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New silicon load cells

At PTB, the technology of conventional strain gauge load cells has been further developed, also for high-precision weighing. The new load cell made of monocrystalline silicon (instead of metal) with sputtered-on (instead of glued) thinfilm strain gauges shows a significantly improved time and hysteresis behaviour, as well as a better reproducibility.

Silicon load cell with sputtered-on thin-film strain gauges

With an annual turnover of 500 million euros, weighing technology makes up a large share of the market in Germany. A large part of this annual turnover is achieved with conventional load cells for low to medium precision. These load cells are made of metallic mechanical springs with glued strain gauges. The sensor which was further developed by PTB works according to the same principle. Its spring bellow, however, is made of silicon instead of metal. Since, under the influence of a load, monocrystalline silicon deforms ideal-elastically, the time-dependency and hysteresis of such a spring bellow is negligible. The application of the strain gauge by means of the thin-film method leads to a more direct connection with the spring bellow than in the case of the conventional glueing method. Thus, also time-dependencies occurring during the transmission of the strain from the spring bellow to the strain gauge could be significantly reduced, and the reproducibility of the strain measurement was clearly increased.

These fundamental advantages were confirmed by investigations on the load- and time-dependency behaviour on five of these new load cells at temperatures from 10 °C to 40 °C. Compared to those of conventional load cells, the characteristic curves of the silicon load cells achieve values which are better by more than one order of magnitude with regard to hysteresis, zero-point behaviour and reproducibility. The non-linearity is comparable to that of conventional load cells.

In order to evaluate the application range of the new load cells, the measured data were analysed on the basis of the OIML International Recommendation on the testing of load cells for applications subject to legal verification. The silicon load cells which were analysed by means of creeping and correctness tests achieve more than 30,000 intervals for applications subject to legal verification and are, thus, suitable also for precision weighing operations such as, for example, in the case of laboratory balances.

Contact at PTB:

Phone: +49-531-592-0