Process Control

1.1 Explain the cyclic operation (execution of the program) of a PLC. At what time will the output signals change?

1.2 Which parts are necessary to build up a PLC? Explain the modules of a compact and of a modular PLC.

1.3 What is a so called Soft-PLC und in which way are the process signals connected to the control device?

1.4 What has to be done to change an ordinary PC to a Soft-PLC?

1.5 Think of a desktop operating system and a real-time operating system running on our control device. Explain two different applications with a Soft-PLC using in your first application the desktop and in your second application the typical real time operation system.

1.6 Which kind of work can be done with a PC in an industrial control application? Discuss relevant quality efforts to such a kind of PC.

1.7 Which aspects from computer sciences are considered in the standard IEC61131 for the programming of a PLC?

1.8 Name two textual and three graphical programming languages for a PLC listed in the standard IEC61131.

1.9 Explain the software model in the standard IEC61131 using the terms configuration, resource and program.

Programming

2.1 Explain the aim and usage of arrays and structures in the programming language Structured Text (ST).

2.2 Explain the necessary steps to use different kinds of variables in a ST-program, a ST-function and a ST-function-block according to the standard IEC61131.

2.3 What is the difference between a Function and a Function Block? How do you implement a so called instance of a Function Block in a ST-program?

2.4 What are direct address variables and what is necessary to use them in a ST- program?

2.5 What does the attribute RETAIN in combination with a variable express?

2.6 Write a short example that explains the usage of a CASE-statement to build up a finite state machine / Petri net in a ST-program.