5 General Information on Weighing Technology and OPC UA ToC Previous Next

5.1 Introduction to Weighing Technology Companion Specification ToC Previous Next

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 4is described in this Companion Specification. It defines two different modes (ProductHandleMode/AccessRestrictionMode).

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Figure 4 – Overview of a Product handle

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 8.7 - 8.8). 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 AccessRestritionMode 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 behaviour of the scale is application-specific and must be specified separately.

NOTE 2: The combination of the “Processing” mode and the “Writeable” mode should be used with caution, as the writeable element may be in an inconsistent state.

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