Dependability analysis of PLC I/O modules

The paper presents a technique for analyzing the dependability of programmable logic controllers (PLCs) I/O modules. The technique is based on the mode in which the I/O modules fulfill their tasks and not on their structure. Such an approach allows a unified analysis of I/O modules, regardless of their type, for almost the entire analysis work. The particularization of the I/O module type becomes necessary only at the final stage of the analysis. There are realized qualitative & quantitative analysis of I/O modules dependability. For this, and because reliability is not an eloquent parameter in any situation, there are defined probabilistical parameters both for one I/O point and for I/O points systems and are made comparisons between some I/O points configurations. Finally there are pointed out several architectures considered optimal and the processes for which they may be suitable.