27 July 2016 Published in Abstracts

PLC5 - VME Conversion NOT an ordinary PLC5

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History helps to manage risk. A fourteen year partnership with a Southern steel mill built the necessary confidence to choose Prism Systems, Inc. to tackle a critical problem on the plant floor. The mill was built in 2002 with steel-making equipment from international suppliers that included three PLC5- VME processors in the rolling end of the mill. While much of the original controls equipment had been upgraded to an AB/Rockwell standard as the mill has expanded and modernized, the PLC5-VME processors were not well understood and left untouched due to elevated risk.

This upgrade would not be a standard PLC5 conversion. Having a successful history completing difficult projects corporate-wide, Prism Systems was tasked to assist. The customer preference was an AB/Rockwell conversion, but all were unsure if conversion was possible due to non-standard communication protocols and methods of control. The original program was written in Italy, and was historically only supported through OEM international support. Existing communications included: DH+, Remote I/O, Profibus, and Reflective Memory on a high speed bus. The PLC5-VME solution was central to the Rolling Mill and touched a pile of I/O, engineered drives, and other custom PC applications via Reflective Memory. Oh yeah, and that international thing… documentation was a mix of Italian, German, and English.

With obsolescence, and NO spare parts availability, the mill knew they were running their process on borrowed time. Something had to be done soon while managing risk. Due to the complexity of this conversion, production demand, and limited downtime, the plan would be to run the new system in parallel to the old system, until all components were operational, fully tested, and verified.


  • PLC5-VME Obsolete with NO direct replacement
  • Risk – not well understood and international documentation
  • 24/7/365 production schedule with limited downtime – installation in parallel
  • Tight network update times for coordinated motion over multiple PLC’s
  • Maintain existing communications on several networks: DataHighway +, Remote I/O, Profibus, and Reflective Memory on a high speed bus Work with international integration project partner, and plant engineering resources
  • New solution to be supportable in-house with local integration support


  • ControlLogix PLC platform
  • Maintain all existing I/O networks - replacing I/O too costly and time consuming
  • Maintain Reflective Memory network via a custom PC Ethernet/IP solution

All hardware in the new solution is now connected to a current ControlLogix PLC processor allowing maintenance personnel to use a familiar program for future support. Replacing I/O was determined too costly and time consuming during this critical stage and therefore remains in place. The steel mill has the expertise and the flexibility to upgrade I/O in the future, at their leisure, and spare equipment is now readily available in local distribution. Further, performance of the new ControlLogix solution is well within the network update requirements.

Critical to the success of this project was a custom solution required to support the existing high speed data on Reflective Memory. Prism Systems designed a communication protocol over Ethernet/IP to communicate between the PLC and a standalone PC, and then using the PC to directly access Reflective Memory networks. In this way, Prism Systems was able to maintain the Reflective Memory network and data shared with other custom PC applications critical to operation of the Rolling Mill.

Upon completion of commissioning, the massive risk to production as a result of any unplanned failure with obsolete hardware has been eliminated. The steel mill can now leverage local integration support relationships currently in place, as needed. Commissioning of this replacement PLC5-VME solution is the latest success in our historical partnership with this Southern steel mill. We certainly appreciate the partnership and the confidence in Prism Systems, Inc. Now if we only could do something about foreign steel and fair trade.


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Last modified on Wednesday, 17 August 2016 10:28

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