Know your options: 6 Key considerations when replacing a PLC-5
Programmable Logic Controllers (PLCs) control multiple systems, so replacing one (or many) can seem daunting. There are a few options and considerations to make before jumping in.
The Front-End Engineering Design (FEED) is an audit that identifies the gaps in OT control systems, this service pinpoints needs and considers the capability and capacity of your facility. This includes:
- prioritizing the critical components that will need to be replaced,
- confirming the site infrastructure capacity (power and electrical, environmental control, network connectivity (IT and OT), location and space requirements),
- identifying what improvements can be realized during the reprogramming,
- identifying how HMIs will be impacted,
- identifying whether alarms will be impacted by peripheral work, and mitigating any impacts,
- confirming how and what data will be historized,
- and ensuring networks are up-to-date and compatible.
1. IO Migration
There are multiple ways to replace the controller: completely rewiring the new one or using the conversion tool to connect existing swing arms to the new controller.
Swing arm method
Pros
- Time saving: Rather than spending time on rewiring, the swing arm method allows you to simply connect the new IO modules directly to the existing PLC-5 IO chassis with the use of an IO adapter plate, conversion modules, and pre-wired cables. The wiring of a single PLC can be completed in less than 10 minutes.
- Reduces errors: Because the same swing arms will be fitted to the new system, there is a reduced chance of errors occurring when rewiring.
- Unlikely damage: The chance of breakage is reduced since the wires will not be worked on individually.
Cons
- Accessibility: Because the replacement PLC chassis mounts directly over the existing PLC-5 chassis, accessibility is limited. The system must be powered down if access to the PLC-5 chassis is required.
- Costly: This requires purchasing the IO adapter plates, conversion modules, and specialized pre-wired cables.
Rewiring
Pros
- Reliable: Having IO wired directly into the new IO modules means that the connections are re-terminated and more reliable. This ensures greater safety for plant processes.
- Facilitated troubleshooting and accessibility: Single IO connections can be accessed for troubleshooting. With adequate planning, it’s possible to conduct a live swing over or hot swap.
Cons
- Time-consuming: The time it takes to rewire is extensive and requires system expertise.
- Room for error: The more connections to wire, the more room for errors.
- Potential damage: Depending on when the system was last updated, there may be brittle wires and handling them could cause breakage. Replacing wires can be costly and time consuming if they need to be re-run.
2. Software Migration
Along with changing out the hardware, migrating to a new controller also requires reprogramming. This can be done the traditional way, writing the code, or using a conversion tool, which automates this process.
Using a Conversion Tool
This is only an option if converting within Allen-Bradley products.
Like installing the conversion tool hardware, the software conversion tool converts code simply by automating the logic migration, rather than rewriting the program. However, this method will not make use of all the software capabilities, such as User Defined Datatypes (UDT) or Add-on Instructions (AOI).
Standard Reprogramming
This allows users to take advantage of new function block programming for greater optimization and software capabilities, such as User Defined Datatypes (UDT) or Add-on Instructions (AOI)). Also reprogramming allows for updating to a tag-based naming system within the program which will reduce troubleshooting and will support future project expansions.
Manually reprogramming the logic will also allow the user to implement any site programming standards that the client has, ensuring consistency with other PLC programs across the organization. This program standardization not only helps with troubleshooting but also allows new staff to adapt to the system easily.
3. Human Machine Interfaces (HMIs)
Applicable only if you connect your PLC-5 to an HMI.
At a minimum, your HMI will need to be updated. If it is integrated with a SCADA, a DCS, or other PLCs, it will need to be migrated. For HMIs there is a choice between a modern solution, like a touchscreen, sticking with a legacy system with pushbuttons, or choosing a hybrid solution which can utilize both.
Legacy
Pros
- No changes: There’s less of a learning curve for operation staff if your current system continues to be used.
- No extra cost.
Cons
- Outdated.
- Less flexible: When IO is added or moved around, altering pushbutton displays and adding new labels makes this a much greater task.
- Finnicky programming: Reworking legacy graphics may take more effort or not be as intuitive as expected. If the program fails to convert the code properly, it can be detrimental to your facility.
- Graphic scalability: Legacy graphics may not be compatible with new monitors (display may be stretched or distorted, the resolution may not be compatible, etc.)
Modernized
Pros:
- Standardization: Layouts can be aligned with company standards, facilitating use for operators.
- Remote accessibility.
- Flexibility and compatibility: Touchscreen HMIs allow for more flexibility and adaptability when setting up new equipment and IO. If other external control systems (like DCS, SCADA, or other PLCs) need to be added, or if operators could benefit from new trending tools, these can be easily integrated.
Cons:
- Costly: A new HMI is a costly piece of equipment, especially when considering purchasing alongside a new controller.
4. Hardware
Power infrastructure and communication modules: Not all controllers have the same power requirements so it’s important to confirm that the site power infrastructure is adequate for the new hardware and cabinet design, and whether the communication modules that the program uses are compatible with the ones currently used on site.
Location and fit: Cabinets each have their own individual constraints (its size, location, accessibility to power), and these must be taken into consideration when designing and working on them. In a brownfield facility, adding new hardware or combining or adding PLCs (which means doubling the IO) may be more complicated than it seems or may not even be possible. Additionally, the cabinet location should be optimal for field wiring. Cabinet design requires confirming the interior dimensions of the cabinet and location of the cabinet for optimal integration.
5. Alarming
Alarms are highly important in a facility to alert operations staff of events or situations that need attention. If alarms are not properly re-configured when conducting a PLC migration, the impacts for site safety and operational efficiency can be severe. Alarms do not convert well with the conversion tool, so it is best to work with an integrator who can ensure your system will function correctly.
6. Network Design
Network Architecture: If the site’s communication type needs to be updated (for example: from RS232/serial connections to Ethernet/IP based), this can introduce the requirement for firewalls and network switches for extra layers of protection.
Cybersecurity protection: Upgrading control systems and software and designing networks to meet new cybersecurity standards will reduce external threats and increase security.
Remote access: A new system introduces the ability to operators to control site assets remotely, improve their visibility on site and of alarm occurrences, reducing potential windshield time. Reducing the amount of time spent in hazardous locations, increases safety for operation staff.
Conclusion
There are many factors to consider before migrating your PLC-5s, and there is no one-size-fits-all; you need a solution that is specific to your facility and company needs. At InnoTech, we’ve completed projects in varying sizes, all using our scalable and standardized project execution processes. Find out more about our migration process, download our guide to modernizing obsolescent PLC-5s in industrial facilities (below), or speak to one of our experts today!
Sources:
InnoTech SMEs
Larson, K. (2023, June 20). Lessons chevron learned in modernizing its plcs. Control Global.
Magill, K. (2022, October 12). Schneider Electric moves to modernize equipment and machinery at 2 US plants. Supply Chain Dive.
Nicolas. (2023, March 16). Industrial Equipment Modernization. Solutions TREXO.
PLC-5 controllers: Allen-Bradley. Rockwell Automation. (n.d.).
ABB Top aluminum producer and recycler novelis to increase uptime following ABB Modernization. News. (2023, August 16).
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