Remote IO distribution or Local PLC... your thoughts, please

Hello,



Late this year I'll be preparing the replacement of old Rockwell PLCs (SLC, Micrologix, one S5 and some compact logix) to Control Logix. A total of about 20 PLCs exist on site. Some are for dedicated machines which I won't want to take on liability and get the manufacturer (if still existing) to take over, there will be about 5 of these in total.



The project started with someone that has left and I took over and their plan was to create a power and optical ring around the entire site and then replace the PLCs in the panel by IO and have the PLCs in a central location talking to the IO over the site's newly laid network.



Although I have no doubt that it would work, it leaves me somewhat concerned as there won't be any "smart" device in the switchrooms should we have a loss of network.

My view is that it would be best to have a dedicated controller per switchroom taking over all the processes in it and replacing the existing controllers by remote IO for a local PLC. Should the main ring fail, the PLC could happily keep the process going and the only thing affected would be the SCADA.



What are your thoughts on this? The site has about 4 batch processes and one continuous process and in total 9 panels where all the network points will lead to were installed.

Since you have 5 main processes, I would go with 5 controllers, one for each. Then if for some reason you need to shut down a controller, it only effects one process.

Hi I would look at the intention of the equipment..for example a stand alone line, and consider that one PLC. It helps also that you mention handing off some of the work to others so they have there own PLC for their own machine etc

Then you can link everything together for SCADA and OEE, also consider essential controls at local machine level also such as Panelview or similar thing

No harm in trying to define common controls (PLC type, RIO type, VFD type etc) and also common AIO and sequence methods at the PLC /HMI faceplate level so maintenance and production have same look and feel across the plant

Ken Moore said:

Since you have 5 main processes, I would go with 5 controllers, one for each. Then if for some reason you need to shut down a controller, it only effects one process.

Click to expand...

This is a good point. Although read below.

cjd1965 said:

Hi I would look at the intention of the equipment..for example a stand alone line, and consider that one PLC. It helps also that you mention handing off some of the work to others so they have there own PLC for their own machine etc

Then you can link everything together for SCADA and OEE, also consider essential controls at local machine level also such as Panelview or similar thing


No harm in trying to define common controls (PLC type, RIO type, VFD type etc) and also common AIO and sequence methods at the PLC /HMI faceplate level so maintenance and production have same look and feel across the plant

Click to expand...

I don't think I made my point.

My problem is not really the separation of process into PLCs, that will be split per functional area to avoid having to shutdown what doesn't have to be to make a change.


My point is that the current plan is to have all PLCs in one room and then, out of the remaining 9 network panels in the ring have only IO (segregated through VLANs).

I see that as a weakness of the system as any network issue will inevitably affect the process, whilst if the PLC is in the switchroom and the remote IO network is confined to that room only, the process (if correctly implemented) could carry on and the only thing to be lost would be the connection to the SCADA. So the system could either keep chugging along, or shutdown gracefully.

Another colleague that got involved is seriously ill so I haven't had a chance to run this through him, so I'd like your opinion on this separation.

I should have mentioned that we're going with Rockwell and PlantPAX.

I would want plc local to machine to keep machine functioning in a safe and expected manner in the event of a network fault so I would not put plc into a re.ote control room or switch room away from IO