Upgrading PLC Hardware

PLCs, or programmable logic controllers, have been around for over 50 years. Not many industrial automation systems will actually have PLCs as old as that, but chances are there are many elderly and ageing PLCs still in use. This means many companies are faced with a decision: whether and when you should update old hardware – and how best to do so.

Why Do You Need To Upgrade PLC Hardware?

PLCs are just another computer and, like any computer, they become obsolete whenever new versions are released. Unlike your desktop PC or tablet, PLCs are used in much more complex and critical applications. They need to be kept running for automated systems to function optimally. They’re also much more specialised than your average PC and can’t easily be swapped out if they go wrong.

If you suspect that your PLC is approaching the end of its useful life, there are two main ways of dealing with the issue:

1. If you decide to do nothing, you may be able to retain functionality for a while. But you’ll always be wondering how long it’s going to last, when something may go wrong and whether you’ll be able to replace obsolescent parts. There are two solutions to this problem.

One is to contact a specialist like Rowse to source obsolete parts , which is an efficient delaying strategy.

2. Migrating existing legacy code into upgraded PLC hardware keeps your control system intact. It also allows control functions to keep working while you’re upgrading the hardware. You’ll still maintain the original functionality and can tweak the software and codes if necessary to adapt to the upgrade.

How Do You Know if You Need an Upgrade?

If you’re considering an upgrade, you can perform a risk assessment to decide if it’s really necessary. Perhaps you might get away with running repairs, but you may discover an upgrade is needed. In this case, these steps will help to minimise downtime:

1. Collect all the part numbers
2. Check if the parts are still available
3. Decide which new platform you want
4. Check the program to see if it works for conversion
5. Check the communications
6. Check communications compatibility

1. Collect All the Part Numbers

PLCs are not a single entity, but a whole conglomeration of parts, so you won’t have just one part number. The first thing you should do in your risk assessment is to catalogue all your system’s parts numbers.

2. Check if Spare Parts are Still Available

Once you’ve compiled a list of part numbers, you must check each and every part number to see if they’re still available. This is because manufacturers might continue to produce a PLC platform, but with individual components within it that have become obsolete. If it’s still possible to use your PLC, you’ll want a catalogue of all the parts that can still be replaced.

3. Decide Which New Platform You Want

If after this you realise that your PLC is obsolete or unrepairable, then you need to upgrade. Some PLC manufacturers produce new versions that directly replace their predecessors, so migrating your system is fairly simple. If your PLC is not one of these models, however, look for one with similar IO capabilities and locally supported services.

4. Check the Program to See if it Works for Conversion

PLC platforms with a defined, manufacturer-recommended migration path are the easiest to convert. You’ll probably have to run the program code through some specialised conversion software, but be aware that not all the codes will convert correctly. Make sure you check that all parts of the code are functioning correctly – and fix any parts that aren’t.

If your chosen PLC doesn’t support conversion software, it’ll mean rewriting the whole code to recapture the control strategies you had with your legacy system. This is a specialist process. If that’s your only option, you might want to choose a different brand of PLC. Some manufacturers offer conversion utilities to convert code from other brands to their own PLC platform, but you’ll still find errors when you run your checks.

5. Check the Communications

Your system is probably connected to one or several networks for communicating with other devices. When you upgrade your PLC, all these links will be broken. You’ll therefore have to identify every device with which the PLC is communicating. The communication hardware will give you some indication, but not a complete picture: a single ethernet communication card can handle hundreds of other devices. You’ll have to look in the PLC program to discover what devices are referenced in the program code.

6. Check Communication Compatibility

Once you’ve identified all of the networked devices on your system, you need to see whether your new hardware will communicate with them. You can usually get a manufacturer’s compatibility chart for this. Then you need to see whether the converted PLC code is able to communicate with them too. It’s not unusual to have to tweak converted code to make it work properly with existing devices.

Then you have to see whether they’ll talk back. You’ll need to check each individual device to ensure that it can communicate back to the new PLC. It might require you to modify the code on each one to ensure proper compatibility.

Once you’ve completed these six steps, you should understand whether your PLC is obsolete, what upgraded PLC platform you want and what it will take to convert it. Although this seems demanding, such a process is essential to making an informed decision about upgrading a PLC.

Conversion or Rewiring?

The simplest way of upgrading PLC hardware is to choose a PLC that has its own conversion kit. This requires little downtime and is very low risk. You won’t have to do any rewiring, or the consequent error checking and I/O checks. The swing arms of your old system will slot straight into the conversion modules, then you can prepare and pre-assemble the conversion kit.

But a complete rewiring is worth considering, if you have the time. It’s a more painstaking approach, but offers more future-proofing than a conversion. Rewiring and recoding will give you a clean and complete break from your legacy PLC hardware.