Beijer Electronics (formerly QSI Corporation)

Manufacturer of Mobile Data and Human Machine Interface Terminals.
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PostPosted: Mon Oct 17, 2011 8:56 am 
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I am currently using Modbus TCP on an A12 running Qlarity. Normally I am communicating with 3 to 4 slaves. Communication runs fine and updates values for about a week and then quits communicating. After a screen reboot the communication is restored. Any thoughts about why this may be?


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PostPosted: Mon Oct 17, 2011 9:59 am 
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This is not something I've experienced or had reported on the QTERM-A12 before.

Can you describe the behavior you are seeing when communication stops. Are you getting error messages? Is the display locked up? Are you able to ping the QTERM-A12? Are you able to ping all of the other Modbus devices?

It would also be helpful to see a packet sniff of the communication when this happens from a program such as "WireShark".
http://www.wireshark.org/

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PostPosted: Mon Oct 17, 2011 10:41 am 
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I have not tried to ping the terminal yet, we had a client come across this problem and are trying to reproduce the issue now. The screen is not giving any error messages and is not locked up, it just appears as if it is not reading the new values. All buttons and commands that are internal to the screen are still operational.

If we reproduce the issue with our bench test I will ping and packet sniff the terminal.


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PostPosted: Mon Oct 17, 2011 1:08 pm 
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It sounds like you have changed the "messagefilter" property of the ModbusComm to hide error messages. I would recommend turning that on to see what communication errors are occuring.

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PostPosted: Mon Oct 17, 2011 1:45 pm 
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Thanks for the reply. I turned the error messages back on and get the following error on all slave devices:

Parsing error, or possible out of sync. packet, resetting modbus comm.


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PostPosted: Mon Oct 17, 2011 1:51 pm 
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That's a strange error message to get. I would not expect that unless the device you're talking to is not adhering to Modbus protocol. I'd be curious to see what the communication looks like between the two devices from a packet sniff program such as "WireShark". Are you using the ModbusV2 library included with Qlarity Foundry 2.63?

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PostPosted: Mon Oct 17, 2011 2:53 pm 
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I am using the modbusV2 library included with Qlarity Foundry 2.63. I am also able to receive and send data on the modbus network despite the error messages posted earlier. I have some data collected from the wireshark program. I am unable to attach the pcap extension on the forum however. Please advise.


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PostPosted: Mon Oct 17, 2011 3:10 pm 
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Try zipping it up. The forum software only allows certain extension, but .zip should be fine

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PostPosted: Tue Oct 18, 2011 6:26 am 
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Ron,

My e-mail was sent back. Here is what we have so far:

These two files are from the wireshark program. One prior to the comms failure on our bench test and one after the failure which occurred sometime last night. The file labeled ashdown comms fail is after the failure. Two of the devices we have are showing up on the A12 (111.111.111.106 and 111.111.111.107) The third device (111.111.111.109) is the one that is no longer communicating. Is there any other info you need? Thanks in advance for your help in this matter.


Attachments:
ashdown_comms_fail_10_18_11.zip [2.33 KiB]
Downloaded 173 times
test_ashdown_1.zip [36.05 KiB]
Downloaded 184 times


Last edited by Dano.oh on Tue Oct 18, 2011 8:00 am, edited 1 time in total.
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PostPosted: Tue Oct 18, 2011 7:52 am 
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I do show IP address 111.111.111.109 reseting its TCP/IP connection for no apparent reason.

Were you seeing an error message displayed during this sniff? If so, what was the exact text?

Everything else looks normal. Can you narrow this down to a Single Modbus Comm object and Single MRegister object. The error message that appears might indicate which objects query failed.

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PostPosted: Tue Oct 18, 2011 8:12 am 
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The errors we are getting (during the sniff also) are:

"modbuscomm983en1: Parsing error, or possible out of sync. packet, resetting modbus comm."
"modbuscomm983en2: Parsing error, or possible out of sync. packet, resetting modbus comm."

We had a similar error message before the comms failure which was:

"modbuscommDECS1: Parsing error, or possible out of sync. packet, resetting modbus comm."

Now we are still getting the first two error messages, but the third device 'modbuscommDECS1' won't send or receive.

The first two devices are send only.


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PostPosted: Tue Oct 18, 2011 8:18 am 
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Can you create a workspace with two objects that causes the error message: 1 ModbusComm and 1 MBRegisterV2? Then send me a packet sniff of this communication and a copy of the simplified workspace?

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PostPosted: Tue Oct 18, 2011 9:56 am 
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Unfortunately we aren't able to duplicate the failure with a simplified workspace. The simplified workspace has no errors. Do the error messages we are getting help us narrow the search for where this error is occurring?


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PostPosted: Tue Oct 18, 2011 10:09 am 
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Are the objects: modbuscomm983en1, modbuscomm983en2, modbuscommDECS1 ModbusComm objects? What are there IP Address of them?

If the "wordsize" set to mb_16bit? (this is what 99% of the Modbus devices use).

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PostPosted: Tue Oct 18, 2011 10:31 am 
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Yes those are modbuscomm objects. The IP of each respectively are: 111.111.111.107, 111.111.111.106, and 111.111.111.109. The wordsize is set to mb_16bit.


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