The OPC Data Access Specification is the first of a group of
specifications known as the
OPC Classic Specifications.
OPC Data Access is a group of
client–server standards that provides specifications for communicating real-time data from
data acquisition devices such as
PLCs to display and interface devices like
Human–Machine Interfaces (HMI),
SCADA
Supervisory control and data acquisition (SCADA) is a control system architecture comprising computers, networked data communications and graphical user interfaces for high-level supervision of machines and processes. It also covers sensors and ...
systems and also
ERP/
MES systems. The specifications focus on the continuous communication of data.
The OPC Data Access specification is also known as OPC DA. OPC DA deals only with real-time data and not historical data (for historical data you need to use
OPC Historical Data Access, or OPC HDA) or events (for Alarms and Events you need to use
OPC Alarms and Events, or OPC AE). There are three attributes associated with OPC DA data. These are
# a value,
# the
quality of the value, and
# a
timestamp.
The OPC DA specification states that these three attributes have to be returned to an OPC client making a request. Therefore, if the data source is not capable of providing a timestamp, for example, the OPC DA server must create a timestamp.
The OPC Classic specifications are based on the
Microsoft COM
Com or COM may refer to:
Computing
* COM (hardware interface), a serial port interface on IBM PC-compatible computers
* COM file, or .com file, short for "command", a file extension for an executable file in MS-DOS
* .com, an Internet top-level d ...
technology and define a
C/
C++ interface. A standard
Automation wrapper interface is also defined for access from
Visual Basic,
Delphi
Delphi (; ), in legend previously called Pytho (Πυθώ), in ancient times was a sacred precinct that served as the seat of Pythia, the major oracle who was consulted about important decisions throughout the ancient classical world. The oracle ...
and other automation-enabled languages. Several vendors offer
.NET toolkits to make the OPC interface accessible in .NET
applications.
The newer OPC .NET (
OPC Xi
Open Platform Communications (OPC) is a series of standards and specifications for industrial telecommunication. They are based on Object Linking and Embedding (OLE) for process control.
An industrial automation task force developed the original st ...
) specification is based on WCF (
Windows Communication Foundation) and defines a .NET interface with the functionality of the OPC Classic specifications OPC DA, OPC HDA and OPC AE (Alarms&Events).
The more recent
OPC Unified Architecture
OPC Unified Architecture (OPC UA) is a cross-platform, open-source, IEC62541 standard for data exchange from sensors to cloud applications developed by the OPC Foundation. Distinguishing characteristics are:
* Standardized data models freely a ...
allows the same functionality but offers platform independence and optionally complex information modelling capabilities.
See also
*
OPC Foundation
*
Distributed Component Object Model
*
OPC Unified Architecture
OPC Unified Architecture (OPC UA) is a cross-platform, open-source, IEC62541 standard for data exchange from sensors to cloud applications developed by the OPC Foundation. Distinguishing characteristics are:
* Standardized data models freely a ...
References
External links
OPC Programmers' Connection
{{DEFAULTSORT:Opc Data Access
Industrial automation