Process engineers understand function charts that look like their own plant. So APT so the APT graphical programming language was developed by Siemens with sequential and continuous function charts, which can be produced by engineers, using a graphics based language. APT focuses exclusively on control system design and the programmer doesn’t have to work with ladder diagrams.
This makes it easier for people who are familiar with a process, but who aren’t programmers, to develop working batch or continuous control systems, quickly and accurately. Kodak estimates that the changeover from MOD300 to TIStar would have taken two years’ programming work using ladder logic. APT reduced this by half.
The engineers who designed the plant went on to write the software. These are the people best placed to understand the chemistry of a process and know about any potential weak points in the plant configuration.
APT allows binary PLC code to be viewed as modules of English – or any other language – statements and its relational database allows real device names to be used, which helps process engineers. The code is self documenting and the recipe tables within the programming structure allow constants to be changed readily.