Programming in Connected Components Workbench

I am working on a 440C-CR30-22BBB in Connected Components Workbench. It is a simple set of interlocking switches. If Gate A is open, B is locked and vice versa. Also, neither gate can be opened if both are not confirmed closed. The first part is simple enough, but I'm struggling to get this (XIO Door_A XIO Door_B OTU Door_A OTU Door_B) programmed on the CCW side. I have the both switches going into an AND gate, but am not quite sure how to do the output. Any help would be greatly appreciated!

Can you confirm my understanding of your setup?


You have two gates, A and B.
Both are fitted with locking interlock switches.
Only one door is permitted to be open at a time.
Before unlocking either door, the other must be closed and locked.


I'm not sure what you mean by "...neither gate can be opened if both are not confirmed closed." That seems like a paradox. Do you mean that neither can be unlocked unless both are confirmed closed? Then you can unlock and open one of the doors? Then close and lock it so the other can be unlocked and opened?


What kind of switches are you using?

joseph_e2 said:

Can you confirm my understanding of your setup?


You have two gates, A and B.
Both are fitted with locking interlock switches.
Only one door is permitted to be open at a time.
Before unlocking either door, the other must be closed and locked.


I'm not sure what you mean by "...neither gate can be opened if both are not confirmed closed." That seems like a paradox. Do you mean that neither can be unlocked unless both are confirmed closed? Then you can unlock and open one of the doors? Then close and lock it so the other can be unlocked and opened?


What kind of switches are you using?

Click to expand...

Sorry, let me explain some more. If both doors are closed, then both interlocks are not locked. If one door opens, the opposite interlock will lock preventing both doors from being opened at the same time. Unless the relay has a signal from both switches that the doors are closed, it will lock both (this is the line of logic I typed out). The issue I'm having is I can't have multiple "Immediate Off" Safety Output Function Blocks referencing the same Safety Output.

I feel the a better question would be, "How do I reference the same output twice using CCW."

Gotcha. You want to keep the doors unlocked the whole time unless one is open, then lock both.
Are you wiring both unlock coils to the same physical output? Are you monitoring the status of the door locks separately from the doors being closed (you must be...)?



Based on the locks being power to release and being monitored separately from the gate status, I threw together a quick program that would energize an SOF for the locks if both gates are closed and de-energize it if either is open. There's another SOF for the hazard that will be energized if:
1) both doors are closed
OR
2) Gate A is closed AND Gate A is locked
OR
3) Gate B is closed AND Gate B is locked


However, it's probable (almost certain) that there would be a race condition that could cause the hazard's SOF to de-energize in the window of time where Gate A is opened before Gate B has a chance to show locked. You may be able to put in some time delays or use an OFF_Delay output for the hazard to compensate for that, but you'll have to be really careful to make sure your gates are far enough from the hazard for that to be ok.
I would strongly suggest leaving both gates locked all the time until an operator presses a button to open one of them. That will unlock the gate they want to open for a time, maybe 5 or 10 seconds. You would have to use a separate SOF for each unlock coil.


It's been a while since I used one of these, and I found them to be pretty limited and expensive. By the time their cost covered enough of the simple SI relays, the I/O count was too limited. Just tinkering around quickly with it here, I'd forgotten how limited it really is. I've found that other brands are more capable and a lot more cost effective. My current go-to is the Keyence GC-1000.

plcgrasshopper said:

I feel the a better question would be, "How do I reference the same output twice using CCW."

Click to expand...

I think the answer is, "You don't." You can arrange AND and OR gates but each EO point can only be controlled in one place.

That's what I was afraid of, thank you.

joseph_e2 said:

Gotcha. You want to keep the doors unlocked [i.e. not prevented from being opened] the whole time unless one is open, then lock both.

Click to expand...

Am I interpreting that correctly?

Because does not make sense (to me, anyway), in that

• IF [neither door is open]
  • i.e. both doors are closed
• THEN [both are unlocked]
  • i.e. both are not prevented from being opened,

but

• IF [one is opened],
• THEN both are locked
  • i.e. both are prevented from being opened
    • but how can both be prevented from being opened if one is already opened?

Seems like a paradox; am I missing something here?

Also, as @joseph_e2 mentioned, there is a race condition:

• if both doors are initially closed,
  • and therefore both unlocked, and
• if both doors are also pulled open at the same moment (i.e. during the same scan cycle),
• then both doors will open before the locks engage,
  • unless the locks engage so quickly that the doors are not fully opened and remain impassable
    • In which case, if just one door was opened and the other left closed, then that door's lock would engage too quickly to allow that one door to fully open.
    • As @joseph_e2 said, this can be resolved with timers, i.e.
      • if only one door transitions from closed to open, then the locking of the other door could be immediate and the locking of the door being opened could be delayed enough to allow it to open
      • but if both doors transition from closed to open simultaneously, then both are locked immediately and remain impassable.
      • Although whether the PLC can execute "immediately" fast enough is an open question.

drbitboy said:

Seems like a paradox; am I missing something here?

Click to expand...

What OP actually stated:

If Gate A is open, B is locked and vice versa

Click to expand...

If one door opens, the opposite interlock will lock preventing both doors from being opened at the same time.

Click to expand...

He then confused the issue by adding

Unless the relay has a signal from both switches that the doors are closed, it will lock both (this is the line of logic I typed out).

Click to expand...

(emphasis added)

This last does indeed beg the question, 'why lock a door you know is open?' You don't need to lock both, just the one that's still shut.

And of course, as noted, the potential for the doors to be opened simultaneously must be considered.

Assuming this is some type of lift or there would be a danger if both were open then it is simple logic,.
If at floor A & not moving then door A should be unlocked, the same goes for Door B & lift at B in other words if a lift is not at a floor or moving then all doors must be locked.
If any door is open then lift cannot move.
If this is a type of lift or access where both doors should not be open then I hope it is an assignment & not a real application.
For safety, there would be double safety contacts, overtravel limits etc.
Also, in this type of application the locks should be Normally locked i.e. loss of power the doors stay locked, access in case of emergency is by a manually operated unlock system only issued to trained personnel.