Reading a few WonderWare (RSLinx?) tags from LabVIEW 6.1

[Tim Erickson]

We have a customer that uses WonderWare and Net DDE. We need to read a few WonderWare tags from a LabVIEW application running on a separate computer. I am sure this has been done before but I cannot find a good example that demonstrates the format to use for computer name, service, topic, item name when talking to WonderWare. I could only find an Access and Excel example.

All we need to do is connect to and monitor a few existing tags in WonderWare from another computer on the LAN running a LabVIEW application.

I would prefer to use OPC but they have been using Net DDE for years and do not want to change.

We cannot use LabVIEW DSC.

[Rolf Kalbermatter]

We have a customer that uses WonderWare and Net DDE. We need to read a few WonderWare tags from a LabVIEW application running on a separate computer. I am sure this has been done before but I cannot find a good example that demonstrates the format to use for computer name, service, topic, item name when talking to WonderWare. I could only find an Access and Excel example.

All we need to do is connect to and monitor a few existing tags in WonderWare from another computer on the LAN running a LabVIEW application.

I would prefer to use OPC but they have been using Net DDE for years and do not want to change.

We cannot use LabVIEW DSC.

Well, without LabVIEW DSC you will have to write your own DDE server. Let me tell you that that is no fun at all, as DDE has a few drawbacks nowadays. First it is an old technology and in some areas rather strange to use for nowadays understanding. Second it has a few quirks including in the LabVIEW interface and there is NO support for it anymore. Nobody at NI is going to look into a problem if you can't get something to work and there very likely won't be a bug fix of some sorts if it turns out to be not working due to some obscure DDE incompatibility with your Windows system.

That said an Excel example is more or less all that is needed. It should show you the service name as well as the topics. What you may be running into is the NetDDE setup that is needed for networked DDE communication. There have been tutorials on NetDDE configurations for LabVIEW DDE on NI's site, but they were written for Windows 3.1 and Windows 95. You may be likely running into access right problems on more modern Windows NT based systems and need to figure out how to setup your system right to get around them before being able to access a remote DDE resource.

Do the Excel examples work over the network, because that would indicate that the NetDDE configuration is more or less correct.

Rolf Kalbermatter

[Tim Erickson]

Thanks for the reply.

I do not think that I need to write a DDE server as our application will only be reading tags, i.e. client only. There will be no communication back to WonderWare.

I will try the Excel example over the network and see if I can get it to work.

[Khalid]

Hi Tim,

Are you interested in (computed) tags from Wonderware, or IO tags from RSLinx? If it's the latter, and if the RSLinx is an OEM version (or better), then it is an OPC Server by default. You could browse to it using the front-panel DataSocket item browser.

If you _have_to_ use DDE, try the following in Excel (first, on the same machine as RSLinx):

Cell formula - "=RSLinx|topic!address"

E.g.: "=RSLinx|PLC1!N7:0"

If that works, you should then try the NetDDE in Excel. And then in LabVIEW.

If it's the former, i.e., computed tags from Wonderware itself, maybe you should contact Wonderware to get the DDE Application, Topic, Item, etc. (I don't think Wonderware/InTouch is an OPC Server by default... at least it wasn't a few years back).

Hope this helps.

-Khalid

[Tim Erickson]

Thanks for the reply, those are some great suggestions. I will implementing this early next year and now have some information.