PROFIBUS in Practice consists of four parts. Part I covers the installation of PROFIBUS devices and cables. Part II looks at PROFIBUS system engineering, commissioning and maintenance, Part III PROFIBUS system architecture and design and Part IV PROFIBUS operation, protocol and applications. This book is Part III of this series. PROFIBUS are field networks connecting motors, pumps, transmitters and controllers. These devices and systems represented a huge advance and intelligence over the conventional systems of early 1980s when fieldbus technology was introduced in the automation industry. Field networks bring a cost saving in cabling, take up less space for electrical cabinets, give operators visualised diagnostic information, and simplify electrical and control system designs. It has been an ongoing journey of learning by experience as these networks have been applied in new factory designs, replacing old systems and in updating and extending existing installations. Initially, there were operational losses due to signal reflection and interference getting into such networks. We started to train electricians to observe the rules collected and issued by PROFIBUS & PROFINET International (PI). Next, we experienced frequent shutdowns due to uncertainties over finding and diagnosing faults and some started to train engineers how to use software and engineering tools to analyse and better understand networked field devices. However, it has taken almost fifteen years in the industry to fully appreciate how many issues are actually caused by poorly thought-through designs. This book answers the need for some guidelines on optimising design of PROFIBUS DP and PA networks covering installation, trouble-shooting, maintenance, system availability, and life cycle costs. The aim of this book is to bring about improved and standardised engineering practice in the field through sharing a greater understanding of the basics, the components and exploring detailed examples of PROFIBUS systems.