Compact Logix and PLC5 Comms

[encoder 0]

Hi All, We are currently upgrading one of our machines which is controlled with a PLC5/40E I think it is Series E Rev A. The reason I'm not 100% is that it also says DH+/RIO Comm Plug #1 Series/Rev: A/A. (I have included a screen shot of this) Anyway, we are looking at replacing some of the older drives with servo drives in a Master/Slave configuration. For this type of setup we communicate to the drives with a DeviceNet Scanner. Our plan is to use a Compact Logix Processor to control the drives and communicate with the PLC5 over Ethernet via messaging. I have not had any experience with this type of setup and am wondering if anyone knows of any problems we might face. My first concern is the PLC5 FW I believe it will need to be upgraded to at least D.1. I was also wondering what sort of Lag we might experience with the messaging between PLC's setup? Any advice/comments are gratefully accepted

[paulengr 44]

A couple of things...first off, the extra information you are showing is showing you the software revision number of the IO card in the PLC. PLC-5's have processors on board their I/O ports. Actually the whole PLC-5 system is very distributed in terms of processing power internally. As to upgrading, you need to upgrade to a recent enough version to be able to deal with CIP packets between the PLC-5 and the CompactLogix. Use the Ethernet port for speed if you can keep it isolated (keep outside traffic off of it with a managed switch). I've done it. You simply request the firmware upgrade from AB. It will come as a ControlFlash file (works the same as flashing a CLX processor) but depending on the version of Ethernet you have, you may also have to split open the PLC-5 processor and replace a ROM on the Ethernet board. This is easy. The programming is easier to do from the CLX side of things in terms of setting up the message blocks. Typically you can probably achieve at least 100 ms response times on Ethernet but you may be able to push for a little more. If you are planning on having the servo drives handle all the ugly details of controlling the system, then the PLC is just sending commands (stop, start, ramp up, etc.), then it doesn't matter if it's a PLC-5 or a CompactLogix. I'd suggest you look at your overall long term strategy with this because there's a couple more options... 1. Configure PLC-5 to "adapter mode". Install a DHRIO card in the PLC-5. Use all existing remote I/O, and treat the PLC-5 as remote I/O as well. Run the PLC-5/CLX converter (if you don't want to recode everything by hand) and fix up the code so that 100% of the code is actually in the CLX processor. This will ease maintenance long term. 2. Simulate "adapter mode". Basically do it all with message blocks but leave the PLC-5 in place. You can also take the schizophrenic route this way (half of the system is CLX, half is PLC-5). 3. Install a 1771-SDN in the PLC-5 and do it 100% in the PLC-5. Don't get a CLX. 4. Perhaps consider using ControlNet or Ethernet/IP (with an appropriate managed switch that supports PTP such as a Hirschmann rail switch). I'm not sure about the CompactLogix family but you can at least implement the motion controls logic directly in a ControlLogix card and skip doing it at the drive level. In addition, there's also the proprietary high speed optical network (HSC I think...I forget the names) that you can use if latency/jitter/speed is an issue. From a long term point of view, that PLC-5/40E is now going for close to $10,000 list and all of the I/O cards are similarly overpriced. AB will probably not stop selling PLC-5 parts for another 10-20 years or more. So there's nothing stopping you from staying where you are at. But long term, AB has made it very clear that you need to try to transition over to the CLX family some time in the near future. I'm going through similar gyrations right now and in the end, I'm going with converting the PLC to adapter mode (since it has lots of both local rack and remote I/O) and migrating the PLC-5 to CLX entirely. Scratch that. Actually, I have 4 PLC-5 processors and they are being upgraded to a single CLX processor with several backplanes in a large distributed process-oriented facility. One of the PLC-5's has 31 Remote I/O nodes and NO local I/O. Another has 5 local I/O points (the rest are buttons and lights that are being phased out) and a dozen remote I/O nodes. Another has all of 5 local I/O points and 2 remote I/O nodes. Finally another has a dozen remote I/O nodes and close to 150 local I/O points but only about 25 of the local I/O points will be reused in the new project...so a local chassis with 2 DHRIO cards and couple more remote racks will suffice to displace ALL of that old stuff.

[BobLfoot 302]

Paul has responded very well as usual so I'll jsut add my humble 2 cents and not rehash the entire idea. I've done or been involved in 6 conversions of multiple PLC 5's to a single controllogix. I really like the DHRIO in the CLGX and an ASB repalcing the PLC 5 CPU or a COntrolNet Adapter repalcing the PLC 5 CPU. THis approach allows you to run your PLC 5 based system during the production week and test your Controllogix system {I/O checkout, Dry Run, Wet Run} on weekends before you go fully CLGX.

[encoder 0]

Thanks for your responses its great to get some really constructive feedback when making these decisions and certainly easier to decide when properly informed. We have a very small window of opportunity to get this system in and running and because there is also a major mechanical refit, there will be no going back so our solution absolutely must be one that is tried and tested. The upgrade basically removes large shafts which drive multiple gearboxes with smaller drives that are electronically linked and work together in master/slave configuration. The nitty gritty is handled by the servo drives (SEW Drives & motors) but we monitor and compare positioning to check for lag error and sending basic commands, target positions etc. The add on PLC5 DeviceNet scanner is expensive, and not that great so we prefer to use a CMPLGX with DeviceNet Scanner as this allows us to also utilize our most recent methods of servo drive control. Thanks again for your comments and I will continue to add to this topic as decisions are made. Edited 12 May 2008 by encoder