PLC/PC Communication Standard ???

I have red many questions for PLC/PC communication problems on this forum and I have had them myself quite enough.
Common Standard missing for PLC/PC Communication.

OPC is method when data have got to PC, but it is one level too late. OPC-Server polls feched variables from PLC, it is not modern way and Causes unnecessory trafic.
In modern way PLC sends data to PC when data has changed (Change Of State). PC do not fetch (or Read) from PLC! PC applications just waits events 'data_has_changed'. PLC can send data in selected interval if necessory and includes some counter or timestamp for cummunication checking as PC can sent to PLC.

I have attached proposal table for common and open data communication method for PLC/PC. Attach: http://www.kolumbus.fi/sepala/plc_Pc_Comm.htm

I hope your responds.

One day Sep I aim to know half of you know!

I agree, there are too many protocols.

Seppo, have you looked into Ethernet/IP? Is has many of the features you have on your wish list.

Protocols such as Ethernet/IP require a lot of memory and processing power. Any protocol that similar to that on your wish list will also require a lot of processing power and will not be cheap to implement.
AB's ENBT cards have a Power PC chip with a built in Ethenet interface. This is not a cheap processor, but it does provide plenty of processing power.

Automation Direct communicates between PLCs using raw Ethernet packets and is very easy to implement as there is no TCP/IP stack. The Automation Direct Ethernet modules are also very fast for the amount of processing power they have because the protocol they use is very simple. By reducing the amount of procesing power and a code size, Automation Direct ( actually Host Engineering ) has manage to make a very in expensive Ethernet interface.

I don't think that PLCs should waste their time sending web pages. A local application should run on the client so that formating data does not need to be sent over the Ethernet.

Peter, I find something common for all manufacturers and common
powerful interface for local and remoted applications. There could be more than one PLC and many Computers where needed communication.

One way is use Broadcasting from PLC or from anyone else to all the others, sometimes we must know all of PLC memorys for BlackBox as in aeroplane or for researchers.

Could not agree more about the web page nonsense but a lot of people disagree. They want web pages so they can view information from all over the world.
Wherever possible I use Omron Controller Link. Most SCADA systems have a copy of Omron Cx-Server middleware built in. The SCADA requests information from the middleware and the middleware returns the results to the SCADA. This will communicate with all Omron PLCs via Ethernet (YUCK), Controller Link, Sysmac Link or serial (YUCK). Controller Link is fast and seamless. One project I did recently with Controller Link and Citect had Citect kurnel reporting 15,000 digital reads per second at 2 meg network speed. There was also plenty of traffic PLC to PLC. Very impressive, cheap, seamless and easy to set up.
Generally I try to use a proprietary comms into a SCADA as it usually works better and mostly is far cheaper.
Not impressed with Ethernet IP yet as it is in it's infancy. ODVA have taken over formulation of the standards for IP so there is some hope for it. They are really well organised.
zzzzz

BobB, I have used FinnsGateway for broadcasting with Fiber optic Ethernet with 4 pcs Omron CS1, 4 pcs SCS-Scada station and 2 other PCs. We sent 2000 bytes data in every 200 ms. Capacity was much more, but Scadas can updates their views in 200 ms.

seppoalanen said:

Peter, I find something common for all manufacturers and common
powerful interface for local and remoted applications. There could be more than one PLC and many Computers where needed communication.

One way is use Broadcasting from PLC or from anyone else to all the others, sometimes we must know all of PLC memorys for BlackBox as in aeroplane or for researchers.

Click to expand...

Again, check out Ethernet/IP.

Ethernet/IP Library

It supports multi casting. It runs on Linux.

It is also possible to have an Ethernet application stack. This is a software package that included the protocols of several PLCs. This way the Ethernet port can be 'multi lingual'. Our product can communicate with Omron's, ABs, Automation Directs and TI505s all at the same time. Every connection can detect which protocol being used to communicate with it and reply using that protocol. I have posted our little demo/test program a couple of times that does this.

seppoalanen said:

Not impressed with Ethernet IP yet as it is in it's infancy. ODVA have taken over formulation of the standards for IP so there is some hope for it. They are really well organised

Click to expand...

Why, it works well. Many of our customers use Ethernet/IP to do get 5 millisecond update rates between our product(s), RSView and Control Logix plcs. That is pretty quick updates for Ethernet.

We have been involved early on with Ethernet/IP. We had a specification a year before it was formally released. I know there were some change between the pre release document and the final release specification. Since then, I don't think the have been any changes and that was a few years ago. So what do think is going to get better, the specification or individual implementations?