If we could enforce one coding habit on every TIA Portal project we inherit, it would be this: define a UDT for every physical thing in the machine. A motor, a valve, an axis, a zone — each gets a type.
Why types beat loose tags
A typeMotor UDT containing command, feedback, fault and configuration fields means every motor in the machine looks identical to the code, the HMI and the maintenance engineer. Faceplates bind to the type once and work for forty motors. Adding a motor becomes a declaration, not an afternoon of copy-paste.
The alternative — dozens of individually named bools like Motor3_Start_Cmd — works right up until the machine grows, and then every change touches twenty places.
Practical rules from the field
- Separate command, status and config sections inside the UDT. It keeps HMI write access controllable.
- Version your UDTs in a library, not per-project. When the type improves, machines inherit the improvement deliberately.
- Do not nest deeper than two or three levels. Deep nesting is elegant in the editor and miserable in a crisis at the machine.
- Reserve spare fields. Adding a member to a UDT changes its memory layout; a couple of reserve words save an online-change headache on running machines.
FAQ
Do UDTs cost performance on S7-1500? No — with optimized block access the compiler lays out the type efficiently. The performance cost of clean structure is effectively zero; the maintenance saving is enormous.
Can the HMI see UDT members? Yes, WinCC binds to structured tags naturally, and faceplates plus UDTs are the standard pattern for scalable HMI engineering.
Zone Otomasyon builds TIA Portal machine software on typed, library-based standards. Inheriting a messy project? We refactor those too.