OPC Data Access

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The OPC Data Access Specification is the first of a group of

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

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.

The OPC Classic specifications are based on the

The more recent OPC Unified Architecture allows the same functionality but offers platform independence and optionally complex information modelling capabilities.^[7]

See also

• OPC Foundation
• Distributed Component Object Model
• OPC Unified Architecture

References