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Old June 13th, 2018, 05:57 AM   #1
jfrye
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SLC5/05 IO TimeOut Reading

We are having an issue with a SLC5/05 timing out reading from the IOs on the backplane. Very briefly the setup is, 1747-L551 (SLC5/05), with 1746-IA16, -OW16, -NI4 (x2), and -NO41, with a PVP1000 as an HMI. Issue started a month or so ago with the original PLC, "Timeout reading N15:0 from SLC... Timeout reading from O0:0 from SLC... Timeout reading from T4:10-T4:11 from SLC... list goes on." We replaced the PLC, first time different rev/series number, and bad data tables, ended up PLC ran for maybe a day and then was completely incommunicable; tried battery reset, etc. nothing, but whatever. We replaced with another PLC with rev/ser no. closer to the existing, installed, programmed, and has been working well for close to a month now. Until last night, we received the same timeout alerts. In the past a reboot would reset the condition and the machine would run for 1-2hrs, I am assuming that holds true today but I have not verified yet this morning.



We added a PID block to control the speed of a pump several months ago but I would have thought if that were an issue it would have cropped up sooner, as we had a math error due to an infinite loop from the PID that we resolved with a reset block, can provide specifics if needed but don't recall offhand. That was in Feb 2018. Timeout issue started in early-mid May '18.


Any help would be appreciated, thanks!


Jeremy
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Old June 13th, 2018, 06:27 AM   #2
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Quote:
In the past a reboot would reset the condition and the machine would run for 1-2hrs

Jeremy,

Have you done a full reset of the PLC and not just a 'reboot' and how much memory are you using? im just guessing but maybe you are running out of memory and need to go up to a L552

Are you storing a lot of data in the PLC ?
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Old June 13th, 2018, 06:28 AM   #3
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I would change the backplane first. Low hanging fruit etc.
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Old June 13th, 2018, 06:58 AM   #4
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make SURE that the chassis is PROPERLY grounded ...
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Old June 13th, 2018, 07:06 AM   #5
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Are those faults showing as major faults in RSLogix or showing on the HMI?

"Timeout reading N15:0 from SLC... " is a read from the SLC's memory, as if the HMI is timing out reading from the SLC.
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Old June 13th, 2018, 08:56 AM   #6
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We replaced the back plane, and checked the memory: Memory used 582 ins. words used - 1076 data table; 11706 ins. words left. We found a resistor scorched on the power supply in the process, we replaced this with a refurb edition. Grounding to chassis and power supply.



The HMI and PLC are ethernet connected via a switch, the HMI has been replaced in the past, both ethernet cables have been replaced, and the switch has been bypass i.e. direct PLC to HMI connection; same results. This bit of work was done during the first occurrence in May,the replacement of the PLC is the step we determined to have resolved the issue at least temporarily.


We have not done a full reset on the CPU. We could reset the original CPU that had the issue and try it, but I kind of hate to do that because it is a spare that will at least allow my operators to wash down the machine. This is on a rotary drum thickener in a wastewater treatment plant, so when it fails it makes a horrible mess.
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Old June 13th, 2018, 09:12 AM   #7
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Quote:
Originally Posted by Aabeck View Post
Are those faults showing as major faults in RSLogix or showing on the HMI?

"Timeout reading N15:0 from SLC... " is a read from the SLC's memory, as if the HMI is timing out reading from the SLC.

^^^ This.


This has nothing to do with your rack, it is a communications fault between the PLC CPU and the HMI. That is all it is.


I'm actually surprised that you can even read the output and input images directly, I haven't used an SLC is a long time, but I seem to remember that the I and O image tables can't usually be read by most communications software.
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Old June 13th, 2018, 09:35 AM   #8
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Quote:
Originally Posted by jfrye View Post

We have not done a full reset on the CPU. We could reset the original CPU that had the issue and try it, but I kind of hate to do that because it is a spare that will at least allow my operators to wash down the machine. .
I would reset the PLC then reload the program... maybe swap them out so they have a 'working' PLC

Any chance you have noise on your ethernet cable(s) or a issue with the switch causing your timeouts ?
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Old June 13th, 2018, 09:40 AM   #9
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Quote:
Originally Posted by rdrast View Post
I'm actually surprised that you can even read the output and input images directly, I haven't used an SLC is a long time, but I seem to remember that the I and O image tables can't usually be read by most communications software.
I have had problems, and there have been more than one thread here, about problems with a HMI reading SLC I/O directly.

I always do a mirroring of all digital I/O to a B19: file and have the HMI check there instead of the I:1 and O:0 files. Also if direct reads of analog I/O is read I mirror those to an integer file for the HMI
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Old June 13th, 2018, 10:09 AM   #10
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I've bypassed the switch and ran comm cable directly between the HMI and PLC, PLC and HMI are both new in case the ports were bad. Currently the setup is PLC to switch and switch to HMI, I do not believe we setup a direct connection since the two units were replaced.
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Old June 13th, 2018, 10:10 AM   #11
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The HMI was programmed by a vendor, and the original config/program is proprietary.... We can get into the PLC in development mode, but not the HMI.
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Old June 13th, 2018, 10:20 AM   #12
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Originally Posted by jfrye View Post
The HMI was programmed by a vendor, and the original config/program is proprietary.... We can get into the PLC in development mode, but not the HMI.
Now that sucks...
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Old June 13th, 2018, 10:56 AM   #13
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Now that sucks...
Yes, yes it does. We are planning to sometime in the future recreate the HMI in CMore and abandon the overpriced PVP... but that doesn't help the immediate future.
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Old June 13th, 2018, 12:29 PM   #14
jfrye
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Originally Posted by rdrast View Post
^^^ This.


This has nothing to do with your rack, it is a communications fault between the PLC CPU and the HMI. That is all it is.


I'm actually surprised that you can even read the output and input images directly, I haven't used an SLC is a long time, but I seem to remember that the I and O image tables can't usually be read by most communications software.
We tested this theory, unplugged the HMI from any connection with the PLC and tested function. The PLC/machine kept in operation the entire time the HMI was disconnected, the timeout alarms did output on the HMI...


We are going to verify that the PID output(s) are not running through the HMI before going to a VFD as a speed input.
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Old June 14th, 2018, 12:25 AM   #15
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I would download Advanced HMI, add in some tags from the SCL and get it running on a laptop, if Advanced HMI works whilst the original HMI produces errors, you have shown the SLC is good and the HMI is bad.

Move on and add in your own HMI. You have many options for a replacement HMI available to you.
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