Frey, G.:
Software Quality in Logic Controller Programming.
Proceedings of the IEEE SMC 2002, Hammamet (Tunisia), Vol. 1, pp 515-520, Oct. 2002.

    Today the hardware of Logic Controllers, the PLCs (Programmable Logic Controllers), provide a more or less standard functionality and the control strategies and algorithms are implemented in software. Nevertheless, concepts from Software Engineering are rarely applied in this application area. In this contribution it is shown that, besides the fact that the term is rarely used, several methods that are quite common in controller design can be seen as means to improve the software quality as defined in ISO 9126. For the quality characteristics portability and maintainability a new metric is presented. The proposed transparency metric evaluates different aspects of a logic control algorithm to check if this algorithm is easy to understand. The metric is defined for controllers programmed via Signal Interpreted Petri Nets but can be adapted to other graphical methods like for example SFC. The validity of the metric is experimentally proofed.