Migration Paths

Review Your Options for PLC-5 Conversions

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Major Decisions in Mapping Out Your Upgrade Path

As you evaluate your options and map out your PLC-5 migration path, you have two major decisions to make. First, you must decide whether you will rewrite your PLC-5 software or convert the existing code into the ControlLogix software. Second, you must decide whether you will upgrade all of your hardware at the same time or do a phased migration using the PLC-5 to ControlLogix conversion kit or remote I/O. The sections below provide more detail on each of these choices.

PLC-5 Software Decision

When determining whether to rewrite or convert your PLC-5 processor application code, major considerations include budget, schedule, and functionality and maintenance requirements. The sections below provide details for each option. 

PLC-5 Code Rewrite

Rewriting the PLC-5 program allows it to be recreated using current programming methods. Although rewriting is the more expensive and time-consuming of the two options, it enables manufacturers to take advantage of the latest programming techniques and instruction set. In addition, it makes the application code more readable.

After completing over 200 system conversions for Fortune 500 companies, we recommend this option for your PLC-5 migration path as it provides the following advantages:

  1. Enables the use of functional tags: Including more descriptive functional tag references in the program flow makes the software easier to maintain — especially for staff members other than the program author
  2. Opens the hardware platform for improvement: By enabling the use of current communication protocols such as Ethernet rather than proprietary Allen-Bradley interfaces, a PLC-5 code rewrite allows data collection and database interaction.



PLC-5 Code Conversion

The second software option involves converting the existing PLC-5 processor code using the Allen-Bradley PLC-5 conversion tool. Converting the code saves time and is less expensive, however it leaves you with older register tags and proprietary interfaces. To minimize these disadvantages, a hybrid approach can be used by first converting the old PLC-5 code into ControlLogix software. Then, some of the logic — such as recurring sections of code — can be rewritten and improved using Add-On Instructions (AOI). 

PLC-5 Hardware Decision

Depending on the length of your downtime window and your upgrade budget, there are two ways to complete your PLC-5 hardware migration:

Total Hardware Conversion

The PLC-5 processor, 1771-series cards and chassis are upgraded all at the same time.

Phased Migration

There are two ways to do a phased migration: 

  1. Add a new ControlLogix Processor and Communication Modules and configure the original PLC-5 I/O as a Remote I/O Rack 
  2. Use the Allen-Bradley Hardware Conversion Kit to link the new ControlLogix PLC-5 hardware to the existing wiring 

PLC-5 Total Hardware Conversion Migration Option


Total Hardware Conversion

The PLC-5 processor, 1771-series cards and chassis are upgraded all at the same time. This option requires the longest conversion window and the largest budget; however, it brings your hardware completely up to date. Completely updating your hardware allows you full access to Rockwell Automation service and support and reduces the cost and risk associated with retaining obsolete hardware.

Original control panel with PLC-5 and PowerFlex 40 VFDs with discrete I/O

New background panel being fabricated with ControlLogix PLC and PowerFlex 525 VFDs with EtherNet/IP Communication

PLC-5 Phased Migration Options

There are two ways to do a phased migration.

Phased Migration Option Using Remote I/O Module

For this option the existing PLC-5 chassis and 1771-series I/O cards and chassis remain in place, and a smaller chassis is added which contains the new ControlLogix processor and a remote I/O communications module to talk to the existing PLC-5 and 1771 I/O. This option allows the upgrades to be phased according to your downtime windows and budget; however, obsolete hardware remains in place and will need to be upgraded at a future time.



New ControlLogix Processor and Communication Modules with original PLC-5 I/O as a Remote I/O Rack

Phased Migration with Hardware Kit

The Allen-Bradley hardware conversion kit links the new ControlLogix PLC-5 hardware to the existing wiring. This approach allows manufacturers to first upgrade the processor and HMI, followed by the remote I/O racks and the rest of the plant.

In addition to allowing the upgrades to be phased to fit your schedule and budget, an advantage of this approach is that communication can easily be switched between the old and new PLC-5 processor and HMI hardware. Upon installation and commissioning of the new hardware, the I/O can be switched over to it and an offline trial can be conducted. If issues occur, communication can quickly be switched back to the old processor until the issues can be resolved and tested. Disadvantages of this option include difficulty troubleshooting and maintaining the old wiring, as well as the cost and risk of retaining obsolete hardware.


Reduce Your Cost and Downtime — Plan Your Migration

Regardless of which migration option you choose, we encourage you to plan your migration ahead of time – don’t wait until an issue occurs to start your upgrade. Planned migrations are less expensive and can be done when it best fits your production schedule. Need help planning? Schedule a complimentary call with our migration experts to get your questions answered.

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