ControlLogix5K 2nd Ethernet Card

[DaveW]

I want to add a second 1756-ENBT to the PLC local rack to handle critical data transfer to/from a SCADA system. The 1st card is already loaded with the typical SCADA data collection stuff. Will this work and give me the priority I need for these critical tags? Should I put the 2nd card on it's own network?
Thanks
DW

[PhilipW]

There are several aspects to the kind of performance gains you are looking for:

1. The capacity of the network.
2. The capacity of the ENBT's
3. The capacity of the CLX processor.

In the first case I will assume that if you are using decent switches at 100M then the network capacity will not be an issue, so whether the second ENBT is on the same network segment will make little difference.

The ENBT's can handle 5000 frames/sec which is reasonably fast. Unless the existing card has an average load of more than 40% of that, then adding another ENBT is not likely to show much performance gain.

The bottleneck may well be the CLX processor. The CPU handles all comms asynchronously during the "System Overhead Time Slice" set in the Processor Advanced Properties. By default this is set to 20%, but increasing it to say 40% will open up more bandwidth for comms. Of course this comes at the cost of longer scan times for the Continuous Task.

What you want to do is perfectly reasonable, I have seen many CLX systems with two ENBT cards, but the reason for this is usually to segregrate point to point PLC to HMI comms, from a general sitewide PLC prgramming and data collection network. This is done for ease of administration reasons as much as performance reasons.

[Contr_Conn]

Previous post already covered most important things to consider.

I've seen multiple ENBTs in one rack and this will help with your communications.

Most important to keep in mind that processor services ALL comms druring "overhead time slice", not just HMI/Scada requests.
This include all message instruction processing, serial port service, etc.
Also just keep in mind that it is not reasonable to incerease time slice above 40%.

Also watch ENBT CPU utilization: you most likely will hit 100% before reaching 5000 packets/per limit. Keep CPU at 75-80% max.

[KCDave]

The ENBT can only handle a fixed number of connections. Once you exceed this you must add a second ENBT. I forget what the limit is but its in the documentation.

Also, there are other factors that affect the network, the switch is a big ticket item. It must be full duplex capable on all ports, have IGPM snooping and port mirroring. Most switches have these today.

[Contr_Conn]

Originally Posted by KCDave

The ENBT can only handle a fixed number of connections. Once you exceed this you must add a second ENBT. I forget what the limit is but its in the documentation.

Also, there are other factors that affect the network, the switch is a big ticket item. It must be full duplex capable on all ports, have IGPM snooping and port mirroring. Most switches have these today.

With ENBT and HMIs you most likely hit CPU limit before reaching connection limit.

You definately need an industril type switch , but IGMP snooping necessary ONLY if you doing Produced/Consumed tag ot I/O control over Ethernet to block UDP multicast. It is not necessary for HMI traffic as it uses TCP messaging

[DaveW]

Originally Posted by Contr_Conn

Also watch ENBT CPU utilization: you most likely will hit 100% before reaching 5000 packets/per limit. Keep CPU at 75-80% max.

Where can I monitor this? Are you talking about the Windows task manager on the pc polling the data? In this case, I guess it's the RSLinx service.

Thanks for all the advices!

[Peter Nachtwey]

I have customers that use 4 ENBTs in the same rack.
1 for the HMI.
1 for the digital I/O ( flex i/o )
1 for the motion controllers.
1 for the scanner/optimizer

This is for a saw mill or veneer application. I know this seems like overkill. I think it is too but then they didn't need to bother with routers.

[PhilipW]

Just to add to Peter's comment above...I have worked on one of these systems that he is referring to and they are really quite something.

To top it off we would not only have RSViewSE hammering away at it, but in addition we could have up to FOUR engineers doing on-line edits at the same time via Wireless 802.11 network connections. A properly set up 1756-L6xx processor has fantastic bandwidth.

[Contr_Conn]

Originally Posted by DaveW

Where can I monitor this? Are you talking about the Windows task manager on the pc polling the data? In this case, I guess it's the RSLinx service.

Open Internet Explorer and type IP address of your ENBT module.
Module has internal diagnostic webpages, were you can get a lot of usefull information.
With FW ver 3.x layout of these pages changed for easy navigation and gives more accurate info.