DesigntrendsinPLC-basedcontrolsystems.docVIP

Design trends in PLC-based control systems Advances in electronics manufacturing are supporting higher functionality levels in industrial automation hardware. Equipment used in industrial control, such as a programmable logic controller (PLC), has increasing levels of connectivity and embedded processing. Additionally, there is a desire to make machinery functionally safe to operate. A few key functional product specifications for a small sample of automation vendors, summarized in Table 1, illustrates the emphasis on features in connectivity, embedded processing, and functional safety. Delving deeper into the architecture and design of I/O modules in these systems, we observe a mutually reinforcing cycle between advances in automation and proliferation of electronic technology. Let’s examine each of these automation trends and the corresponding effect on the underlying electronics. Connectivity From a simple industrial control system to a large-scale processing plant, automation infrastructure is usually classified into three levels (Figure 1). At the top is the operations and enterprise level. Next is the control level, consisting of the main processing units used to control machinery and processes on the factory floor. Finally, the actual sensors and actuators are located in the field level. There is a high level of connectivity between these levels, and the underlying theme to inflection today is a need to embed intelligence in the field devices and to control and communicate with them for better efficiencies and planning. Automation trend: Previously, the main mode of communication between field devices, controllers, and other equipment was 4-20 mA loops or industrial fieldbuses. While these will continue to be used for many years, Ethernet is being adopted in industrial control systems with several fieldbus protocols having corresponding industrial Ethernet versions. Variants include Profinet, EtherNet/IP, Eth