OPC DX anyone ?

Hi all

A little background first:

I use OPC in several applications to connect HMI software and database software to various PLCs. This kind of OPC is actually called "OPC DA" (DA = Data Access), and is probably the most common variant of OPC out there. The connection is from OPC Server to/from OPC Client.

There are other variants though, one is "OPC DX" (DX = Data Exchange).
OPC DX allows direct OPC Server to Server data exchange which in turn means that two PLCs can exchange data with each other without any OPC Client in the setup.

Here is the problem:

I can find plenty articles that explains what OPC DX is in broad terms.
And I can find some articles on how to write applications that support OPC DX in C or C++.
But I cannot find ANY hands-on documentation how to do this as an enduser.

In Simatic Net I cannot find any reference to OPC DX at all. But OPC DX must be possible because there is a "DX" selection available in the Configuration Console.

In Rockwell RSLinx there is NO reference to OPC DX at all (I dont know if RSLinx supports OPC DX though).

Anyone ?

Aha. There is a manual + sample code on Siemens Support site (entry ID 21523569).

I am studying it now.

It appears that DX connections has to be setup with a special OPC DX Client. It is not part of the standard Simatic Net software but has to be downloaded separately (it is contained in the sample programs).

hmmm... When I try to run the DXClient program I get an error "The image could not be added to the image list".
It would be nice if someone else would try to run that DXClient program.

Isn't Simatics "OPC-DX" their 'Data Exchange' software? If it's what I'm thinking of, it is identical in funtion to Rockwell's RSSQL, in that it automates transactions from a source to a client.

Generally, the source is a PLC, and the client is a database, but that doesn't have to be the case.

No, OPC DX is an open standard.

Siemens equivalent to Rockwell RSSQL is the "Industrial Databridge" (I think, not sure).

I have now tried the DXClient program on another PC and I get the same error message.

On a collegues PC however it works fine.
I think that it is some kind of Microsoft framework file that is missing on my PCs.

I was unaware of the OPC DX mode, thinking OPC was always client-sever, until Jesper MP mentioned it.

I searched the Kepware site, which has some info on their OPC DX bridging software. They use the graphic below to show how they accomplish it
http://www.kepware.com/Products/DX-OPC.htm under the OPC-DX tab



Given what Kepware does - software implementation - getting peer-to-peer by going around the red loop makes sense.

Does it appear that Siemens method is going directly peer-to-peer, like the arrow connecting the A-B to the Siemens PLC above?

Dan

It is neither a Kep method or a Siemens method. OPC DX is an open standard. It must work with any OPC Server that supports "DX".
That an OPC Server supports DX isnt a given thing.
Simatic Softnet does, but I am afraid Rockwell RSLinx does not. These are the two OPC packages that I use the most.

An OPC DX Client is needed to setup the connections between the OPC DX Servers.
The ones from Kep and others are comercial and cost money, whereas the one that is linked to in the Siemens FAQ is free including source.
But I cant get it to work on my PC, something is missing and I dont know how to proceed.

I noticed that the example was written in .net. Every .net program needs the .net framework to run. Try to install the framework hopefully it will solve your problems...
http://www.microsoft.com/downloads/...e3-f589-4842-8157-034d1e7cf3a3&displaylang=en

Have done that. Didnt help though.

I think I will have to wait until it is released as a real product or included in the real Simatic Net software.