PLC Upgrade Using the Existing IO Rack

Are you wondering how to tackle your PLC retrofit project and avoid hours of rewiring?  Here’s a strategy you can use when upgrading from a legacy PLC to the same manufacturer’s latest and greatest CPU.

In the video above, we show you how to save substantial time and cost in a PLC upgrade.  Can’t listen?  Follow along with the text below.

Below we have a representation of a legacy-model PLC with an older, slower CPU and rack-mounted I/O modules.

Each module can contain as many as 32 inputs or outputs, potentially adding up to hundreds of wires to relocate. If we want to change out the CPU to take advantage of faster processing speeds and/or state-of-the-art communication protocols, a traditional rip-and-replace procedure is not only time consuming but could introduce new wiring issues that would need to be sorted out.

Instead, add to your panel a new, superfast CPU from the same PLC manufacturer, and as shown, a multi-port Ethernet switch.

Keep your PLC rack, I/O modules, and wiring intact and replace the CPU with a communications module such as Rockwell Automation’s Ethernet IP, Siemens Profinet, Beckhoff’s Ethercat, or one of the many others available in the automation marketplace.  Next, connect the remote I/O rack and then the new CPU to the Ethernet switch.

Move the PLC program from the old CPU to the new one.  Of course, this is easier said than done, but you will need to do this, regardless.  Now the new CPU can communicate with the remote I/O rack and “see” the status of the I/O, read analog values, or encoder inputs.

If for example, input #7 is pulled high on one of the modules of the rack, it will show up as such in the new PLC program without ever having to move a single wire.  Remember, the new CPU doesn’t even need to be in the same enclosure or mounted on the same panel.  It could be hundreds of feet away, connected to the remote rack’s Ethernet switch by a Cat 5 or Cat 6 cable.

Need help with your PLC retrofit project? Give Electronic Drives and Controls, the nationwide PLC and drives integration specialists, a call or click.