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plurals

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2013-11-13T23:38:47.567
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<p>This may give you a run down on OPC servers work, I'm not too sure how much you know, so sorry if I relay. A OPC Server polls rather than a request/reply style of communication. It polls for tags rather than devices. </p> <p>Check this link for Java - OPC Deve - <a href="http://www.opcconnect.com/java.php#javacom" rel="nofollow">http://www.opcconnect.com/java.php#javacom</a></p> <h2>OPC 101</h2> <p>You will need to develop:</p> <ul> <li>Channel</li> <li>Device </li> <li>Variables</li> </ul> <p>Each channel specifies two things. The two aspects being specified are the : 1. Physical medium (Network adapter such as your standard Ethernet device or a Serial port) 2. Protocol being used (MODBUS, Allen Bradley, GE-Fanuc etc). This means each channel cannot host devices on either different mediums or protocols. </p> <p>The Device This field specifies a few things. These being:</p> <ol> <li>Address. This can be an IP address (for Ethernet passed protocols – such as IDEC Serial Encapsulated Protocol), or an identification number for serial communications such as Profibus or Modbus ASCII/RTU.</li> <li>Driver Specific information - This may include specifying a CPU model, or I/O card being used. This varies among drivers. </li> </ol> <p>The Variables are where the “Tags” are defined.</p> <ol> <li>Tag Name</li> <li>PLC Address. Such as M1 or RW1 or 49075 (Driver specific though)</li> <li>Data Type – Boolean, Word etc. </li> </ol> <p>Each tag or process variable has both data and meta-data. This can includes variable, last updated, the health of the tag etc, engineering units.</p> <h2>Finally</h2> <p>I haven't actually programmed my own OPC Server, but the above might help. I am not sure how much that Java SDK above gives, but consider security in your application. </p> <p>Is it possible to run an OPC server, polling the data, then your application interfaces with the OPC Server? This could help with not having to mess (too much, at least) with OPC. You can get Java based OPC servers than run on any platform and I'm confident most have an API, or at least a way to communicate the data. </p> <h2>Edit</h2> <p>Check out the software package Pi (<a href="http://www.osisoft.com/" rel="nofollow">http://www.osisoft.com/</a>). That might help with this. </p>
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