Distributed control system upgrades for process control systems
There are many reasons to upgrade a distributed control system (DCS) for a process control system, but there are many considerations and challenges to consider when doing so.
The process control system is the brain running behind any automated process facility being core system behind the overall process; distributed control systems (DCSs) control the process directly together with integration of packaged process units having independent programmable logic controllers (PLCs).
DCSs were built on proprietary protocols historically, but as the technology is reshaping very quickly and customers are becoming more demanding, the requirement of integrating everything (control systems) under one system (DCS) has become the key to success (together with cost effectiveness) causing the DCS original equipment manufacturers (OEMs) to move towards more open systems.
As the DCS has become open in terms of ease of integration with almost all types of systems, its lifecycle has decreased. There are several more reasons to upgrade a DCS.
End of life
The most common factor in upgrades is the product's end of life, which will push users to stock more operational spares in order to continue using the current DCS or buy refurbished hardware from the open market.
End of support
The OEM stops providing support on old systems, or the level of support is reduced to the bare minimum, which pushes end users to upgrade.
Lack of knowledge
Skilled resources are not easy to find especially when it comes to older or legacy systems. If there isn't a specialist on-hand who is familiar with the old system, it may be time to consider replacing the existing system.
Performance matters a lot. Obsolete or older hardware can't perform to meet today's needs and requirements.
Lack of openness for expansion or integration with newer systems
It becomes very difficult to integrate new systems with older ones due to integration limitations.
Lack of features required for enhancing the control philosophies
Process control techniques are always evolving and enhancing ways of optimizing the process and its efficiency. This requires newer functionalities in the systems to be used and implemented which either are not available in older systems or are very complex/difficult to implement.
Maintaining older systems is always expensive whether it's obsolete components, availability of specialists, or retention of older employees, and so on.
Paths to upgrade
There are many paths that could be opted for by the end user while deciding on an upgrade. Most of the DCS OEMs have already designed their upgrade paths accordingly.
One of the simplest approaches is to replace all of the existing DCSs at once—including all human-machine interfaces (HMIs), control hardware, and input/output (I/O) modules. This path might seem easier to deploy, but it has some factors like longer downtime, reduced efficiency of operational staff as they have to switch to newer systems in one go, and so on.
The most commonly used approach is upgrading in steps or phases.
Phase 1: Supervisory layer component upgrade
Supervisory layer components involving HMIs and communication network elements between control systems and HMIs are upgraded in phase 1. This enables the end user to get familiar with the new system operationally. Having the old HMIs run in parallel with the new HMIs is beneficial because it gives the operators a chance to become familiar with the new system.
Phase 2: Control system upgrade (except I/O modules for some OEMs)
Phase 2 involves upgrading DCS control hardware. This is a critical phase and has to be planned in more detail as compared to phase 1. It may involve downtime based on DCS configuration and upgrade limitations.
Phase 3: I/O modules upgrade [Optional]
Phase 3 involves upgrading I/O modules and relevant hardware in a DCS. It may also involve downtime based on I/O module configuration and upgrade limitations.
Additional considerations for DCS upgrades
DCS upgrades are always complex and require thorough planning. The core components of any upgrade consist of an HMI, control hardware, and I/O hardware, but these are not the only areas to be considered while planning. There are a few other important areas that can become potential risks if they aren't properly worked out. These risks include:
Interface with field I/Os
- How existing hardware is interfaced with field I/O and the upgraded hardware's compatibility level
- Availability of final documentation including drawings, design documents, wiring layout, and so on
- Physical condition of marshalling panels including termination details, tagging, grounding, etc. This will help assess the volume of changes needed in existing panels if these are being retained.
- DCS systems available today work on various communication networks associated with multiple layers. It is important to understand the existing system's network infrastructure.
- Physical components (switches, cables, firewalls. etc.) of the existing network need to be thoroughly scanned to identify all items that need to be upgraded.
Documentation of the existing system
- All documents of the existing system should be identified, marked, and updated at the end of the upgrade. Having documentation of the existing system will minimize the volume of work needed during the upgrade process.
Operational and functional issues in existing system
- Every system has its pros and cons. It is very important to identify all problems and potential areas of improvement. These functional issues should be minimized, and operational requirements should be catered as much as possible.
DCS upgrades require more rigorous analysis and systematic approaches, but the benefits will make all of the hard work up front even more worthwhile in the end.
- Aneel Shahzad Baig is senior project manager at Intech Process Automation. Intech Process Automation is a CFE Media content partner. Edited by Chris Vavra, production editor, CFE Media, Control Engineering, firstname.lastname@example.org.
- See additional stories about distributed control systems (DCSs) linked below.