OPC – OLE for PROCESS CONTROL

By:

Mugdha More.

Swagata Bhaumik

Introduction (statement of problem)

The microprocessors based devices in plants, often

do not work together, because: • Application software do not readily communicate

with digital plant-floor devices as well as other applications.

• Making these systems work together is the most pressing need of process manufacturers.

Why do we need OPC ?

• A pressing need in both factory automation and process manufacturing is making production and business systems work together.

• Barriers are incompatibilities and proprietary communication interfaces.

• OPC gives production and business applications across the manufacturing enterprise access to real-time plant-floor information in a consistent manner, making multi-vendor interoperability and "plug and play" connectivity a reality.

Why do we need OPC ? Contd…

• Interfaces are not standard.

• Proprietary systems are fairly common.

• Hardware and software choices reduced due to limited connectivity.

Solution – OPC: OLE for Process Control

• Real plug-and-play software technology for process control.

• Every system, every device and every driver can freely connect and communicate.

• Easy enterprise-wide communications between systems and devices, from plant floor to MIS (Management Information System) and beyond.

History• OPC (OLE for Process Control) is an industry standard.• The organization that manages this standard is the OPC Foundation.• The objective of the OPC Foundation is to develop

– An open, flexible, plug-and-play standard.– End users to enjoy a greater choice of solutions.– Sharply reducing development and maintenance costs for hardware and software

suppliers.

• The OPC Foundation has released two sets of interfaces: – OPC Data Access (V2.0, October 1998)– OPC Alarms and Events (V1.0, December 1998)– A third one is in preparation.

What is OPC ?OPC™ (OLE for Process Control) is a defined set of interfaces, based on OLE/COM and DCOMtechnology, for truly open software applicationinteroperability between automation/controlapplications, field systems/devices and business/officeapplications.(See fig. 1).

Instead of having to learn how to use 100 or more custom toolkits, users will only have to learn one set of tools, because all OPC drivers will work the same way.

What is OPC? Contd..

• OPC defines a standard interface that allows applications to access data from a variety of process control devices.

• The applications must implement one OPC compliant driver to access data from any OPC compliant server.

• OPC provides for a high degree of interoperability between client and server applications supplied by different vendors.

What is OPC? Contd..

• OPC provides for a high degree of interoperability between client and server applications supplied by different vendors.

• OPC allows software modules from a variety of vendors to inter-operate through a standard interface. This concept is shown in Figure1.

Term Meaning

OPC OPC stands for OLE for Process ControlOPC is based on the core OLE technologies COM and DCOM.

OLE Object Linking and Embedding.

COM In order to make objects implemented on different platforms or computer architectures compatible with one another, it must be determined how these platforms interpret an object. For this, something called an ‘object model’ is required.OLE uses the COM model (Component Object Model). This defines the standard for interaction of components. COM enables calls within a process, to another process and even to another computer.

DCOM The object model for inter-computer calls is known as DCOM (Distributed Component Object Model) which is integratedinto the operating system in Windows NT 4.0 and above.

OPC Server• The OPC server is responsible for acquiring the data

requested by a client from the process control device. • Each server contains OPC groups, which are logical collections of data to be gathered. • The groups in a server may be shared by many clients or be private to a single client.

OPC Client/Server SystemThe OPC server is the component which provides standardized

methods for the following services, for example:

• reading, changing or monitoring process variables (Data Access)

• monitoring of interrupts/alarms with optional filters (Alarm & Event)

• extracting or changing archive data (Historical Data Access) security and batch functions

OPC group object

• The OPC group object holds the OPC items that contain the values retrieved from the process control device.

• The client adds items to groups. The client may want to group all process temperature values into a group.

• The client can specify to the server the update rate for the group that defines the rate at which the server will check to see if the exception limit for a value has changed. The client also specifies the exception limit used for items in the group to determine if the value should be reported back to the client.

OPC groups & OPC items.

OPC clients use the standardized OPC interface of the OPC server to access process data. The following are some examples of OPC clients:

· SCADA systems

· Manufacturing Execution Systems

· Microsoft Office Tools

OPC’s interfaces for application• The OPC standard defines two interfaces for applications:

– One interface is designed for high volume/high throughput applications. This is an OLE custom interface.

– A second interface is provided for ease of access to the data.

What is COM?

• The Component Object Model provides standard interfaces and inter-component communications.

• Through COM, an application may use features of any other application object or operating system, or allow for software component upgrades without affecting the operation of the overall solution.

• COM can be used by developers and system integrators to create customized solutions.

• A binary standard, COM is generic and is the core of DCOM,ActiveX, and OLE technology.

What is OLE?

• Object Linking and Embedding is used to provide integration among applications, enabling a high degree of application compatibility, even among diverse types of information.

• OLE technology is based on COM, and allows for the development of reusable, plug-and-play objects that are interoperable across multiple applications.

• It also provides for reusable, component-based software development, where software components can be written in any language, supplied by any software vendor.

What is OLE Automation?

• OLE Automation and the underlying COM technologies were designed by Microsoft to allow components (written in C and C++) to be used by a custom program (written in Visual Basic or Delphi).

• Through OPC, application developers can write code in any language necessary (C and C++) to request and utilize plant-floor data.

What is DCOM?

• The Distributed Component Object Model extends COM to networks (remote objects).

• It is a new, highly optimised protocol, where remote components appear to be local.

What is ActiveX?• ActiveX is a term for broad range of

technologies that used to be known as OLE Controls, all of which rely on COM.

• It is object-based rather than object-oriented.

• ActiveX is an open, integrated platform that lets developers and Web producers create portable applications and interactive content for the World Wide Web.

• It’s open, cross platform, and is supported on Mac,Windows, and Unix systems.

What is DDE?

• Dynamic Data Exchange, is a method of dynamically moving data among applications in the Microsoft Win32 application programming interface (API).

DDE OPCPasses 1 value per request

Can pass multiple values per request

No time stamp Time stamp standard part of response

No quality flag or indicator on data

Indication standard part of response

No underlying structure Similar to OLE based on OLE/COM structure

Does not support OLE Automation

Supports OLE Automation

Benefits

• OPC technology can eliminate the need for expensive custom interfaces and drivers for moving information easily around the all parts of the enterprise between different computing solutions and platforms both horizontally and vertically in the enterprise. It cuts costs, speeds development and promotes increased operating efficiency. Here's how:

* Eliminate custom interfaces and drivers*Write one software component instead of multiple drivers*Create re-usable modules*Communicate data locally over the enterprise network* Communicate data remotely over the internet

Benefits

• In the past, client application vendors had to develop a different driver for each control device. The OPC standard

• provides the greatest benefit to client vendors in that they now only have to develop one driver to access data from

• a process control device. Both of these situations are diagrammed

OPC Summary• Combine different devices from different manufacturers in one

system • Reduce installation time • Add devices without stopping existing software and systems • Quickly replace a device from one vendor with one from another • Share information around networks • Device drivers rendered obsolete • Factory, laboratory and office applications can all access the same

data • Reliable data as any number of OPC software applications can

simultaneously read a device

• Single, industry-standard, data interface