Autopro Blog

Evaluating Vendor Recommended Programable Logic Controller Upgrade Procedures

July 17, 2019


It is an often-misconceived notion that when upgrading a programmable logic controller (PLC), it is a mandatory requirement to remain with the same vendor. This is not always the case, and at times may not be the best solution when faced with adapting to any new requirements placed on the PLC. You may not always be looking for a one-to-one replacement of an existing system, but also looking to add value to your current installation.

The recommendation Autopro provides to customers when upgrading PLCs, is to review the differentiations of vendors and their technologies during the FEED stage of any project. We work closely with our clients to develop a detailed technical survey and thorough investigation of their current system. When working through this process, there are two overarching technical aspects that need to be considered.

1. Uninterruptible Power Source Load

During the technical survey for an existing system, it is recommended that you revisit the Uninterruptible Power Source (UPS) load calculation. This is used to validate that the existing UPS capacity and power distribution will be able to support the new control system after any proposed migration. (It can also prove useful to review the use of two independent UPS sources to supply the new control system. This is most beneficial when faced with system segregation or redundancy in the new system.)

2. Communication Network Functionality

The existing communication network functionality and infrastructure should be evaluated to ensure that it would suit a new control system post migration. In some cases, there may be existing network problems that must be resolved before designing and installing a new control system.

As well; you may determine that the existing network infrastructure requires changes to the network cabling. This could entail merging from copper to fiber, replacing older fiber technology like OM1 (with limited communication bandwidth and less transmission distance) to OM3/OM4 Multimode Fiber or even OS2 Single Mode fiber (with wider bandwidth and longer transmission distance). Another important consideration should be the communication equipment redundancy, which may require adding extra fiber strands, communication channels and/or network switches.

Pros and Cons of Vendor Recommended PLC Upgrade Tools

PLC vendors are often known to recommend specific migration strategies tied to toolkits when migrating from an obsolete control system to the latest and greatest on the market. However, it is important to understand the advantages and disadvantages of using such tools, and how they may affect your current installation. These migration toolkits should be used as temporary solution to complete the migration in a compressed timeframe. The results provided by some toolkits are not always recommended as a long-term solution.

The photos below show the before and after scenarios when using a migration tool kit. This example is specific to PLC-5 migrations, but the concepts are applicable with other technologies as well.

kit pic 1    arrow      kit pic 2 


  • Easy design work allows for quick installation on-site
  • If no I/O re-assignment is required, this would be a go-to option when under a time constraint
  • The ability to utilize the current footprint and wire ducts on the cabinet backpan
  • There is no change required for cross-wiring


  • Increased risk due to using obsolete swing arms from the current PLC
  • Inconvenient maintenance and troubleshooting of cross-wiring terminals; after the initial installation, access to the wiring will be underneath the newly installed PLC
  • Limited room for future improvements and no opportunity to use varying technologies
  • If re-assignment to the IO points, modules or system segregation is required according to HAZOP/LOPA recommendations, implementation will be difficult by using a migration kit.
  • If future installation of a new system with clean cross-wiring is desired, the toolkit must be removed. This would require another stage of engineering and site installation, with proper review to the best system migration options

Review Your Current Situation with Your Main Automation Contractor

There should always be an open dialog between you and your MAC, with a review of the current control system situation in hand. There are certain cases in which using a migration tool kit may be what is called for in a time constrained environment. The justifications for implementing, or not implementing a migration kit is something your MAC can easily and efficiently provide guidance on.

Autopro Can Help

As a vendor-independent service provider, Autopro is able to offer cost-effective turnkey solutions to support the full scope of our clients’ requirements. By removing the need for multiple service suppliers, we minimize risk of costly scope changes and schedule delays. With desirable locations, Autopro’s offices are well-situated to our clients’ facilities. We provide local staff and flexible, cost-effective solutions.

For more information on this and our other services,
please contact us:
+1 (888) 539-2450