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Introduction to OPC Device Support for EPICS in Bessy Installation

Learn about OPC (OLE for process control) in device support for EPICS at Bessy Installation in Berlin, Germany. Understand OPC data flow, client/server communication, features, and future capabilities.

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Introduction to OPC Device Support for EPICS in Bessy Installation

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  1. OPC - Device Support Bernhard Kuner, Carsten Winkler BESSY, Berlin, Germany

  2. Introduction to OPC • OPC: OLE (COM) for process control DCOM: Distributed Component Object Model • Client/Server scalable and distributed over network • “Data Access” specification read/write, time stamps, quality polled or callback • “Alarm and Event” specification Existing OPC servers support only a subset of the defined OPC features

  3. Data Flow • Device - OPC server communication: proprietary, vendor dependant • OPC client - OPC server communication: via DCOM (Microsoft) • OPC libraries available for: all Windows, Unix, not vxWorks

  4. Client Data Access • Connect to server Client will start/stop the server • Add group Client defines groups with common parameters for all items within the group • Add items Client subscribes for several data objects

  5. Bessy Installation • Connect PLC controlled beamlines to EPICS - 30 PLCs: c. 6,000 PVs - 4 OPC servers • Currently 600 PVs with the new iocShell • In the future: 30,000 PVs • Data volume One PLC: 6 kB/s, polled with 50 ms - > 2 GB/d raw data over the network - > 200 kB Channel Access data

  6. Former Approaches • OPC_CAS • Doesn’t work reliably • Several crashes a day • VisualBasic program with Kepware OPC client and ActiveX_CAS • Proper handling of values, alarms and graphic limits • Crashes ALH and other clients • No access security • OPC can’t set STAT and SEVR • XCas • Another CAS based solution

  7. Device Support for EPICS 3.14 • For these record types: - ai, ao - bi, bo - mbbi, mbbo - mbbiDirect, mbboDirect - longin, longout - stringin, stringout - (waveform) • OPC client with - Softing OPC Toolbox 3.01 - Other client libraries possible

  8. opcDevSup Features • Data conversion for all integer and float data types • Timestamp generated by OPC server or EPICS determined by the record‘s TSE field • Map OPC quality to records STAT/SEVR fields • Out records may be written by the PLC and by EPICS in - records: read only records out - records: read/write records • Record processing: SCAN field: „I/O Intr“ or „.1 second“ to „10 second“ OUT records are not „Passive“, but „I/O Intr“

  9. Conclusions • Portable CAS solutions never satisfy EPICS clients. • For full range of EPICS functionality EPICS records are required.

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