Legal-for trade weighing instruments for industrial applications need to comply with the European Measurement Instruments Directive (MID 2004/22/EC) which has been transposed into national law in the German Weights and Measures Act (Eichgesetz).
Modern weighing instruments increasingly incorporate digital load cells such as HBM's FIT load cells (Fast Intelligent Transducer). The measured value is digitized directly in the load cell and transmitted to a display and analysis unit. Encryption of the measured value is an appropriate means of preventing manipulation of the measured value during transfer.
HBM's DIS2116 digital scale electronics used in combination with digital load cells enable legal-for-trade, manipulation-proof weighing machines to be implemented. Data is sent from the load cells to the scale electronics in encrypted form.
However, analog load cells, too, enable legal-for-trade, automatic weighing instruments to be implemented. For this purpose, HBM offers the AED transducer electronics which digitizes the signal supplied by an analog load cell and then sends it to the scale electronics or a superordinate control system. In this case, too, securely encrypted transfer to the scale electronics ensures both protection against manipulation and legal-for-trade capability.
The transducer electronics offers many more advantages. A wide range of fieldbus interfaces that are optionally available allow easy integration of the weighing equipment into automation environments, for example, based on a PLC. CANopen, Profibus DP and DeviceNet are currently supported. In addition, serial RS232 or RS485 interfaces can be used. This allows for high flexibility in system integration and enables legal-for-trade weighing technology to be incorporated into existing applications.
In these applications, the transducer electronics can directly perform control tasks. This results in significantly increased processing speed in comparison to solutions involving communication at first via the scale electronics and subsequently via the PLC. In particular in filling machines this enables direct control of the feeding device and this accelerates the filling process.