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Old December 20th, 2002, 03:51 AM   #1
ganutenator
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the answer to which PLC is the best...

Its easy...


The one with the best programming software...


duh...


Best programming software you ask???


ummm..... well.....umm.......
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Old December 20th, 2002, 05:06 AM   #2
BobB
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200 brands on the market - you will probably get 200 answers. My preference is Omron for software, networking (Controller Link), speed (CS1 & CJ1), Device Net & Profibus support (prefer Device Net) and huge function set. I am lead to believe that they are addressing the USB/serial port problem also with a new release of the above 2 PLCs with a USB port interface. HURRAH!!!!!!!!!
Oh by the way, HATE Ethernet as an industrial network although GE-Fanuc, Omron and no doubt others now have a "Global Bit" protocol that runs below TCPIP so that evryones favourite huge print file does not stuff up our precious PLC communications.
Another pi$$ing competition??????????
BobB
beerchug

Last edited by BobB; December 20th, 2002 at 05:22 AM.
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Old December 20th, 2002, 06:36 AM   #3
Matthias Von Zorn
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Hate ethernet?

Why do you hate ethernet so much? I find it very useful indeed, and have replaced all other protocols with it, where possible. Ive never used it for device to PLC comms tho, just inter-PLC and PLC-HMI connections.
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Old December 20th, 2002, 06:40 AM   #4
Matthias Von Zorn
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after a re-read

Is it because the network gets clogged with other traffic (your print file complaint)? First off, never share your ethernet network with the office network. The PLCs should be on thier own network. And, if the network topography is proper, it should be very fast.
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Old December 20th, 2002, 12:26 PM   #5
akreel
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Re: after a re-read

Quote:
Originally posted by Matthias Von Zorn
Is it because the network gets clogged with other traffic (your print file complaint)? First off, never share your ethernet network with the office network. The PLCs should be on thier own network. And, if the network topography is proper, it should be very fast.
Yes. If your process matters to you, set up a separate highway for data communication. If that's too pricey for you, use ethernet switches rather than hubs. That will help a little bit with traffic control.

Did I just say traffic control??? Sorry guys!

AK
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Old December 20th, 2002, 03:55 PM   #6
BobB
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The last time I used Ethernet it was specified. The PLCs were GE-Fanuc 90-30. There were 4 PLCs controlling 3 diesel generators for emergency power and co-generation. The Ethernet reads only had to take place every 2 seconds but even at that meager rate, the PLCs were reporting "full mail boxes". The only other device on the network was a computer with FIX-Dynamics on it. Unfortunately, this was not good enough as the generation was at 11kV, the generation system had a neautral earth switch connected to keep the system grounded. If the neutral earth switch opened, the whole system had to be taken offline very quickly to stop the 11kV "floating" to dangerous levels above ground. If that did not happen very quickly, there would have been the potential for cuasing major problems at the sub-stations in the reticulation system. Finished up hard wiring all critical signals from PLC to PLC. The local GE-Fanuc distributor was not surprised at our problem and considered what we saw as normal for that version of their Ethernet.
I have found it non-deterministic and fine for collection of data into a SCADA system or something similar but until I see evidence of a project where the "global bit" idea works effectively, I will not use Ethernet for a critical system, such as generators, where you really do not have any room for "network collisions" to slow down PLC to PLC exchanges.
My preference for these systems is definately a token ring based PLC to PLC network. The network does not clog up and there are no collisions. Data transfer is reliable, seamless and fast.
I have developed many systems with Omron's Controller Link networks. The network is Manchester encoded token ring and, even though the network's maximum speed is 2mB/sec over a twisted pair, I have one system controlling a base load power station with a total of 9 Omron C200HS PLCs, (these are older slower PLCs these days), all with remote I/O, and a 4500 tag Citect data base drawing information from the network, the Citect SCADA still reports in excess of 12,000 digital reads per second and the PLC to PLC I/O update is taking place at the same rate. The Controller Link network also has a certain amount of redundancy built in. One of the PLC cards takes charge of token and communications control. If that PLC is taken off line, another unit takes over.
The setup is seamless. A table is developed that is loaded into each PLC. If one sets up each PLC on the network with, say, 30x16 bit channels of digital data and 50 channels of data memory (register) data for exchange, and loads the same table into each PLC, the same address numbers from one PLC to another are used. For example, PLC1 is setup with digital channels 400-429 for network exchange, then PLC2 reads exactly those channels and can use the bits for information and control.
Quite frankly, it is the easiest and best PLC to PLC network I have used, although I have not experienced GE-Fanuc's global I/O yet. I am lead to believe that it behaves in much the same way. Seamless and reliable with no send or receive commands required.
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Old December 20th, 2002, 04:43 PM   #7
Jay Anthony
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Quote:
I have developed many systems with Omron's Controller Link networks. The network is Manchester encoded token ring and, even though the network's maximum speed is 2mB/sec over a twisted pair, I have one system controlling a base load power station with a total of 9 Omron C200HS PLCs, (these are older slower PLCs these days),...
This is the second time I have seen you mention this system, but for the life of me, I can't figure out how you got ControllerLink to run on C200HS. Are you sure these aren't C200H Alphas?
Quote:
Seamless and reliable with no send or receive commands required.
That's the real beauty of ControllerLink.
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Old December 20th, 2002, 06:33 PM   #8
BobB
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Sorry Jay they were Alphas. Becoming old and feeble.
Have used Sysmac Link on C200HS PLCs.
beerchug
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Old December 20th, 2002, 10:14 PM   #9
Jay Anthony
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I was kinda hoping that you'd tell me you had found a way to make ControllerLink run on C200HS. I've got a bunch of clients that would love to see it happen. Oh well......
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Old December 21st, 2002, 08:46 AM   #10
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I don't think the problem is ethernet, so much as you guys lack of understanding of it. There are collisions if you use hubs instead of switches. There will be mail boxes full, if you don't understand the messaging structure, buffering, send receive speeds etc.
Did you know... If you are using a hub and all devices on the network are communicatin at 100mb full duplex and you were to install an AB SLC5/05 with enet, the entire network will slow down 20 times slower. Why?
I would suggest you talk to someone who really knows what and how ethernet works, before dismissing it.
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Old December 21st, 2002, 12:47 PM   #11
Peter Nachtwey
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Ethernet

