1 Scope

The joint VDMA and OPC Foundation Working Group “VDMA OPC UA Weighing Technology Initiative” developed an OPC UA information model for communication of scale systems. Scale systems are defined as devices within a value chain that measure the weight or mass flow of a product or Object containing several additional parameters (e.g., price, tare of packaging, etc.). Scale systems stand for a complete weight measuring device that includes one or multiple scales. The scales may fulfill different use cases within one scale system (e.g., filling and price labeling). Each scale consists of one or multiple load cells which capture the weight. It is the smallest unit regarding the components of a scale system within this Companion Specification.

The OPC UA Weighing Technology Companion Specification covers the following scale system types directly: Automatic Filling Scales, catchweigher (Automatic Price Labeling Scales, Automatic Weight Labeling Scales, checkweigher), Continuously Scales, Hopper Scales, Laboratory Scales, Piece Counting Scales, Simple Scales, Totalizing Scales and Vehicle Scales.

Other scale systems including weighing bridges may be modeled based on this Companion Specification, but probably need to be extended by certain parameters.

NOTE: The scale system class “Retail Scales” is excluded by this information model. At this time there is no relevance for an OPC UA interface and therefore there is no information modelled for representing these devices.

2 Normative references

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) applies.

OPC 10000-1, OPC Unified Architecture - Part 1: Overview and Concepts

OPC 10000-3, OPC Unified Architecture - Part 3: Address Space Model

OPC 10000-4, OPC Unified Architecture - Part 4: Services

OPC 10000-5, OPC Unified Architecture - Part 5: Information Model

OPC 10000-7, OPC Unified Architecture - Part 7: Profiles

OPC 10000-8, OPC Unified Architecture - Part 8: Data Access

OPC 10000-9, OPC Unified Architecture - Part 9: Alarms and Conditions

OPC 10000-100, OPC Unified Architecture - Part 100: Devices

OPC 10000-100

OPC 10000-200, OPC Unified Architecture - Part 200: Industrial Automation - Basics

OPC 10000-200

OPC 30050, OPC UA for PackML

http://www.opcfoundation.org/documents/30050

OPC 40001-1, OPC UA for Machinery - Part 1: Basic Building Blocks OPC 40001-1

http://www.opcfoundation.org/documents/40001-1

3 Terms, definitions and conventions

3.1 Overview

For this specification it is assumed that basic concepts of OPC UA information modelling are understood. This specification will use these concepts to describe the OPC UA for the Weighing Technology Companion Specification Information Model. For the purpose of this document, the terms and definitions given in OPC 10000-1, OPC 10000-3, OPC 10000-4, OPC 10000-5, OPC 10000-7, OPC 10000-100, OPC 10000-200, OPC 30050, OPC 40001-1 as well as in the following apply.

NOTE: OPC UA terms and terms defined in this specification are italicized in the specification.

3.2 OPC UA for Weighing Technology terms

The terminology used in this specification conforms to

The International Vocabulary of Legal Metrology (VIML)

Basic and General Terms in Metrology (VIM)

D 11 General requirements for measuring instruments - Environmental conditions

R 76 Non-automatic weighing instruments,

D 31 General requirements for software-controlled measuring instruments.

In addition, the following definitions apply.

3.2.1 General Terms

3.2.2 State machine terms

The terms for state machine defined in OPC 30050.

3.3 Abbreviations and symbols

3.4 Conventions used in this document

3.4.1 Conventions for Node descriptions

Node definitions are specified using tables (see Table 3).

Attributes are defined by providing the Attribute name and a value, or a description of the value.

References are defined by providing the ReferenceType name, the BrowseName of the TargetNode and its NodeClass.

If the TargetNode is a component of the Node being defined in the table, the Attributes of the composed Node are defined in the same row of the table.

The DataType is only specified for Variables; “[<number>]” indicates a single-dimensional array, for multi-dimensional arrays the expression is repeated for each dimension (e.g. [2][3] for a two-dimensional array). For all arrays the ArrayDimensions is set as identified by <number> values. If no <number> is set, the corresponding dimension is set to 0, indicating an unknown size. If no number is provided at all the ArrayDimensions can be omitted. If no brackets are provided, it identifies a scalar DataType and the ValueRank is set to the corresponding value (see OPC 10000-3). In addition, ArrayDimensions is set to null or is omitted. If it can be Any or ScalarOrOneDimension, the value is put into “{<value>}”, so either “{Any}” or “{ScalarOrOneDimension}” and the ValueRank is set to the corresponding value (see OPC 10000-3) and the ArrayDimensions is set to null or is omitted. Examples are given in Table 2.

