hello, i'm working on a project where by if our dock door is open, a production door must stay closed. Only when the dock door is closed can the production door open. I was told to use interlocking? can someone please help me, it would be greatly appreciated.

 

You don't need a programmable device for this application. Install a solenoid-operated lock on the production door and a normally open limit switch (electomechanical or magnetic)on the dock door. If you need an emergency override (to allow someone to exit the production area if dock door sticks open), put a pushbutton on the wall so the door can be opened while the button is depressed. Run the solenoid power through the limit switch and optional pushbutton. You might need a relay. You should work out the details of the circuit on paper in a ladder diagram.

If you use a PLC, the program will be the same connections, only in software.

 

Since the logic is simple enough, a ladder example (1 rungs) is all that is needed. You will have to have a prox or some other kind of limit switch on the open side of the dock door in this example. Otherwise replace Dock_Sensor with the open command sent to the dock door (if it is tied in with the PLC). If this ladder is below all other rungs that can write to Prod_Open_Command, it will be interlocked.


Prod_button Dock_Sensor Prod_Open_Command
-| |-----------------|\|---------------------( )

 

Well one way to do it is with an electromagnet (assuming they are steel doors or use a steel plate) to hold the door shut. This would assume the door is already closed and then via a limit switch, reed switch or whatever the the other door then cannot be opened. You could also add a mechanism to close the door automatically if the other one is open.

 

Use limit switch or proximity switch for sensing the door close and you can easily make the interlock with PLC.One door is close then only Open command for other door will go use AND gate for that viseversa

 

Many industrial doors have an E-Stop input, or a form of external cutout (interlock) input, into which a normally closed contact is wired. If you dock door is closed, this switch should be closed, and in any other position this contact should be open. A simple limit switch can be installed on the dock door if this type of output is not already available.

This same sequence can be repeated if the dock door is required to not open if the production door is already open.

Tom Reiter
ASI Technologies, Inc.
Makers of high-end industrial and pharmaceutical door systems.

 

thank you for your help, but i'm still a little confused. what would the actual logic look like for the interlock? and how would the AND gate tie in?

 

thank you for your help, i was woundering if you could though help me with what the actual circuit would look like? i'm not too sure how to construct the ladder diagram? or if you know a web site i could visit, or give me any info on where i can learn more it would be greatly appreciated, thank you for your help already.

mike

 

mike,
If this is a safety issue then you ought not to use a PLC. hard wire each door enable via contacts on the other door. better still use a mechanical interlock if possible, a sliding bar
which only allows one door at a time to open.
if it is just a matter of stopping a through draft then it's still easier to use hard wiring, or an intelligent relay, like a LOGO

marc

 

Mike,
The interlocking just means that you basically put contacts in series. This prevents a contact from affecting an output unless the 'permissive' contact is made.

A possible rudimentary method to interlock the system you described might look like this:

Assumptions:
You have a normally-open limit switch on your dock door closed position.
I'll call it DockClosedLimitSW.
You have a normally-open pushbutton that the operators use to open the production door. I'll call it ProdOpenPB.
You have a coil that will open the production door when on. I'll call it ProdOpenCmd.
I assume that no other interlocks, latches, or bypasses are required.

Ladder Logic:

ProdOpenPB DockClosedLimitSW ProdOpenCmd
-----||-------------||--------------()

This will allow the operator to open the production door only if the dock door is closed.
Hope it helps,
Curt