One of the main challenges in the food and beverage as well as in the packaging industry is the production of high-quality products at acceptable market prices. To remain competitive, an effective IT assistance for their in-company processes is used in form of production management systems, so-called Manufacturing Execution Systems (MES). The MES is responsible for refining the production orders, which are roughly planned in the Enterprise Resource Planning (ERP) by assigning them to production lines and monitoring the order in production. The functions also include reporting efficiency parameters back to the ERP and optimizing production processes.
The strength of the Weihenstephan Standards is that they are practical and specifically adapted to a domain.
The Weihenstephan Standards are currently available for four different domains:
- WS Pack for the packaging and bottling industry, published in 2005
- WS Food for the food processing industry, published in 2010
- WS Bake for the baking industry, published in 2015
- WS Brew for the process area of breweries and beverage companies, published in 2019
The advantages of the Weihenstephan Standards are that they greatly simplify the definition of MES functionalities and the data points required for them during the project planning phase. In the implementation phase, the time required can be greatly reduced by using WS tools, which leads to a considerable reduction in costs.
This is possible because the Weihenstephan Standards take on three tasks (see Figure 1):
- exemplary definition of MES functionalities that are specifically tailored for a WS domain
- definition of data points derived from the MES functions
- definition of the communication protocol and information model between the data sources and the MES
Figure 1 – Communication via Weihenstephan Standards
On the way to Industry 4.0, the hierarchical structures of the automation pyramid are breaking down more and more. This is also reflected in the Weihenstephan Standards, the data points required for the MES functionalities are not only provided directly by machines. Instead, the data is already aggregated and made available by process control systems, for example. Figure 1 illustrates the structured communication between an MES and different communication partners in a heterogeneous system for the provision of data according to the Weihenstephan Standards.
Within a WS domain, the processing of machine and process data is defined for various MES functions that are required in the respective domains. The standard shows how data points can be used to calculate parameters, track batches or create clear production reports.
The Weihenstephan Standards cover exemplary the following areas for MES functionalities:
- Efficiency analysis
- KPIs
- Production control
- Material management
- Batch tracing
- Quality control
In addition, WS DataPoints enable extensive visualization functions or continuous production monitoring, e.g. with regard to production efficiency and machine performance.
An example of such visualization is the quick comparison of production efficiency shown in Figure 2.
Figure 2 – Visualization of states and OEE with Weihenstephan Standards
Both the WS BrowseName and the WS TagNumber are unique for the identification of a data point. In OPC UA for Weihenstephan Standards the WS BrowseName is used for identification; in WS Protocol this is mainly the WS TagNumber. The prefix WS_ in the WS BrowseName indicates that it is a data point of the Weihenstephan Standards. Members of the WS Industrial User Group can add more data points to their machines with their own vendor-specific prefix. The assignment of the WS TagNumber is defined in the WS Protocol. The WS DisplayName of a WS DataPoint can be defined in different languages and serves as a short description for e.g. the labelling of fields in an HMI. The description of a data point contains the exact definition of this data point. The description can also be provided in different languages. The WS DisplayName and the description of a data point are available at least in English. Each data point is assigned to a category. The available categories are listed and described in Table 10. The Access permission property determines whether a data point can only be read or can also be written via the interface.
The data type of a WS DataPoint is defined depending on the interface used. See chapter 4.1.4.
WS DataPoints of all domains in the Weihenstephan Standards are structured according to the same scheme (Table 9).
Table 9 – Definition of a WS DataPoint
|
Property |
Description |
Example |
|
WS BrowseName |
The WS BrowseName is used to uniquely identify a WS DataPoint. In OPC UA this corresponds to the Browse-Name. |
WS_Temp_Min |
|
WS DisplayName |
The name is used to describe a WS DataPoint and can be displayed in different languages. In OPC UA this corresponds to the display name. |
EN: Minimum Temperature DE: Minimale Temperatur |
|
WS Category |
The WS DataPoints are divided into different categories. An overview of the categories can be found in Table 10. |
Computed values |
|
WS TagNumber |
The WS TagNumber is mainly used to uniquely identify a WS DataPoint in WS Protocol. In WS OPC UA the WS TagNumber can be added to each WS DataPoint optionally. |
2006 |
|
Access permission |
Access rights of a client to a WS DataPoint. |
Read only |
|
Description |
Definition of the content of a WS DataPoint. |
EN: This data point gives the minimum temperature value during an operation/procedure. DE: Dieser Datenpunkt gibt die minimale Temperatur während einer Operation/Prozedur an. |
|
Base quantity/engineering units |
Informs about the base quantity of the WS DataPoint and gives a recommendation for the engineering units used for this WS DataPoint. The recommendations follow the UNECE code or domain-specific recommendations. |
°C / °F or Packages / Minutes |
|
WS OPC UA type definition |
The type definition that is used for a WS DataPoint in WS OPC UA. |
WSAnalogUnitType |
|
WS OPC UA data type |
The data type that is used for a WS DataPoint in WS OPC UA. |
UInt32 |
|
WS Protocol data type |
The data type that is used for a WS DataPoint in WS Protocol. |
Real |
|
WS Protocol annotation |
In the WS Protocol, information about a WS DataPoint can be added in the annotation. For example, the unit of a variable. WS OPC UA provides this information directly in the data type. |