The TypeDefinition is specified for Objects and Variables.

The TypeDefinition column specifies a symbolic name for a NodeId, i.e., the specified Node points with a HasTypeDefinition Reference to the corresponding Node.

The ModellingRule of the referenced component is provided by specifying the symbolic name of the rule in the ModellingRule column. In the AddressSpace, the Node shall use a HasModellingRule Reference to point to the corresponding ModellingRule Object.

If the NodeId of a DataType is provided, the symbolic name of the Node representing the DataType shall be used.

Nodes of all other NodeClasses cannot be defined in the same table; therefore, only the used ReferenceType, their NodeClass and their BrowseName are specified. A reference to another part of this document points to their definition.

Table 3 illustrates the table. If no components are provided, the DataType, TypeDefinition and ModellingRule columns may be omitted and only a Comment column is introduced to point to the Node definition.

Components of Nodes can be complex that is containing components by themselves. The TypeDefinition, NodeClass, DataType and ModellingRule can be derived from the type definitions, and the symbolic name can be created as defined in 3.4.3.1. Therefore, those containing components are not explicitly specified; they are implicitly specified by the type definitions.

3.4.2 NodeIds and BrowseNames

3.4.2.1 NodeIds

The NodeIds of all Nodes described in this standard are only symbolic names. Annex A defines the actual NodeIds.

The symbolic name of each Node defined in this specification is its BrowseName, or, when it is part of another Node, the BrowseName of the other Node, a “.”, and the BrowseName of itself. In this case “part of” means that the whole has a 0:HasProperty or 0:HasComponent Reference to its part. Since all Nodes not being part of another Node have a unique name in this specification, the symbolic name is unique.

The namespace for all NodeIds defined in this specification is defined in Annex A The namespace for this NamespaceIndex is Server-specific and depends on the position of the namespace URI in the server namespace table.

NOTE: This specification not only defines concrete Nodes, but also requires that some Nodes shall be generated, for example one for each Session running on the Server. The NodeIds of those Nodes are Server-specific, including the namespace. But the NamespaceIndex of those Nodes cannot be the NamespaceIndex used for the Nodes defined in this specification, because they are not defined by this specification but generated by the Server.

3.4.2.2 BrowseNames

The text part of the BrowseNames for all Nodes defined in this specification is specified in the tables defining the Nodes. The NamespaceIndex for all BrowseNames defined in this specification is defined in Annex A.

If the BrowseName is not defined by this specification, a namespace index prefix like ‘0:EngineeringUnits’ or ‘2:DeviceRevision’ is added to the BrowseName. This is typically necessary if a Property of another specification is overwritten or used in the OPC UA types defined in this specification. Table 18 provides a list of namespaces and their indexes as used in this specification.

3.4.3 Common Attributes

3.4.3.1 General

The Attributes of Nodes, their DataTypes and descriptions are defined in OPC 10000-3. Attributes not marked as optional are mandatory and shall be provided by a Server. The following tables define if the Attribute value is defined by this specification or if it is server-specific.

For all Nodes specified in this specification, the Attributes named in Table 4 shall be set as specified in the table.

3.4.3.2 Objects

For all Objects specified in this specification, the Attributes named in Table 5 shall be set as specified in the table. The definitions for the Attributes can be found in OPC 10000-3.

3.4.3.3 Variables

For all Variables specified in this specification, the Attributes named in Table 6 shall be set as specified in the table. The definitions for the Attributes can be found in OPC 10000-3.

3.4.3.4 VariableTypes

For all VariableTypes specified in this specification, the Attributes named in Table 7 shall be set as specified in the table. The definitions for the Attributes can be found in

3.4.3.5 Methods

For all Methods specified in this specification, the Attributes named in Table 8 shall be set as specified in the table. The definitions for the Attributes can be found in OPC 10000-3.

4 General Information on Weighing Technology and OPC UA

4.1 Introduction to Weighing Technology Companion Specification

Scales are used in a wide range of applications. Therefore, this section describes the schematic structure of a scale and includes a simple classification of scale types.

