OPC custome and automation I/F

[Maryam]

Hi all,

Sure it's clear I'm just a beginner in OPC. I wanna know what are OPC custom and automation interfaces?

Thanks... 

[Sreedhar_T]

Me too... I also want to know about the speed and other constraints in using labview with OPC.

[SachaE]

Hi Maryam,

  a fabulous resource for opc programming is here : http://www.opcconnect.com/

http://www.opcconnect.com/history.php mentions the custom and automation interfaces so they're part of the standards which can be found here at the opcfoundation

http://www.opcfoundation.org/Default.aspx/01_about/01_whatis.asp?MID=AboutOPC

there's a forum there with lots of answers on it.

Another great resource for Process control stuff is http://www.control.com/

These should give you some pointers about what's involved at the lower levels.

Thanks

Sacha Emery

National Instruments (UK)

[SachaE]

Hi TSreedhar,

Can you be more specific?

Timing will be relative to the OPC server you're communicating to and it's update rates. If networks are involved too, then there could be jitter in the system timing, so actual response rates can vary cycle to cycle.

Also, since the code is running on what I'm going to assume to be a normal PC, then there's the system dependencies on hardware (motherboard, processor, memory etc) that you would see from any programming setup, i.e. how fast can it execute a line of code....

Thanks

Sacha Emery

National Instruments (UK)

[Sreedhar_T]

Well thank  you SachaE, we have matricon , B&R, PVI manager etc types of OPC servers. Still yet to start working on the OPC part as I am just entering into that, I want to have some prior knowledge about the connectivity and how well can I interact.

[SachaE]

Hi,

  for connecting to OPC, you can simply use Datasocket. If you're designing a larger system, then you might want to have a look at LabVIEW Datalogging and Supervisory Control, which prior to LabVIEW 8.0 runs with a tag engine to connect to the various external data sources, including OPC, and then you write your code to talk to the tag engine. 

Here's the link to a search results page that will allow you to find out more about Datasocket and OPC connections.

http://search.ni.com/nisearch/nisearchservlet?nistype=default&ddown=0&filter=%2Btaxonomy:top+%2B(met...

(from ni.com, top right hand corner and type in "OPC datasocket" (without the quotes)

Hope that helps

Sacha Emery
National Instruments (UK)

[Maryam]

thank you Sacha, we're developing an HMI system and just start with OPC . for connecting to OPC we use DSC on LABView 7.1.... so I would like to have some knowledge on using OPC via DSC, I really want to know how exactly these two works with eachother.I mean the implementationof of interfaces.

[REM1]

All this info is for pre-8.0

As far as the interaction between the OPC world and DSC goes, DSC establishes an two way OPC connection to communicate with the OPC world and then moves the data into its data engine.  Once in the engine DSC transports the values around inside LabVIEW (or uses Logos - the pre-cursor to LabVIEW 8.0s PSP) for DSC-to-DSC communications.

Slightly more specifically on the DSC/OPC connection, DSC establishes an asynchronous OPC connection to the external server/client.  When DSC sends data across the OPC connection, that data packet is assigned a confirmation number.  This confimation number goes into a container DSC holds while waiting for confirmation.  The software on the other end of the connection responds that message x has been processed and DSC removes the confirmation number from the container.  Should the container become full, DSC assumes that communication is irrevokably lost, posts a message to the UI and discontinues trying to communicate with the external connection. 

Does this answer your question?