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Old March 15th, 2019, 05:41 PM   #1
stallone
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L62 controller fault program fault code 32

Hi all,

i have a 1756-L62 processor, it keeps going into fault mode when i put it into run.
I went to check major faults and i see the program fault (type 04) (code 34) a timer instruction had a negative value for its PRE or ACC.

So from what i understand (basic PLC knowledge) it means the timer has a negative value, which it does, i reset it to 0 but when i place in run mode, it happens again immediately with the same value (-15200)
In the timer there is an expression, and i see the value coming from the machine set speed is -29, so this is where i think the negative value is coming from.

I think it happened today when i technician fixed something in the panel and moved the servo's, is it possible it needs to be set to 0 again somehow?

Also i clear this value but it immediately goes to -29 as i put the plc into run mode and the controller goes into fault and shows the same error as above.

Any guidance is welcomed, thank you.
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Old March 16th, 2019, 07:03 AM   #2
tarik1978
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Did you do a cross reference to check where this value is coming from, it could be an HMI, another PLC , servo drive .....
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Old March 16th, 2019, 07:08 AM   #3
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I did and it is coming from a valur from the hmi but the hmi appears stuck amd wont allow me to change the -29.

I put in another processor from an exact same line and it works. And this plc with the -29 doesnt workin the other line.

The fault is with this processor but im not sure if its a program fault why does it work on the other line.
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Old March 20th, 2019, 09:21 AM   #4
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Is it possible if someone can have a look at the program,

for some reason it has a major program fault and it wont clear.

There seems to be a negative value and i cant clear it, it keeps coming back.

also when this program loads onto the plc, the hmi freezes with a minus speed point of -29 and i think thats whats causing the negative value.

i have attached the plc program, from a 1756-L62 processor version 17.


i csnt attach the file, it says too big
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Old March 20th, 2019, 10:52 AM   #5
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Do you have a back up version of the program for the PLC?
(From before this problem started.)

What happens if the back up program is loaded into the PLC?
Poet.
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Old March 20th, 2019, 11:03 AM   #6
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No i dont,

Its a new customer, i went to help and they didn't have the plc program, so i did an upload, and all the comments came with the upload also, maybe because there was a cf card in the plc.
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Old March 20th, 2019, 11:33 AM   #7
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If the file is too big you can upload it to WeTransfer and post the link here. It will be there for 7 days (select the FREE option)

If the HMI is writing a negative number I would suggest adding a line before the timer and if the .PRE is LES 0 then MOV 0 to it before the timer executes.

EDIT: All of the ControlLogix PLC's keep the comments and descriptions in the PLC, not related to a CF card.
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Last edited by Aabeck; March 20th, 2019 at 11:47 AM.
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Old March 20th, 2019, 01:02 PM   #8
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Im new to the whole process, forgive my ignorance.

I have sent the wetransfer link to the plc program.

Can someone have a look at the rung that has the major fault and advize what to do.

thank you for any suggestions or comments.

https://we.tl/t-Yoxk3tMR1w
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Old March 21st, 2019, 05:28 AM   #9
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Stallone > I put in another processor from an exact same line and it works. And this plc with the -29 doesnt workin the other line.


OK.
Are both PLC's supposed to have the same program?
If the problem can't be found, resolved . . . You might try pulling the program from the
working one and dumping it into the non-working one.

(Or try comparing the two programs to see what the differences are.)

Poet.
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Old March 21st, 2019, 05:35 AM   #10
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in theory the lines are identical with identical plc equipment.


update note, i took this plc with the program fault and put in the working lines plc rack and the processor still has major fault.

I then took the working lines plc and slotted into the rack of the line not working and it did work, which basically i wanted to see if the negative reference was coming from the line somewhere and would also put this plc into fault but it did not.

so basically the program faulted plc didnt work in the working line,
i also put the program onto brand new processor and same program fault comes up.
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Old March 21st, 2019, 06:11 AM   #11
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A timer will cause a major fault if the PRE or the ACC has a negative value when the timer instruction is executed.

It is not "normal" to manipulate the ACC in code, although it may be done, so it is more likely that some math is being done to change the timer's PRE.


There are two ways of dealing with this issue...

1. Place a rung in front (above) the rung with the timer, and if PRE less than zero, MOV zero to it.

2. Create a Fault Routine that gets (GSV) the fault code, checks it for 4, 34, clears them, and puts them back (SSV).

In most circumstances I would prefer to do no.1, constraining the PRE to be >= 0, and the timer will execute correctly, setting the DN bit immediately if the PRE is 0.

If you use approach no.2, the timer instruction is ignored after clearing the fault, so you will never see a DN bit from it.
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Old March 21st, 2019, 06:14 AM   #12
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@daba thank you for the detailed help,

im unfortunatly a bit lost as im new to this all.

Have you got a chance to look at the program and see if you can see why the rung has a fault?
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Old March 21st, 2019, 06:40 AM   #13
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Quote:
Originally Posted by stallone View Post
@daba thank you for the detailed help,

im unfortunatly a bit lost as im new to this all.

Have you got a chance to look at the program and see if you can see why the rung has a fault?

There is a CPT (Compute) instruction on rung 8 of program file "A10_SBR_OuterWrapper_Reel_On" that is creating the negative value that is then loaded into TIMER022.PRE when it is less than 5000.

A negative number will always be less than 5000.

The culprit then is the expression in the CPT instruction, and the negative is being produced by the -29 in "PV_Motion_McSpeed". This value comes from the Add-On instruction "Machine_Speed_Position" in MI06_PanelViewMotion, rung 16. I unfortunately cannot open this add-on instruction due to my limited licensing.

The same applies to TIMER023 on the same rung, but of coursew the processor will fault out on the first occurrence found.
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Old March 21st, 2019, 06:44 AM   #14
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Quote:
Originally Posted by stallone View Post
i also put the program onto brand new processor and same program fault comes up.
I would do as Poet suggests and do a compare of the working and non-working projects.

If you only swapped the PLC and not the HMI that you said was getting stuck the problem lies somewhere in the program. Something may be writing the -negative number to the timer. If you did also swap the HMI with the PLC I would suggest a swap of one without the other.
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Old March 21st, 2019, 06:47 AM   #15
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I only swopped the processors, not the HMI's.

When i loaded the working program from the other line onto this plc then hmi was responsive and working, it even loaded a recipe from the plc.

But as soon as i load the program in question, the plc has -29 on the screen and stuck in a running mode. nothing can be done.
But the hmi works fine with the other plc

how do i compare both programs.
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