Retain output state in Program Mode

I'm curious..
I have an 1768-L43 Rockwell Controller that communicates via one of the ENBTs to an Intellicenter MCC. The MCC controls certain conveyors/elevators, but also use a 1769-OA8 module to manage a permissive hold/bypass for equipment ahead of the MCC controlled equipment. I was asked to put this in place because the equipment ahead of the conveyors involves 2 large gas fires dryers with 4 burner controllers each, and restarting that equipment for minor maintenance was very time consuming. Usually these are put into low-fire for short periods when maintenance is performed. Since the permissives for the dryers are handled through the 1769-OA8, is there a way to retain an output's status, if I chose to put the controller into "Program" mode to make major changes to the program? I have several drives I was wanting to add some links to in my program, but can only do while in "Program" mode.
I've Thought about maybe wiring the permissives through my NC connection on the relays in my cabinet, and then just having my program keep the relays energized during normal operation....the problem with that being that my fail state then would be a bypass, which is not what I want.

Check this PDF out and see if it's what you're looking for (particularly pages 34 & 35):

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1769-um020_-en-p.pdf

Program Mode (PM)
This configuration selection provides individual Program mode
selection for the output channels. When this selection is disabled
(PM = 0), the module holds the last state. This means that the output
remains at the last converted value prior to the condition that caused
the control system to enter Program mode.

I strongly urge caution with what you propose !!

you said the magic word - GAS !!
All gas fired equipment that I have dealt with has a start up, shutdown, and purge procedure to prevent explosions.
In my opinion, what you propose is bypassing those safety procedures.

You will have to get with the Dryer Manufacturer, local osha people, management, safety, engineering, maintenance, and operators to discuss what you want and do a risk assessment. that will let you know what you can / cannot do. If the dryer manufacturer says no, you're done ! they will document what you propose and keep in in their files to cover themselves in case you go against their recommendations and something goes wrong.
management will then have to get with your insurance company to discuss the changes.

As for the plc process, I will leave that to others who know your unit better than I do.

regards,
james

Fair point James. I haven't dealt with much gas fired equipment and am not sure of the regulations on it.

The gas dryers have 4 burners each, and each burner is managed by a Honeywell controller that monitors flame, ignition, dryer rotation combustion air.....
The output I wish to retain are are permissives to an elevator from the dryers, and if it shuts down, the dryer gearboxes shut off, and kill the flame controllers...an on, and on. In total about 30 things shut off through all the conveyance permissives. What I purpose has nothing to do with the actual flame controllers.

Thanks for the information....It's what I was looking for.

Thank you.

What I would do is to draw a line diagram of the plant processes involved.
Expand on the line diagram and detail what needs to be kept on.
If the dryer is bypassed, Is the dryer gearbox part of the dryer?
you may not be able/allowed to shut down part of the dryer and leave another part running !!

You may need a keyed selector switch position 1 - run.
position 2 - maintenance mode - key removed or vice versa.

use the keyed switch to enable the permissives.
simulate the program using a dummy program and get what you want running.

the problem I see is how to switch states from maintenance mode to run mode without shutting down everything.

you will still have to have a meeting and do the risk assessment.
we do something similar, but it took a good while to make everyone happy.

james

I agree with James, this is not a simple question.

My preference would be to make the changes on the burner system. "Maintenance Mode" needs to exist on this control system. If it is appropriate to go to low fire when the outputs from the PLC all go off, then the burner controls is the right place to do it. Make the modifications here. This way you can choose what to keep running. If it is preferred to stop that elevator, but go to "low fire" it is possible.

I would strongly resist "fooling" the burner controls by maintaining outputs while the PLC is in program mode. That just doesn't sound like a safe thing to do. Nothing about this approach causes the burner controls to behave in a safe manner.