4.1.1 Schematic Structure of a Scale system

In addition to the definition of a scale of OIML R76 the following definition applies:

A scale is a computer system, device or measuring instrument used to determine the mass or mass flow of a quantity of material and consisting of one or more weighing modules (including load receptor, load-transmitting device, load cell and data processing device) and additional modules or peripheral devices (see Figure 1). Each weighing module determines a mass. The weighing result of the scale may be the result of one weighing module or the addition of several weighing modules. Not all partial results need to be included in the result.

In addition, a scale can also have subdevices such as printers or feeder systems. Each scale needs a data processing device and at least one interface like a display or field bus. Thus, an interaction other than OPC UA is always possible.

Each scale provides a specific set of functions. These functions can be divided into three categories. The basic set of functions is available for all scales and behaves the same way for all scales. The scale type functions depend on the scale types (see Section 5.1.2) and behave the same within this type. An example is the administration of zones at the checkweigher or the administration of recipes at the recipe scale. In addition, further functions or applications can be specifically defined by a vendor.

A scale system is the combination of several scales that are addressed by a common interface and can have additional functions, such as a state machine or a production preset. However, a scale must be included in any case.

The schematic described here is a significant simplification of scales and focuses on the external representation of entire scale systems. It does not include any metrological details. In addition, real systems can deviate significantly from this schematic.

4.1.2 Introduction into scale classification

This classification of the scales is based on the aspect of communication via OPC UA. If possible, existing classifications (e.g., from OIML) were used. However, further conflicting classifications may exist. Since the boundaries are partly fluid, some devices can be assigned to several scale types. The resulting classification is shown in Figure 2.

The definitions of the individual types can be found in Table 9.

4.1.3 Product Handle Handling of product-related information

In addition to measuring, scales may also perform other tasks such as managing product data (production presetting and statistics/production output). To ensure that product-related information does not become inconsistent during the weighing process, it must be protected accordingly. For this purpose, a corresponding product information handle model shown in Figure 4 is described in this Companion Specification. It defines two different modes (ProductHandleMode/AccessRestrictionMode).

The ProductHandleMode indicates if a product can currently be processed by the scale or not. It is possible that the product-related information can be writeable or read only in both modes. The transition between the two states of the mode can be triggered internally in the scale or via the OPC UA methods SelectProduct, DeselectProduct, SwitchProduct (see sections 7.7 - 7.8). In some cases, it is possible that several products are in the "Processing" mode. For example, a catchweigher can process different products in parallel, while a continuous scale can only process one product at a time.

The AccessRestrictionMode can be used to define the access restriction of the product. A client can make a set of changes (e.g., multiple write operations and method calls) only when the mode is in "WritableMode". This mode applies to the entire product Object, including all components such as zones. The access level of all child nodes of the product Object should at least have written access and the method should be executable. The AccessRestritionMode is used via the LockingService descripted in OPC 10000-100.

NOTE 1: When a physical product is to be processed but is not in the correct mode or has no OPC UA representation, the behavior of the scale is application-specific and must be specified separately.

NOTE 2: The combination of the "Processing" mode and the "Writable" mode should be used with caution, as the writable element may be in an inconsistent state.

4.2 Introduction to OPC Unified Architecture

4.2.1 What is OPC UA?

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 Weighing Technology Companion Specification, 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.

4.2.2 Basics of OPC UA

As an open standard, OPC UA is based on standard 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 example of 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 5.

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.

4.2.3 Information modelling in OPC UA

4.2.3.1 Concepts

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 0: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 6.

Object and Variable Nodes represent instances, and they always reference a TypeDefinition (ObjectType or VariableType) Node which describes their semantics and structure. Figure 7 illustrates the relationship between an instance and its TypeDefinition.

The type Nodes are templates that define all the children that can be present in an instance of the type. In the example in Figure 7 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.

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 8 depicts several References, connecting different Objects.

The figures above use a notation that was developed for the OPC UA specification. The notation is summarized in Figure 9. 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.

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 expected 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 functionalities (see OPC 10000-7).

4.2.3.2 Namespaces

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. Namespaces in OPC UA have a globally unique 0:String called a NamespaceUri, and a locally unique integer called a NamespaceIndex. The NamespaceIndex is only unique within the context of a Session between an OPC UA Client and an OPC UA Server. The Services defined for OPC UA use the NamespaceIndex to specify the Namespace for qualified values.

There are two types of values in OPC UA that are qualified with Namespaces: NodeIds and QualifiedNames. NodeIds are globally unique identifiers for Nodes. This means the same Node with the same NodeId can appear in many Servers. This, in turn, means Clients can have built in knowledge of some 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.

4.2.3.3 Companion Specifications

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.

