Know when to upgrade a facility's control system

Upgrading control systems is costly and expensive and should only be done when necessary. Signs such as increased energy use, current renovations, and the system reaching the end of its life are clear indications an upgrade is needed.


Image courtesy: Bob Vavra, CFE MediaHow old is a facility's control system? In most processing plants, the control system consists of field instruments wired to input/output (I/O) cards which feed to a central programmable logic controller (PLC). Operators communicate with the PLC through a human-machine interface (HMI) computer.

While the lifespan of an HMI computer is about the same as a typical desktop computer, the instruments, field wiring, I/O boards and PLC controllers last a lot longer - and the mentality of most operators is: "If it ain't broke, don't fix it." Upgrading a control system is a costly investment, and, as a result, many facilities have field hardware that is decades old. 

When to upgrade a control system

Control systems should be upgraded for the following reasons: 

  • Their system has reached the end of its life and/or no longer functions
  • An upgrade would result in significant energy savings
  • They're already undergoing other major plant renovations or upgrades.

There are a few red flags to keep in mind. When software versions are no longer supported or will not run on currently supported versions of the Microsoft Windows operating system, it's time to upgrade. The risk is too high for virus and cybersecurity issues.

Another indicator is when hardware is no longer being manufactured and spare parts are difficult or impossible to find. The risk of a minor failure taking down an entire facility because spare parts aren't available is too high.

Partial upgrade vs. full upgrade

A new control system can get expensive, but sometimes costs can be minimized by upgrading in phases.

In a partial upgrade, users can replace individual components while keeping the rest of the system intact. However, there are limitations. For example, the technology in the old and new components must be able to talk to each other. In the right situation, this allows plant owners to take advantage of features offered by more modern computers and software without the expense of fully replacing all the control hardware.

Some potential partial upgrades would be:

  • Replace the HMI computer and software and keep the existing control hardware in place. This allows the control system to communicate on a modern Windows network for printing temperature reports, saving historical data, doing remote alarming, etc. However, the PLC program stays the same, so you won't get the benefit of improved functionality and energy efficiency.
  • Replace the PLC controller and program and leave the I/O, field instruments and wiring in place. This option takes advantage of the newest energy-saving algorithms and control functions.

A full upgrade may be required if the control system is obsolete. Legacy systems—often 20+ years old—were frequently manufactured as proprietary, stand-alone systems. When the control hardware is too old to communicate with a new HMI on a modern network, it generally can't be upgraded in phases. Replacing the entire system is inevitable.

Benefits of upgrading

Control systems aren't like the newest iPhone: Replacements aren't done when the next-gen model comes out. When the time does come for an upgrade, the features can be a big advantage to your business and the quality of life for plant personnel. Here are some of the biggest benefits with newer automation systems: 

  • Energy efficiency. Modern refrigeration systems have advanced controls for efficiently sequencing compressor and controlling the head pressure at its optimum point. If your system is more than 10 years old, you're probably missing out on some energy-saving benefits.
  • Communication. There are great labor-saving benefits to be gained from integrating all equipment and sensors from the basement to the rooftop. Operators can see the entire plant from one screen and can make better choices about how to spend their time, and managers can monitor and improve energy usage.
  • Mobile access. Today's cloud-based software allows for remote alarming and mobile access. A refrigeration engine room is frequently staffed with only one operator and is often not staffed at night. When an alarm goes off after hours, someone—like a security guard doing their rounds—would have to notice and call the off-duty operator to come onto the plant and investigate. A control system with remote capabilities will alert the off-duty operator, who can log in and address the alarm from home. This increases efficiency, saves time and improves quality of life for operators.

Today, people increasingly expect all controls to be integrated and to be controlled from one central location. A modern control system should be expected to be fully integrated—including process equipment, tank level controls, pump controls, skid-mounted equipment, etc.—on a common control network. An operator should be able to view the same information from every control screen around the plant. Older systems don't do that.

Allen Casteel is operations manager at Stellar. This article originally appeared on Stellar Food for ThoughtStellar is a CFE Media content partner. Edited by Chris Vavra, production editor, Control Engineering, CFE Media,

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