science

OPC Data Access

OPC Data Access is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand OPC Data Access rather than just read about it. In short: 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 systems and also ERP/MES systems.

Key takeaways

OPC Data Access belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect OPC Data Access to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of OPC Data Access from memory before moving on to harder problems.

Reference excerpt

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 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 technology and define a C/C++ interface. A standard Automation wrapper interface is also defined for access from Visual Basic, Delphi 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) 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 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

References

External links OPC Programmers' Connection

Worked examples

Example 1 — a first encounter with OPC Data Access

Start with the simplest possible case. Write down what OPC Data Access claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to OPC Data Access before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about OPC Data Access ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of OPC Data Access

In research: OPC Data Access appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses OPC Data Access in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: OPC Data Access is common in secondary-school and first-year university syllabi. It links to neighbouring topics Industrial automation, so understanding it makes those chapters shorter.
In everyday life: Look for OPC Data Access outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study OPC Data Access in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what OPC Data Access means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain OPC Data Access out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is OPC Data Access in simple terms?

Why does OPC Data Access matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study OPC Data Access?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on OPC Data Access.