Conditioning of weighing cells in the climatic test chamber

The reference list of MULTIPOND makes you hungry for more. Well-known companies from the food industry use fully automatic MULTIPOND multihead weighing systems to weigh the ingredients for their sweets, snacks, yoghurt, cereals, coffee, tea, nuts or cheese, before transferring them to the packaging machine. The adjustment of the strain gauge weighing cells is done in a Memmert climatic test chamber CTC, as well as in a TTC temperature test chamber.

Up to 450 weighing procedures per minute

The MULTIPOND multihead weighing system weighs the goods several hundred times per minute with an accuracy of up to 0.5 gram. In addition to this, the all-rounders can combine, dose and count depending on the given requirements. Robust design, intelligent control technology, as well as customer-specific design of the weighing systems are essential for the high standards required in the food industry. Nevertheless, the core components of the MULTIPOND weighing systems and thus the guarantee for precision are the in-house-developed strain gauge weighing cells.

Weighing cells developed in-house at MULTIPOND   

A strain gauge is a device used to measure strain. It consists of thin conductors on a foil, firmly glued to a spring bellow. If the spring bellow is loaded with weight, i.e. if it is stretched, the strain gauge is stretched as well, increasing its electrical resistance and sending an electrical signal to the control technology. There you go! In practice, however, things are never that simple - especially when maximum precision is required. For this reason, MULTIPOND develops all their strain gauge weighing cells themselves. The design of the spring bellow, application of the foil adhesive and the exact positioning and clean gluing on of the strain gauge require a lot of development work by the engineering team as well as accuracy in production. Cables have to be shielded from interference and the entire weighing cell has to be protected from contamination, humidity and other external influences.

Conditioning of weighing cells in the climatic test chamber

Especially temperature deviations and humidity must not influence the weighing performance at all. For this reason, the calibrateable MULTIPOND weighing cells have to complete a 14-hour test session inside the Memmert TTC temperature test chamber or in the CTC climatic test chamber for combined temperature and humidity tests. Zero point measurements are performed at different temperatures, with the ramps varying between 12 temperature points between 5 °C and 50 °C. Possible deviations are offset with the detuning values and an additional test run is done until all the weighing cells have been exactly adjusted. The decision in favour of the Memmert CTC climatic test chamber and TTC temperature test chamber was mainly down  to the excellent price/performance ratio, easy operation, controllability via Ethernet and USB as well as the optimal utilisation of the entire chamber during measurements.

AtmoSAFE would like to thank the MULTIPOND Wägetechnik GmbH, especially Mr. Hegel and Mr. Hammerl for their kind support during the preparation of this article.