4.1. Introduction

Ordinary sensors, as described in other chapters of this book, were used for a long time and are still used in many applications. Thanks to the explosive progress in microelectronics in the final three decades of the 20 ^th century, sensor technology moved to a completely new level of quality. The functionality of the ordinary sensors has been expanded in many ways and a new group of so-called intelligent sensors has appeared, providing a number of additional properties. They include higher accuracy, better immunity to environmental conditions, application flexibility and especially the possibility of easy integration into the industrial distributed systems.

In contrast to a common centralized approach, nowadays control, measurement and data acquisition systems are widely based on the distribution of a system's tasks among a number of nodes (e.g. intelligent sensors, actuators, controllers), interconnected using an appropriate communication network. It is not enough to acquire the information; it has to be transferred from the sensors to the place where the decisions are made and results have possibly to be transferred back. The behavior of the communication network between the nodes of a distributed system has a significant influence on overall system performance. Maximum node distance, communication speed, response times, determining of data transfers, resolving of transmission errors and a number of other parameters should be taken into account when the suitable communication network standard for a particular application is being selected. Communication networks used to interconnect intelligent sensors and...