PLC Trouble

[cwal61]

Ken, No Doubt you should be able to Back Trace the event from the Reset Button. I thought the machine would restart but re-stopped after time if not online. I just thought that maybe a file was being logged to PC and possibly that file had been removed and Logic could not find it so stop. He stated he replaced hardware and CPU but same result which leads me to believe it's in the logic. Message's waiting for response? (You know this area better than anyone.) I'm just guessing. This is definetly an odd ball. But for sure if The Reset Button Resets the Stoppage then you should be able to isolate the problem. Still if OP would post program as requested someone would find the issue.

 

[tomalbright]

I'm finding it nearly impossible to believe it's in the logic. Unless they hired the same guys who wrote the mess I work with...

PC and PLC operation should be totally independent. Yeah, we definitely need the logic, then we can rule that out and find the fat-finger button.

Have you had a "guest programmer" online with your system? These things don't just change by themselves.

 

[DBONN]

No one was in this program prior to the problem. I had a programmer in this weekend to look at this with me. We found nothing. He also said he has never heard of such a thing but he saw it happen when we went offline. The reset button is a hardwired button that goes back to program to unlatch fault software. If we stay offline and hit the reset we fault right away. If we go back online and hit reset we run again.

 

[DBONN]

I will see if my company will allow posting of their logic. This program is huge. It resides in a 10 slot rack with a slc 5/04

 

[Lancie1]

DBONN,

One thing you haven't mentioned is whether or not the RSLogix500 computer has now (or has ever had) any type of link to the Internet. Is there any outside comm connection, or have any used flash drives been employed to move programs to this computer? If so, all bets are off.

What type of plant is this (not the company name, but what does it produce - automotive parts perhaps)?

 

[Lancie1]

PLC worms have been around for years, but the damage has been kept off the radar of most PLC users, for various security and political reasons ("don't want to panic the ignorant masses"). Check out the first example in this article about the Davis-Besse nuclear power plant near Sandusky, Ohio in 2003:

http://www.systemsafetyskeptic.com/notebook

 

[harryting]

This is a weird one. I haven't read everything in detail but DBONN said when he go back online THEN hit the reset button, the thing runs.

So, when he first go back online, does he see what is locking up the machine in the logic?

Did OP do a comparison between the data when the machine is running vs when he first go back online after a stop?

 

[Lancie1]

So, when he first go back online, does he see what is locking up the machine in the logic?

No, but if the computer is running and "ONLINE", the normal operator RESET button will allow the PLC to run again. If the computer is running but OFFLINE, the RESET button seems to do nothing. Of course, it should not matter whether a programming computer is running or not - the PLC should work the same - unless the PLC has malfunctioned or was sabotaged.

DEBONN: The computer is used to monitor and make changes to the program. One day we hooked up, then we couldn't take the computer back off without the equipment stopping.

Tomalbright: This would be in the RSLogix 500 software? You ARE taking it "offline" and not changing to "PROGRAM"? Offline should have no effect on the PLC, and it's shutting down with the PC turned ON, and going "offline" with RSL500 causes it (to stop running)?

DEBONN: Everything you described is correct. Any ideas?

Ken Roach: From what I understand, if he does not put RSLogix 500 back online but presses the Reset button, the machine does not restart.

 

[DBONN]

Ken, That is right. One other thing I was told to look at was if there was a terminating resistor in the DH+ wiring. I found no resistor. I don't this would be the problem because it seems it never had one. What size resistor needs to go in and where? Thanks

 

[dmargineau]

It depends of the DH+ network configured communications rate (baudrate):

57.6 kbps or 115.2 kbps -> 150 Ohm
230 kbps -> 82 Ohm

to be installed at both ends of the "blue hose daisy chain" between the Blue and Clear conductors.

 

[wrager69]

I know this is off topic, but I am looking for help with a Toshiba EX100.

 

[Mickey]

I know this is off topic, but I am looking for help with a Toshiba EX100.

wrager69,
You should start a new thread. And explain what kind of help you need.

 

[The Plc Kid]

Ken, That is right. One other thing I was told to look at was if there was a terminating resistor in the DH+ wiring. I found no resistor. I don't this would be the problem because it seems it never had one. What size resistor needs to go in and where? Thanks

As I said in post # 14 it may be that the computer is the terminating resistor. Many DH+ pc interface cards had the abilty to be the last device which would mean needing a resistor. Many times it's built into the board and you have to turn a dip[ switch on/off to enable or disable it. This is true for RIO and DH+ on many drive interface cards also. You may not see a physical resistor connected to the terminals.

Part number and brand from the DH+ board in the pc would help a lot.

 

[DBONN]

PLc Kid, Do you have any idea why being online or not makes a difference? I can't find anyone that can answer that question. Everyone says they have never heard of a problem like this before.
Thanks

 

[Lancie1]

One thing you haven't mentioned is whether or not the RSLogix500 computer has now (or has ever had) any type of link to the Internet. Is there any outside comm connection, or have any used flash drives been employed to move programs to this computer? If so, all bets are off.

You could have caught a PLC worm. There are a lot going around, and new ones are arriving every day.