Upgrading Allen Bradley PLC


Thread Starter


Our existing Allan Bradley PLC 5/40 processor Hot standby configuration. 1785 BCM module need to be upgraded with latest version.
Can somebody please recommend which is the suitable version and procedure to upgrade? Since the system is controlling/monitoring of fuel supply to airport, the system cannot be shutdown at any cost.

Bob Peterson

My first question is why does it need to be upgraded? This is an obsolete hot standby system on an obsolete platform. You go in and mess with it and who knows what will happen. You really do not want to have an unplanned shutdown due to trying to install modules AB took off the market and very few people know much about anymore.

I would leave it alone unless there was just no way around it. OTOH, it was a very simple system as hot standby systems go. Basically not much more than some block transfer channels for data synching and a relay to switch the backup processor online if the primary processor failed. before they had the BCM module, we used to do something quite similar with just a relay. very cheap and simple, and remarkably effective.

You would be wise to consider an upgrade path to something like a controllogix or compactlogix hot backup system. You could likely reuse the existing I/O, so there would be minimal rewiring involved.

I would point out that there are some issues with some 1771 hardware in trying to use RIO with contrologix via a DHRIO card that you might want to research very closely if you try to reuse the old I/O. keep in mind you not only have an obsolete PLC you have obsolete I/O that is getting older by the day.

In the end, it might make sense to do a phased transfer of control from the PLC5 to a new platform using redundant controllogix and point I/O, probably with redundant controlnet as the I/O link. There are some point I/O modules that have some diagnostic capabilities that might be helpful in your application.