OLE for Process Control

Talk Outline u OPC Overview u What is OPC? u Why OPC at CERN? u OPC functionality and architecture? u OPC Data Access u Access to process data u OPC Alarms & Events u Notification of special conditions u Conclusions

OPC Overview Version 2.0, October 1998 u What, Why, Where? u Architecture u Functionality

What is OPC? u An industry standard for process control, comprising: u A model for interactions and data u A set of interfaces u Standards for u data access (read/write of propeties) u alarms and events u Supported by companies u Implemented on Windows NT, (D)COM

Why OPC at CERN? u First industrial standard u Integration of industrial systems (LHC) u Supported by SCADA systems u Used by Experiments u Input for building our own JavaAPI

Where does OPC fit? u Access of u Devices u Databases u Applications (e.g. SCADA) GUI (Browser) SCADADatabase Physical I/O Controls Application OPC Device OPC device server

OPC Architecture u Client Server Paradigm u Client (e.g. browser, control system, SCADA) u OPC server on Windows NT u PLC u ### here goes an image ###

Functionality u OPC data server u holds process data for clients u client can read/write or subscribe to data u OPC event & alarm server u administrates events and alarm for clients u client can subscribe to event notifications u Both provide meta-information u Client can browse available information

OPC Data Access Version 2.0, October 1998 u Data Model u Interactions

OPC Data Model u Data structured in u OPC items (~ device properties) u OPC groups = collection of items u OPC item u connections to data sources u triplet: value, quality, timestamp u OPC groups u collection of data items u exclusive access to data Group item1 item2 item3

OPC Data organization Server Group OPC/COM Interfaces Group Group(s) OPCItem(s) Item(s) OPCItem(s) Item(s) OPCItem(s) Item(s)

OPC Items u Connections to data sources u Information (provided through I/O) u Value u Quality u Timestamp u Attributes (provided by browsing) u Name u Type u Units u Descriptions

OPC Groups u Logical container for clients to organize and manipulate data items u Client accesses data only via groups u Group has attributes: u Deadband (minimal variation considered as a change) u Update rate (frequency at which cache is updated) u ACTIVE flag (whether data is used & updated) u Group can be u public or private (“local”) u fixed or dynamic

OPC Data Access Version 2.0, October 1998 u Data Model u Interactions

Data Access u Read/write u Default: read from cache => efficient u cache is updated regularly u possible to read from device directly u Subscription-based u client registers with group u server sends data upon u change in value or u change in quality

Group Administration u Server administers groups for clients u Client tells the server... u to create/delete groups u to add/remove items u Groups are private (“local”) to one client u Groups can be made “public” u => Clients can share groups u Clients can browse u available groups u items in a group

Meta-Information Access u Look up… u groups by name u Browse... u items available on the whole server u (public) groups defined on a server u items defined in a group u item properties

OPC Alarms & Events Version 1.0, December 1998 u Architecture u Data related Concepts u Interactions

Architecture u Client-Server u Alarm/event server types: u Simple servers, elementary, attached to device u Management servers: intermediate level u ### here goes an image ###

OPC Alarms & Events Version 1.0, December 1998 u Architecture u Data related Concepts u Interactions

Data Related Concepts u Condition = well-defined, interesting state of a device or subsystem u Examples: system health, operational state, special value of data item(s)### u Event/Alarm = well-defined interesting behavior of device or subsystem u 3 Event Types: u Related to condition (e.g. alarm state changed to HighAlarm) u Related to client action (e.g. operator changing data item) u Other (e.g. failure of underlying device) u Event Notification: the information passed

Details ("Attributes") u Condition Attributes u Name, Description u Severity, Quality (=accuracy) u Time of last condition change u Acknowledgement: when and by whom u Event Notification Attributes: u Message u Severity, Quality u Source, Timestamp u Type of event u Acknowledgement: required or not

OPC Alarms & Events Version 1.0, December 1998 u Architecture u Data related Concepts u Interactions

Subscription u Subscribe u Client tells server to create subscription object u Client chooses events to subscribe to u Subscription management u Enable/Disable subscriptions u Set up filters u End subscription u Client: delete subscription object u Server: send shutdown request to client

Event notification u Event Notification u if a subscribed condition becomes "active" => server passes event notification to client u Some event notifications require acknowlement u "Refresh event notification" u Client actively requests latest condition state => server sends #condition-related# notifications u Filtering u Events can be filtered based on various criteria

Meta-level browsing u Client can browse server for: u areas (= groups of equipment) u condition categories ( = types of conditions) u conditions ( = named u condition attributes u available filters

Conclusions u Very interesting concepts u We can learn from them u Needed for industrial system integration u Industrial devices u other SCADA u Many interfaces are only optional u Microsoft dominated u Needs Windows NT near devices u Based on DCOM