In the process control services industry, a system that generates unwanted, preventable or false alarms is quickly rejected by plant operators regardless of the added value generated by the system during its uptime. High network availability and reliability need to be the building blocks of an industrial wireless network DNA. Solutions should offer wired-like data availability, ensuring that no alarms or alerts are caused by data packet losses or communication disruption. A network-meshing algorithm should be optimized so that data packets can be efficiently rerouted through the wireless mesh network in case of a link failure, and the system can quickly recover from a network wide shutdown.
Reliability Features of an Industrial Wireless Network Meshing Technology Wireless Local Area Networks (WLANs) allow industrial plants to extend their PCN into the plant. They are used to support a wide range of process automation applications that improve the plant's efficiency, reliability and security. This includes perimeter and process video monitoring, personnel and asset location, handheld apps and, of course, process optimization using industrial wireless field instruments.
Distributed vs. Centralized Meshing WLAN There are two types of meshing industrial wireless local area networks: centralized and distributed meshing WLANs. A centralized WLAN requires a WLAN controller to manage traffic through the network, as well as other functions such as security policies, intrusion prevention, RF management and Quality of Service (QoS. With the distributed meshing approach, the wireless traffic load is distributed across the MAPs and does not depend on a centralized element for processing.
Duocast Duocast is one of the key elements improving the confidence in, integrity of and availability of data sent by a wireless transmitter in an industrial environment. Duocast allows two receivers to receive and acknowledge data sent by I/O devices.
Integrated Backbone Router The ISA100 standard has defined a standard interface allowing users to route field instrument data through any backbone, including high-speed backbones such as meshing WLANs. Most backbone routers are used with Internet Protocol (IP) networks such as an IEEE 802.11 mesh network or a 4G network. The most common backbone routing implementation consists of encapsulated ISA100.11a IPv6 packets inside IPv4 packets following RFC2529.
Gateway Redundancy Each multinode can be configured either as a Multinode or WSG. A multinode connects wireless devices to the WSG or to a wireless bridge, which is a multinode connecting the industrial wireless network to the wired network. A WSG connects wireless I/O (transmitters or actuators) to the wired process control system, enabling data exchange with the various control system applications.
Gateway Located in a Control Room Networks should allow plants to locate the gateway for industrial wireless field instruments, either a WDM or WSG, in the control room. WDMs and WSGs are the heart of the sensor network, since they host system, security and gateway functions. Such critical pieces of network communications are typically located in a safe and secure environment.
Quality of Service Quality of service is the ability to provide different priority to different applications, users or data flows, or to guarantee a certain level of performance to a data flow. For example, a required bit rate, delay, jitter, packet dropping probability and/or bit error rate may be guaranteed.
Conclusion A network should be designed by automation professionals for automation professionals. High network availability and wall-to-wall redundancy make it the industrial WLAN capable of supporting critical monitoring and control applications. Industrial plants can then extend their process control network with, enabling them to implement multiple applications from apps running on handhelds to wireless field instruments used to improve process efficiency.