OPC Data Access
Encyclopedia
The OPC Data Access Specification is the first of a group of specifications known as the OPC Specifications.
OPC Data Access is a group of standards that provides specifications for communicating real-time data from data acquisition devices such as PLC
s to display and interface devices like Human-Machine Interfaces (HMI). 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). There are three attributes associated with OPC DA. These are (1) a value, (2) the quality of the value, and (3) 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.
OPC Data Access is a group of standards that provides specifications for communicating real-time data from data acquisition devices such as PLC
Programmable logic controller
A programmable logic controller or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many industries and machines...
s to display and interface devices like Human-Machine Interfaces (HMI). 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
OPC Historical Data Access
This group of standards, created by the OPC Foundation, provides COM specifications for communicating data from devices and applications that provide historical data, such as databases. The specifications provides for access to raw, interpolated and aggregate data .OPC Historical Data Access, also...
, or OPC HDA). There are three attributes associated with OPC DA. These are (1) a value, (2) the quality of the value, and (3) 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.