4.2.4 RelativePath

A RelativePath is a structure that describes a sequence of References and Nodes to follow. Annex A of Part 4 Services describes a text format for a RelativePath that can be used in documentation or in files used to store configuration information

The components of a RelativePath text format are specified in Table 10.

5 Use cases

5.1 General

This Weighing Technology Companion Specification describes how a scale system is addressed via OPC UA. For this purpose, the following primary use cases for the different scale types from section 4.1.2 were considered. Other use cases can also be covered or specified in other standards (vendor or Companion Specification).

In all defined use cases the scale system usually has the role of an OPC UA server. Therefore, this specification describes and defines the way an OPC UA client can read or write data and control the scale system via OPC UA. A scale system may also have a different interface (e.g., an HMI) that can control the scale as well. Some peripheral devices (e.g., printer, feeder) are also described in this specification but the communication between the peripheral devices and the scale is not part of the description.

NOTE: The OPC UA Companion Specification for Weighing Technology does not consider any use cases that are affected by legal requirements (like official verification). For example, further parameters may be necessary for external data access or existing parameters may not be read out. A country-specific extension of the Companion Specification would be conceivable.

5.2 Accessing Data of measurement results and statistics

An important application of a scale is the data access of individual measurement results. In many cases, the measurement result is a weight value with a unit derived from the weight (e.g., flow rate, volume, ...). A distinction can be made between the continuous display of the measured value (called “current Weight”) and a measurement (internal or external) that has been registered (called “registered Weight”). A registration could be triggered from an OPC UA-Client. The use case also includes the needed meta-data (e.g., product ID, unit) for identifying the result in further processing.

In some cases, the individual measurement result is not relevant or only of minor relevance. In some cases, a statistic (mean value, standard deviation) over several measured values or over a period of time is required.

5.3 State Machine of the Scale

A defined state machine enables the user to obtain a uniform overview of different devices from different manufacturers. This is useful in applications with a large number of machines. The interaction between a client system and the scale system depends on the current state of the device. Transition between two states can be triggered by method calls from an OPC UA client, by another interface or internally. Each state change creates an event in the OPC UA server. The PackML state machine is used for the scale system, as it is already in use in Weighing Technology, e.g., for checkweighers, and can be adapted accordingly for other scales. A more detailed description of the state machine can be found in the Companion Specification PackML for OPC UA. NOTE: Scales do not have to implement the SubStateMachine within the state "Execute".

5.4 Production Preset

Part of the access of a higher-level system to a weighing system is the management of products. This standard describes a way of creating, editing and selecting products on the scale. The entire information flow via OPC UA can also run completely or in parts via different interfaces. The schematic structure of production management is described in Section 5.1.3.

NOTE: For recipe scales, this use case also includes the creation, editing and administration of recipes. Recipe management is based on the OPC UA Companion Specification for machine vision. The structure and concept for recipes are described in section 5.1.4 and Annex B.

6 Weighing Technology Information Model overview

6.1 General

The information model for Weighing Technology has three main aspects: the generic part for all scale devices, the production management and the scale type specific part.

6.2 Overview of generic Scales

Figure 10 shows an overview of the different ObjectTypes for the Weighing Technology devices and the references to the types from the Companion Specification for devices. Four subtypes of the ComponentType are defined:

FeederModuleType

PrinterModuleType

ScaleSystemType

ScaleDeviceType

The entry point of a server is an instance of the ScaleSystemType or a ScaleDeviceType. The ScaleSystemType represents a multi-scale system and includes one or more scales and has some common information (e.g., serial number). The ScaleDeviceType is abstract and only subtypes of it can be instantiated (see section 6.3). Both Types (ScaleDeviceType and ScaleSystemType) can optionally have an Object of the ProductionPresetType (see section 7.7) and/or an Object (called ProductionOutput) of the StatisticType.

Figure 10 shows the most important Object types used in the information model and the relations between them.

6.3 Modular scale devices

A modular scale device is represented by a (subtype of) ScaleDeviceType or ScaleSystemType that is composed of a top-device and a set of subdevices (modules). It uses the modular devices concept of OPC UA Companion Specification for Devices (see OPC 10000-100 9.2). The modules (subdevices) of modular scale devices are aggregated in the SubDevices Object. The SupportedTypes folder for SubDevices is used to maintain the set of modules that can be added to the ScaleDevice or scale system (see Figure 11).

