Messaging between 3 fixed I/O SLC500

[ssommers 20]

Ancient history question... I have a DH485 network with 3 fixed I/O SLC500's already hooked up using AICs. Is there a way to have them message to each other directly without adding any more hardware? (Note: I've already looked at my RSLogix500 and the MSG & SVC icons are greyed out for these processors.) The reason for this question is that I have to upgrade the current process from manual pushbuttons to an automated system and parts of the process are in each different PLC. It's over a 500 ft run between PLCs so just rewiring the inputs to a central PLC isn't an option. All suggestions are welcome... Thanks, Susan

[jstolaruk 9]

I believe you're going to have to add another piece of equipment - A PC acting as a go-between (I know, not an option) or another "concentrator" SLC with a SN card and DCMs in the brick SLCs, etc. Edited 31 Oct 2008 by jstolaruk

[Ken Moore 23]

How about a small Redlion data station as the gateway? http://www.redlion.net/Products/HumanMachi...tationPlus.html

[ssommers 20]

After I posted, I went hunting thru my stash of SLC parts and found a 5/03 with a 7 slot rack. It turns out to be exactly the same size as my largest fixed I/O SLC with a 2 slot adder. I also have the right I/O cards to make the whole thing work. I think that if I swap that fixed one out with the 5/03, I'll have my messaging functionality. Could someone give me a sanity check on what I'm thinking about doing? Here's the application... I have a tube mill where a tube is running about 600 ft from a seam welder to a coiler. I have an eddy tester that sets a bit in PLC1 when there's a hole in the tube. PLC1 has a spray marker & buzzer that spray marks the flaw at a later point in the line as determined by an encoder. Shortly after the spray marker, PLC2 controls the cutter and the coiler tubs based on pushbutton signals from the coiler operator - right now he's watching the spray marker. PLC3 controls the footage counter & a printer based on pushbutton signals from the mill & coiler operators. They would like the system to cut out only the buttweld flaw (I have the requirements) and that requires PLC1 & PLC3 to send signals to PLC2 which will cut out the flaw and move to the next coiler tub. (Again, I've got more details and know the sequence) The flaw signal into PLC1 is about 450 ft before PLC2 & PLC3. The machine is going about 530 ft/min so I have about 50 sec between flaw trigger & flaw cut. I have encoders in PLC1 & PLC3 - not PLC2. If I change PLC2 from a fixed I/O to a 5/03, I think it would have to continuously read from PLC1 & PLC3. What pitfalls am I getting into by using reads from PLC2 instead of writes from PLC1 & PLC3???

[ssommers 20]

If I needed the info to go to ethernet, that would be a sweet little converter! In this case, I want to keep the data & control local and DH485 handles the distance ok. I will keep it mind for future projects... like when I want to monitor & program those local networks in my office!

[JeffKiper 9]

Susan I would look a having a read and write from each. I do this alotto verify that we still have comms. with tah target nodes. I know on large systems that with a lot of network traffic that will be a problem. With your 3 node system why worry?

[BobLfoot 301]

Susan avoid writes especially on DH485 if you can avoid it. The reason is time consumed. I'll illustrate. READ Step 1 - "PLC2 to PLC1 give me N7:0" Step 2 - "PLC1 to PLC2 here is N7:0" WRITE STEP 1 - "PLC1 to PLC2 I want to write N7:0" STEP 2 - "PLC2 to PLC1 I am ready for N7:0" STEP 3 - "PLC1 to PLC2 Here is N7:0" STEP 4 - "PLC2 to PLC1 I received a good N7:0" In you case I see one issue. PLC1 and PLC3 have encoders. PLC 2 will receive a flaw signal, but how will it know when to cut? You cannot count on the flaw pulse timing being exact given the hardware you are using.

[danyost 0]

Unfortunately, the DSP cannot access the I/O of the SLC with fixed I/O. That is at least accroding to our documentation, I have never actually had a fixed I/O unit to try. However, we can talk to the rest of the data files within the PLC. Regards, Dan

[ssommers 20]

I have to cut out at least 40-50 ft of tube to make the switch between tubs since the mill is running at 500+ ft/min. The buttweld doesn't have to be exactly in the middle of the cutout either. I was thinking that since I have about 40 sec from the time the buttweld passes the eddy tester & sets the flaw bit, I'd have plenty of time to read from PLC1. PLC3 would actually get the mill operator's signal at about the same time as the flaw bit gets set too. The problem is (and has always been) variability of the mill speed & signal coordination. I've been rethinking this project over the weekend and have a few new thoughts & options... #1 - I have to change at least one of the fixed PLCs to a 5/03 to use the read/write capability. (That's our standard PLC now so I have a couple in stock.) #2a - I could combine the fixed PLCs 2 & 3 (they currently live in the same panel) into a single 7 slot 5/03, I get an encoder in the cutter PLC and instant access to all of PLC 3's I/O. Then all I would have to do is read the flaw bit array from PLC 1 ad infinitum. Since my cut has to start well ahead of the flaw actually reaching the coiler, I can do a bit of math & determine when the buttweld is close enough to start the cut. (In this case, close enough will probably be a lot more consistent than what the operators have been doing manually!) OR #2b - I could change PLC 1 to a 4 slot 5/03 and write the flaw signal + mill speed to PLC 2 only when a flaw is coming (about every 45 minutes). I would also need to wire the mill operator buttweld signal into PLC 2 from PLC 3. OR #2c - The solenoid valve that is currently spray marking the flaws is about 100ft away from the panel with PLCs 2 & 3. I could add a relay to pick up when the solenoid is active and send that input to PLC 2 to activate the cutter. I'm not sure if I could start the cutter quick enough before the 1st spray mark gets past it, but it shouldn't let too much past. Timing would be more consistant, but I still have to read the other 2 PLCs to know the difference between small hole (no cut, just mark) & a buttweld (big 50 ft cut). Yeah... I know it's probably not enough information to really evaluate things, but it's a start. I still don't know if read or write is more appropriate to get the info between PLC 1 & 2, but I think I can make it work in either direction. If you've read this far... congratulations! And thanks for hanging in there with me. Susan