OLE for Process ControlOLE for Process Control

Talk OutlineTalk Outline

OPC Overview What is OPC? Why OPC at CERN? OPC functionality and architecture?

OPC Data Access Access to process data

OPC Alarms & Events Notification of special conditions

Conclusions

OPC OverviewOPC OverviewVersion 2.0, October 1998Version 2.0, October 1998

What, Why, Where? Architecture Functionality

What is OPC?What is OPC?

An industry standard for process control,comprising: A model for interactions and data A set of interfaces

Standards for data access (read/write of propeties) alarms and events

Supported by 150-200 companies Implemented on Windows NT, (D)COM

Why OPC at CERN?Why OPC at CERN?

First industrial standard Integration of industrial systems (LHC) Supported by SCADA systems Used by Experiments

Input for building our own JavaAPI

Where does OPC fit?Where does OPC fit?

Access of Devices Databases Applications (e.g.

SCADA)

GUI(Browser)

SCADA Database

PhysicalI/O

ControlsApplication

OPC

Device

OPC deviceserver

OPC ArchitectureOPC Architecture

Client Server Paradigm Client (e.g. browser, control system, SCADA) OPC server on Windows NT PLC

### here goes an image ###

FunctionalityFunctionality

OPC data server holds process data for clients client can read/write or subscribe to data

OPC event & alarm server administrates events and alarm for clients client can subscribe to event notifications

Both provide meta-information Client can browse available information

OPC Data AccessOPC Data AccessVersion 2.0, October 1998Version 2.0, October 1998

Data Model Interactions

OPC Data ModelOPC Data Model

Data structured in OPC items (~ device properties) OPC groups = collection of items

OPC item connections to data sources triplet: value, quality, timestamp

OPC groups collection of data items exclusive access to data

Group

item1item2item3

OPC Data organizationOPC Data organization

Server

Group

OPC/COMInterfaces

Group Group(s)

OPCItem(s)OPCItem(s)Item(s)OPCItem(s)OPCItem(s)Item(s)OPCItem(s)Item(s)

OPC ItemsOPC Items

Connections to data sources Information (provided through I/O)

Value Quality Timestamp

Attributes (provided by browsing) Name Type Units Descriptions

OPC GroupsOPC Groups

Logical container for clients to organize and manipulate data items

Client accesses data only via groups Group has attributes:

Deadband (minimal variation considered as a change) Update rate (frequency at which cache is updated) ACTIVE flag (whether data is used & updated)

Group can be public or private (“local”) fixed or dynamic

OPC Data AccessOPC Data AccessVersion 2.0, October 1998Version 2.0, October 1998

Data Model

Interactions

Data AccessData Access

Read/write Default: read from cache => efficient cache is updated regularly possible to read from device directly

Subscription-based client registers with group server sends data upon

change in value or change in quality

Group AdministrationGroup Administration

Server administers groups for clients Client tells the server...

to create/delete groups to add/remove items Groups are private (“local”) to one client

Groups can be made “public” => Clients can share groups

Clients can browse available groups items in a group

Meta-Information AccessMeta-Information Access

Look up… groups by name

Browse... items available on the whole server (public) groups defined on a server items defined in a group item properties

OPC Alarms & EventsOPC Alarms & Events Version 1.0, December 1998Version 1.0, December 1998

Architecture Data related Concepts Interactions

ArchitectureArchitecture

Client-Server Alarm/event server types:

Simple servers, elementary, attached to device Management servers: intermediate level

### here goes an image ###

OPC Alarms & EventsOPC Alarms & Events Version 1.0, December 1998Version 1.0, December 1998

Architecture

Data related Concepts Interactions

Data Related ConceptsData Related Concepts

Condition = well-defined, interesting state of a device or subsystem Examples: system health, operational state, special

value of data item(s)###

Event/Alarm = well-defined interesting behavior of device or subsystem 3 Event Types:

Related to condition (e.g. alarm state changed to HighAlarm)

Related to client action (e.g. operator changing data item) Other (e.g. failure of underlying device)

Event Notification: the information passed

Details ("Attributes")Details ("Attributes")

Condition Attributes Name, Description Severity, Quality (=accuracy) Time of last condition change Acknowledgement: when and by whom

Event Notification Attributes: Message Severity, Quality Source, Timestamp Type of event Acknowledgement: required or not

OPC Alarms & EventsOPC Alarms & Events Version 1.0, December 1998Version 1.0, December 1998

Architecture Data related Concepts

Interactions

Subscription Subscription

Subscribe Client tells server to create subscription object Client chooses events to subscribe to

Subscription management Enable/Disable subscriptions Set up filters

End subscription Client: delete subscription object Server: send shutdown request to client

Event notificationEvent notification

Event Notification if a subscribed condition becomes "active"

=> server passes event notification to client Some event notifications require acknowlement

"Refresh event notification" Client actively requests latest condition state

=> server sends #condition-related# notifications Filtering

Events can be filtered based on various criteria

Meta-level browsingMeta-level browsing

Client can browse server for: areas (= groups of equipment) condition categories ( = types of conditions) conditions ( = named condition attributes

available filters

ConclusionsConclusions

Very interesting concepts We can learn from them

Needed for industrial system integration Industrial devices other SCADA

Many interfaces are only optional Microsoft dominated

Needs Windows NT near devices Based on DCOM