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.
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.
Figure 1 – Schematic view of a scale system
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.