Dual rendundancey and DF1 communications for controllogix HELP

[paulb67]

does anyone know how many DF1 cards a ControlLogix can handle. I have designed a system with 6 plcs. The specification states that the comms MUST be point to point and it must have dual redundancey at the SCDADA connection. This means that i have 1 node in the network which requires 2 control logix plcs that are connected to 2 systems and eachother and each is connected to SCDADA meaning 6 DF1 connections. Can this be acheived ?????

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[davidg68124]

I have not seen anything like this personally, but I will ask this, when you are referring to DF-1, are you referring to the Serial connection? IF so, I had a situation that was going to require this, so I am curious as to how to do this as well.


I had some ideas, but never any time to pursue it.

David

 

[Contr_Conn]

ControlLogix has only one DF1 port.

You may be able to expand this with 56-MVI module from prosoft

 

[davidg68124]

Actually, that is what I have right now. But IF I set up redundant CL racks, with the Proper MVI cards in each, how would I handle the switch of the COmms?


Like I said, I had some ideas, but never pursued it.

David

 

[Contr_Conn]

You can't put MVI in redundand rack. only in I/o rack.
BTW, redundand processor can't use serial port also.

 

[Ken Roach]

This doesn't make sense, Paul. You're saying that the specification requires you to use point-to-point connections to perform the functions of a network.

You could conceivably put six MVI56 modules in a remote ControlNet chassis, but that is a waste of money and brainpower. Ethernet is the way to get this done correctly.

ControlLogix redundancy allows EtherNet/IP modules to "swap" IP addresses, making them easy to communicate with from SCADA and other controllers.

If the specifiers say "that's what the spec says, you have to comply with it", buy them a Dilbert calendar and consider finding another project to spend your time on.

I've been in plenty of situations where the specifying engineers manage to put mutually exclusive requirements into a spec. I've always dealt with it by choosing the proper design for my system, and never had them come back and demand that I redesign to the impossible.

 

[gluca]

Hello Ken,

do you know if is possible to connect an Operator Panel (third party one) to a ControlLogix Redundancy System through the DF1 port?
In other terms, how the redundancy system deals the serial communications in case of a switchover?

Thank you,
Luca

 

[RSL]

It is my understanding that you can use the local serial port in a redundant system.

You have to "build" a switch that uses a cube relay or similar. This switch will transfer your serial devices connection to the primary controller. The relay is operated by a signal from the SRM module. If you look at the SRM module it has a set of dry contacts that change states on switchover.

I cannot recall the details, but that is the basic premis. I read this in the documentation a LONG time ago. Just can't remember the details.

I have not ever seen this, and I have never attempted it myself.

I agree with Ken, the correct way to connect HMI's,SCADA etc. is with Ethernet. I have done this, it does work, and it is super easy to configure. Ethernet is THE way to go.

RSL

 

[gluca]

Thank you, RSL

 

[Sheldn]

When using redundant PLC racks with EtherNet cards in the I/O racks or other communications modules, the CNET communications is managed by the hardware/firmware. You can plug the comm modules into the redundant PLC racks, but the redundancy will expect the same modules in each rack. Fail over of a rack is based on single point failure of any module in the rack. For example if a Ethernet module fails in the primary, it will fail over to the secondary.

The system architecture that you are describing sounds like a problem that is not only waiting to happen, but happened. I would suggest you get more details from the designer regarding what they want to accomplish. Two Ethernet cards in the I/O racks will give you more redundancy of the communications bus than you could ever hope to use. I would guess that the MVI modules could handle the switch over of the PLC also so locating these in the I/O racks sounds like the best bet.

Serial - Point to Point using DF1 protocol is very common in connecting to modems or radios.

I would not recommend connecting an HMI through the serial port to redundant PLC processors and then using an Ice Cube relay to switch the serial port on failure. It may work though.