Currently I have a SLC5/04 that will be connected to a 1761-NET-ENI/B and there will be a PC at the other end.

Eventually I will replace this SLC5/04 to a SLC5/05 and connect it through a hub. Later on there will be a total of five or six SLC5/05.

My worry is that reading through AB's literature: 1761-UM006E-EN-P august 2005 on page 38, it states that when using the 1761-NET-ENI devices I can only hook up 4 devices. With node 1 to 4.

I understand that...at least I believe I do!

My worry is that if I replace the SLC5/04 to SLC5/05 how many 05 can be on the same network (separate network obviously)? First step would be 5 ovens, there is another one already with a SLC5/05 CPU (this CPU is connected to PC for the HMI using VB6, actually it's on the network where any there computer with VNC can take control of the computer at a distance, this uses a second Ethernet card on the motherboard). I would like to add other machinery to it to be able to monitor the entire activity in the factory.

I know that I have got some other topics about this project. I had many advices and I appreciate it. I have a laptop with RSView software on it with which I can build a HMI for the supervisors. Basically is just to gather a minimum of information on stop times on the production.

Thank you to all of you experts.

Pulsar that limitation of only 4 is in the net-eni module and due to the number of "connections" the module will support. The SLC5/05 supports several more "connections" than the net-eni but it is also not infinite. You'll find a lot more and the exact specifics about "connections" on the RA websites. The high strokes follow below.

1. A "connection" refers to a link between 2 devices to exchange data.

2. More then 1 "connection" may be generated depending on the type of machines and the amount of data being exchanged. {For example - a single slc 5/05 and a single pc could consume 8 "connections" if the PC were running an HMI and RSlogix simultaneously.

3. "Connections" can be cached or unchached meaning persistent or renewed each time needed.

4. Processors will refuse "connections" when they have reached their allowable limit.

5. The web page of newer SLC's can be used to monitor the connection counts.

Pulsar,

I'm not an expert, so I hope someone else will weigh in on this, too... But with a NET-ENI, you can still have a large number of PLC's together on the same network. But I believe the 4 device limit refers to the number of active TCP/IP sockets that the unit supports. I think this means that a single NET-ENI will allow the SLC5/04+NET-ENI to have a maximum of 2 peer-to-peer connections with other PLC's on the network. You could increase this by going with a different type of gateway device instead of the NET-ENI, such as the Digi One IAP, which allows up to 64 peer-to-peer connections, which is another option. Will each PLC be talking via message instruction to every other PLC on the network? If so, then yes -- you will need more than the 2 connections. If not, then you may be OK.

Hope this helps!

(Edit: After switching to linear view, I just saw Bob's response that explained it better than I could.)

The mentions about connections counts may be accurate, but there's another limitation as well. The number of "virtual nodes" that you can program into the NET-ENI (these are outgoing connections which appear as additional node numbers across the NET-ENI device to allow serial-only PLC's to send data to TCP/IP capable PLC's) is limited to 4.

If the number of connections becomes a problem, you can always use one PLC to act as a "data aggregator". Not ideal but it works.

As far as Ethernet networks go, the number of nodes is limited to theoretically 281474976710656, but not all addresses are allowed so the real limit is probably maybe only 1% of that.

Do NOT use a hub as you mentioned. These are a really, really bad idea. Some switches (Cisco in particular) will see the amount of packet collisions that hubs cause as a sign of a bad connection and diable the port (errDisable). Also, the TOTAL throughput on a hub is 33% of the bandwidth at best with infinite latency for the entire network segment, so even if you connect 2 hubs together, it affects all devices on all ports of both hubs. With PLC-5's and SLC 5/05's since they are half-duplex only, using a switch gives you full 100% of the bandwidth available on every port. With ENBT's and other devices that properly implement full duplex Ethernet, you get 200% of bandwidth (one packet in each direction) and no collisions thus you get a deterministic network rather than a nondeterministic one.

The only theoretical use for a hub these days is if you are too poor to afford a managed switch for troubleshooting and thus you decide to use a hub to be able to do port sniffing (port mirroring), which a hub does "for free" (actually at a very high throughput cost). All other hubs should be tossed in the garbage can before they cause you massive networking grief down the road.

Ethernet hubs do have another purpose: to look exactly like some models of good switches so that they all get marked with the same price down at the Re-PC technology recycling center where I do my toy shopping.

Ken Have we been burnt by these look alike hubs?

Hey!

I'm glad to see that this topic has been revived.

Can any body suggest a particular model to do the correct job?

Now a days there are mother boards with two Ethernet connections, I was wondering if all the PLC could be wired directly to the supervisor's computer. I want to point out that it is located somewhat in the middle of all the five ovens...

Now here is the question: Can there be many Ethernet card on a motherboard? Will a Visual Basic application be able to communicate?

Thanks.

Best to simply not try to get a PC to survive there. Most aren't rated for anything >100 F, and the so-called industrial PC's end up not working as advertised frequently.



Yes. I have a couple servers with 8 Gbps Ethernet ports. Half are TOE SCSI and half are TOE. This means that the actual TCP/IP stack is implemented inside the Ethernet card itself, freeing up the processor to focus on other things. Why do this? Well, if you connect to a hard drive array via multiple Ethernet cards, it becomes the speed bottleneck. Why do that? Faster and cheaper than the alternative, FibreChannel. What's the upper limit? Well, Windows/DOS isn't particularly efficient at doing this. So you may want to run a higher performance OS such as a Xen hypervisor (which is a modified Linux kernel) even if you put Windows on top of it. The Linux protocol stack is highly optimized and much more efficient than Windows if you are doing very high bandwidth Ethernet I/O.



Routing among multiple ports is handled within the TCP/IP protocol stack. The software on your PC simply looks at the IP address and sends it to the appropriate port. This is done by comparing the IP address of the destination with the Ethernet ports. Best match wins. There are some ways to manually program this too if absolutely necessary.