PE Energy Management comprises all services allowing to obtain energy related information and to control the state of all energy manageable entities contained in the PE Energy Information Model. The PE Energy Information Model is based on the PROFIenergy profile[PE CAP]. The PE Energy Management functions defined in this specification are separated into three main categories: Standby Management, Energy Measurement, and Sleep Mode WOL.

Standby Management allows a device or parts of a device to switch into an Energy Saving Mode if not in operation or engaged. If a Standby Management Entity supports more than one Energy Saving Mode (with different levels of energy consumption), transitions from one Energy Saving Mode into another might be possible. For the smooth integration of devices with Standby Management functionality into a production process, Standby Management offers commands to issue the transition into an Energy Saving Mode and the termination of an Energy Saving Mode with switchback to normal operation.

Devices might also support Sleep Mode WOL functionality allowing to completely switch off a device. If this Sleep Mode WOL functionality is active, the device in Sleep Mode WOL is not reachable for network communication and can only be ‘awakened’ by receiving a ‘WOL magic packet’.

Standby Management defines a state model determining the possible state transitions. Figure 1 shows the state model.

Figure 1 – Standby Management State Model

When in ‘Energy saving disabled’ state, the device is in normal operation and does not accept standby commands. In the ‘Ready to operate’ state the device accepts standby commands. When in transition to or from an Energy Saving Mode, the device has a ‘Moving to …’ transition state. Thus the state model reflects the physical properties of a real-world device: Changes in energy consumption imply changes of some physical processes which will always be time consuming.

Standby Management is made available for OPC UA Clients with the ObjectTypes defined in chapter 8.1 ”Standby Management”.

Status information functionality of Standby Management provides information about the current state of a Standby Management Entity, the current energy consumption, the available Energy Saving Modes and their detailed characteristics.

The current state information of a Standby Management Entity is made available for OPC UA Clients with the EnergySavingModeStatusType (chapter 8.1.3) referenced by the EnergyStandbyManagementType.

Detailed information about a specific Energy Saving Mode is provided by the EnergySavingModeType defined in chapter 8.1.4.

Energy Measurement functionality allows the retrieval of energy related measurement values. Possible Energy Measurement values offered are energy counters, current power consumption, active and reactive power, frequency, voltage, current, information about maximum and minimum values of the former, and more. Furthermore, the Energy Measurement is not limited to electrical energy. In addition, different Metering Points of a device can be distinguished.

In general, the number and type of Energy Measurement values provided are vendor specific. For simplification and standardization, specific EnergyProfile types are defined which comprise a predefined set of measurement values together with a guaranteed measurement accuracy. However, when proxying the PROFIenergy Profile, additional measurement values are already defined (See [PE CAP] for details).

Energy Measurement is made available for OPC UA Clients with the ObjectTypes defined in chapter 8.2 ”Energy Measurement”.

The Sleep Mode WOL functionality allows to entirely switch off the device, including the network interface, and to switch on again by using the standard WOL (Wake-on-LAN) mechanism. The transition to the Sleep Mode WOL state is initiated by invoking the SwitchOffWOL Method of the EnergyDevicePowerOffType.

If the switched off device contains the OPC UA server, the connection of the OPC client to the server disconnects. The server will be reachable again after a wake up of the device by Wake-on-LAN (sending the WOL magic wake-up packet).

OPC UA is an open and royalty free set of standards designed as a universal communication protocol. While there are numerous communication solutions available, OPC UA has key advantages:

• A state of art security model (see [OPC 10000-2]).
• A fault tolerant communication protocol.
• An information modelling framework that allows application developers to represent their data in a way that makes sense to them.

OPC UA has a broad scope which delivers for economies of scale for application developers. This means that a larger number of high-quality applications at a reasonable cost are available. When combined with semantic models such as PROFIenergy, OPC UA makes it easier for end users to access data via generic commercial applications.

The OPC UA model is scalable from small devices to ERP systems. OPC UA Servers process information locally and then provide that data in a consistent format to any application requesting data - ERP, MES, PMS, Maintenance Systems, HMI, Smartphone or a standard Browser, for examples. For a more complete overview see [OPC 10000-1].

OPC UA is an open standard based on internet technologies like TCP/IP, HTTP, Web Sockets.

As an extensible standard, OPC UA provides a set of Services (see [OPC 10000-4]) and a basic Information Model framework. This framework provides an easy manner for creating and exposing vendor defined information in a standard way. More importantly all OPC UA Clients are expected to be able to discover and use vendor-defined information. This means OPC UA users can benefit from the economies of scale that come with generic visualization and historian applications. This specification is an OPC UA Information Model designed to meet the needs of developers and users.

OPC UA Clients can be any consumer of data from another device on the network to browser based thin Clients and ERP systems. The full scope of OPC UA applications is shown in Figure 2.

Figure 2 – The Scope of OPC UA within an Enterprise

OPC UA provides a robust and reliable communication infrastructure having mechanisms for handling lost messages, failover, heartbeat, etc. With its binary encoded data, it offers a high-performing data exchange solution. Security is built into OPC UA as security requirements become more and more important especially since environments are connected to the office network or the internet and attackers are starting to focus on automation systems.

