If I have a legacy 984 PLC system what is my best migration strategy? Should I look at other suppliers as well - if I am going to have to move, why not move to someone new? Can we rely on the future of the tools I am comfortable with and what will be discontinued next?

 

There are a number of things which you should consider before migrating.

1. Are there any special things you are doing with your PLC that needs special consideration? If so then you may be limited on your options.

2. Who is going to be around for the next 20 - 30 years to help provide you support? If you consider who has the most popular products they are Allen Bradley, GE, Modicom & Siemens. Then looking at the size of these companies they will probably still be around in 20- 30 years. So if support is a concern you are probably limited to these manufacturers.

3. Do you plan on upgrading your I/O system? If so you need to consider which type of I/O system you would like to upgrade to: DeviceNet, ControlNet, Genius Bus, Remote I/O, Advantys or Simatic to name a few.

4. What type of communications does your system require? Are these communications in a standard format or do they require special consideration?

5. Will your system require and HMI or user interface? What capablities will the user interface require? With HMIs and user interfaces quite often it is benefical to get one made by the same company that made the PLC. Since it is easier to get support when there is a problem with them?

6. Do you need to consider future expansion into the system? If so by todays standards you should get one with TCP/IP capability.

This is a list of what I consider some of the most important considerations before upgrading a PLC. The PLC should be the last thing to consider.

Mike McCowan
Automation Specialist
Industrial Automated Systems
[email protected]

 

Dear Jeff,

If you want to stay with reliable Modicon family, then definetely I suggest the Modicon Quantum family. If you really want, you can keep your old 800s I/O drops under Quantum CPU.

By the sw point of view: If you want to use longer term solution start with Unity Pro. HSBY solution is also supported. Definetely these are the Schneider ways.

If you are not happy, then Allen Bradley Controllogix or Siemens S7-400s are the answers.

Good Luck

 

You can retain your 800 series I/o for the time being and later upgrade 984 CPU to Quantum PLC system. Later on you can change the 800 I/O with quantum I/Os. Contact your local Schneider office. Give your details, i can help you more on this.

 

I think you have the right idea. While you are trying to decide what to do, look around and see what else is available.

While sticking to Modicon processors allows you to keep your old I/O, that may not be your best long term strategy. Do you really want 20 year old I/O and the problems of maintaining obsolete I/O technology? You will get a modern CPU out of the deal, but unless you are willing to do a LOT of reprogramming, you will end up with the same old 984 style ladder logic. If you want the new style programming, the time it will take you to convert over might make swapping out the I/O to something else look pretty attractive. That means you are no longer tied to modicon.

That does not mean that modicon might not turn out to be your best choice, but you are not tied to them. I almost hate myself for saying this but as far as I am concerned, there are only two good choices for CPUs if you are going to swap out a lot of existing stuff. Both are IEC style ladder logic and both have user defined function blocks so you can make and reuse chunks of predeveloped and pretested code. Siemens S7 and Modicon Quantum are the only two CPUs that support this to my knowledge. I would thus seriously consider switching to either one. Having used both, i can tell you I consider either to be acceptable, with both having slight advantages over the other in different areas.

This from a long time AB fan, who is really disappointed AB has not put this functionality into ControlLogix and shows no interest in doing so. It's a really sad thing too, because Clx has a lot going for it, but AB just does not want the user defined function blocks for some reason. My guess is that they plan to chargte extra for it at some point when the product becomes untenable without it. Just the cynic in me I guess.

 

One plus for staying with Modicon is that Schneider has a conversion tool which will automatically convert you old Modsoft programs to IEC, and you will be able to use new hardware

 

what you need is an easy to deploy instrumentation application development environment which based on platform and protocol can communicate to your legacy PLC and any other devices on serial, e-net, 1394 or bluetooth.
The best to do this is with LabVIEW, more information is available at: http://www.ni.com/labview
you can also download a labview eval. copy.