1771 Profibus vs ControlNet

[infineum]

I am starting a new project to upgrade a manufacturing suite that consists of four PLC5/Es. Each major piece of equipment has its own PLC (dryer,mixer, solution kettles). The SCADA is Wonderware InTouch 7.0 on NT. My plan is to upgrade SCADA (probably WW 9.5) and replace the PLCs with one Controllogix using distributed I/O. My question revolves around the I/O racks. Downtime is a very big issue so I thought I would leave the existing 1771 I/O racks and either replace the PLC with a ControlNet adapter or use a Profibus card as a slave in the PLC rack. I would then have to maintain the PLC5s but simplify the program just for block transfers and data concentration. The other advantage would be that I could install the Profibus cards and connect into the Controllogix for testing. If there are issue, I could easily go back to the old state. I have a lot of experience with profibus and feel confident with installing it. Not so with ControlNet. However, it would seem more logical to use the ControlNet setup eliminating the PLCs. Any thoughts? Thanks.

 

[Oakley]

Question ... Is your plan to keep the PLC5's and have a CLX as a data concentrator? Or is it to replace the PLC5's with an IO bridge module (either CNET or Profibus)?

 

[Michal_dk]

Have a look at Technote 26821 on the AB support website. If your I/O racks are compatible with the ControlNet of today go for the ControlNet option.


You will not need to keep servicing the old PLC5's and should some of the 1771 IO's die it 's fairly easy to switch a rack with a new C-Net IO solution.

C-Net isn't that complicated, there is a very useful technote on how to set it up and after that, it runs by it self.

If you go for the profibus solution, make sure that either you yourself know all that is to be known about profibus on AB equipment or make sure that your local AB support centre is able to and can in fact help you with your eventual problems. I'm saying this as you are putting in an third party solution and as the technology isn't AB they might not be able to do much other that saying that their products work fine and so will SST (or whoever makes the Profibus adapter) and you will find your problem landing between two chairs.

Michal Rudbeck-Rønne
M2R

 

[infineum]

The Plan

I plan to write all of the control code within the controllogix PLC. The ladder logic code is not well written and hard to modify and support. It does not make sense to me to rewrite all of the code within the PLC5s in ladder logic. This application is a batch process with a good deal of batch sequencing and PID control. The controllogix has great tools for accomplishing this. In an ideal world, I would be able to remove all of the 1771 I/O and replace it with either Flex or Controllogix I/O. To minimize downtime, I thought that I would utilize the 1771 I/O. The most direct solution is to use control net adpaters in the I/O racks and a control net scanner in the controllogix. Since there are no profibus adpaters available for 1771, the only solution is to place a profibus module in the 1771 rack and configure it as a slave. However, this arrangment requires a PLC5 CPU to reside in the rack. I would then access the PLC5 CPU and I/O via the profibus module.

 

[Oakley]

I would definitely go the ControlNet route - sounds like too much "layering" to implement the profibus solution.


ControlNet is not difficult to implement.