OPC UA provides a framework that can be used to represent complex information as Objects in an AddressSpace which can be accessed with standard services. These Objects consist of Nodes connected by References. Different classes of Nodes convey different semantics. For example, a Variable Node represents a value that can be read or written. The Variable Node has an associated DataType that can define the actual value, such as a string, float, structure etc. It can also describe the Variable value as a variant. A Method Node represents a function that can be called. Every Node has a number of Attributes including a unique identifier called a NodeId and non-localized name called as BrowseName. An Object representing a ‘Reservation’ is shown in Figure 3.

Figure 3 – A Basic Object in an OPC UA Address Space

Object and Variable Nodes represent instances and they always reference a TypeDefinition (ObjectType or VariableType) Node which describes their semantics and structure. Figure 4 illustrates the relationship between an instance and its TypeDefinition.

The type Nodes are templates that define all of the children that can be present in an instance of the type. In the example in Figure 4 the PersonType ObjectType defines two children: First Name and Last Name. All instances of PersonType are expected to have the same children with the same BrowseNames. Within a type the BrowseNames uniquely identify the children. This means Client applications can be designed to search for children based on the BrowseNames from the type instead of NodeIds. This eliminates the need for manual reconfiguration of systems if a Client uses types that multiple Servers implement.

OPC UA also supports the concept of sub-typing. This allows a modeller to take an existing type and extend it. There are rules regarding sub-typing defined in [OPC 10000-3], but in general they allow the extension of a given type or the restriction of a DataType. For example, the modeller may decide that the existing ObjectType in some cases needs an additional Variable. The modeller can create a subtype of the ObjectType and add the Variable. A Client that is expecting the parent type can treat the new type as if it was of the parent type. Regarding DataTypes, subtypes can only restrict. If a Variable is defined to have a numeric value, a sub type could restrict it to a float.

Figure 4 – The Relationship between Type Definitions and Instances

References allow Nodes to be connected in ways that describe their relationships. All References have a ReferenceType that specifies the semantics of the relationship. References can be hierarchical or non-hierarchical. Hierarchical References are used to create the structure of Objects and Variables. Non-hierarchical are used to create arbitrary associations. Applications can define their own ReferenceType by creating subtypes of an existing ReferenceType. Subtypes inherit the semantics of the parent but may add additional restrictions. Figure 5 depicts several References, connecting different Objects.

Figure 5 – Examples of References between Objects

The figures above use a notation that was developed for the OPC UA specification. The notation is summarized in Figure 6. UML representations can also be used; however, the OPC UA notation is less ambiguous because there is a direct mapping from the elements in the figures to Nodes in the AddressSpace of an OPC UA Server.

Figure 6 – The OPC UA Information Model Notation

A complete description of the different types of Nodes and References can be found in [OPC 10000-3] and the base structure is described in [OPC 10000-5].

OPC UA specification defines a very wide range of functionality in its basic Information Model. It is not required that all Clients or Servers support all functionality in the OPC UA specifications. OPC UA includes the concept of Profiles, which segment the functionality into testable certifiable units. This allows the definition of functional subsets (that are expected to be implemented) within a companion specification. The Profiles do not restrict functionality, but generate requirements for a minimum set of functionality (see [OPC 10000-7])

OPC UA allows information from many different sources to be combined into a single coherent AddressSpace. Namespaces are used to make this possible by eliminating naming and id conflicts between information from different sources. Each namespace in OPC UA has a globally unique string called a NamespaceUri which identifies a naming authority and a locally unique integer called a NamespaceIndex, which is an index into the Server's table of NamespaceUris. The NamespaceIndex is unique only within the context of a Session between an OPC UA Client and an OPC UA Server- the NamespaceIndex  can change between Sessions and still identify the same item even though the NamespaceUri's location in the table has changed. The Services defined for OPC UA use the NamespaceIndex to specify the Namespace for qualified values.

There are two types of structured values in OPC UA that are qualified with NamespaceIndexes: NodeIds and QualifiedNames. NodeIds are locally unique (and sometimes globally unique) identifiers for Nodes. The same globally unique NodeId  can be used as the identifier in a Node in many Servers – the Node's instance data may vary but its semantic meaning is the same regardless of the Server it appears in. This means Clients can have built-in knowledge of what the data means in these Nodes. OPC UA Information Models generally define globally unique NodeIds for the TypeDefinitions defined by the Information Model.

QualifiedNames are non-localized names qualified with a Namespace. They are used for the BrowseNames of Nodes and allow the same names to be used by different Information Models without conflict. TypeDefinitions are not allowed to have children with duplicate BrowseNames; however, instances do not have that restriction.

An OPC UA companion specification for an industry specific vertical market describes an Information Model by defining ObjectTypes, VariableTypes, DataTypes and ReferenceTypes that represent the concepts used in the vertical market, and potentially also well-defined Objects as entry points into the AddressSpace.