An OPC UA FX drive

OPC UA FX (Field eXchange, OPC 10000-80 and following) describes how controllers, drives and I/O devices exchange data with each other. The modeler knows its three information models as standard namespaces:

Alias	Namespace URI	Defined in
fxData	http://opcfoundation.org/UA/FX/Data/	OPC 10000-81, data types and FxRoot
fxAc	http://opcfoundation.org/UA/FX/AC/	OPC 10000-81, AutomationComponent
fxCm	http://opcfoundation.org/UA/FX/CM/	OPC 10000-81 §6.7, ConnectionManager

fxAc and fxCm depend on di and fxData: the modeler loads them for you. This page names fxData too, because the instances it creates go under its FxRoot folder.

namespaces:
  - di
  - fxData
  - fxAc
  - fxCm

The functional entity

A functional entity is the part of a device that takes part in the exchange: here, the control function of a variable-speed drive. It publishes what it measures in OutputData and receives what the controller commands in InputData. Both folders come from the IFunctionalEntityType interface; declaring them is what activates them, and a subtype is the way OPC 10000-81 §6.4 expects them to be filled.

AuthorUri, AuthorAssignedIdentifier and AuthorAssignedVersion identify the functional entity: a client compares them with what the system engineering expects before it connects (OPC 10000-81 D.3.8).

DriveFunctionalEntityType

objectTypes:
  - browseName: DriveFunctionalEntityType
    subtypeOf: fxAc:FunctionalEntityType
    description: The control function of a variable-speed drive, exchanged with a controller over OPC UA FX.
    components:
      - browseName: fxAc:OutputData
        components:
          - browseName: ActualSpeed
            dataType: ua:Float
            engineeringUnits: revolutions per minute
          - browseName: MotorCurrent
            dataType: ua:Float
            engineeringUnits: ampere
      - browseName: fxAc:InputData
        components:
          - browseName: SpeedSetpoint
            dataType: ua:Float
            engineeringUnits: revolutions per minute
            accessLevel: CurrentRead | CurrentWrite
    properties:
      - browseName: fxAc:AuthorUri
        value: http://acme.com
      - browseName: fxAc:AuthorAssignedIdentifier
        value: DriveControl
      - browseName: fxAc:AuthorAssignedVersion
        value:
          major: 1
          minor: 0
          build: 0
          subBuild: 0

The automation component

The automation component is the device as the network sees it. Its FunctionalEntities folder organizes the functional entities, and its Assets folder organizes the hardware they run on. The functional entity names the Asset that executes it with an IsHostedBy reference (OPC 10000-81 Table 5).

Every OPC UA FX instance goes under FxRoot, the folder fxData adds to the Objects folder (OPC 10000-81 §12.2). The instance Drive1 takes its members, and the IsHostedBy reference between them, from its type.

DriveAutomationComponentType and its instance under FxRoot

objectTypes:
  - browseName: DriveFunctionalEntityType
    subtypeOf: fxAc:FunctionalEntityType
    components:
      - browseName: fxAc:OutputData
        components:
          - browseName: ActualSpeed
            dataType: ua:Float
            engineeringUnits: revolutions per minute
      - browseName: fxAc:InputData
        components:
          - browseName: SpeedSetpoint
            dataType: ua:Float
            engineeringUnits: revolutions per minute
            accessLevel: CurrentRead | CurrentWrite
  - browseName: DriveAutomationComponentType
    subtypeOf: fxAc:AutomationComponentType
    description: A drive that offers its control function as an OPC UA FX Automation Component.
    components:
      - browseName: fxAc:FunctionalEntities
        organizes:
          - browseName: DriveControl
            typeDefinition: DriveFunctionalEntityType
      - browseName: fxAc:Assets
        organizes:
          - browseName: DriveAsset
            typeDefinition: fxAc:FxAssetType
            optionals:
              - di:Manufacturer
              - di:SerialNumber
              - di:ProductCode
    references:
      - referenceType: ua:IsHostedBy
        source: /fxAc:FunctionalEntities/DriveControl
        target: /fxAc:Assets/DriveAsset
instances:
  - browseName: Drive1
    typeDefinition: DriveAutomationComponentType
    organizedBy: /ua:Objects/fxData:FxRoot

The connection manager

A connection manager establishes the connections between automation components, from a configuration an engineering tool writes into it. A server has at most one, and it has a fixed name: fxCm already provides it, as FxRoot/ConnectionManager (OPC 10000-81 §12.3). A model that imports fxCm does not declare another one.

Conformance checks

A model that imports an OPC UA FX namespace is checked against OPC 10000-81 when it is compiled, in the command line and in the editor. Each check points at the node that breaks it:

Code	Checks that	OPC 10000-81
DSL-E-FX-001	FunctionalEntities holds only FunctionalEntities	§6.2.2
DSL-E-FX-002	Assets holds only Assets	§6.2.2
DSL-E-FX-003	every Asset a FunctionalEntity is hosted by is listed in Assets	§6.2.2
DSL-E-FX-004	InputData and OutputData hold only Variables, capabilities and groups	§6.4.4, §6.4.5
DSL-E-FX-005	Variable names are unique in an Inputs or Outputs folder	§6.4.4, §6.4.5
DSL-W-FX-006	String and ByteString data carry a maximum length	§6.4.4, §6.4.5
DSL-W-FX-007	AutomationComponents are under FxRoot	§12.2
DSL-W-FX-008	no second ConnectionManager	§12.3

An error is a "shall" of the specification. To turn a warning into an error, or silence one, use the model's lint: section like for any other rule.

Going further

• Samples from OPC 10000-81 Annex D, rebuilt in the DSL: a temperature monitor with a ControlGroup, an analogue input module, an AGV and a full Raspberry Pi automation component.
• The types each namespace defines are listed in the gallery, under OPC UA FX Data, FX Automation Component and FX Connection Manager.
• The specifications: OPC 10000-81 and OPC 10000-82.