The backup plan in industrial Ethernet automation

Redundancy in industrial Ethernet should be addressed seriously to avoid disasters

As more and more types of industrial equipment now come with Ethernet interface, redundancy has become a hot topic for many industries. In fact, with the rapid development of hardware and software, administrators have been forced to think more carefully about various requirements for backing up systems in an unstable environment. In this article, we discuss different recovery requirements for redundant solutions and ways to keep redundant hardware and software running reliably.

Power Redundancy
Power backup is a basic redundancy requirement for every part of the communication network in control systems. In case of a power outage, the backup takes over, thus minimising the possibility of damage caused due to the system shutting down. The system’s hardware should be compatible with unregulated DC and have reverse power protection. Two most common methods of sending power failure alarms to the administrator are by an email or relay output, both of which send the alarm automatically when power supply fails.

Media Redundancy
Media redundancy is another basic requirement for automation. This involves forming a backup path when a part of the network becomes unavailable. A recent technology for media redundancy known as Spanning Tree Protocol, or STP, uses an Ethernet ring topology with backup paths. Earlier, it was difficult to create an Ethernet ring topology, as they were not allowed. Moreover, using a readily available dual-star topology to create an automation system network was expensive. The technology used today identifies one of the switches in the network as the “root switch” and then automatically blocks packets from travelling through any of the network’s redundant loops. In case one of the paths gets disconnected from the rest of the network, the STP automatically readjusts the ring and uses the redundant part.

Although STP has helped solve many problems in the Ethernet network, it has the limitations of bridge diameter, lower convergence speed, VLAN insensitivity, etc. The Rapid Spanning Tree Protocol (RSTP) technology was developed in order to deal with those limitations. Not only does this new protocol have all the advantages of a STP, it also provides higher performance. Media redundancy by ring topology also cuts costs, especially in the case of long distance wiring such as windmill monitoring and management. With ring topology, one can decrease the cost of wiring to a large extent, making the wiring cost-effective.

Network and Network Node Redundancy
Companies suffer a great deal of loss when a network disaster takes place. For this reason, all network administrators need to implement a network that is available all the time to let all network nodes continue to operate in case an accident occurs. After implementing media redundancy in an industrial Ethernet network, a problem that arises is of including every point in the control systems. Therefore, switches that are connected to critical devices need to set up dual network nodes, one of which is the second Ethernet switch. Both these network nodes should connect to a dual-homing controller. When a network problem occurs, the controller that supports two Ethernet interfaces to connect both redundant switches, should establish connections with certain critical end devices.  Here, the cost of the redundant equipment is also much less than buying a duplicate of the network switch.

Complete system redundancy
Even though one may decide not to establish redundancy for all devices in a network due to space and cost constraints, it is still advisable to have the knowledge of how to create a system that is completely redundant. A completely redundant system consists of redundant ports, switches and device pairs. All Ethernet workstations are connected to both independent ring network architectures. Complete system redundancy can help form a reliable network that minimises data loss and has fast recovery time. A dual homing controller should exist that is able to distinguish which Ethernet device is active – the primary or secondary.

Constructing a Reliable Architecture
Different vendors have proposed different criteria for redundant network systems that ensure 100 percent system availability of the plant floor for industrial automation. To avoid your networks from being damaged by power failure, one should establish power redundancy in every component of the network. Some Ethernet switches are connected to several devices where data transmission to the central controller cannot be afforded. Here, one will need node redundancy instead of media redundancy since backing up paths isn’t enough to meet higher demands. However, will a dual network solve the problems with efficient recovery in all industrial automation applications? The answer could lie in the fact as to why administrators wish to establish complete system redundancy.

Check Availability: After understanding the methods of redundancy required for present control systems for industrial automation, the importance of availability needs to be emphasized upon. Earlier, though the newly-developed equipment reduced the need for workers, yet it was common for administrators to work long hours in the field collecting data, fixing transmission hiccups and dealing with network disasters. A company can prepare a table listing the entire redundancies and use them as a reference for system redundancy. They can select the most suitable option based on their need and budget.

Conclusion: ince Ethernet has become integral to automation hierarchy and industrial Ethernet switches have started playing a crucial role in setting up Ethernet LANs, one can only expect the technology available for plant floor systems to keep improving. The power, media, network, node and complete system redundancy talked about in this article certainly help create a more convenient kind of industrial automation control. A careful attention to redundancy concept and its involvement as a central part of the design of networks can help companies avoid all disasters, big and small.

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