Proceedings of 2021 4th International Conference on Computer Science & Education
OPC Server Software Design in DCS
Tundong Liu, Gangquan Cai, Xiafu Peng
Automation Dept.
Xiamen University, Xiamen, China 361005
xfpeng@xmu.edu.cn
Abstract—In order to meet the application of OPC for
process control, a set of OPC server interface software is
designed with OPC specification in this paper. This software
organizes the device data as OPC standard data for other
equipments which also support the OPC standard, and it
successfully solves the communication between different
equipment manufacturers. The software is applied in the
Distributed Control System (DCS), so as to realize the data
exchange between the management configuration software and
the control device, which enhance the compatibility and
interoperability of the system.
Keywords—OPC Technology, COM, Interface
I. PREFACE
For a long time, many different hardware manufacturers
usually use different communication mechanism, which easily
leads to “information island“ phenomenon. In order to
integrate the data of different equipments in a system, software
developers have to invest considerable time and effort to
construct the underlying software, and delay the development
cycle. To this end, the industrial control field needs an open
standard to conduct a data access mechanism and management
that enable communication between various types of
equipment more flexible [1].
In 1990s, some of the world”s leading suppliers of
hardware or software develop a set of OPC specifications with
Microsoft. OPC is an industry standard, which is based on
Microsoft”s OLE (now ActiveX), COM and DCOM
technology, includes a set of interfaces, properties and
methods for the process control and manufacturing
automation systems [2].
In August 1996, the version of OPC 1.0 specification
published by the OPC Task Force was passed. In 1998, OPC
Foundation organizations launched OPC 2.0 version [3], and
amended some errors in the last version, added a few
interface and adjusted the means of data communication,
making programs to run more stable and reliable.
OPC technology is to bring the advantages of separating
software development and hardware development
completely, leaves access interface task to the hardware
manufacturer or third-party manufacturers, and offers OPC
server for users. OPC technology will be widely applied to
control filed [4]. Many well-known international hardware
manufacturers added OPC interface in their own
products. On the basis of
the introduction about OPC technology and OPC server
interface software in this paper, OPC application on fertilizer
plant in the gas furnace Distributed Control System is
presented later.
II.
OPC TECHNOLOGY
INTRODUCTION
A. COM Technology
OPC technology is mainly based on Microsoft”s COM
technology. COM is a component tool that widely used,
provides a wealth of integrated services for software
designing [5]. COM uses binary canonical form, and can
establish components to communicate with each other. As
long as in accordance with the norms of COM, any software
functions will be implemented very well with high-level
program language. DCOM is COM’s seamless expansion in
the distributed computing, realizes the transparency of the
network.
B. OPC Technical Specifications
There are three kinds of OPC specification: (1) OPC Data
Access specification; (2) OPC Alarm and Event norms; (3)
OPC Historical Data Access specification. The OPC Data
Access Specification is mainly applied in this paper.
The OPC Data Access Specification is based on the logic
of the object model of OPC, the model includes three types:
OPC server object, OPC group object and OPC item object.
OPC server object: It is at the most top-level of the logic
model, and maintains information on the server and acts as a
container of OPC group object, each OPC server object can
contain many group objects.
OPC group object: It provides the mechanism that
contains and manages many item objects. A group object can
provide a way to allow customers to “subscribe“ list, so
customers can be notified when changes are happened in the
project.
OPC item object: it represent a connection which connects
with data source, including the value, quality, timestamp, the
3 basic attributes. All the OPC item operation is controlled by
the OPC group object that contains related items.
III.
OPC S
ERVER
INTERFACE DESIGN OF THE SOFTWARE
A. OPC Server Overall Structure
The overall framework of OPC server is shown in Figure 1.