In order to provide measured energy consumption, either current values or aggregated values (counters), the information model enables to create Objects of ObjectType EnergyMeasurementType with potentially several measurements measured at the same point in a system represented by Variables of VariableType EnergyMeasurementValueType. Those Objects may have a Method to reset the aggregated values. How those Objects are connected to other parts of an information model (e.g., for a device or a machine) is not addressed by this specification. The EnergyMeasurementValueType provides additional meta data of the measurement like the engineering unit.
In Figure 8, an overview of the EnergyMeasurementType and the EnergyMeasurementValueType is given. They are formally defined in 7.1.1 and 8.1.
Figure 8 – Overview EnergyMeasurementType and EnergyMeasurementValueType
In Figure 9, an example of the usage of those TypeDefinitions is given. The “X:SampleObject” contains two instances of EnergyMeasurementType, one measuring the electrical power and one the air extraction. Both contain different measurement values, like pressure, volume, and temperature.
Figure 9 – Example of usage of EnergyMeasurementType
Instead of defining the different type of measurements in a large variety of TypeDefinitions or InstanceDeclarations, this specification defines a container for measurement identifiers (MeasurementID) and a list of those standardized identifiers. In Table 15, the format of the table containing the standardized IDs is given. The file, as comma separated value file is published in addition to this document (see Annex A).
Table 15 – Format of Definition of standardized Measurements
|
MeasurementID |
BrowseName |
Description |
EngineeringUnits |
MeasurementPeriod |
DataType |
HasStatisticComponent |
|
|
|
|
|
|
|
|
The MeasurementID is a unique numeric identification. The BrowseName (leaving out the NamespaceIndex, which is always the one of this specification (see Annex A)), is a unique identification that is used as BrowseName for instances of the EnergyMeasurementType. Those BrowseNames are also used for the interfaces (see 6.2.3). The Description (in English) may be used as the Description Attribute for those Nodes.
For all instances of EnergyMeasurementType using the BrowseName as defined in the table, the EngineeringUnits shall be used for the 0:EngineeringUnits Property, the DataType shall be used as DataType (Attributes DataType and ValueRank), and the MeasurementPeriod shall be used for the MeasurementPeriod. If no EngineeringUnits is provided in the table, the 0:EngineeringUnits Property shall not be provided as well. If no MeasurementPeriod is provided in the table, the MeasurementPeriod Property shall not be provided as well. The MeasurementPeriod is the interval of time over which the data is collected and at the end of the period being reported. If the MeasurementPeriod is defined as “user-defined”, the MeasurementPeriod Property shall be provided, but the value is not pre-defined. If it is defined to start in the full hour (see Description), a multiple of the value shall fit into one hour.
The HasStatisticComponent defines, if the 2:HasStatisticComponent ReferenceType shall be used to reference the Variable of EnergyMeasurementType (YES), or the 0:HasComponent ReferenceType shall be used (NO). Using 2:HasStatisticComponent indicates, that the Variable is aggregating values over time and may be reset, potentially using the 2: ResetStatistics Method (see 7.1.1).
Note that the referenced file is part of the specification, and changes in the file are considered as changes in the specification, requiring the normal update process.
In general, measurements of voltage and current are RMS values calculated over 3 seconds or 10 minutes as described in IEC 61000-4-30. Note: 3s corresponds to 150 cycles on a 50Hz system or 180 cycles on a 60 Hz system.
Energy values are calculated over a period of time, typically 15 minutes, as described in IEC 61577-12.
Values described as minimum or maximum values are calculated over the period since the last reset.
For measurements defined in this companion standard that do not have a specific measurement period, the system integrator or manufacturer may use any period that is appropriate or available.
The BrowseNames of the standardized measurement identifiers follow the following naming conventions:
- AcPe: Phase to Neutral
- AcPp: Phase to phase
- Lp: Low Precision (Float DataType)
- Hp: High Precision (Double DataType)
- Total: concerns all phases
- Sum: concerns the sum of all measured import and export parts (sum = import - export)
Some explanations to the Description text in the table:
- Qtot is according to IEC61557-12 [4] the reactive power calculated by the triangle formula, also known as Fryze's definition (harmonics are specified vendor specific)
- Qn is according to IEC61557-12 [4] the reactive power calculated according to the Budeanu's harmonic definition (harmonics are specified vendor specific)
Measurements defined to have the DataType Int16[5] represent values as defined in [8].
Some combinations of measurement values are reasonably provided together. This specification standardizes some of those combinations by defining interfaces containing all those combinations. Applications may implement those interfaces and thereby provide the combinations of measurement values.
Standardized interfaces are defined in 7.1.3 An example, how standardized interfaces are used is shown in Figure 10. The interface can either be used directly on an instance, like on MyMeasurementPoint, or on a ObjectType like on MyEnergyMeasurementType.
Figure 10 – Example of usage of interfaces
Individual measurements (Variables of EnergyMeasurementValueType) have a specific accuracy class defined by a specific accuracy domain. This specification defines accuracy domains in a way, that it is possible to add additional accuracy domains. Each accuracy domain is represented by an Object of AccuracyDomainType (see 7.1.2). The Objects can be browsed from the standardized AccuracyDomains Object (see 10.1), allowing a Client to receive all accuracy domains used by the Server (see Figure 11). This specification defines standardized accuracy domains in 10.
The Object representing an accuracy domain contains the EnumValues Property containing the different accuracy classes defined by the accuracy domain. Each measurement of EnergyMeasurementValueType references its accuracy domain by the Property AccuracyDomain of DataType NodeId. The accuracy class is provided in the AccuracyClass Variable. This Variable of MultiStateValueDiscreteType shall either reference the EnumValues Property of the referenced accuracy domain Object (see VariableA in Figure 12 as example) or it shall contain a copy of that Property containing the same values (see VariableB in Figure 12 as example).
