LabVIEW RSLinx and DH485

[LV_Pro]

Good Morning All,

    LabVIEW 8.0 woo wee!

   Sorry, my question is about using LabVIEW 7.1 with RSLinx. Specifically my customer wants to build a LabVIEW user interface that can both receive information from and send values to a AB microLogix 1500 over DH485. He wants to know if this can be done using the RSLinx OPC server and datasockets from within LabVIEW without adding the DSC toolkit, just native LabVIEW. I'm not sure myself and the my research hasn't completely cleared up the question. As an example, the LabVIEW examples shipping with 7.1 have this statement "This example uses the DataSocket VIs that shipped with versions of LabVIEW prior to version 6i.  These VIs are provided with LabVIEW 6i for compatibility.  The DataSocket primitives shipping with LabVIEW 6i are not currently fully compatible with OPC.  When using DataSocket to connect to OPC Servers, use the older compatibility DataSocket VIs."  This seems a bit dated as I'm using LabVIEW 7.1, it appears that this problem either wasn't fixed, or the examples weren't updated. So has anyone experience talking to a Micrologix 1500 with LabVIEW, over DH485, with or without using RS Linx (customer hasn't purchased that yet, has the RS Linx lite, which appears not to have the OPC server according to a literature search)?

  Any help/suggestions (with in limits   ) will be welcomed!

As always, thanks!

Putnam Monroe

North Shore Technology, Inc.

[Khalid]

Hi Putnam,

Not sure if you've seen the following post on LAVA..  it has some discussion on this topic:

http://forums.lavausergroup.org/index.php?showtopic=1663

Regards,

-Khalid

[Donald]

Putnam,

“This seems a bit dated as I'm using LabVIEW 7.1, it appears that this problem either wasn't fixed, or the examples weren't updated.”

I think it’s the latter (not updated). There have been a few posts like this one indicating that the problem with the DataSocket primitives was fixed in LV7. I thought there had been something about the fix in one of the LV or DSC upgrade notes, but I couldn't find anything in a very brief look.

[LV_Pro]

Thanks to both of you. I'm still in the research phase prior to presenting a proposol to the customer, don't want to get burned from not knowing some of the "gotchas".

P.M.

[Ben]

gotcha's

A)

DataSocket overhead scales linearly with channel count. This is not the case with DSC.

I took on a project that was prototyped using DataSockets. It was OK for a couple of I/O points but testing showed that scaling it up would lead to disaster.

DSC on the other hand was able to handle the 3000 tags with time to spare.

B)

Handshaking via datasockets and DSC is not a blazingly fast operation.

C)

OPC servers and Tag engines do not neccessarily execute your write and read requests in the order you post them. Watch for possible race conditions.

Ben

[LV_Pro]

Good Morning Ben,

    Thanks for the input. At the moment the customer is saying that there should only be "a couple of dozen" tags, but I will be sure to try and get a feel from him whether this is firmly fixed or just a preliminary. Of course if it works at a couple of dozen and they come back in 6 months, having been suitibly warned up front, and need to go to a couple of hundred, well it will require a redesign of the concept.

Hope things are going well with you!

P.M.

[unclebump]

Don't forget the storage capabilites of Citadel as well. The ability to combine numerous plc variables(even from multiple plc's with OPC) into a cluster of unique data. Then save this clump of data into a memory string tag and Citadel for historical purposes. Show them how you can turn labview DSC into a multichannel logic analyzer. I bought the professional control edition of Labview/DSC and have not been disappointed.