• Defines per state, how each zone behaves

• Operands:

  • 0 = Don’t care – no relevance

  • I = Interlock – condition must be fulfilled

  • S = Sequence Check – action is expected and monitored

  • M = Monitoring - like interlock, but without shutdown - documents deviation

• Basis for automatic enable, state transitions, and error diagnostics

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🔍 2. Sequence Check

• Expected action in automatic mode

• Is compared with the actual signal

• In case of deviation: Diagnosis with blue hint in the HMI as info for the continuation condition per signal

• Leads to the release of the next state, when all S are fulfilled

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🛑 3. Interlock Check

• Monitors critical conditions in every state

• If an I is violated: Automatic mode stops immediately, red error message

• Also visible in manual mode → targeted correction possible

• Monitoring is the same function, but does not shut down

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🚨 4. CMZ (Constantly Monitoring Zone)

• Permanent monitoring of safety-relevant signals

• Faults have cross-cutting effects on:

  • Sequence (SEQ errors only)

  • Hardware Zone (all SEQ errors in the HWZ)

  • Plant (all HWZ errors)

• Leads to immediate blocking of automatic mode and Manual mode

• Errors are not overrideable

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✋ 5. MXIC (Manual Cross Interlock Check)

• Controls in manual mode whether a manual movement is permitted

• If not permitted: → no movement, → diagnosis with explanation, why not

• Safety logic: no manual movement against logical conditions

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👁️ 6. HMI linking (automatic)

• Each zone is HMI text linked

• Errors are automatically localized and color-coded:

  • Red = Interlock error (No automatic mode)

  • Blue = Sequence Check active (Automatic possible or active in automatic)

• Operator can always see what is expected and what is missing

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⏱️ 7. Steptime

• Time monitoring for certain states possible

• Used e.g. for waiting times, safety sequences, etc.

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🔁 8. Sequence Cross

• Synchronous transitions between multiple sequences

• Enables synchronization e.g. with robot or additional stations

• Modular structure across sequence boundaries

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🧠 9. Parameter Layer

• Enables definition and use of non-binary values:

  • Times

  • Speeds

  • Number of repetitions

• Parameters can be written directly from the HMI

• Flexibilization of the process sequence with parameters (positions, lengths, etc.)

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📋 10. Automatic diagnostics

• Errors, warnings, and states are derived from the model

• No manual programming of diagnostics necessary

• Errors are contextual, localized and visually recognizable, bit-precise information

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✅ What the Selmo Standard delivers

Benefit	Description
Structure	Uniform, reusable control architecture
safety	Interlocks, CMZ and MXIC as integrated safety mechanisms
Transparency	Automatic diagnostics with clear HMI feedback
Modularity	Machines can be divided into and combined from sequences
Maintainability	Every process is transparently modeled, not programmed
Determinism	Behavior is clearly defined in every state