Companies in the food and packaging sectors must comply with strict legal requirements in accordance with the EU Prepackaging Directive 76/211/EEC. The German Pre-packaging Ordinance (§ 22 FPackV) contains clear specifications in this regard: On average, the specified nominal filling quantity must not be undercut. In practice, this means that manufacturers may always overfill, but filling less than the specified quantity is critical. Example: chocolate bars with 100 g: Only 2% of chocolate bars may be lighter than 95.5 g and none lighter than 91 g. The consequence of this strict regulation is that a large number of food producers work with expensive overfilling. This can cumulatively lead to high additional costs, especially for high-quality products such as olive oil, ice cream or cosmetics. In addition, underfilled products are rejected, which also means more effort, additional processes and therefore additional costs. These inaccuracies can be avoided with more precise, reliable weighing technology during filling and dosing, but at the latest in the checkweighers at the end of the production line.

Digitization of weighing technology

The more precisely the weighing technology works, the higher the productivity of the filling processes and the lower the overfilling. The load cell is a crucial component here. It is the central element of dynamic weighing and packaging processes.

The FIT7A load cell with IP66 protection and waterproof, hygienic connectors meets the special requirements of the food industry - such as being completely covered in foam or cleaned with a powerful jet of water.

© HBM

Until now, manufacturers of checkweighers have relied on load cells that work according to the principle of electromagnetic force compensation (EMF). Up to now, they have scored highly in terms of precision compared to load cells based on strain gauge technology. At the same time, however, they are expensive, vulnerable and very complex to commission. This is why HBM has continuously developed its strain gauge-based load cells: The latest generation, such as the FIT7A, ensures precision and high speed in the processing of measurement data as well as simple operation - combined with significant cost savings compared to EMFR load cells.

The FIT7A load cell from HBM has been optimized for checkweighing. It has a high natural resonant frequency, which results in a fast settling time. In addition, the run-in behavior after switch-on is negligible and the load cell delivers low-noise and high-resolution measured values with the 24-bit A/D converter and the HBM-typical carrier frequency measurement. Thanks to the integrated filters and procedures for determining the dynamic measured values, it contains all the functions required for dynamic weighing - and does not require any additional PLC or weighing electronics. For example, a checkweigher with the FIT7A load cell can achieve a standard deviation of just 0.1 g for a nominal weight of 1 kg. Depending on the checkweigher design and nominal weight, 100 to 400 measurements per minute can also be achieved.

Digital load cells have further advantages over EMF load cells:

- With their now similarly high precision, they increase output and reduce overfilling in applications for which EMFR load cells are too expensive.
- Internal filters and inputs/outputs make an additional PLC obsolete.
- The robust design leads to fewer failures.
- Connectors allow quick and easy replacement.
- Integrated overload protection against physical forces that can damage the load cell.
- Hygienic due to smooth stainless steel surfaces.
- Active temperature compensation allowing less temperature drift and negligible run-in behavior after power-up

Digital load cells also enable food producers to use the gravimetric filling principle. In contrast to the volumetric approach (flow measurement) or filling according to fill level, this leads to significantly more accurate filling results. The gravimetric filling principle is particularly convincing when high accuracy is required or when microbiologically sensitive products are involved. This is because volume tolerances of the container, different physical properties of the product (proportion of pieces, viscosity, conductivity, number of gas bubbles) are not included in the filling result. Filling via weight determination offers optimum hygienic conditions and reduces foreign particles because the sensor does not come into contact with the filling product.

Digital platform as a basis

HBM has developed the PanelX software as a digital platform to integrate both digital and analog load cells into machines and processes in the best possible and most user-friendly way according to the gravimetric filling principle. This allows the user to quickly commission weighing systems such as checkweighers, dosing systems and multihead combination weighers. A wide variety of strain gauge-based load cells can be configured using standardized command sets, which reduces effort, costs and susceptibility to errors.

Digital weighing electronics PAD - turns any analog transducer into a smart digital load cell.

© HBM

In addition, with PanelX and the digital inputs/outputs of the load cells and weighing electronics, a PLC is no longer necessary. However, if such a controller is to be used, the command sets of the platform can be transferred to a PLC.

Further advantages of this digital platform are the visual display of the measurement and control signals as well as evaluation functions, for example for frequency analysis. The analysis functions are also helpful during maintenance and servicing in order to find faults that are not caused by the load cell itself but are visible in its measurement signal in the event of a malfunction. The platform also supports the development, planning, design and parameterization of weighing applications with analysis tools. Online help on functions, interfaces and command sets is already integrated into the software via a web browser; the interface is intuitive to use. PanelX therefore saves time and costs. At the same time, the software exploits the optimization potential of weighing applications and thus increases their overall performance.

Digitizing analogue load cells

The PanelX software user interface for all digital load cells and weighing electronics: Among other things, it is used to configure fillers, dosing systems and checkweighers.

© HBM

HBM has developed the PAD digital transducer electronics to take advantage of the benefits of digitalization for analogue load cells as well. The range of functions is almost identical to digital load cells. PAD can be connected to all analogue load cells in order to digitize them and then configure them with PanelX. A stainless steel housing protects the transducer electronics against liquids and adverse environmental conditions up to protection class IP68/IP69K. With a measured value resolution for 2 mV/V of up to 5,120,000 digits and complete measurement signal processing with selectable or automatic filters, PAD works precisely even in the event of interference from vibrations. The transducer electronics can be easily integrated into various system environments via the RS485 and CANopen interfaces.

With PAD and its integration into the PanelX platform, analogue load cells benefit from all the advantages of digitalization. This means that dynamic filling and dosing applications in harsh environments can be visualized and analysed just as quickly and, if necessary, readjusted immediately during the process. This technology is the plug & play connection for analog force transducers and load cells to Industry 4.0.

Chinese machine manufacturer Best Crown shows how digital weighing technology can work in the food industry and save considerable costs. For its customer Shanghai Dairy Milk, it equipped a rotary filler for coconut milk with the FIT5A digital load cell from HBM.

The key to more productivity

Thanks to the increased precision of gravimetric filling, safety overfilling has been reduced by several grams per bottle. With a production volume of around 100,000 bottles a day, coconut milk manufacturer Shanghai Dairy Milk saves several million euros a year.

Companies in the food and packaging sectors can benefit disproportionately from the digitalization of weighing technology. This is because digital strain gauge-based load cells are now equivalent to EMFR load cells in terms of precision and are cheaper, more robust, easier to install and more durable. A uniform, intuitive digital platform not only simplifies the configuration of digital load cells, but also enables the digitization of analogue load cells, such as those required for sensitive hygienic areas, via transducer electronics. This means that digital weighing technology can be used for almost any application in the food industry within or at the end of the filling process and can readjust the filling process if necessary.

Author: Thomas Langer is Product Manager at Hottinger Baldwin Messtechnik.