Legal-for-trade commercial weighing instruments

• Secure Legal-for-trade Weighing Systems in Open Automation Applications
• The advantages of digital weighing technology
• Off-centre load compensation in a few minutes
• Communication with control systems
• Easily integrated digital weighing technology

HBK provides weighing technology components and systems to allow scales to be flexibly integrated into filling or loading systems. The digital weighing electronics and terminals are a typical example of this. The optional fieldbus modules used to implement the different fieldbus interfaces simplify integration into a wide variety of automation architectures.

In Germany, the weighing instruments used in commercial applications must be verified. One of the reasons for this verification (statement of conformity) is: “... to create conditions for accurate measurement in commercial transactions, in the interests of fair trading.”(www.eichamt.de) Wherever commerce involves goods that are weighed, there is a great temptation to manipulate the scales. When a ship is unloaded, for example, automatic weighing instruments quickly weigh goods to a value of several million euros.

Therefore, Germany and the European Union apply a series of laws and regulations, designed to ensure that all the weighing instruments used in commerce are verified. The requirements of the European Measuring Instruments Directive MID 2004/22/EC are implemented in German law by the Weights and Measures Act.

Modern weighing instruments increasingly make use of digital load cells such as HBM's FIT® load cells (Fast Intelligent Transducer). Here, the measured value is digitized directly in the load cell and then transferred to a display and evaluation unit, the so-called scale electronics. The big advantage of digital data transfer is that there is practically no interference on the measuring leads.

A suitable way to prevent manipulation of the measured value during transmission is to encrypt it. The series WTX110-D digital weighing terminals from HBM, in conjunction with type C16i digital load cells, for example, allow legal-for-trade, manipulation-proof weighing instruments to be set up.

As digital load cells also transfer status and error messages in addition to the actual measured values, it is very easy to implement asset and facility management at the same time. Faulty transducers can be easily identified and replaced, if necessary. This greatly reduces service and maintenance expenditure.

Additionally, a complete measurement chain including the calibration can be conveniently and independently set up – either on site or remotely via PanelX or the WTX Mobile app. All communication data is optimally protected thanks to HTTPS encryption.

The weighing electronics have an electronic compensation for the off-centre load error. To compensate for mechanical off-centre load errors, a load is simply placed on each corner. The process takes only a few minutes – a considerable time saving compared to the same process for analogue scales, which can last two or three hours.

In industry, measuring instruments are often integrated into automated systems based on a PLC via fieldbus or serial interfaces, for example Profibus/Profinet/ Ethernet/IP or EtherCAT. Modern HBK weighing electronics additionally offer a free-of-charge dot NET-based weighing API to transfer data and measurement results via standard Ethernet (TCP/IP) to a Windows PC-based application vie encrypted communication (https).  So-called automatic weighing instruments frequently work without intervention from an operator. The measuring process starts and stops automatically. So, as well as manipulation protection, it is particularly important for this type of scale application that the weighing technology can easily communicate with the controller over modern and secure interfaces and bus systems. This is firstly because it controls the functions of the weighing instrument, and secondly reads out the measured values and continues to process them.

HBK is a competent system partner for weighing technology, providing all the requisite components for legal-for-trade, industrial applications, from the load cell to the matching weighing electronics. Practically all industrial weighing applications can be implemented.

The extensive options of the WTX110 weighing terminal, particularly for communication, simplify the integration of weighing technology into a primary control architecture, such as one based on a PLC or PC, through to modern smart weighing technology in mobile applications.

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