CLX Ethernet Comms Issue

I had a problem today with a CLX and ethernet IO rack.

The CPU is a 1756-L55 ControlLogix5555 Controller Rev 10.24.

I should point out, that this has been a working application
for quite some time now, there may have been intermittent problems of a similar nature, but only became apparent today.

Comms had been lost to the remote rack, upon attempting to
'ping' the remote rack, there was inconsistent results,
request timed out etc.


The Main rack was connected to a netgear switch, which then had
a moxa EDS-305 media convertor connected to connect to the
remote rack. This media convertor had 4 ports on it.

The Moxa unit is an un-managed switch.

The only way I could get the system up and running again, was
to plug the Moxa unit directly into the main rack, then the
scada server into one of the spare ports on the Moxa unit,
ie. take the netgear switch completely out of the equation.

I tried different port combinations etc, even tried the little
cheapy that I carry in the car with me, still didn't work.

I have brought both switches with me now, and seem to have
no major issues using them to connect on this network. As it
stands at the moment, there is only the moxa switch in the
circuit, and the system is working honky dory, except that
none of the original hardware is in place.

The obvious answer, is that the netgear switch is the issue, but
if it works fine where I am now, what is the difference? I am
going to try and get a managed switch for them anyway, but am
reluctant to unplug the moxa from the direct connection to the
main rack, for fear that it may not work again.

Is there anything else I should be looking out for? I guess the
first thing would be to update the revision?

Was the Netgear switch connected to a plant network? How about the Moxa switch? What are/were the IP addresses and subnets?

Heat, Power supply, noise, connectors...
Netgear makes okay stuff for home use, but it does not hold up well at all in an industrial enviornment. For that matter, almost all 'home/office' switches will have problems. Try some serious, industrail, 24VDC powerered switches, like from NTron, or Phoenix, etc.

Another possibility is that your getting too many packet losses running at 100 m/bit I would try setting everything down to 10 mbit this will actually end up being a faster connection on longer runs. I've even had a few network cards that would not connect at all at 100 mbit at those long runs

I've seen similar things before and it's either been the length of the run or a "noisey" leg that has been the culprit.

Was the Netgear switch connected to a plant network?

Click to expand...

I think it was, the information on what ports/outlets are what was non-existent.

How about the Moxa switch? What are/were the IP addresses and subnets?

Click to expand...

The Moxa switch was connected to the netgear switch also. IP address's for this network were something like
172.31.1.1 Main Rack EBT
172.31.1.2 Remote Rack EBT
172.31.1.151 Scada PC

Netgear makes okay stuff for home use, but it does not hold up well at all in an industrial enviornment. For that matter, almost all 'home/office' switches will have problems. Try some serious, industrail, 24VDC powerered switches, like from NTron, or Phoenix, etc.

Click to expand...

This is what I plan to do, I thought netgear were one of the better 'home/office' models though?
I should note, the moxa switch is 24vdc powered, but un-managed.

Another possibility is that your getting too many packet losses running at 100 m/bit I would try setting everything down to 10 mbit this will actually end up being a faster connection on longer runs. I've even had a few network cards that would not connect at all at 100 mbit at those long runs

Click to expand...

Ok, this is something that I could try, this could of been the
cause of all the intermittent problems that they have been having.

I've seen similar things before and it's either been the length of the run or a "noisey" leg that has been the culprit.

Click to expand...

Don't think that this is the case in this situation though, the remote rack is on fibre, so no interference possible. The moxa
switch is almost right beside the main rack, with the netgear sitting on top of the Main rack by means of a piece of perspex, a quality installation.


This still doesn't settly my query as to why the configuration will not work with either 'home/office' switch, but will when plugged directly into the moxa switch, whereas it worked before.

The bad experience I had was with a certain model of network adaptor this circuit was also going through a fibre weird part was that we tested the physical lines with a data acquisition tester which showed all lines as being capable of 100 mbit however any time we tried to set that we had packet losses 6 out of 10 we ended up setting everything on that line to 10 mbit half duplex