PLC Trouble
- Thread starter DBONN
- Start date
James Mcquade
Member
DBONN,
we did this where i used to work. the pc was an integral part of the machines operation doing data collection and passing data between plc's.
we used rsview32 for the data collection and recipe function. we alsu used excel on another machine. you might have some other type of program running.
regards,
james
we did this where i used to work. the pc was an integral part of the machines operation doing data collection and passing data between plc's.
we used rsview32 for the data collection and recipe function. we alsu used excel on another machine. you might have some other type of program running.
regards,
james
Bit_Bucket_07
Member
What do you mean by "host computer"?
If you are referring to an HMI workstation, then it is quite likely that the programmer designed the control system to shut down equipment in the event of a loss of communication with the operator interface.
If you are referring to an HMI workstation, then it is quite likely that the programmer designed the control system to shut down equipment in the event of a loss of communication with the operator interface.
Ken Roach
Lifetime Supporting Member + Moderator
Okay, but what software are you running on it ?
You're hinting that this is editing software, but you need to come out and say what it is, unless you're intentionally being obscure.
I've written HMI "watchdogs" to verify that an operator interface is running before allowing some machine functions, but I've never seen a controller that required the logic editor to be online to run its program.
You're hinting that this is editing software, but you need to come out and say what it is, unless you're intentionally being obscure.
I've written HMI "watchdogs" to verify that an operator interface is running before allowing some machine functions, but I've never seen a controller that required the logic editor to be online to run its program.
icky812
Lifetime Supporting Member
My guess would be grounding or floating neutral where the PLC is deriving it's ground from the PC.
Ken Roach
Lifetime Supporting Member + Moderator
Hey, good point, Icky !
I assumed an Ethernet connection, but it could be serial with a ground pin or grounded shield.
If it's Ethernet and it's grounding through the computer... oh, boy.
I assumed an Ethernet connection, but it could be serial with a ground pin or grounded shield.
If it's Ethernet and it's grounding through the computer... oh, boy.
Yeah, I'm with Roach on this one. It seems like a watchdog. If you have some kind of HMI running, it may be continually poking a bit on/off to keep a timer from expiring, which may trigger some "all outputs off" bit in the PLC. One way to test this is to shutdown or disconnect the computer and immediately try to run something. If you can in the first few seconds, then it dies shortly after, you have a watchdog. You may still have a watchdog if you get an instant cutoff. It depends on the timer length. Look for timers in your program while online. Look for one that always seems on, yet never really increments much.
bernie_carlton
Lifetime Supporting Member + Moderator
Does the PLC die when you turn off any communicating applications or when you physically unhook the PC?
At what point does the PLC die?
1. Stop all applications.
2. Turn off the PC, but don't disconnect the communication link or unplug the PC - leave it off for the following steps.
3. Unplug the communication link.
---- If it dies plug the communication link back in, does it come up?
4. With the communication link still plugged in unplug AC power to the PC.
At what point does the PLC die?
1. Stop all applications.
2. Turn off the PC, but don't disconnect the communication link or unplug the PC - leave it off for the following steps.
3. Unplug the communication link.
---- If it dies plug the communication link back in, does it come up?
4. With the communication link still plugged in unplug AC power to the PC.
FrancisL
Member
Well, if you have a PLC running phases with a PC orchestrating the phases - as in many batch systems - that would happen. But I am sure you would know about that!
Ken Roach
Lifetime Supporting Member + Moderator
The tantalizing part is that DBONN says that this is new behavior for this system.
I assume that if it did this intentionally that it would have done so from the start, or that he'd be aware of the change and correlate it with the new behavior.
DBONN, tell us as much as you can about the PLC, the software, and the network connection.
Otherwise we'll just spend more time guessing. I enjoy guessing.
I assume that if it did this intentionally that it would have done so from the start, or that he'd be aware of the change and correlate it with the new behavior.
DBONN, tell us as much as you can about the PLC, the software, and the network connection.
Otherwise we'll just spend more time guessing. I enjoy guessing.
The Plc Kid
Member
The pc could be the last node in a DH+ network ( terminating resistor ) for example. Should not be a problem to tun off but if you unplug then BOOM I/O racks and drives stop talking, etc.
OkiePC
Lifetime Supporting Member
I recall using many DH+ devices with 6 pin connectors but they had to be unplugged to break communication and that normally would not stop a machine, just disconnect other downstream devices if you wired through the connector.
The program can monitor for activity on a channel and take action, detecting when serial communications are established and broken, for example...I had to do this once to set up a portable HMI and enforce data to be read each time communications were established. This way the battery powered thing could be carried from machine to machine, and when you plugged it in, would refresh the values and not overwrite them with data from the previous connection.
I am struggling to think of what may have happened that changed this behavior suddenly...looking forward to the result...
The program can monitor for activity on a channel and take action, detecting when serial communications are established and broken, for example...I had to do this once to set up a portable HMI and enforce data to be read each time communications were established. This way the battery powered thing could be carried from machine to machine, and when you plugged it in, would refresh the values and not overwrite them with data from the previous connection.
I am struggling to think of what may have happened that changed this behavior suddenly...looking forward to the result...
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