This Companion Specification defines the following supported types (including the subtypes) for the ScaleDeviceType:

FeederModuleType

PrinterModuleType

WeighingModuleType

This Companion Specification defines the following supported type (including the subtypes) for the ScaleSystemType:

ScaleDeviceType

The SupportedTypes folder may only refer to a subset of all possible subdevices for the modular device. Other vendor-specific modules or modules of other Companion Specifications can be defined. For more details of the concept see OPC 10000-100.

6.4 Subtypes of the ScaleDeviceType

In the information model different subtypes of a ScaleDeviceType are defined for the different scale types (see section 4.1.2). For many subtypes of the ScaleDeviceType, a subtype of the ProductType exists as a counterpart. The ProductFolder defined in the ScaleDeviceType is overload and can only contain the specific subtype of the ProductType or a subtype of them.

Figure 12 shows the main Object types used in the information model and the relations between them.

7 OPC UA ObjectTypes

7.1 FeederModuleType Definition

7.1.1 Overview

The FeederModuleType defines the structure of an Object of the FeederModuleType. Figure 13 shows the hierarchical structure and details of the composition. It is formally defined in Table 11.

An Object of the FeederModuleType represents a feeder system. A feeder system is a subdevice of an automatic scale for conveying the product (e.g., a belt or a screw conveyor) to or from the WeighingBridge. A feeder must be part of another device (e.g., an Object of the ScaleDeviceType).

The Type defines a general communication interface for a feeder system. It contains only variables and methods.

7.1.2 ObjectType Definition

The components of the FeederModuleType have additional references which are defined in Table 12.

7.1.3 ObjectType Description

FeederLoad defines the current loaded weight on the feeder system.

FeederRunning indicates that the feeder system is running.

FeederSpeed defines the current speed of a feeder system. The unit of the FeederSpeed depends on the construction system. Possible values are velocity or a flow rate (kg/s).

MaximumFeederSpeed defines the maximum possible speed of the feeder.

MinimalFeederSpeed defines the minimal possible speed of the feeder.

The Identification-AddIn contains information about the identification and nameplate of a feeder.

MachineryItemState is used as defined in OPC 40001-1. Shall also be referenced as AddIn in the MachineryBuildingBlocks Folder

MachineryOperationMode is used as defined in OPC 40001-1. Shall also be referenced as AddIn in the MachineryBuildingBlocks Folder

MachineryBuildingBlocks is used as described in OPC 40001-1.

7.1.4 Method SetFeederSpeed

Allows to set a new value for the speed of the feeder system. The OPC UA server must check if the value is between the minimal and maximum allowed speed and if the unit is allowed. The signature of this Method is specified below. Table 13 and Table 14 specify the Arguments and AddressSpace representation, respectively.

Signature

	SetFeederSpeed(
	[in]	Float		FeederSpeed
	[in]	EUInformation		EngineeringUnits);

7.2 PrinterModuleType Definition

7.2.1 Overview

The PrinterModuleType defines the structure of an Object of the PrinterModuleType. Figure 14 shows the hierarchical structure and details of the composition. It is formally defined in Table 15.

An Object of the PrinterModuleType represents a printing device. A printing device is a subdevice of a scale that prints labels or other documents related to the scale or to the measurement results. The variables of the module are only readable. So, the primary use case of the module is to monitor the label and print media status.

7.2.2 ObjectType Definition

The components of the ObjectType have additional subcomponents which are defined in Table 16

7.2.3 ObjectType Description

LabelLength defines the length of the labels in stock.

LabelStock indicates the level of labels in stock in percent.

LabelTypeId defines the Id of the label to be printed.

LabelWidth defines the width of the labels in stock.

PrintMediaStock defines the level of the print media in percent (e.g., ink, wear of thermal element, etc.).

The Identification-AddIn contains information about the identification and nameplate of a printer.

MachineryItemState is used as defined in OPC 40001-1. Shall also be referenced as AddIn in the MachineryBuildingBlocks Folder

MachineryOperationMode is used as defined in OPC 40001-1. Shall also be referenced as AddIn in the MachineryBuildingBlocks Folder

MachineryBuildingBlocks is used as described in OPC 40001-1.

7.3 ScaleSystemType Definition

7.3.1 Overview

The ScaleSystemType defines the structure of an Object of the ScaleSystemType. Figure 15 shows the hierarchical structure and details of the composition. It is formally defined in Table 17.

