PTF – Process · Technology · Function
PTF is the methodical foundation of Selmo. It describes how one must think about a machine before it is modeled.
PTF is:
no modeling
no technical description
not a tool
not a diagram
But:
A structured thinking and analysis process, which necessarily precedes modeling.
Why PTF is necessary
Without upstream analysis, the following often happens:
modeling is started too early
thinking in technical instead of functional terms
complexity is shifted into the model
safety is compensated afterwards
This leads to:
overloaded sequences
implicit assumptions
states that are hard to explain
unnecessary special cases
PTF exists to systematically avoid these errors.
Overview: The three levels of PTF
PTF deliberately separates three levels of consideration:
P – Process What should happen professionally?
T – Technology Which physical and technical principles are used?
F – Function What verifiable requirements result from that?
These levels are:
logically separated from each other
not interchangeable
necessarily to be considered in this order
P – Process
What does “Process” mean?
The process describes the professional sequence:
from the perspective of product, material, or task
independent of automation
independent of the technology used
Examples:
Insert workpiece
Fix part
Perform processing
Check result
Release part
The process answers not:
how something is implemented technically
which sensors are used
which actuators are moved
The process describes what happens – not how it happens.
Typical errors without a clear process view
Technology determines the sequence
PLC structures define the process
Process logic is no longer explainable
Special cases arise uncontrolled
T – Technology
What does “Technology” mean?
Technology describes:
physical principles of operation
machine technology used
relevant forms of energy
mechanical, electrical, pneumatic or hydraulic relationships
Examples:
Clamping via pneumatics
Positioning via servo axes
Gripping via vacuum
Measuring via sensors
Technology answers:
what is physically possible
what must be monitored necessarily
where risks and limits lie
Why technology must be understood before function
Without understanding the technology:
wrong functions are formulated
unnecessary safety assumptions arise
monitoring is placed incorrectly
Functions can only be derived from technology – not the other way around.
F – Function
What does “Function” mean?
Functions are formalized requirements for the behavior of the machine.
They are derived from:
the professional process
the technological boundary conditions
Examples:
"Workpiece must be clamped before processing"
"An axis may only move if the protective condition is met"
"Processing may only start when position is reached"
Functions are:
not implementations
not PLC function blocks
no states
Functions are verifiable statements about expected behavior.
Result of well-formulated functions
From clear functions arise:
necessary states
meaningful sequences
relevant zones
required monitorings
This makes modeling:
not a creative activity
but a consistent derivation
PTF and the Selmo model
The roles are clearly separated:
PTF
Thinking & Analysis
Selmo model
Formal description
PLC / HMI
implementation
PTF decides:
what is modeled
why it is modeled
Selmo decides:
how this behavior is described formally
PTF limits the model. Selmo structures it.
Typical errors without PTF
Modeling starts too early
Sequences take over process decisions
Zones are defined technically instead of functionally
Safety logic compensates for missing analysis
Models become unnecessarily complex
Rule of thumb:
When a model becomes confusing, PTF is almost always missing.
Summary
PTF is:
the methodical entry into every Selmo project
Prerequisite for explainable models
Protection against implicit logic
Reduction of complexity
PTF is not a substitute for Selmo and no alternative to the model.
Think first. Then model. Then automate.
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