OPC evolution toward Unix

Mark Beharrell IT/CO, CERN, Geneva, Switzerland ICALEPCS ― October 12th, 2005

►Communication standards within a DCS►OPC Data Access►OPC on Unix►The future

From Windows to World Wide Domination?

2

Data Flows within a Detector Control System

DevicesDevices

Supervisor(SCADA)

Accelerator

Accelerator

ExperimentExperiment

SafetySafety

General Services

General Services

Web Access

Web Access

DCS

3

Device communication

• Device access protocols vary between:-• Manufacturers• Models• Versions of models

• Want an ‘interpreter’• Hide device differences• Developed by 3rd party

• What protocol to use with the interpreter?

4

Middleware

General solutions• CORBA• Java RMI• DCOM

• General solutions are not sufficient• Must solve a specific problem in standard way

• Need Standardize to level of the device• “Data Acquisition”• “OPC Data Access”

5

The OPC DA solution

• 1996 - OPC Data Access 1.0

• Well defined specification giving• Device model• Data model• Communications model

• Acceptance • Wide user base

• Uses DCOM middleware

6

Why OPC on Unix

MotivationSingle protocol for all device oriented

communications

Possibilities1. DCOM on Linux

2. OPC XML DA

3. OPC Unified Architecture

7

1. DCOM on Linux

• 1996 – Microsoft release the DCOM Spec.• Implementations on Solaris, VxWorks, Linux

• DCOM → OPC

• OPC DA (DCOM) Servers on Linux• Performance?• Stability?

8

1. DCOM-Performance & stability

• Test• Windows OPC server ported to Linux• Measured time to read OPC items (float) on both

platforms

• Result• Windows OPC ~ 100,000 items per second• Linux OPC ~ 76,000 items per second

• Problems• OPC server itself was stable• ‘System issues’

9

2. OPC XML DA

• 2003 – OPC XML DA released

Similar to the DA specification• Same device and data model• Different communication model

• Based on Web Services• OPC XML DA on any TCP/IP enabled processor

10

2. XML-Performance & stability

• Test• Wrote OPC XML server using toolkit.• Measured time to read OPC items (float) on both platforms

Result• OPC XML DA ~ 6,000 items per second

• Verses 76,000 with OPC on Linux!

Problems• ~5 items per second for single OPC item reads!• Interface definition does not always translate to code

correctly.

11

3. OPC Unified Architecture

• 2005 – OPC UA introduced• But not yet released

• Fusion of OPC interfaces• “Integration of plant floor data into enterprise

systems and the internet”• Provide secure, reliable and efficient services• Protocol and platform independence

• DCOM to be ‘retired’• Replaced by SOAP based alternatives

12

It works but is it useful?

• Several solutions to OPC servers on Unix. • DCOM based• OPC XML DA• OPC UA

• Waste of time ? - NO• OPC DA clients on Linux based SCADA systems.

Low industrial acceptance

Not yet available

13

Into the future

• OPC DA lives for the time being

• OPC XML will be replaced by UA

• OPC UA holds promise.

Platforms

But World Wide Domination?Enterprise

Factory

Internet

For device access – maybe!