An Object of the ScaleSystemType represents a scale system and contains one or more scales. The ScaleSystemType defines a general communication interface for a scale system and is the entry point for clients. This interface makes it possible to interact with this system independent of the knowledge of the internal structure and the underlying processes of the scale system.

The system is modelled with a finite state machine and contains primary information about the state and the status of the system. It optionally can also contain the objects ProductionPreset and ProductionOutput.

7.3.2 ObjectType Definition

7.3.3 ObjectType Description

The Identification-AddIn contains information about the identification and nameplate of a machine.

A scale system can contain one or more scales. The scales must be a subtype of the ScaleDeviceType but must not be of the same type. The ScaleDeviceType is described in section 7.4.

Policy defines the legal guidelines that apply for the scale or need to be complied by the scale.

ProcessStateId contains a relating identification for the occurring ProcessStateMessage.

ProcessStateMessage contains the message of the current overall state of the scale.

ProductionPreset contains the production presets. See section 7.7 for the complete definition of the ProductionPresetType.

SystemState provides information about the current state of the scale system and methods for controlling it. PackMLBaseStateMachineType is defined in OPC 30050.

ProductionOutput defines the overall statistic for the scale production.

The modules (subdevices) of a scale system are aggregated in the SubDevices Object (see section 6.3 and OPC 10000-100).

MachineryItemState is used as defined in OPC 40001-1. Shall also be referenced as AddIn in the MachineryBuildingBlocks Folder

MachineryOperationMode is used as defined in OPC 40001-1. Shall also be referenced as AddIn in the MachineryBuildingBlocks Folder

MachineryBuildingBlocks is used as described in OPC 40001-1.

The components of the ScaleSystemType have additional references which are defined in Table 19.

7.3.4 Method ResetGlobalStatistics

All statistics relating to the scale system but not to a product are reset.

Signature

	ResetGlobalStatistics(
	);

7.4 ScaleDeviceType Definition

7.4.1 Overview

The ScaleDeviceType defines the structure of an Object of the ScaleDeviceType. Figure 16 shows the hierarchical structure and details of the composition. It is formally defined in Table 20.

The ScaleDeviceType is an abstract ObjectType. An Object of a subtype of the ScaleDeviceType represents a scale. The ScaleDeviceType contains all information that is relevant for most of the scale types. The system is modeled with a finite state machine and contains primary information about the state and the status of the system.

7.4.2 ObjectType Definition

The components of the ScaleDeviceType have additional references which are defined in Table 21.

7.4.3 ObjectType Description

AllowedEngineeringUnits contains an array of engineering units that can be handled by the OPC UA server. A server that supports a method with the input argument EUInformation must also provide this array.

CurrentWeight defines the current value that is measured at the sensor at the current timestamp. This might be a highly fluctuating value.

MaterialClass defines the allowed material the scale may measure. It is only relevant for certain scales (e.g., totalizing hopper scale or continuous scale).

The MinimalWeight is the smallest sample quantity required for a weighment to just achieve a specified relative accuracy of weighing (see also EURAMET Calibration Guide No. 18). So it is the smallest load or component of a recipe that may be weighed on the scale. SubDevices: the modules (subdevices) of a modular scale are aggregated in the SubDevices Object. See OPC Unified Architecture for Devices for more information.

ProcessStateId contains a relating identification for the occurring ProcessStateMessage.

ProcessStateMessage contains the message of the current overall state of the scale.

ProductionOutput defines the statistic for the scale prodution related to this ScaleDeviceType instance.

ProductionPreset contains the production presets. See section 7.7 for the complete definition of the ProductionPresetType.

RegisteredWeight defines the last valid measurement that was recorded and will be used for further processing.

<ListOfWeighingRanges> defines the weighing range and resolution the scale may operate in with a structure of range and resolution.

Policy defines the legal guidelines that apply for the scale or need to be complied by the scale.

ScaleStateMachine provides information about the current state of the scale system and methods for controlling it. PackMLBaseStateMachineType is defined in OPC 30050.

MachineryItemState is used as defined in OPC 40001-1. Shall also be referenced as AddIn in the MachineryBuildingBlocks Folder

MachineryOperationMode is used as defined in OPC 40001-1. Shall also be referenced as AddIn in the MachineryBuildingBlocks Folder

MachineryBuildingBlocks is used as described in OPC 40001-1.

The components of the ScaleDeviceType have additional subcomponents which are defined in Table 22.

7.4.4 Method ClearTare

The tare value is set to zero or deleted.

