ethernet problems

I work on a industrial manufacturing line that has multiple machines each with AB SLC 500s and have them all connected by ethernet to a hub. This connection serves as a connection for SCADA tracking each machine as well as a PC that is used to monitor and troubleshoot the equipment.Two of these machines have a PC at the machine that also is connected to the PLC at the machine , which means that I have a external hub at these two machines to connect the PC at the machine and the PLC to the network. These two machines are constantly locking up the ethernet communication causing a power down to get them reset. I can watch them go off and on with RSLinx. Is there another way that I can connect the PC at the machine to the processor without using a hub, such as a module that would let me eliminate the extra hub? There also is a twin to this line in another building that has exactly the same problem on the same machines.

Is the SLC-5/05 controller failing to communicate with the supervisory and diagnostic PC's, or is the local PC the one that seems to be "locking up" the Ethernet communications ? Do you cycle power to the SLC, to the local PC, or to both ?

I know there was a bug in some early 5/05 firmware that resulted from the controller's attempt to protect itself from stack overflow due to Ethernet messaging; if the buffers were getting full, the SLC-5/05 would throttle back the TCP/IP stack and start ignoring messages, then try at 10 ms intervals to accept all messages again. The problem was, it sometimes didn't throttle back up. This was fixed in OS501 Series A firmware revision 4, in early 1999.

I have had some success sniffing out SLC-5/05 connection problems with a tool called an MIB-II browser. No, not the Will Smith movie, but a set of data tables maintained by almost all Ethernet devices which respond to the Simple Network Management Protocol (SNMP) protocol.

SLC's, for example, have a limited number of TCP Connections they can make to other controllers and to PC's. This used to be limited to 16 in any direction, with up to 12 in or out and the rest opposite. This could be a problem when a lot of SLC-5/05's were trying to message all to one another. The limit has been raised to 24 connections, but it's still worth trying to sniff out how many are in use. There's no way to get that in ladder logic, but an MIB-II browser can tell you how many TCP ports are open at any given time. Hook up the MIB browser, then fire up RSLinx and do an RSWho... bingo, another TCP Connection.

You might investigate hooking up the local PC to the controller using the controller's serial port. Then you'd be sure the local PC wasn't the culprit if the Ethernet problems continue.

As you explained, the Ethernet ports on two PLCs are called from two or three "masters" : 1)SCADA, 2)monitoring PC and 3)local PC.

- Perhaps should you quickly replace your "hubs" by "switches". Sounds quite similar, but in fact is not at all ! Switches manage your Ethernet packets and turn them only towards their addressee, avoiding unbalanced or overloaded networks. With basic hubs, everyone linked "hears" all frames : your network could be locked by some machine continuously attempting to reach another one. Your network seems to be frozen until those two equipments can communicate.

- Secondly, be sure that all your simultaneous connections (or services) use different Ethernet ports on a same device.
Usually, as Ken wrote, the number of TCP connections or simultaneous services is limited on PLCs. But if you don't exchange datas directly between PLCs, only two services should run on your PLCs, and max 3 services on those with local PCs. So, be sure that there is no conflict generated by sharing the same Ethernet port number between two services or more.

Regards

I have found that all I have to cycle power on is the PLC and from what I can tell the PC at the machine is getting locked up some of the time. Most of the time I do not have to reboot this PC.

Is there any evidence that your local hub is part of the problem ? If it has a COLLISION indicator and that's flickering, you might know that there's a lot of traffic on the network and that simple Ethernet switches can divide the system traffic up to reduce that problem.

Check out the OS number, OS Series letter, and OS firmware revision in the SLC. SLC-5/05's are very convenient to FLASH upgrade and a single copy of the firmware will upgrade unlimited numbers of processors.

Before you do that, though, you really, really do need to characterize how much traffic is going around your IP network. I use a simple tool called LANScan Network Monitor to get statistics overall on network traffic in the office, especially when somebody starts streaming a RealAudio Mariners baseball broadcast while I'm trying to do server backups.

