3 Terms, definitions and abbreviations ToC Previous Next

3.1 Terms and definitions ToC Previous Next

For the purposes of this document, the terms and definitions given in The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments and errata) applies.

OPC 10000-1, OPC 10000-3, and OPC 10000-4 as well as the following apply.

3.1.1 DataItem

link to arbitrary, live automation data, that is, data that represents currently valid information

Note 1 to entry: Examples of such data are

  • device data (such as temperature sensors),
  • calculated data,
  • status information (open/closed, moving),
  • dynamically-changing system data (such as stock quotes),
  • diagnostic data.

3.1.2 AnalogItem

DataItems that represent continuously-variable physical quantities (e.g., length, temperature), in contrast to the digital representation of data in discrete items

Note 1 to entry: Typical examples are the values provided by temperature sensors or pressure sensors. OPC UA defines a specific VariableType to identify an AnalogItem. Properties describe the possible ranges of AnalogItems.

3.1.3 DiscreteItem

DataItems that represent data that may take on only a certain number of possible values (e.g., OPENING, OPEN, CLOSING, CLOSED)

Note 1 to entry: Specific VariableTypes are used to identify DiscreteItems with two states or with multiple states. Properties specify the string values for these states.

3.1.4 ArrayItem

DataItems that represent continuously-variable physical quantities and where each individual data point consists of multiple values represented by an array (e.g., the spectral response of a digital filter)

Note 1 to entry: Typical examples are the data provided by analyser devices. Specific VariableTypes are used to identify ArrayItem variants.

3.1.5 EngineeringUnits

units of measurement for AnalogItems that represent continuously-variable physical quantities (e.g., length, mass, time, temperature)

Note 1 to entry: This standard defines Properties to inform about the unit used for the DataItem value and about the highest and lowest value likely to be obtained in normal operation.

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