Usually, Model-in-the-loop (MiL), Software-in-the-loop (SiL) and Hardware in the loop (HiL) simulation approaches are used in industry and all of them have to deal with the inter process communication issues between system's components. In this paper it is intended to describe the construction of a prototype workbench for testing and validation of Programmable Logic Controllers' (PLC) programs, using HiL simulation approach, focusing this study on guaranteeing adequate plant models to be used. This work is inserted in a bigger project that deals with creation of a flexible automation platform that is used for controlling any kind of networked industrial automation systems. This platform considers several industrial protocol communications and different kind of sensors and actuators, usually used in industry, and it was developed on the context of WALC (Web Assisted Laboratory for Control Engineering on-line) project.