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Unread December 2nd, 2019, 09:33 PM   #1
dcam
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Networked PFlex525 Start command issue

This is an issue I see occasionally.The logic tells a drive through Ethernet to start but it does not see the start command at the drive. There is no indication on drive display above FWD. If I cycle power it goes away. It is intermittent, I cannot repeat the issue consistently........Here are some picts. Please note this drive operates normally almost all the time. All control settings are Ethernet
Attached Images
File Type: jpg chill output.jpg (157 Bytes, 14 views)
File Type: jpg chilllogic.jpg (222.0 KB, 10 views)
File Type: jpg chillpanel.jpg (255.5 KB, 10 views)
File Type: jpg chillvfdface.jpg (159.2 KB, 11 views)
File Type: jpg chillproject.jpg (223.7 KB, 11 views)
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Unread December 2nd, 2019, 10:26 PM   #2
seth350
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Have you tried trending the Start and Stop bits?

Just because the instruction doesn’t turn green doesn’t mean it didn’t turn on. The software, bless its heart, is trying its best to keep up with a PLC scanning every [insert scan time].

Also, how is your fault reset bit programmed? I ask because I’ve seen people place a rung with an XIC for faulted and an OTE for reset fault. Naturally as soon as the drive faults, it is then cleared.

I thought the PF525 had a display parameter to show where the last start command came from, as well as the stop. May only apply to the 755s.
There are fault history parameters you can look at though.

Verify you got a good Ethernet cable as well and all duplex settings match for Ethernet interfaces. This unlikely to be the problem, but best to verify rather than go bald.
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Unread December 2nd, 2019, 10:38 PM   #3
dcam
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This is a situation where the start OTE is energized and the bit associated with it is a 1. Your first sentence in your reply tells me you do not understand my problem....".Just because the instruction doesn’t turn green doesn’t mean it didn’t turn on"............the logic is working, the output table for that drive command is a 1.....The 525 is not recognizing the TABLE_CHILL_PUMP:O.Start command....thank you for replying though.
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Unread December 2nd, 2019, 10:44 PM   #4
Ken Roach
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Thanks for posting those photos !

This is a common problem related to the STOP bit logic and the asynchronous I/O scan of the ControlLogix / CompactLogix operating system. It's common enough that there might be comprehensive PLCTalk threads or Rockwell documents addressing it, but it's not my job to write those anymore, so I'll just wing it.

In A-B drives, a STOP command from any source prevents the drive from starting.
In A-B drives, START must transition from 0 to 1 while STOP is 0.

If the I/O connection RPI timeout occurs after the rung that sets .START = 1 but before the CompactLogix has gotten back around to the rung that sets .STOP = 0, then both .START and .STOP will go out in the Command word as = 1.

Even though on the next scan STOP has gone to 0, the transition of Start from 0 -> 1 was not done with STOP set to 0.

The easiest solution is to write your STOP logic so that it only asserts STOP if the .Running or .Active bit is true. That way STOP will stop the drive when you need it to, but it won't still be true when you send that 0 -> 1 transition of the START command.
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Unread December 2nd, 2019, 10:47 PM   #5
seth350
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Not if your stop output is coming on simultaneously for some reason or the start output turns on then drops then turns back on.

The drives do require some amount of time, although minimal, to recognize a command, do something, then be ready for the next command.
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Unread December 2nd, 2019, 10:49 PM   #6
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My money is on the same thing that's tripped up many a programmer. Check this thread for a quick overview (the cause of the problem is described in post 2) and this thread for a more detailed look at it, including a "how to do it better" screenshot in post #12. Both from the indubitable Ken Roach. [edit: who has poked his head in and beaten me to the punch anyway]
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Unread December 2nd, 2019, 11:12 PM   #7
GaryS
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It looks to me like the stop command is not getting reset correctly
the stop command always overrides any run command
in your ladder program you show the Stop command as _LE_CHILL_PUMP.O.STOP
an the Start command as _E_CHILL_PUMP.O.START
if that is true then the stop command and start command are 2 different tags to on 2 different drives and do not have a relationship to each other.
I normally maintain the stop command until I set the run command then I don't get any surprise restarts the start / rum command and the stop should be programmed interactively activating the stop command will reset the start / run command
Repowering the drive clears the stop command it will work until the next time the stop is set

Last edited by GaryS; December 2nd, 2019 at 11:15 PM.
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Unread December 2nd, 2019, 11:18 PM   #8
Ken Roach
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The first time I encountered this, it was on a corn chip packaging line at Frito-Lay in Jonesboro, Arkansas. An integrator in my area had bought a bunch of the then-new PowerFlex 40P indexing drives, and was using them to rapidly start and stop conveyors that sealed and opened and positioned Dorito bags underneath the chutes that filled them with chips.

It was part of a new "in-line seasoning" system that would take fresh chips and hit them with seasoning just as they fell into the chute. Seasoning is the most expensive part of a corn chip, and this wasted far less of it getting stuck to conveyors and chutes and bins. It also enabled the multiple flavors in one bag that was all the rage in the early 2000's.

This system had ControlLogix L55 controllers and ControlNet. The factory even sent a bunch of specialized network equipment down via the Company jet to drop it off for me because we assumed there were network signal issues. Pepsico has some pull.

The end of the story has the usual finger-pointing and refusal to pay invoices for engineering work, but I prefer to remember the midnight that I drove back toward town from this corn chip plant in the middle of the cornfields and saw searchlights surrounding an island of light in the darkness off the highway.

Big football game ? Movie premier ? Neither seemed likely on the outskirts of Jonesboro in the middle of July.

So I pulled off the highway and followed the lights to find a line of people stretched across the parking lot in front of a Barnes & Noble, for the midnight release of the hardback of "Harry Potter and The Half-Blood Prince".
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Unread December 3rd, 2019, 01:43 AM   #9
dcam
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You guys are great. I love this site. Ken's advice of putting a TABLE_CHILL_PUMP:I.Active
permissive operand in the stop rung seems to have corrected the issue. Thanks again my Automation brethren. Heres a final fix pict
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Unread December 3rd, 2019, 01:44 AM   #10
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TABLE_CHILL_PUMP:I.Active

TABLE_CHILL_PUMP:I.Active
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Unread December 3rd, 2019, 02:07 AM   #11
GaryS
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I think that putting the active permissive in the stop command could get you in a lot of trouble in time.
A stop command should remain set until you are ready to start the motor that way you prevents an unexacted start then on a start command rung reset the stop and set the start then you know for sure what to exect
I never liked leaving a stop unset when you don't wan it to run it could result in an unexacted start
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