Quote:
Originally posted by RRobbins
Did you know... If you are using a hub and all devices on the network are communicatin at 100mb full duplex and you were to install an AB SLC5/05 with enet, the entire network will slow down 20 times slower. Why?
1. The 10MB SLC5/05 takes 10 times longer to send a packet the same size as 100MB device.

2. The SLC5/05 is half duplex. It can send or receive but not both.
A full duplex device can potentially transfer twice as much data as a half duplex device.

This just means that a SLC5/05 is potentially 20 times slower than a 100MB full duplex device. However, I doubt that it slows down the net work that much because the other devices still would operate at there normal speeds unless colisions started to become a problem. How much the whole network slows down is more dependent on how heavily the network is loaded.

We have a SLC5/05. We have done a lot of Ethernet testing measuring times, collisions, and missed packets when communicating to one, two, or three other devices. The SLC can initiate a Ethernet transfer than about one every 27 milliseconds so one SLC cannot tie up the network that much. However an HMI can tie up the network because it may be able to poll the SLC at a faster rate. To check this out, use the program below.

Ethernet testing program.

Last edited by Peter Nachtwey; December 21st, 2002 at 12:52 PM.
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Old December 21st, 2002, 08:38 PM   #12
RRobbins
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Right on Peter.
But I think you will find the entire segment that is on that hub slows to 10mb. The network can only run as fast as the slowest node. I grabed your test program an will play with it next week when I get my SLC5/05 back from a show. Everything else runs 100mb / full duplex. I have a network packet sniffer to check the packet size also. I do have a Siemens S7-400 that I checked and it will send and receive a packet 8,196 bytes in one shot @ 100mb full duplex.
I have seen the problem with HMIs also, when they are running 100mb and polling data from PLCs that are on the other side of a switch that are at 10mb. I have also seen data between ethernet modules and over run the buffer because the data tranfer to and from the PLC CPU was too slow. If you are using an HMI on an office LAN with hubs to run critical data to and from a PLC, shame on you. A switch will solve a lot of your problems.
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Old December 21st, 2002, 11:00 PM   #13
Peter Nachtwey
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More Ethernet

Quote:
Originally posted by RRobbins
Right on Peter.
But I think you will find the entire segment that is on that hub slows to 10mb. The network can only run as fast as the slowest node.
Hubs usually work at one speed only. Usually only 10MB.

Quote:
Originally posted by RRobbins

I have seen the problem with HMIs also, when they are running 100mb and polling data from PLCs that are on the other side of a switch that are at 10mb.
Most people let the HMI poll the PLCs, and other devices, way too often. Updates every 200-250 milliseconds would be fast enough for human eyes.

Quote:
Originally posted by RRobbins

I have also seen data between ethernet modules and over run the buffer because the data tranfer to and from the PLC CPU was too slow.
I have seen this too. It takes a lot of processing power to handle 100MB Ethernet. Rockwell's ENBT Ethernet card for the Control Logix has a Power PC CPU with built in Ethernet to process the data. That is more processing power than many PLCs. Rockwell rightly figured that this processing power is required for the future.

Quote:
Originally posted by RRobbins

If you are using an HMI on an office LAN with hubs to run critical data to and from a PLC, shame on you. A switch will solve a lot of your problems.
Amen. Now how do we clear up the confusion about Ethernet.

Last edited by Peter Nachtwey; December 21st, 2002 at 11:08 PM.
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