Protecting the investment
Any capital spending on your control system undoubtedly had to promise an acceptable return on investment (ROI). Without reliable signals you don’t have trustworthy control — and you imperil your investment. So, there’s significant economic incentive to maintain the system so you can achieve the ROI. More than that, though, any control system has a risk management aspect — that is, dealing with the threat of unplanned outages and, just as importantly, effectively managing the frequency and duration of each stoppage of plant production. A predictive maintenance system and associated data are the keys to being able to accurately forecast when a device is likely to fail — allowing for proactive action at a convenient time instead of an emergency outage resulting from a component failure. The system must be able to analyze and interpret the data and then act, such as, at a minimum, initiating the appropriate work order for any required repairs.
Independent research has shown that predictive maintenance typically costs only one-fifth as much as preventive maintenance. However, predictive maintenance systems need to be properly installed and maintained, often by fewer people than in the past but by those with higher skill sets.
Today’s facilities are truly integrated operations, with modern digital systems often extending from the sensors through the business network and beyond to key outside suppliers. As such, they play a key role in keeping a company competitive. However, to be effective, the systems must get proper maintenance.
Wireless comes with strings
Wireless mesh networks are starting to gain greater acceptance at plants and are changing the communications landscape for industrial networks (see “Wireless Starts to Mesh,” www.ChemicalProcessing.com/articles/2008/208.html). Such mesh networks, which generally rely on low-cost battery-powered devices, add significant benefit such as flexibility in change-outs, faster uptime, increased mobility and lower installed costs. Wireless gives plant management access to data historically not available — turning data into strategic information.
Just like its wired counterpart, though, a wireless network requires a certain amount of care and maintenance to retain peak operational performance. While a mesh network should be “hands-free” because it automatically organizes and manages itself, in reality you always need to have a clear picture of what the mesh is doing. For instance, you should continually check latency (the length of time it takes data to move from one point to its intended destination). Basically, the more nodes that connect, the more bandwidth needed.
Commercially available software can monitor the mesh in real-time. At a minimum, the software should give visibility to all interconnections, provide upgrade capability for new firmware and enable control over the dynamic configuration mode and security of the mesh network. Software allows tuning, troubleshooting and maximizing overall network performance. It continuously observes the health of the sensor and system, including batteries, to enable predictive maintenance and hence the high reliability expected of the system.
ANSI/ISA-95, “Enterprise-Control System Integration,” provides standard terminology and a consistent set of concepts and models for integrating control systems with enterprise systems that will improve communications among all parties involved. The models and terminology emphasize good practices for integrating control systems with enterprise systems during the entire lifecycle of the systems. The ISA-95 committee has developed and is continuing to work on a multi-part series of standards that defines the interfaces between enterprise activities and control activities, focusing predominantly on the interface between Layers 2, 3 and 4.
Ian Verhappen is Edmonton, Alta.-based director, industrial networks, for MTL Instruments. Frank Williams is CEO of Elpro Instruments, San Diego, Calif., a subsidiary of MTL Instruments. E-mail them at firstname.lastname@example.org and Frank.Williams@elprotech.com.