Signature

	ClearTare(
	);

7.4.5 Method RegisterWeight

Triggers the registration of a measured value and a new value for the RegisteredWeight will be calculated.

Signature

	RegisterWeight(
	);

7.4.6 Method SetPresetTare

The method set the current PresetTare.

Signature

	SetPresetTare(
	[in]	Double		PresetTare
	[in]	EUInformation		EngineeringUnits);

7.4.7 Method SetZero

The method sets zero point. It uses the gross value of the CurrentWeight value.

Signature

	SetZero (
	);

7.4.8 Method SetTare

The method triggers the tare operation. The CurrentWeight value is used as the tare.

Signature

	SetTare(
	);

7.5 WeighingRangeElementType Definition

7.5.1 Overview

The WeighingRangeElementType defines the structure of an Object of WeighingRangeElementType. Figure 17 shows the hierarchical structure and details of the composition. It is formally defined in Table 25.

7.5.2 ObjectType Definition

7.5.3 ObjectType Description

ActualScaleInterval defines the difference between two consecutive indicated values.

Range defines the range within the scale that may be operated depending on the additional parameters within this type.

Range.EngineeringUnit defines the engineering unit of the range.

VerificationScaleInterval defines the value, expressed in units of mass, used for the classification and verification of an instrument.

The components of the WeighingRangeElementType have additional references which are defined in Table 26

7.6 StatisticType Definition

7.6.1 Overview

The StatisticType defines the structure of an Object of StatisticType. Figure 18 shows the hierarchical structure and details of the composition. It is formally defined in Table 27.

The StatisticType is a container for the different statistic values. All variables are optional so that the statistics can be instantiated in an application-specific way. The StatisticType can be instantiated with parent nodes (e.g., ScaleDeviceType, …). Parent nodes other than those described in this Companion Specification are possible.

7.6.2 ObjectType Definition

7.6.3 ObjectType Description

StartTime defines the point in time at which the system starts acquiring the statistic (e.g., 15:00). This value is relevant for time statistics. For example, it can be used to create statistics for the last 3 hours.

ResetCondition is a vendor-specific, human readable string that describes the reason and context for the reset of the statistics. For example, after 4 hours or after 1000 items. Please note that the subtype FloatingStatisticType is used for floating statistics.

	Examples:
	ResetCondition::= “AFTER 4 HOURS”
	ResetCondition::= “AFTER 1000 ITEMS”
	ResetCondition::= “OPERATOR”

Tare defines the last occurring tare value of the period of time which is used for the statistic.

Throughput defines the number of items registered over the period of the statistic (e.g., packages/min).

TotalPackages defines the totalized number of packages of one cell for weight determination. Contains packages that were sorted out but were physically transported via the scale. This value may be calculated by TotalPackagesAccepted + TotalPackagesRejected.

TotalPackagesWeighed defines the totalized number of packages for which a weight was measured. No reference to acceptance or rejection of the package.

LastItem contains the values of the last item.

7.7 ProductionPresetType Definition

7.7.1 Overview

The ProductionPresetType defines the structure of an Object of ProductionPresetType. Figure 19 shows the hierarchical structure and details of the composition. It is formally defined in Table 28.

ProductionPresetType provides methods to manage the production preset.

7.7.2 ObjectType Definition

7.7.3 ObjectType Description

CurrentProducts is an array containing the Ids of all product objects currently in processing mode. The product process can be started using the SelectProduct method or another interface or an external trigger signal.

Products contains the products used in the scale aggregated in the Products Object. The objects in the folder should have the type ProductType or a subtype of it. The subcomponents of the Products Object are defined in Table 29.

7.7.4 Method AddProduct

The method creates an Object with a subtype of ProductType from the address space. The Object needs a reference of the type "0:HasComponent" to the product folder of the scale device. The signature of this Method is specified below. Table 30 and Table 31 specify the Arguments and AddressSpace representation, respectively.

Note: To simplify the handling, it is recommended that during the creation of the product the object is immediately locked for the client. (see section 7.8)

Signature

	AddProduct(
	[in]	String		ProductName
	[in]	String		ProductId
	[in]	NodeId		ProductType
	[out]	NodeId		ProductNodeId
	);

7.7.5 Method SelectProduct

Selects the product. The scale is now able to process the product. This includes that the ID is saved in the CurrentProducts array and that the ProductMode switches from "Not processing" to "Processing". Table 32 and Table 33 specify the Arguments and AddressSpace representation, respectively.

