PLC Reset Command?

Sprayman

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Join Date
Jan 2020
Location
Chicago
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50
Hi all,

I had an interesting question posed to me. A developer asked me if there was a way to reset/reboot a plc via the plc itself. Not run/stop mode but a physical "reboot" of sorts.

I was unsure so I thought I would check here!

From my understanding that would be impossible but maybe there's a way!

We run a Delta DVP-SX2

Thanks!
 
You could trigger a relay output (or external timer) that is wired in series with the PLC power. This would allow the PLC to hard reboot!
I cannot think of a reason why you would want this to happen.

Regards,
 
A developer asked me if there was a way to reset/reboot a plc via the plc itself. Not run/stop mode but a physical "reboot" of sorts.

Depends on the definition of reset/reboot of the plc.
If a power cycle fits that definition, then program a output to a N.C. timer relay (the relay has a 5sec. or so delay) that will de-energize/energize the power terminals of the plc.
 
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You could wire the power to the PLC through the normally closed contact of a relay, and wire the relay coil to a PLC output. If the PLC ever turns on that output, it cuts power to itself.

Mind you, if someone asked me to implement this for a PLC, my very first question would be "why?"

If I was presented with a good enough reason to *actually* do this, I'd use a delay-off timer instead of a relay. Because with a straight relay, the split second you open that contact, the power will be removed from the coil of the relay, and thus restored to the PLC. A compact logix PLC, for example, takes around 5-10 seconds from loss of power until all the LED's on the front go off - during this time it's using stored energy to perform necessary shutdown tasks. Repeatedly restoring power to is while it's in this state is probably not a nice way to treat your PLC. If you had a delay off timer that has power applied at all times and is simply triggered by your PLC output, then you can set it up so that as soon as it received the trigger it opens the circuit powering the PLC, which also removes the trigger. But then because the timer still has power applied, just not to the trigger, it can hold the contacts open for another 10-20 seconds to make sure it's fully powered down, before closing them and powering the PLC back up.


Edit: Man, beaten to the punch by no less than five people this morning!
 
Hmm, the Delta DVP-SX2 looks like the kind of PLC you would be able to use something like:
SysProcess.SysProcess_ExecuteCommand2(pszCommand:= 'shutdown /r /t 0', pszStdOut:= returnText, udiStdOutLen:= 255, pResult:= dummyResult);
// OR even just:
// SysProcess.SysProcess_ExecuteCommand(pszComand:= 'shutdown /r /t 0', pResult := dummyResult);


Hint, remove the "_" I only added it because the forum doesn't like certain series of characters.
Hint, replace with the appropriate command line reboot command for your system
Hint, ExecuteCommand really does misspell its first operand
 
Sounds like a “developer” that blames the hardware before attempting to debug the trash they call code.

PLCs are designed around the principle of continuous, uninterrupted operation for as long a period as possible. Rebooting the PLC defeats the purpose and places it in the territory of a Windows 10 box getting compulsory updates and reboots ordered by mindless corporate drones with zero clue of how their users operate their tools.

I’d decline any and all hardware design change requests from this monkey.
 
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Dear Sprayman,


Checkout the description of M1035 in the help section. This will definitely help you achieve what you seek
 
Why would anyone want to do this?


it sounds to me like the developer wants to figure out a way to do this and then put a lock in the plc program to keep it from running. then he will password the program so he keeps getting called back. just my 2 cents.
James
 
She tried to explain it to me a few times. It sounds like their end goal is to be able to power cycle the entire system remotely?

I've tried to explain the plc's don't get "hung up" like computer programs do. Either the plc works or it doesn't but that apparently doesn't register in this persons brain.

I will check out these suggestions though! I fee like at the very least its a nice back pocket skill/idea to have just in case there is a need for it. (like a back-back-back up power kill??)
 
Why would anyone want to do this?


it sounds to me like the developer wants to figure out a way to do this and then put a lock in the plc program to keep it from running. then he will password the program so he keeps getting called back. just my 2 cents.
James

I had a legitimate reason to consider this once but in the end just fixed the real problem. We have an assembly machine and RF welder which communicate to each other over serial. About once a shift the machine would go down due to the RF screwing with the serial connection. The only way to get the communications fault to clear and reset was to power cycle either one of the PLCs. The machine would sit down for 15 minutes or more while the OP waited for a technician to come pull the fuse. This idea was considered at some point as a quick fix to prevent downtime.

Keep in mind that at no point did I suggest this was a good idea, but it is an idea anyways.
 
I fee like at the very least its a nice back pocket skill/idea to have just in case there is a need for it. (like a back-back-back up power kill??)

It really isn't a skill at all.

A bit like having the skill of re-decorating your living room with your d!ck because it would save £5 on a roller and brush.

Sure you could do it, by why in gods name would you?
 

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