PLC Re-Engineering

If you are considering upgrading your plant’s PLC systems due to obsolescence, Global Electronics can help develop a migration path and structure an approach that meets your timing and budget requirements.

PLC Re-engineering Solutions

Issue:
The original Allen Bradley PLC-5 or (Micrologic 1000) produced by Rockwell was retired in June of 2017. By 1995 over 1 million were installed. The current migration path recommended by Rockwell is to the Micrologic controller family. The problem is that, in many cases, the PLC-5 is integrated into a larger system. (For example storage retrieval systems where conveyors and cranes are integrated as part of a total system.) In this case a straight forward migration is not possible.

What is required, is to understand how and what to handshake with the Inbound, Outbound, and Safety PLCs to communicate routing decisions without changing the PLC code as well as to help troubleshoot any issues occurring while testing. The PLC’s code should often not be changed because the customer wants the old tracking software to still function in case of a disaster which requires the fall back to the older system.

Case Study:
In this example, there were six PLCs in the system. An inbound PLC5 For controlling the inbound portion of the AS/RS, an Outbound PLC5 for controlling the outbound portion of the AS/RS, a safety PLC5 for the 3 Storage Retrieval Machines (SRMs or cranes), and 3 ControlLogix one for each SRM or crane. There were 3 aisles of storage, with each aisle serviced by a dedicated Storage Retrieval Machine (SRM). Under normal conditions, the SRMs will store and retrieve vehicles from within the rack structures in their own aisles. The SRM retrieves a selected vehicle from a rack location, according to the model rotation pattern decided by the ASC, and deliver it to its associated Outbound Pick-up and Drop off (P&D) Roller Bed near the assigned level of the rack structure. The SRM will then check to see if a vehicle is at the associated Inbound P&D Roller Bed, located in the assigned levels of the rack structure, and store it in a pre-selected bin.

After understanding the AS/RS System, reverse engineering was used to analyze and determine how and which part of the PLC-5 memory and the handshake transaction logic was used between the PLCs and the ASC. A flowchart diagram was generated explaining the PLC logic Transaction part and Excel spreadsheets were created for the PLC5 and ASC memory map.

Solution:
In this instance, it was advisable to perform a Front End Engineering Design(FEED) study to determine the current state of the system, identify risks, and create a migration strategy suitable for the facility.

Global Electronics is uniquely positioned and has experience to complete this process. A FEED study or migration specification would analyze where you are, where you want to go, and how to get there. A FEED study also aids in estimating the hardware and integration costs necessary to complete the project. Electrical contracting work and other disciplines can be folded into the study as well to generate a complete estimate. The resulting benefit is the client is freed from guesswork about the cost of the upgrade.  Instead, the phases are clearly delineated in the study along with timelines and milestone dates.