ControlLogix IO Configuration

[Archie]

I have a machine with a single ControlLogix chassis with (2) L61 processors and each processor has an accompanying ControlNET card with it for controlling some FlexIO. Each processor controls 2 FlexIO racks over its ControlNET card.

The rack is full and I need to free up a slot. If I replace the 2 ControlNET cards with 1 ENBT, then replace the ControlNET FlexIO adapters with AENT adapters, would the 2 processors both be able to route through the same ENBT card to get to their own FlexIO AENT module?

If this is possible, it would free up the slot that I need.

 

[Operaghost]

Yes, this is certainly possible. The EtherNet module does not require "ownership" to one controller or another while in the local chassis.

That is one of the benefits to having multiple controllers in the same chassis. Bandwidth permitting, they can share these communications resources.

OG

 

[Ken Roach]

Why do the two ControlLogix controllers use individual 1756 ControlNet modules to connect to the FLEX I/O ?

If it's for reasons of physical isolation, logical isolation, network bandwidth, or communication module resources, you're going to lose all of those if you combine the functions of both ControlNet modules into a single EtherNet/IP module.

The principal benefit is that you won't have to put both CPUs into PROG mode to "reschedule" the network if you change something.

If it were my system, I'd start by evaluating the network bandwidth and 1756-CNB module CPU capacity to determine if you can just connect the two ControlNet networks together and create a ControlNet schedule that serves both CPUs.

 

[Archie]

The system was designed to be modular. There is a central control cabinet with the PLC chassis. It was originally a SoftLogix5800 system that was converted to a ControlLogix chassis. The original system had PCI ControlNET cards and ControlNET to DeviceNET converters. After the conversion, the CN2DN were replaced with DeviceNET cards in the chassis.

The system was originally designed to handle 2 pressing cells and a finishing cell. Each cell has it's own ControlNET card and DeviceNET card. The idea was to add cells by adding an additional processor with a ControlNET and DeviceNET card.

The latest system is to eliminate the finishing cell and have 4 pressing cells. So 4 processors, 4 ControlNET cards, and 4 DeviceNET cards will not physically fit in the space with the chassis. The other restriction is an older HMI software that can only address processors in a single local chassis. The HMI uses RSLinx and was upgraded from a PLC5 based system, so it inherited this restriction.

I believe the only reason ControlNET IO was used originally was because the CN2DN did not have enough memory to handle another DeviceNET FlexIO. So the decision was made to use a single PCI card and a CN2DN converter and make one IO block use ControlNET.

So now I have to come up with a way to control 4 cells in a 10 slot chassis. One slot is used for Ethernet communications to the HMI and plant network, leaving 9 slots to work with.

One thought was to have a processor with an accompanying ENBT. In the cell, use an Ethernet to DeviceNET converter. This was a less preferred option because the original CN2DN was one of the weak links in the system that caused down time.

So my next thought was a processor for each cell with an accompanying DeviceNET card and one common Ethernet card that would pickup the task that the ControlNET card now does. Ethernet is preferred because daisy chaining through the cells is not always convenient.