OPC Device Support

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
• - gt 2 GB/d raw data over the network
• - gt 200 kB Channel Access data

6
Former Approaches

• OPC_CAS
• Doesnt 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 cant 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 records 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.