PLC 5 / RSLogix 5 Strange things. (With video)

[Oceansoul]

I was troubleshooting as to why a pump wouldnt start the other day and came across some strange goings on in RSLogix 5.

If you watch the video its all there, but, all the criteria for B183:6/3 to be true, are all true. But if i toggle that bit, it goes false and stays that way. There is nothing else "controlling" B183:6/3 (as i show in the xref at the end).

At 17 seconds or so, i toggle this, and as it stays false, you can see in the bottom line the XIC B183:6/3 goes false but the bit at the end of that rung stays true. I can toggle as much as i like, and it always stays that way.

I'm online, processor is in run mode and controlling other equipment.

Youtube link. http://www.youtube.com/watch?v=8PXv3-SmTsQ

Why does it do this?

 

[Mickey]

I was troubleshooting as to why a pump wouldnt start the other day and came across some strange goings on in RSLogix 5.

If you watch the video its all there, but, all the criteria for B183:6/3 to be true, are all true. But if i toggle that bit, it goes false and stays that way. There is nothing else "controlling" B183:6/3 (as i show in the xref at the end).

At 17 seconds or so, i toggle this, and as it stays false, you can see in the bottom line the XIC B183:6/3 goes false but the bit at the end of that rung stays true. I can toggle as much as i like, and it always stays that way.

I'm online, processor is in run mode and controlling other equipment.

Youtube link. http://www.youtube.com/watch?v=8PXv3-SmTsQ

Why does it do this?

Is the subroutine being called?

Post your program if you can, zip it first.

 

[jkerekes]

Is the subroutine where this rung is located, being scanned? Does it have a JSR to this file somewhere?

 

[Ken Roach]

Piling on: that's definitely consistent with a subroutine that is not being executed.

There's room in the infinite universe for this to also be a bug, but let's chase down the most likely thing first.

 

[mutzui]

Yup. I think the subroutine is not executed. Make sure to do it in the LAD 2.

 

[Mickey]

Yup. I think the subroutine is not executed. Make sure to do it in the LAD 2.

That's one way to do it. The Enhanced PLC5's have another feature where by you can have 16"Master Control Programs" which act just like Lad 2. You can also enable/disable them by writing to the assigned status bit.

See exert from help file and picture below.

 

[Oceansoul]

The ladder (58) is being called by JSR in ladder 6 which has a JSR in ladder 2. I have just found a watchdog bit that is a condition to JSR ladder 6. The state of data tables is the last state it was saved in when i was online and found this problem. Could have found whats doing this. I'll have to get online and see whats going on with these watchdogs.

Ive uploaded the programe. But be warned there is alot of **** in there (from old SCADA system etc) and it was origionally written in the late 80s/early 90s on AB6200 software

 

[Mickey]

Looks like ladder 70 controls that watchdog bit, ladder 7 has the JSR for it and ladder 2 has the JSR for ladder 7. My head is starting to spin.

But that is definitely your problem, the subroutine is not being called.

 

[Eric Nelson]

My head is starting to spin

Yes, this is quite the convoluted program...

Working backwards:

Ladder 58 is being called by a JSR in ladder 6
Ladder 6 is being conditionally called by a JSR in ladder 2
The condition (B3:0/10) is turned on by B3:0/6 in ladder 70 (rung 18)
B3:0/6 is being turned on by XIO B181:5/15 in the previous rung (rung 17)
B181:5/15 is being turned on by I:012/17 in ladder 40 (rung 41)

Looks like I:012/17 must be OFF for ladder 58 to be called

Or, I'm way off, and it's something completely different...

Best of luck with this one!



-Eric

 

[Nigasai]

Try to put a rung on the mentioned ladder with XIO and OTE with same bit address you would notice the XIO and OTE blink constanly meaning the scanning is active, if not the ladder is not being scan.

Cheers,

 

[Oceansoul]

UPDATE: A watchdog relay had worn out and welded its contacts closed, causing the timer to timeout. Replaced said relay and it all started working "wonderfully".

 

[The Plc Kid]

This is one of those programs where you want to just press the delete key and start over.

 

[daba]

This is one of those programs where you want to just press the delete key and start over.

ROFLMAO - I have not looked at the program, nor want to after that comment...

Worked on a few in my time that would have you pulling your hair out if you had any.

Wish you luck Oceansoul if you have to maintain it

 

[The Plc Kid]

Take a look Daba it will make your eyes water.

I may have done it the same way if I was smoking crack while laying out the design.

I have quite a few beasts like that in my plant also but I am slowly getting rid of them. That delete key works like a champ.