WS DataPoints and WS Categories – OPC UA for Weihenstephan Standards

4.1.3 WS DataPoints and WS Categories

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

Table 10 – WS categories

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.