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OPC Gateway (Device Support). Ralph Lange – EPICS Collaboration Meeting March 2008 @ SSRF. OPC Gateway (Device Support). Accessing PLCs through EPICS 3.14 Device Support running on a Windows box connecting to a combination of commercially available OPC client and server packages

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opc gateway device support
OPC Gateway (Device Support)

Ralph Lange – EPICS Collaboration Meeting March 2008 @ SSRF

Ralph Lange: OPC Gateway (Device Support)

opc gateway device support2

OPC Gateway (Device Support)

Accessing PLCs through EPICS 3.14 Device Support running on a Windows box connecting to a combination of commercially available OPC client and server packages

Inspired by work from Kay-Uwe KasemirDeveloped by Carsten Winkler and Bernhard KunerWith additional help from Roland Fleischhauer and Ralph Lange

Credits: Main Authors and Contributors

opc introduction
OPC: Introduction

OPC: OLE (based on COM) for Process ControlBased on DCOM: Distributed Component Object Model

Client/Server ArchitectureScalable and distributed over the network

“Data Access” SpecificationRead/write operations, time stamp, data qualityPolled or event driven (callback mechanism)

“Alarm and Event” Specification

Many existing OPC servers only implement a subset of the defined OPC features

Ralph Lange: OPC Gateway (Device Support)

opc data flow

PC Hardware

PC Hardware

PC Hardware

OPC Server

OPC Server

OPC Client

OPC Client





RS 232





OPC: Data Flow

OPC Server ApplicationAlways available from the PLC vendorFor wide-spread PLC series there are alternatives offered by third party vendors (see link list at http://www.opcconnect.com or e.g. http://www.matrikonOPC.com)

OPC Server – PLC CommunicationProprietary, vendor dependant

OPC Client LibrariesAvailable for Windows, Unixes (see http://www.opcconnect.com)Binary distribution of the client library by Softing is royalty-free

OPC Client – OPC Server Communicationvia DCOM (available by Microsoft and others – also for Linux)

Ralph Lange: OPC Gateway (Device Support)

opc client side data access
OPC: Client Side Data Access

Connect to Server

Client will start/stop the server

Browse Server

For debugging purposes or dynamic client configuration

Add Group

Client defines groups with common parameters for all items within the group

Add Items

Client subscribes for several data objects

OPC Server




OPC Browser

OPC Group

Common Parameters, e.g. Update Rate, Deadband



OPC Item

Process Variable



  • Properties are:
  • Value of a common data type
  • Quality
  • Timestamp

Item Properties

Ralph Lange: OPC Gateway (Device Support)

opc device support overview

PC Hardware

OPC Server


EPICS 3.14

OPC Client

Channel Access



To other

OPC clients

From other

OPC servers




OPC Device Support: Overview

Supported Record Types:

- ai, ao

- bi, bo

- mbbi, mbbo

- mbbiDirect, mbboDirect

- longin, longout

- stringin, stringout

- waveform

OPC Client Library:

- Softing OPC Toolbox 3.01

- Distribution as Windows binary is royalty-free

- Other client libraries possible

Ralph Lange: OPC Gateway (Device Support)

opc device support features
OPC Device Support: Features


IOC will connect to multiple and/or remote OPC servers

Data Conversion

For all integer and float data types

Timestamp is Set by OPC Server or EPICS Record Processing

Determined by the record‘s TSE field

OPC Quality Information is Mapped to Record’s STAT/SEVR

In-Records: Read-Only

Value is written by the PLC

SCAN = “I/O Intr“ (event driven mode)


“.1 second“ to “10 second“ (polled mode)

Out-Records: Bidirectional

Value may be written by the PLC (e.g. local control) or by EPICS

SCAN = “Passive“, but record will still be updated when PLC value changes

Ralph Lange: OPC Gateway (Device Support)

bessy installation plc controlled beamlines
BESSY Installation: PLC Controlled Beamlines

33 Phoenix DIN-Rail PLCs with ~700 Channels Each: Approx. 22,000 Channels

Phoenix OPC Server Introduces Serious Limitations

Supports only polling mode: no events in the OPC server – PLC connection

Max. 2 PLCs per OPC server

No third-party OPC server available for this particular PLC type

Windows PC Hardware

4 Dual-processor 3 GHz 19” rack servers (standard high availability servers)

Each server runs 4 virtual Windows PCs (using VMware GSX server software)

Each of the 16 virtual PCs runs one softIOC and one OPC server that connects to 2 PLCs

PLC data is polled every 100ms or 250ms (different OPC Groups)

Servers are running at 40-50% CPU load

Ralph Lange: OPC Gateway (Device Support)

opc device support experiences and status
OPC Device Support: Experiences and Status

The BESSY beamline guys are very satisfied with this solution

“OPC is the spreading integration standard in scada and industrial automation.”

“Vendors simply have to provide OPC servers for a PLC if they want to be commercially successful. For common PLC series, third-party vendors will add competition, leading to better OPC servers.”

“This gateway opens up a window from EPICS to the whole wide world of industrial automation.”

They are very interested to have more facilities use the OPC device support and feedback changes as well as improvement requests

Existing users: BESSY, DESY, PSI, SLS, PPPL, SNSLatest changes by Sheng Peng are evaluated for integration


Roland.Fleischhauer@bessy.de Carsten.Winkler@bessy.de

Ralph Lange: OPC Gateway (Device Support)