This is the second in a 2 part series highlighting the key decision points and recommendations for a successful upgrade from PLC5 Automation Platforms to Logix 5000. In Part 1 we discussed the need for planning prior to the project start. In Part 2, we will discuss the software and interface concerns as well as the necessary training.
There are several aspects of the hardware platform to consider when beginning an upgrade program. If there are multiple systems to be upgraded over time, a uniform approach resulting in minimized spare parts inventory is best.
Determine whether field wiring is run directly to the I/O modules, or to terminal blocks in the panel. If the field wiring goes directly to the I/O module, it may be more efficient to use Allen-Bradley’s conversion kit for wiring arms. This allows use of the existing 1771 wiring arms, mated to a special adapter, which then connects to the new 1756 hardware underneath.
While simpler and quicker in the short term, this method results in a panel that’s harder to maintain in the long run, as the wiring is harder to trace, and some of the hardware is more difficult to access, as it is hidden by the adapters.
If a slightly longer downtime window is available, and if the I/O is wired to terminals in the panel, a good option is complete replacement of the old PLC5 hardware with new ControlLogix equipment, using pre-wired harnesses that snap onto the I/O module and run as a single cable to the termination points.
It is easy to focus on the PLC itself as the target of the upgrade, but all PLCs have interfaces of some sort, whether HMIs, historians, other PLCs, drives, etc. These interfaces need to be modified to be compatible with the new PLC as well. First, consider whether any outdated networks, such as Data Highway Plus or Remote I/O, are being used. If so, now is probably the best time to replace them with Ethernet.
For HMI or SCADA interfaces, there will likely be a tag database that needs to be updated. PLC5 addresses are of the format “N7:1/0”, while the new ControlLogix arrays will look like “N7.0”. Depending on the HMI package, it may be possible to export the tag database to a text file which can be manipulated with search and replace, then re-imported. If not, it may be necessary to change every single animation point within the HMI package.
Any messaging in other PLCs will need to be modified to communicate to the new ControlLogix. Especially note that some older PLC5s are not able to communicate via Ethernet to ControlLogix PLCs at all, and will require a firmware upgrade to communicate.
If the site maintenance staff is unfamiliar with the ControlLogix platform, some form of training should be considered. In addition to formal instruction, it is useful to set up a PLC as a ‘sandbox’ that can be used for self-directed study and familiarization.
Upgrading PLC5 to ControlLogix is usually a straightforward effort, but it is tempting to over simplify by not considering the ancillary work required to make the project successful.