PLC2 and ControlLogix?

I had an earlier post asking about problems with switching between a PLC2 and ControlLogix processor controling our Remote I/O racks. I had determined that was the way to go. The engineer however wants to run in parallel with the two processors. This doesn't seem practical and I want to know if it's possible. I want to do this upgrade and need the engineers okay to do it. I will take whatever steps are necessary. If this is possible could you point me to some tech notes so I can start studying up on what I have to do. Thanks for your help. We are currently using a PLC2/30.

Mike

You can use one processor or the other -- not both.

If you set it up correctly, it's fairly easy to switch between the two. However, you cannot have both a PLC2 and a CLX controlling the same I/O in parallel.

Just as Ozee pointed out, you can use one or the other but not both.

One idea I have used in the past for a changeout is to plan a cutover date and spend a long day testing out the new hardware/logic and if there are any programming issues that need to be resolved, you can always pop the PLC2 back into the rack and continue to run until the next day (works well for 24 hr/day operations). That is a simple way to eliminate downtime and make use of the old hardware until all kinks are worked out. It is real easy especially if you leave all racks with the same addressing as the original setup.

Control Logix does have fully redundant capability if that is something they are looking for. Both PLCs are Control Logix processors and the system is quite a bit more complicated however.

Thanks for your replies, the pop the PLC2 back in method is the way another tech and I want to do it but the engineer doesn't really want to do it that way for some reason. He has suggested running the PLC2 in run and ControlLogix in test. I didn't want to say we can't do that without checking first but I don't think we can. Below is what the engineer wants to do. This is his reply to an email I sent telling him I didn't think it would work.

We could run the PLC2 in run mode and the Control Logix in test mode and compare them with an RS View application. I am looking into installing ControlNet onto the racks first, then route the I/O to the Control Logix PLC rack, and then use a Remote I/O card to feed this information to the PLC2. The key is what are the requirements for the remote I/O to the PLC2 and what hardware is capable of performing this task.

In reality, we don't even need to run the old PLC2 program on the Control Logix but could just use it to transfer the I/O until it all goes through the Control Logix rack. We could then install the new Control Logix program and test. However, my current thoughts are that there is some benefit of rewriting the old PLC2 program on the Control Logix so I would probably recommend doing it as well.

HUH???

There's no way that will work.

There is very likely a lot of benefit to rewriting the old PLC2 code -- It won't translate nicely to CLX anyway...

What about mapping the data from the PLC 2 to the ControlLogix?


Would that satisfy his concern? That way, all you would have to validate when you cut over would be the IO communication.

Will the mapping work? When I looked at what we have and where we want to be I told engineering I wanted to rewrite the PLC2 program or at the very least get it converted and massage the conversion then on weekends unplug the rio from PLC2 and plug in ControlLogix. Leaving the option to plug the PLC2 back in should my program not be right. I posted here asking if anyone could see a problem doing it this way. The response was great and I got tips on "gotchas" to look for. I told the engineer how I wanted to do it. He came up with his own idea, that is what is posted above. I don't know if the mapping would work or not. I need someone that knows how (if it is possible) to tell me where to look to figure out how to do it. If it is possible what will be the problems.

I see where the idea comes from of having the original controller be in full control of I/O and have the replacement controller "listen" and solve in parallel. That's how I have seen some GE Series Six to Logix conversions done, using a special (and very very expensive) "ghost" protocol module on the Series Six I/O network.

I cannot think of a way to do that with PLC2/ControlLogix on RIO, because RIO has no "listen-only" mode like ControlNet does. You can't do it on ControlNet, since the PLC-2 pre-dates ControlNet by ten years.

And the idea of having a ControlLogix handle the I/O on ControlNet and then "map" all the I/O back to the PLC-2 over RIO is deserving of a Rube Goldberg award, but technically not feasible because it would require the 1756-DHRIO module to have a "multi-rack adapter" mode. The module is strictly a scanner.

Your vexing engineer's ideas are interesting and novel, but your idea of swapping over RIO scanner ownership between the original PLC-2 and the new ControlLogix has the advantage of being commonly performed, technically feasible, and of low risk to production.

Thanks Ken, your tips always proves valuable, in this case you said exactly what I had hoped you'd say. I feel comfortable telling the engineer what he wants isn't going to work. Hopefully he will let me do the weekend swap over. Thanks to all that posted.

Mike

Alcoa Tech said:

Thanks Ken, your tips always proves valuable, in this case you said exactly what I had hoped you'd say. I feel comfortable telling the engineer what he wants isn't going to work. Hopefully he will let me do the weekend swap over. Thanks to all that posted.

Mike

Click to expand...

Put it to the engineer , sure it can be done if he has the money and the downtime to provide all the extra RIO racks with cards for the Contrologix to run in parallel with the existing PLC2 inputs. The Clgx outputs cannot be wired in parallel with the existing outputs, but at least this way the theory of the Clgx can be proven.

I somehow thing the engineer won't go for that

Ian

Bit the bullet, wire to the new system and make it work. You will waste too much time and money trying to go back and forth. Test out your application as much as possible. It may be possible to take over control one step at a time on a larger system.

d

Ian, thanks again for posting. Your post when I first asked about the weekend switch over was very helpful. Once the weekend switch over becomes the engineer's idea I will be okay. Now that I can tell him it won't really work I'm hoping he will get the idea to mirror the program and test it on weekends. You've probably seen this situation before.

Mike

Alcoa Tech said:

Ian, thanks again for posting. Your post when I first asked about the weekend switch over was very helpful. Once the weekend switch over becomes the engineer's idea I will be okay. Now that I can tell him it won't really work I'm hoping he will get the idea to mirror the program and test it on weekends. You've probably seen this situation before.

Mike

Click to expand...

Yup, seen it many times. The main factor is production downtime. Whatever has to be done, do it, with minimal production downtime. Thats why the switchovers were always the best. Run one shift on the new stuff, get a 10 minute of downtime to swing back to the old for the next 2 shifts so you can get some rest and not those horrible 2:00am phone calls that the plant is down

Ian

curlyandshemp said:

Yup, seen it many times. The main factor is production downtime. Whatever has to be done, do it, with minimal production downtime. Thats why the switchovers were always the best. Run one shift on the new stuff, get a 10 minute of downtime to swing back to the old for the next 2 shifts so you can get some rest and not those horrible 2:00am phone calls that the plant is down

Ian

Click to expand...

That is what I hope to do. Is there a tech note on settings for the RIO card? I've started a folder of different tech notes and I've printed out various posts from the forum. I've been trying to clear my plate so I can sit down and do some serious studying before the project is started. The only real concern I have is getting CLX to communicate properly with the racks. I'm ready for the octal/decimal problems and other programming issues, once I'm talking to the racks okay the rest is just time and patience.

Thanks,
Mike

Sent you an IM.