Maintain the Magic And Keep Good Data Coming

Properly maintain networks to ensure reliable data transfer.

By Ian Verhappen, MTL Instruments, and Frank Williams, Elpro Instruments

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Without communication between the various components of a control system and, just as importantly, the control system and the corporate network (including manufacturing execution and enterprise resource planning systems), it’s impossible to make product. While plants realize that maintenance of field devices and production equipment is crucial, they don’t always pay sufficient attention to the monitoring and maintenance of the network used to interconnect these components. Yet this is essential for high reliability. Unfortunately for most people using these systems, “all the stuff” that makes them work is “magic” and this magic is becoming more complex (Figure 1).

user perspective of a maintenance system
Figure 1. Merlin at work -- Many users view data
handling and the working of control systems and
networks as magic.
Click on image for a larger illustration.

As we all know, if we don’t have a reliable control system with availability as close to 100% as possible, production staff quickly lose faith in the system and circumvent it with jumpers, loops in manual, etc., that defeat the purpose of the investment. Even “finicky” analyzers have a 95% minimum acceptable availability.
A key part of any control system is the infrastructure that carries the signals from the field devices to the controllers — because without signals there won’t be data on which to control nor a means to manipulate the final control elements (valves, drives, etc.) to adjust process operating conditions. However, as the level of expected interconnectivity increases between the various systems, the degree of difficulty in maintaining them rises exponentially.

Essential monitoring
System reliability depends on proper design — which includes taking into account security and regular maintenance. Correct maintenance requires understanding the condition of the system. A single snapshot in time, say, when the system was started up and commissioned, isn’t good enough. Instead, you must gather and compare data over time so you can predict when one or more components are likely to fail.

Regularly manually capturing these data (at a minimum at the vendor-recommended intervals) forms the basis of a preventative maintenance program to verify everything is within tolerances and hopefully to spot when a component in the system needs to be replaced. The data collected this way normally then have to be manually keyed into appropriate software and, in most cases, interpreted by a knowledgeable end user. Unfortunately, this is labor- and time-intensive, and depends upon staff expertise, which is growing increasingly scarce as old timers retire.

Fortunately, the same systems that form the networks now have components, tools and software to monitor the networks in real time and provide analysis of the data to alert you that the system is degrading well in advance of an incident. In addition, because control systems are incorporating more and more “Commercial Off The Shelf” (COTS) technology as part of their infrastructure, many of the tools used for business networks can serve in the control environment as well.

layers of maintenance architecture
Figure 2. Network architecture -- Plants usually
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