Signature

	SelectProduct (
		[in]	String		ProductId
	);

7.7.6 Method DeselectProduct

Deselects the product. The scale should stop to process the product. This includes that the ID is removed in the CurrentProducts array and that the ProductMode switches from "Processing" to "Not processing". The signature of this Method is specified below. Table 34 and Table 35 specify the Arguments and AddressSpace representation, respectively.

Signature

	DeselectProduct (
		[in]	String		ProductId
	);

7.7.7 Method RemoveProduct

The method removes an Object from the address space with a subtype of the ProductType. The signature of this Method is specified below. Table 36 and Table 37 specify the Arguments and AddressSpace representation, respectively.

Signature

	RemoveProduct (
		[in]	String		ProductId
	);

7.7.8 Method SwitchProduct

Selects the new product and deselects the old product. The scale is now able to process the new product. This includes that the new ID is saved in the CurrentProducts array and that the ProductMode switches from "Not processing" to "Processing". Additionally, the old ID is removed in the CurrentProducts array and the ProductMode of the old product switches from "Processing" to "Not Processing". This method is only possible if only one product is used. The signature of this Method is specified below. Table 38 and Table 39 specify the Arguments and AddressSpace representation, respectively.

Signature

	SwitchProduct (
		[in]	String		ProductId
	);

7.8 ProductType Definition

7.8.1 Overview

The ProductType is an abstract type that defines the basic structure of all objects that represent a product. Figure 20 shows the hierarchical structure and details of the composition. It is formally defined in Table 40. An Object of the type ProductType represents a product related to the scale.

The different subtypes of the ProductType are described in the following sections. The ProductType only contains the basic information about a product. The scale type-specific information is modeled in the subtypes for the different scale types. The Create Method makes it possible that a vendor can add own Variables and extend the Create Method.

7.8.2 ObjectType Definition

7.8.3 ObjectType Description

BatchId is the ID of the batch to which this product belongs.

BatchName is the human-readable name of the batch to which this product belongs.

JobId is the ID of the job to which this product belongs.

JobName is the human-readable name of the job to which this product belongs.

PresetTare defines the predefined tare weight. The value must be written before the item is measured.

ProductId defines a unique ID of this product.

The ProductMode displays the current mode of the product. The ProductType instance can be in the mode "Processing" or "Not Processing". The mode is independent from the Lock. Thus, it is possible that a product is in the "Processing mode" and writeable. The combination of these both modes should be used with care as the writeable element may be in an inconsistent state. If the ProductMode is true the Object is in "Processing". Otherwise, it is in the mode "Not Processing".

ProductName defines the name of this product.

Lock is used as container for the LockingServicesType Methods and Properties. It is defined in OPC 10000-100 (Locking). In addition to this definition, the server can also lock an object of the ProductType. In this case the property LockingClient contains the ProductUri of the server and LockingUser contains an empty String.

NOTE: If an Object is writeable not all variables must be writeable. There can be additional restrictions based on the implementation.

Statistic contains the different statistic values of the product. The statistic can’t be reset manually. All measurements that relate to the product of the job will be used in the statistics.

The components of the ProductType have additional Attributes defined in Table 41.

7.9 AutomaticFillingScaleType Definition

7.9.1 Overview

The AutomaticFillingScaleType defines the structure of an Object of the AutomaticFillingScaleType. Figure 21 shows the hierarchical structure and details of the composition. It is formally defined in Table 42.

An Object of AutomaticFillingScaleType represents an automatic filling scale. It defines additional Methods and Properties required for managing automatic filling scales.

7.9.2 ObjectType Definition

7.9.3 ObjectType Description

Deviation defines the relative amount of over (positive value) or under (negative value) dosed value in relation to the TargetWeight.

ToleranceState describes the state of the tolerance deviation. Under: underneath the lower tolerance value. Over: above the upper tolerance value. In: within the tolerance values. The options “under” and “over” need to be determined via the TargetItemType information of TargetWeight.

ProductionPreset, which is inherited from ScaleDeviceType shall have instances of AutomaticFillingProductType or a subtype in the Products folder.

7.10 AutomaticFillingProductType Definition

7.10.1 Overview

The AutomaticFillingProductType defines the structure of an Object of the AutomaticFillingProductType. Figure 22 shows the hierarchical structure and details of the composition. It is formally defined in Table 43.

An Object of AutomaticFillingProductType represents a product of an automatic filling scale. It defines additional methods and properties required for managing the product.

7.10.2 ObjectType Definition