Maximizing a control system's lifecycle

Extending the lifecycle of a control system requires proper maintenance and effective lifecycle management practices.

07/11/2017


If a control system is at the end of its lifecycle and a company can't afford the time or expense of an upgrade to the whole system, there are some things that can be done in the interim to increase the longevity of an aging system. Whether this is a new installation or a legacy system, many of these tips are useful independent of the system's age.

In most cases, a control system consists of much more than a few programmable logic controllers (PLCs). There are controllers, input/output (I/O) cards, a network infrastructure, gateways or interface devices to allow data to flow between systems, and human-machine interface (HMI) software applications or proprietary consoles. In an effort to maximize the lifecycle of a system, it's important to have good preventive maintenance plans, but users also need a plan for managing the dependence on aging components and software, which are essential to operation. 

Control system maintenance tips

As a whole, keeping up with control system releases and properly maintaining the system over its entire lifecycle is essential to ensuring its reliability and continuous operation. This is an exercise to thwart the rigorous demands of time, manufacturing, and production schedules. 

Control system power

Good, reliable, and clean power is a must to maintain longevity. Nothing stresses power supplies more than brownouts, which lead to premature failure of components. Power surges are another big power supply killer. It's always a recommendation to install an uninterruptible power system (UPS) and run the critical components from it. 

Environment

Keeping tabs on the environment means factoring in temperature, humidity, and dust. Controlling the temperature and humidity around the components in the control system is critical. The warmer the cabinet, the shorter the life of the components inside (above a threshold temperature). This applies to computers as well. Most computers are designed to operate at an ambient temperature of no more than 80°F. Exceeding that temperature means there is not enough physical cooling capacity to keep the components below the design temperature, which may lead to failures.

The same issues can occur with dust accumulation, as dust can act as an insulator, keeping the cooling air from properly removing heat.

  • Ensure enough space for adequate airflow for PCs.
  • Ensure that the server cabinets have enough airflow and are in environmentally controlled rooms. Humidity also should be controlled (this may require external cooling such as fans or an air conditioner).
  • Choose control cabinet design with recommended spacing for components (this includes duct spacing around components) and heat dissipation. (This may require external cooling such as fans or an air conditioner.)
  • Keep components free of dust and dirt. The use of good filters and a preventative maintenance schedule to replace filters is a must.

Network

The network is the backbone of the control system yet it is often the part most overlooked. The data has to make it from the processors to the server/HMI so it can be controlled. More and more systems are adopting Ethernet as the go-to choice for control of distributed components. Variable frequency drives, valve banks, remote I/O, etc., are all reliant on a solid network. In most cases, it makes sense to make this as robust as possible. Users should explore layout topologies, distributing loads, and fault tolerance using multiple links and switches.

Staying up-to-date

Every control system has a life span. Computers should typically be replaced every five to six years and controllers/hardware should be replaced as needed (while still available). For the most part, keeping up-to-date involves upgrading computers and the control software. Companies that follow the latest and greatest version of software supplied by the vendor probably will be upgrading PCs more often due to enhancements and functions offered on the newer operating systems, which usually don't support older hardware.

Replacing computers seems like a trivial process, but with each passing year, a new operating system pops up and an old one no longer is supported. Additionally, since older operating systems may not support the new hardware, this means you're forced to go to the newer operating system and upgrade the control software for a distributed control system (DCS) or PLC. Depending on how many versions of the software you are behind, this could be a really big deal.

It's not all doom and gloom, but there are some tools you can utilize until it's time to make the big switch. 

Virtualize

In most cases, it's possible to virtualize the old system, which would allow users to limp by until a final solution is in place. This works well if you have good control hardware and need an immediate solution to HMI PC replacement problems. 

Phased replacement

Replacement often consists of updating the HMI software to a package that works with the existing and new hardware. Users can replace hardware as part of a phased approach, running the new and old systems side-by-side on the new HMI software until the upgrade is complete and you have all-new hardware. This removes the vulnerability of the old outdated computer hardware running legacy operating systems. 

The value of planning ahead

All control system vendors have a product lifecycle model, which defines a phased approach for support of their hardware/software. If users don't know what the lifecycle is of the current system or what stage of the lifecycle they are in, then it's reasonable to assume they are behind the curve.

Several years prior to when a control system is to be discontinued, users should begin the process of planning the next steps to ensure you minimize the potential for production outages. Most vendors offer migration paths for nearly every system. Some migrate effortlessly while others are much more involved, requiring a re-write of the code for the new controller.

Looking into the future, it's hard to predict what will happen with computers, operating systems, hardware, and networking components. Virtualization is a great way to maximize the life of the overall system, opening the door for added flexibility. Users are able to move their virtualized machines from one piece of hardware to the next with reduced effort or downtime.

Using thin-clients is also a great way to help minimize the impact of replaced hardware because these are independent of operating systems. A very efficient approach to lifecycle management is to couple virtualization of the operating system along with thin-client technology for operator workstations. First, this is a popular choice that decouples the control system from computer operating system so users are not chasing software compatibility like the IT departments. Second, the thin-clients allow for easy replacement with small costs compared to replacement of actual computers and time needed to reinstall the software.

Extending the lifecycle of a control system and squeezing the investment out of production system assets requires proper maintenance but, just as important, it requires lifecycle management practices. This means knowing where you are in your hardware/software lifecycle and having a plan to minimize production outages to allow the assets to continue to meet production schedules.

Both of these elements help reduce the risk of potentially having an unplanned outage, which could be detrimental to a business. Taking advantage of good maintenance practices and proven technology like virtualization can extend the life of the system, decrease disaster recovery time, lower the overall total cost of ownership, and ultimately reduce the risk of unexpected downtime.

David Ward, integration/energy management engineer, Cross Company Integrated Systems. This article originally appeared on Cross Company's website. Cross Company is a CFE content partner. Edited by Hannah Cox, content specialist, CFE Media, hcox@cfemedia.com.

MORE ADVICE

Key Concepts

  • Computers typically should be replaced every five to six years.
  • Virtualization can maximize the life of a control system while providing needed flexibility for a plant manager.
  • Extending the lifecycle model of a control system requires proper maintenance and good management practices.

Consider this

What other methods can plant managers use to maximize a control system's lifecycle?



No comments
click me