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One special feature of load cells is that the environment in which they are used plays a decisive role – in a number of ways.
Every material changes with temperature, expanding in response to heat and contracting in response to cold. Of course the same applies to load cells and their strain gauges. This also changes the electrical resistance of the conductor. Yet load cells must measure the correct weight everywhere in the world, regardless of the ambient temperature. To achieve this, a sophisticated temperature compensation mechanism is built into every HBM load cell. Load cells must be able to withstand various effects. "Consider a truck scale: These scales are exposed to the elements: rain, dirt or heat – they have to be able to withstand outdoor ambient conditions. And we are talking world-wide: A truck scale in Siberia, for example, is exposed to different effects than one in South Africa. But they do have one thing in common: They must be designed for environments with severe weather and must therefore be correspondingly rugged," says Stefan Schmidt.
"It's astonishing how many applications require load measurements." - Stefan SchmidtAnd there are also unusual uses for load cells, as Schmidt points out: "For example, our PW15iA single point load cell is used in the development of high-performance triathlon apparel and swim wear: It measures the water resistance of suits for world class swimmers."
"Weight plays a leading role in industry because goods are sold primarily by weight." - Stefan SchmidtBecause of this, weighing is strictly regulated. Use of different scales is permitted depending on the goods: For goods with low value (such as sand or gravel), the weigher does not need to be extremely precise – accuracy class D is sufficient. For pharmaceutical products, on the other hand, the highest accuracy classes A or B are required. The most common consumer goods such as meat, fruit and vegetables are weighed with accuracy class C, which already places high requirements on the accuracy of the weighing system that is used. But accuracy class C is also required in mechanical engineering or for building materials scale. The strict rules and standards for weighing continually present new challenges to load cell developers. For load cells in the higher OIML accuracy class, a deviation in accuracy of only a few ppm (parts per million) of the measuring range of the load cell is permitted. "It's impressive how accurately you can measure with a piece of steel and a strain gauge glued onto it," notes Stefan Schmidt. "But it can't be done without the necessary know-how. In recent years HBM has systematically achieved to increase the accuracy reached by many load cells. A continuing development process that never ends."