Wireless Sensor Networks in Industrial Automation
Marko Paavola, Kauko Leivisk · InTech eBooks · 2010
Factory Automation 202machinery (Werb & Sexton, 2005).In these conditions, it is important to maintain data integrity for operation-critical data, for example alarms (Low et al., 2005).All these factors set a special emphasis on automation design and the fact that WSN are technically challenging systems, requiring expertise from several different disciplines, emphasizes this.Additionally, requirements for industrial applications are often stricter than in other domains, since the system failure may lead to loss of production or even loss of lives.(Low et al., 2005); (Werb & Sexton, 2005).This Chapter discusses wireless sensor networks in industrial automation, focusing especially on performance issues, both in the design phase and during actual operation.The Chapter will proceed as follows: Section 2 introduces industrial applications.Moreover, a demo system, developed by Control Engineering Laboratory, University of Oulu, is presented as an example.Section 3 concerns the protocols and standards in the industrial WSN.In Section 4, the interferences in industrial environment are discussed briefly.Finally, networked control systems are addressed in Section 5, and a list of references given in Section 6. WSN in Industrial ApplicationsFrom industrial point of view, ISA SP100 workgroup introduces six classes (Class 5 -Class 0) for wireless communications based on analysis of industrial, inter-device wireless communication applications (ISA SP100.11,2006).Class 5 defines items related to monitoring without immediate operational consequences.This class covers applications without strong timeliness requirements.The reliability requirements may vary.Class 4 defines monitoring with short-term operational consequences.This includes high-limit and low-limit alarms and other information that may require further checking or involvement of a maintenance technician.Timeliness of information in this class is typically low (slow).Class 3 covers open loop control applications, in which an operator, rather than a controller, "closes the loop" between input and output.For example, an operator could take a unit offline, if required.The time horizon for this class is in a human scale, measured in seconds and minutes.Class 2 consists of closed loop supervisory control, and applications usually have long time constants, with the time scale measured in seconds to minutes.Class 1, closed loop regulatory control, includes motor and axis control as well as primary flow and pressure control.The timeliness of information in this class is often critical.Class 0 defines emergency actions related to safety, which are always critical to both personnel and the plant.Most safety functions are, and will be, carried out by dedicated wired networks in order to limit both failure modes and vulnerability to external events or attacks.Examples in this category are safety interlock, emergency shutdown, and fire control.(ISA SP100.11,2006) According to survey results (Hoske, 2006), the leading application for industrial networks (both wired and wireless) is supervisory control and data acquisition (SCADA).Next are diagnostics, testing, maintenance; both continuous and batch processing; motion control, robotic equipment; and machine control.Furthermore, the applications include pump, fan, and blower applications; continuous processing; packaging machines; materials handling equipment (elevators, cranes, hoists); and discrete product manufacturing.The most used means of communication are Ethernet TCP/IP, RS232 and 4-20 mA.Ten most used networks, communications and protocols did not include wireless alternatives.