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Old April 21st, 2016, 01:05 AM   #1
Elcan
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HMI communication problem.

Hi all,
We have a control panel with a CompactLogix PLC and two Red Lion G310 HMIs. They communicate via a N-Tron 108-TX. One of the HMIs is installed on one of the panel door, in an air conditioned room. The other HMI is in the plant, about 120 feet away from the panel. Both HMI programs are identical.

The panel has been running a couple weeks every few months for the past year, and no issues were reported with the HMIs or the PLC.
Last week, the remote HMI started going “crazy”. I never had seen this behavior before. I've seen the typical dashes for the numeric values and black background on my motor labels (mine are white when the motor is stopped, green when is running, and red when is commanded to run but is not running). But this was different, there was a combination of dashes, black backgrounds and red backgrounds. I even noticed that before this situation some of the VFD speed labels were shown as zero, and also some temperature values. Also, the labels that are displayed only if the E-Stops are activated, were displayed. In other words, wrong tag values.

Also, after about an hour, some of the VFD speed signals from the PLC were set to zero. There were not a 4-20 mA signal meter nor a way to go online with the PLC at that moment.
If the panel was power cycled, the issue was cleared, but after a few minutes the remote HMI would start with the “craziness” and after an hour some of the PLC analog signals that control the VFDs speed were set to zero.

When I arrived to the plant, I disconnected the bad HMI, and the issues with the VFD signals was gone. Then, I updated the HMI firmware. I connected the HMI back to the network and the problem started in less than 15 minutes. I tried a couple more times with the same result. Then I decided to connect the HMI to the wireless router we use to connect the PLC to the panel, and also our phones to control the plant remotely. This has worked for the past 2 days.

I believe the cable for the remote HMI has noise, since the problem with the HMI starts when a specific set of motors start running. I grounded the Ethernet switch, but the problem persists.

I suspect the problem with the PLC was that the bad HMI forced zeros to the VFD speed values, overwriting the good values sent by the good HMI.
But now that I can prevent the PLC problem from happening, I'm wondering why the problem disappears when I connect the HMI to the router.


Thank you!

Last edited by Elcan; April 21st, 2016 at 01:13 AM.
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Old April 21st, 2016, 03:43 AM   #2
Chris Hasler
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You probably have a noise issue with the existing connection.

The three main culprits are physical damage to the cable, incorrectly configured switch or induced noise. The last one is a pain to resolve correctly.

My diagnostics steps would be as follows:

Step one:
Go get a multimeter and/or an electrician, and start checking for shorts within the Ethernet cables, between conductors and to earth. If you can, check the cable from end to end for conductivity. If possible check the condition of the physical cable.

If this fails to find a problem proceed to step two:

Connect a laptop at the HMI end, open command prompt and run

"ping "PLC IP address" -t"

This will spam packets at the PLC for time = infinite, and let you see how well the network responds. Ctrl + c will stop the command from running. Its a crude and poor quality network diagnostics tool, but good enough when nothing better is present.

If the ping drops lots of packets or packets take a long time to return, you will probably need to replace the Ethernet switch or the physical cable.

Start with getting the IT department to check out the Ethernet switch settings.
Then remake the RJ45 connections on the physical cable and/or pull new cable.

If all this fails - get the IT department to debug the network connection and point the finger at them when anyone asks why the machine is down
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Old April 21st, 2016, 09:00 AM   #3
Elcan
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Thank you for your reply, Chris.
I think there's noise, and I wonder why connecting the remote HMI to the router fixes the problem. Is the router more immune to noise?
Regarding configuring the Ethernet switch, it does have that ability. It's a plug and play switch.
I will try the ping command you suggest.
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Old April 21st, 2016, 09:32 AM   #4
Chris Hasler
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The router is a different "cable" so your troubleshooting so far has isolated the issue down to the part of the network you are bypassing with the router.

The router is not immune to noise, its just working on a different frequency, and via a slightly different path. So the noise that is been induced may not actually be impacting the router in the same way.
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Old April 21st, 2016, 10:50 AM   #5
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Elcan,

This may not apply to your situation, but I had two G315s connected to a similar fashion. One was in a somewhat climate control room while the other sat next to an IR dryer. The remote HMI started to act up (freeze, was unresponsive, send values, and even displaying arbitrary numbers and strings). What I found out is that the HMI does not respond or function well over the operating temperature of 50 C. Hope this will shed some light into your issue.

K
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Old April 21st, 2016, 01:35 PM   #6
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I had a similar problem which ended up being a network problem. The G310 would get stuck in a constant reboot cycle or just freeze up completely. Cycling power would almost always restore it to normal operation for days or weeks. This seemed to correspond with other devices on the network acting up. Our IT department finally discovered a "rogue switch" and a cable that was causing a "network storm". I did not get to see the details of what they found first hand, but they basically replaced one of their switches and moved a cable from one port to another (the port in question was configured for some sort of mirroring or test function) and it solved the problem with my HMI.
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Old April 21st, 2016, 03:57 PM   #7
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It sounds like the Cat5 cable and/or switch that the HMI was connected to is getting noise induced onto it which an AC motor can do. Connecting to the wireless router isolated the HMI from the noise thus eliminating the problem (or at least the symptoms of it). I would be concerned even if you have the HMI working well through the router. If there is noise being induced onto some of the Cat5 cables those cables may also have induced voltage on them which could (probably will) cause other issues with the equipment that is still connected to those cables and/or switch. Something was causing the issue with the HMI and I’d want to find it.
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Old April 21st, 2016, 11:57 PM   #8
Elcan
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Quote:
Originally Posted by Elcan View Post
Regarding configuring the Ethernet switch, it does have that ability. It's a plug and play switch.
I should have written: it does not have the ability.
I mean, I cannot change any settings of the switch.
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Old April 22nd, 2016, 12:00 AM   #9
Elcan
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Thank you everybody for your answers!
I will try to eliminate the noise in the Ethernet cable.
There's a section of the cable (about 2 feet long) that runs parallel to 460 VAC cables and is only around 1 feet away from those power cables.
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Old April 22nd, 2016, 12:35 AM   #10
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Just a thought - if you have two identical HMI's, why not quickly just swap them over and see if the problem follows the hardware or the installation position? A simple test that can at least rule out half your possible causes one way or the other.
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Old April 22nd, 2016, 09:09 AM   #11
Elcan
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Quote:
Originally Posted by ASF View Post
Just a thought - if you have two identical HMI's, why not quickly just swap them over and see if the problem follows the hardware or the installation position? A simple test that can at least rule out half your possible causes one way or the other.
I did that and the problem didn't follow the hardware...
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