The engineering unit must be indicated in the device description file |
|
Categories |
Descriptions |
|
Alarms |
Data points in this category display alarm messages. In the Weihenstephan Standards it is assumed that the affected machine can no longer operate as usual and has been stopped. Only the first-up message is always displayed. This remains until a fault has been rectified. |
|
Batch and article tracing |
These WS DataPoints are used for tracking and tracing. |
|
Computed values |
Computed values are measured values which have been pre-processed by an application-oriented function either on PLC or data acquisition level. For example, a data point reports either a minimum, maximum or mean value of a unit procedure, an operation or a specific timeframe. All data points shall have one engineering unit. |
|
Counters |
Counters are used to record quantities and sometimes also times (e.g. an operating hours counter). The counts become larger with time. Only looping (cycle) counters must be used. The operating cycles of high maintenance components must be recorded for all machines. All data points shall have one engineering unit. |
|
Identification |
This category contains data points that describe a WS machine in more detail. These data points are general and defined in CS OPC UA for Machinery. |
|
Machine communications |
The WS DataPoints in this category are required for the WS Protocol communication interface and are not available for WS OPC UA. |
|
Measured values |
In the Weihenstephan Standard, measured values are understood as the data which are being collected at sensor level. These can be temperatures, pressures or the current speed of a conveyor belt, for example. All data points shall have one engineering unit. |
|
Operating modes |
WS DataPoints in this category describe the operating modes and machine states of the respective machines or units or of individual modules of these. |
|
Operating states |
WS DataPoints in this category describe the operating states of the respective machines or units or of single modules of these. |
|
Parameters |
In the category Parameters data points are understood which are set externally via the communication interface. This can be for example the desired speed of a conveyor belt but also the type of beer currently being processed. All data points should have a engineering unit if possible. |
|
Programs |
WS DataPoints in this category describe the programs of the respective machines or units or of individual modules of these. |
|
Warnings |
Data points in this category indicate warning messages. In the Weihenstephan Standards it is assumed that the machine concerned is no longer working in the target range but has not yet been stopped. The latest warning message will remain until this warning situation is resolved. |
As a link between production and ERP (see Figure 1), an MES requires communication interfaces to the subordinate machines and the higher-level ERP. The communication with the ERP is usually done via standard mechanisms such as SQL or XML, while the connection down to the machines and process control systems is often complex and expensive. There are many different communication standards in automation systems, and the availability of data relevant to the MES varies greatly from machine to machine, requiring complex engineering to connect these different systems.
To meet the challenge of different communication standards in automation systems, the Weihenstephan Standards defines two universal communication interfaces for connecting different machine and process control systems to an MES:
- WS Protocol
- WS OPC UA
With “WS-Protocol - Physical Interface Specifications”, a specified WS communication interface for data exchange between higher-level IT systems was developed in 2005. It is based on Ethernet TCP/IP and provides proprietary communication commands that allow easy implementation independent of hardware, software and platform. For further information please refer to https://www.weihenstephan-standards.com/.
The present document CS OPC UA for Weihenstephan Standards now provides a second opportunity to ensure that the Weihenstephan Standards meets the requirements for communication in an Industry 4.0 environment.
The Weihenstephan Standards consist of a number of individual documents. Each document considers a particular aspect of the WS. Figure 3 gives an overview of the individual document parts. Table 11 briefly describes the document parts.
Figure 3 – WS Document structure
The content of the separate document parts is described in detail in Table 11. The documents can be obtained from the website https://www.weihenstephan-standards.com.
Table 11 – Description of the WS document parts
|
WS document parts |
Descriptions |
|
|
Implementation Guide |
The implementation guide explains both the WS document structure and the workflow for creating a WS Server. |
|
|
Data Evaluation and Reporting |
For each WS Domain there is a separate Data Evaluation and Reporting document. This document describes exemplary MES functionalities. |
|
|
WS Modeler |
The WS Modeler is a modeling tool that covers the following aspects. |
|
|
WS Templates |
For each WS Domain there is a WS Template. A WS Template consists of three parts. |
|
|
WS DataPoints |
Definition of the WS DataPoints. In Table 9 the defined properties of a data point are described. |
|
|
WS Machine / Unit Profiles |
Definition of the WS Machine / Unit Profiles |
|
|
Permutation tables |
This table defines which WS DataPoints are mandatory or optional for a certain WS MachineProfile. |
|
|
|
Modeling Tool |
The modeling tool to create an information model for a WS MachineClass. The tool can export the information model for both WS OPC UA and WS Protocol. |
|
CS OPC UA for WS |
This Companion Specification for the Weihenstephan Standards. |
|
|
WS OPC UA NodeSet |
A NodeSet file describes the information model of a specific machine for transmission with WS OPC UA. |
|
|
WS Protocol |
Description of the proprietary communication standard WS Protocol. |
|
|
WS PDA-Config |
A PDA-Config file describes the information model of a specific machine for transmission with WS Protocol. |
|
|
WS Acceptance Test |
Guideline for the complete documentation of installation, commissioning and the events occurring during operation. This document provides recommendations for clarifying responsibilities and avoiding errors through correct operation. |
|