Re: Ethernet Switch with 48 Ports connected to 48 PLC

Re: Ethernet Switch with 48 Ports connected to 48 PLC

Gentlemen:





The instructions or the command I’m sending to these PLC is not as important as my strong curiosity to find the answer to the following questions. The questions all assume that all the PLC’s are within 50 feet from the Ethernet Switch.

• Will all PLC’s received this instruction or command EXACTLY at the same time?
• Will there be a small delay in milliseconds between one PLC and another receiving the instruction or command, if so how much?
• Can I use my Ethernet Card to send this instruction or command to all 48 PLC’s using the Ethernet Switch?

For the sake of this argument I’m using an AD 260 CPU with an ECOM card.



Thanks all for your answers.



Andy

If you are thinking of doing a 'broadcast' message, this is from the Host Engineering web site -

FAQ0006
01/29/03 qty=1
Q: Can the ECOM do a broadcast message?
A: No, not directly.

Click to expand...

AND TCP/Ip on ethernet is not deterministic. You would need something like ControlNet.

I don't know how AD does this, but here is how A-B Controllogix PLC works
It can do Ethernet muticast using Produced/Consumed tags.

Because this transsmission is done over UDP, it will go to all ports of the switch, unless this is a managed switch and it has IGMP snooping or VLAN enabled. I know that there is a limitation on the amount of consumers, but do not rememeber number - it is less than 48.
This will be scheduled connection with some RPI (Requested Packet Interval) and it will repeat over and over. It is still no guarantee that destination will receive and accept packet.
Conncetion failed only if no response received in 4*RPI time, but it will try to re-establish it.

If message instruction used it wi istablish point to poit connection only and will be transmitted only out switch port with destination PLC connected. Message will fail if did not get respose in 30sec(default)

If you are sending individual instructions to individual PLCs then they are sent at 48 individual times. They can be spaced very closely to each other (since Ethernet transmission is very quick) but each one still takes time. Only some sort of broadcast, in which the exact same message, transmitted once, is heard by all the units at the same time, would have any hope of arriving anywhere near the same time. But, for these one-at-a-time instructionst, if 'EXACTLY the same time' means within the same minute, then probably. If within the same second then possibly not. If in the same tenth of a second then probably not.

I know that there is a limitation on the amount of consumers, but do not rememeber number - it is less than 48.

Click to expand...

I think only limitation in CLX is number of connections. Max should be 250 or 255 as I remember.
But anyway, seems that Ethernet/IP one of the best Ethernet based network (producer-consumer model, etc).

Thanks all, this is what I needed to know.

Andy

I think only limitation in CLX is number of connections. Max should be 250 or 255 as I remember.
But anyway, seems that Ethernet/IP one of the best Ethernet based network (producer-consumer model, etc).

Click to expand...

This is correct, CLX processor has 250 conncetions limit total and ENBT has a limit of 128 connections.
Each tag will use amount of connection equal to amount of consumers it has (47 in your case).

Max amount of produced tags is 127.
See 1756-RM094.
I was not correct in the earlier post, I thought it is 32