At Rewire we have been using PLC’s for the past 30+ years.

All our Technical Field service people are able to troubleshoot PLC programs.


The following is a list of Processors we are familiar with and would have used at one time or another.



Allen Bradley:SLC500
PLC2, PLC5, SLC500, CompactLogix, Controllogix, Micrologix





S5, S7-200, S7-300, S7-1200, S7-1500





Modicon, Honeywell IPC-620, Texas Instruments, Omron CJ-series.

cjHoneywell IPC 620 Programmable Controllermodicon



As products mature corporations buy out smaller corporations such as TI-505 was sold to Siemens and subsequently disappeared from the market place. Some of the Processors or PLC that have evolved are:

  • Allen Bradley PLC5 (1785 series) replaced the PLC2plc5
  • Allen Bradley 1756 Series replaced the 1785 Series
  • Siemens S5 was replaced by the S7
  • Allen Bradley SLC was replaced by Logix Processors.

The replacement trend continues and this pushes the end-user into the latest software. Typically it is a matter of economics that drives a PLC replacement. As the older processor(s) become too expensive to replace and are typically limited in functionality. Some parts are just obsolete and can take weeks to replace. Try finding an Allen Bradley PLC2 Ethernet card. The PLC5 processor (5/40) costs almost $ 18,000.00 new. A new compactlogix 1769-L35E costs around    $ 3,500.00. The 5/40 is limited to 16 bit processing whereas the L35E is a true 32 Bit processor and has an Ethernet port to boot.

cropped-IMG_00000624-e1380752381127.jpgAs machines continue to age the electronics start to exponentially reduce their service life. If you have 15 or more years of usage from a PLC then replacement should be on the horizon. The oldest PLC’s should be the first to be replaced.

Step 1: After a Factory hardware audit has been done the oldest processors would be determined for replacement. A cost to keep the processor running maybe performed as well as preservation of the current software ability may also be audited. Older interfaces also become obsolete as some interface software does not run well on various computer platforms (win3.11, Win95, 2000, NT, XP, WIN7, WIN8, CPM, OS9 etc.)

Step 2: Removal of program from the machine. This is done to preserve the sequential logic within the processor. If the program is written in sub routines, some on site verification maybe required. Watching the program work through the ladder rungs. Any missing comments or address names would also be added at this stage.

Step 3: Purchase of replacement hardware and mounting on a shipping board. This is done so that the purchaser knows exactly what will be added or replaced on his existing machine. Sending small boxes is easier but loosing a small part during a retrofit can delay the changeover.

Step 4: The processor(s) are turned on and all communications are verified. The original logic is ported into the new processor and verified for errors. If all looks good the I/O is now wired. We typically prewire the new Processor I/O so that the customer does not need to spend time making up wire leads (including ferrules and labels).

Step 5: New processor sub plate is shipped to customer and is ready for installation. On arrival shipment is checked and can be verified as power plugs are typically left in place. Shut down of machine is scheduled and retrofit can begin.

Step 6:Typically on large change outs Plant electricians are involved to keep the cost down. Upon installation completion the machine is commissioned with the new program.

cropped-IMG_00000637.jpgKeep in mind that newer processors allow for some other ideas, like new Touchscreens that are Ethernet based, Communications over wireless and Devicenet communication to drives are possibilities. These add-on’s could look expensive but they may result in a lower hardware count and/ or a simpler method of software utilization.


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