S7 OPC VB & DCOM

Hi everyone,



This is my first time in this forum so please be gentle.

Sorry if this is rather long.



My company’s plant has about 12 PLCs: S7 400 & S7300.



The plant is split into several areas with PLCs in each area communicating to remote I/O via ProfibusDP. Communication between the PLCs in each area is also by Profibus .



Each of the areas is controlled by HMIs (In Touch or WinCC) via Ethernet. The Ethernet network extends between each of the plant areas but no inter-PLC communication takes place. Level 2 software in each area is also connected to the Ethernet network but I have no details of the implementation. (I’m told that the software accesses the PLC’s directly and data blocks in the PLCs seem to confirm that this is true) The Level 2 applications are again local to each plant area. (The reason the areas are connected by Ethernet is that Level 2 in each area accesses product analysis data from a remote PC in the plant lab. At the lab the networks connect via a common hub)



Using a PG and Step7 V5.2 sp1 I can communicate with any PLC around the plant from an Ethernet hub in any of the plant areas.



I’m trying to implement an application in VB6 that will read various data from each of the plant PLCs and produce plant wide shift reports. (Individual area Reports are available at each HMI station but I want an automated plant summary.)



I’ve tried the SimaticOPC automation example that came with Simatic net but only with the simulated connection and I’ve just downloaded Kepware’s OPC server which seems easier to configure.



So at last to the questions:



I assume that the existing HMI systems already communicate via OPC.



If that’s the case will adding a PC running the OPC server ‘conflict’ with the existing HMI connections?. (I have no knowledge of the HMI or how to access the software)

(I’ve read a little about collision detection etc but I’m unsure of the impact my application would have on normal HMI operation)



There seems to be a ‘port’ setting in Kepware. Should I use a different port than that suggested by Kepware and if so would I have to change settings in the PLCs? What would I need to change if I used the Simatic OPC server?



I understand I will need to use DCOM if I wish to run my client application from several remotely connected PCs. Any information or hints to point me in the right direction would be appreciated.



And finally if I succeed in writing my application will there be any impact on the performance of the PLCs that run the plant? (My data collection can be very slow if necessary.}



As you can see, I know very little about networking in general so any assistance would be welcome.

If that’s the case will adding a PC running the OPC server ‘conflict’ with the existing HMI connections?.

Click to expand...

You will use one more connection on each acessed CPU. You will have to investigate if there are connections avaliable. It is probably not a problem, and if no connection is available it will only mean that the OPC server cannot connect to the PLC. The allready connected HMIs will remain connected.

For DCOM, search on Siemens support site for "OPC DCOM" and there should be an instruction.

And finally if I succeed in writing my application will there be any impact on the performance of the PLCs that run the plant?

Click to expand...

There can be a slight increase in the scan time on the CPUs where you use "unconfigured connections".
But I doubt that there will be any real impact.

Thanks Jesper,

I've managed to connect using Kepware but I'm still having problems with Simatic Net. (My problem is basically solved but it's annoying that I still can't connect to a Seimens OPC server as my plant is almost totally Siemens}

I've read Jesper's download "How to set up OPC with Simatic Net.doc" and this makes more sense of the Siemens documentation. However the same Siemens documentation "Commissioning PC Stations - Manual and Quick Start" also refers to 'PG Operation' and 'HMI'.

As I'm using a PC with a standard Ethernet card I'm wondering if PG Operation is in fact what I should be using.

I'm still vague concerning configured/un-configured connections. I was under the impression that by using an OPC Server that all I needed to know was the PLC address.

If anyone can suggest a good textbook or can offer an understandable explanation I'd be appreciative.

Ray4242

Where do you see the "PG operation" and "HMI" ?
If you are referring to the setting in the COnfiguration Console where you can choose "PG operation" (I think from memory that it is what it is called) and "Configured mode" then for OPC you must allways use the "Configured mode".
Anyway, there is no problem with using a normal ethernet port.

The configured connections can only be made with a project that is integrated in STEP7. S7 PLC and PC Station in the same project.
The difference is that the CPU will have to do more of the work with an unconfigured connection. With a configured conection, the CP will do all the work. (that is how I understood it).
Dont worry too much about it. Use an unconfigured connection.

For ethernet via Softnet I vaguely remember a Siemens FAQ about having to specify the slot of the CP and not the slot of the CPU. You may have to check up on that.

Have you come so far that you can test the connection with an OPC test client ?

Thanks again Jesper,



My OPC Client program is working fine using the Kepware OPC server. I can read data from DBs etc on any of my networked PLCs with no problems but I still have no success using the Simatic NET OPC.



The reference to "PG operation" and "HMI" comes from the Siemens manual:

SIMATIC NET Commissioning PC Stations - Manual and Quick Start (Release 8/2004 C79000-G8976-C156-05) which I believe I downloaded as ‘mn_ncm-pc_76.pdf’ from Siemens web site. Section 3: PG Operation contains the 'HMI' reference.



Using Kepware I didn't need to use Step 7. I just 'told' Kepware the address of the CP and the CPU rack and slot number. I'm led to believe that performance is good but for reasons stated earlier would prefer to use the Siemens server.



The HMI systems on my plant (IN touch & Win CC) have no configured connections visible in Step 7 (hardware or network view) and these applications run on PCs with standard Ethernet cards.



It seems to me (but I’m often wrong) that the ‘PG Operation’ is what I really need. My application is relatively simple in terms of OPC as I only need to poll the PLCs at fairly lengthy intervals



The first part of ‘PG Operation’ setup seems straightforward but unfortunately the manual (p45 & 46) refers to ‘adding an item’ and shows an input box with a syntax that I can’t get to grips with: (S7Verb|VFD_OPC|…etc). Apparently information regarding this entry is in the OPC manual but it’s either unclear or I’ve not been able to find it.



Siemens (in my view) produce excellent PLC products and for those who know how to use them properly they provide enormous versatility and reliability. I just wish they could write understandable manuals!



Ray 4242

I dont have the manual at hand.

If you follow my guide you will see that you have to switch from "PG mode" (or something like that) to "Configured mode" for the "index" in the PC station that contains the ethernet card.

"PG mode" means that the ethernet card will follow the settings set at S7ONLINE in the "Set PG/PC interface" utility. PG mode is sufficient for programming, and sometimes also for HMI software but not for an OPC connection.

"Configured mode" means that the ethernet card will follow the settings that is set for the PC station project. You need this because of the configured OPC connection.

Dont get confused because of the refernces to "Configured mode" as well as "Configured connections" and Unconfigured connections". The firstv doesnt have anything directly to do with the last two.

You can set up an Unconfigured Connection. That only means that you have to manually specify such things as PLC address, rack number and slot number.

So, to sum it up:
In the Configuration Console, select Configured mode for the index you have assigned to the ethernet card.
When setting up the OPC connection in NetPro you can choose to set it up as an Unconfigured Connection.

I’m finally communicating with my client application with VB6 and the Siemens OPC server. Thanks to Jesper for your help and patience.

Thanks also to plctalk.net for the forum and the members for sharing their knowledge. Hope I can contribute some answers in the future.

It appears that to fully participate in plctalk.net I need an ‘Avatar’. As I’m new to forums of any kind I looked the word up (I thought Avatar was some type of god!)

Dictionary,com states:

avatar \AV-uh-tar\, noun:
1. The incarnation of a deity -- chiefly associated in Hinduism with the incarnations of Vishnu.
2. An embodiment, as of a quality, concept, philosophy, or tradition; an archetype.
3. A temporary manifestation or aspect of a continuing entity.

It’s a tough choice!

Ray4242