When the SLC-5/05 "locks up", go unplug it and substitute your laptop PC for the PLC on that local Ethernet hub. If you can PING other nodes on the network, you know the SLC-5/05 is the problem and not the network hardware.

Have noticed that when this lockup occurs, this PLC is the only one that I cannot logon to from network. The green communication light is on solid. After cycling power the communication light goes back to blinking. Looked for firmware update that was suggested at AB site. Did not find specific update, but found information that these updates can cause many problems. Am thinking about trying the ethernet switch instead of hub first.

While reviewing technical support case logs, I've found that the use of the first person passive voice with implied subject is very common. Sentence fragments abound, as well.

I shall, therefore, extend and revise my comments.

The SLC-5/05 firmware upgrade kit is not free for download from AB.COM, because it includes significant feature upgrades as well as bug fixes. The list price for the kit is $150, and a single upgrade kit can be used on an unlimited number of controllers.

Often you may obtain a firmware kit free of charge by calling A-B Technical Support and describing a bug that matches one fixed by a firmware kit, but it is typically required that you describe the problem in more detail than " have to reboot [the SLC]".

The principal problem I foresee with upgrading your SLC is that the new firmware may not be supported by the version of RSLogix 500 which you own. If you have a support contract, that is an obstacle which will be easily overcome.

If you do choose to upgrade your SLC, I strongly recommend you do so on an isolated Ethernet segment on which your MMI and other computers are not active. The upgrade utility uses a built-in BOOTP server to manage the SLC-5/05's IP address during the upgrade, which can be interfered with by a systemwide BOOTP or DHCP server.

I am surprised by your first conclusion about firmware upgrades.

I suggest strongly that before you run out and spend money on either a firmware upgrade or a new Ethernet switch that you first spend no money on the demo version of LANScan, and run it to obtain some traffic statistics on your Ethernet network. You'll learn a lot about this IP network, and will have some empirical information on which to base your future network architecture decisions. It will also be neat for the PLCTALK.NET community to see a small industrial Ethernet network diagnosed.

Before you do anything else, go to your local computer store and buy the fanciest Category 5 Ethernet cable you can find there, and replace your existing SLC -> Hub cable. 70% of Ethernet problems are cable-related, and it's very cheap to replace in-cabinet runs.

The principal problem I foresee with upgrading your SLC is that the new firmware may not be supported by the version of RSLogix 500 which you own. If you have a support contract, that is an obstacle which will be easily overcome

Click to expand...

Quick question Ken, I have RSLogix500 and wasnt aware that any firmware upgrades or for that matter that it wouldnt work with any slc500 or Micrologix, is this incorrect? IS this something that relates to starter software? I didnt think AB did the limited versions (for specific models) or online/offline with RSLogix500 like they did with previous software versions. I have 5.20.00 now that works on my XP laptop but the original cd is 5.00.00, if that makes a difference. My RSLinx is 2.30.02

I have several SLC models that so far I havent seen a need to connect too but need to be able to when/if necessary. I have more cables on order for my PCMK just for that reason.

Appreciate any clarification you may offer.

RON-
What Ken is talking about is if you have a significantly older version of RSLogix and try using it with some of the "latest and greatest" firmware/OS revisions, there will be problems......

I had this problem while attempting online with RSLogix 3.XX and a SLC 5/04 that had the "latest and greatest" firmware/OS.

To sum up my problem (example): The SLC I was attempting online with was using Block Transfers over RIO, something that the old RSLogix 3.XX didnt support. A quick upgrade of RSLogix and I was on my way!!

thanks

In addition, Brian, the SLC-5/05 can tell you some things about conditions on the Ethernet link.

If you define a Channel Diagnostics file for the Channel 1 port on the controller (you'll have to do this offline and reload the program), you get a window that displays a lot of Ethernet statistics, including the number of packets sent and received, as well as collision and error counters.

Often, none of the counters on this page increment except the packets in/out and octets in/out. If there are a lot of collisions indicated, you may be able to cure your problem with an Ethernet Switch. If there are alignment errors, carrier sense errors, or MAC Rx/Tx errors, there may be noise or cable problems.