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OPC Group Control in Flex

Created by: Captive Engineer at: 7/24/2008 11:55 PM (2 Replies)

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7/24/2008 11:55 PM	Rate (0)
Captive Engineer Experienced Member Joined: 1/30/2006 Last visit: 7/26/2023 Posts: 103 Rating: (15)	Hello, Folks, I'm using Flex 2007 advanced. This project will utilize Flex RT on some sort of industrial PC. Per the normal recommendations of forum courtesy, I have searched using the words "OPC" and "Flex" for information about using Flex with OPC. While there are some threads addressing this to a small extent, I've not found one that deals with the question that I now submit. Also, I have examined the chapter on OPC in the manual, WinCC Flexible 2007 Communication Part 1. This also does not provide the details I seek. The OPC Data Access Interface (OPC-DA) specifies a class model consisting of the OPC Server, OPC Group(s), and OPC Item(s). The Item class object is essentially the process variable or OPC Tag Name that I link into my HMI [Flex] tag list. The OPC server object is what I define in Flex's Connection Parameters as the OPC Server Name. What does not appear to be explicit in Flex, however, is the OPC Group. If the reader knows all about OPC Groups, skip down about three paragraphs to my first question. A Group object is arranged by the OPC Client -- theoretically, Flex runtime in this case --to logically handle read and write access to a particular set of process values. Thus,with one command, an OPC Group can be activated for reading and/or writing, deactivated for the same, or have its cyclic update rate changed, assuming that the group is cyclically updated at all. So, for example, when I navigate to a particular screen, all tags in a group associated with that screen could be activated. Upon exiting that screen, the same group might be deactivated, since that group is no longer necessary for display. In addition to this, the OPC Group class defines several different methods for access. These include: Synchronous -- the OPC Client calls for the group values and awaits response, Asynchronous -- the OPC Client calls for the group values and performs other tasks while awaiting response, Refresh -- the OPC Client reads all active items inside an active OPC Group, and Subscription -- the Client Group is configured so that, after the initial data transfer,the OPC Server transmits values defined in that Group only as they change in the process. This is very efficient as it relieves theClient of performing read cycles on tags which may rarely change, and, furthermore, as it reduces the amount of communication generally. So my first question is, since Flex Runtime is the OPC Client, does Flex have any support for OPC Groups? Or, is the group functionality that I have described only carried out on the Item (Tag) level? If there is no OPC Group functionality, then my second question is, using the Acquisition Mode = Cycle on Use, which of the OPC Group access methods does Flex most closely resemble? (Synchronous, Asynchronous, Refresh, or Subscription)? I'd like to know these details since the results of my first project relying entirely on OPC communications are fairly critical to my business. Thanks, The Captive Engineer
	Last edited by: Captive Engineer at: 7/25/2008 3:03 PM
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7/29/2008 5:50 PM	Rate (0)
ZAK Gold Member Joined: 5/8/2006 Last visit: 2/22/2023 Posts: 1085 Rating: (77)	Hi, WinCC flexible can work as OPC DA Client and as OPC DA Server. Maybe this Information will help you: 1. WinCC flexible Getting started: http://support.automation.siemens.com/WW/view/de/18657078/0/en 2. OPC - see attachment: Bye Attachment WCF07OPCenUS.pdf (31 Downloads)

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7/30/2008 2:55 PM	Rate (0)
Captive Engineer Experienced Member Joined: 1/30/2006 Last visit: 7/26/2023 Posts: 103 Rating: (15)	Thanks, ZAK, For the processor I am using, my Flex application needs to be set up as a client. The document that you attached also has its content in Flex's help files. Furthermore, I have examined the link you provided. If these represent the totality of the information on OPC with Flex, then it is apparent that there is no particular support for OPC DA groups. In that case, my second question still remains: which access mode in the OPC-DA standard is Flex's tag access most like when a tag is configured for cycle-on-use? Thanks, The Captive Engineer

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