Load cells are the key components within the electromechanical scales measurement chain. They are, as such, force transducers or even force sensors, which are used as transducers.
They convert the mechanical variable (force) proportional to the electrical variable (tension).
However, load cells thus differ from standard force sensors in the fact that they are calibrated in grams, kilograms or tonnes, not in Newtons (N) like other force sensors.
They are similar to other force sensors in that they also contain a spring body, a suitably shaped piece of metal, the geometry of which changes slightly when weight is applied. The elastic deformation is picked up by strain gauges and converted to an electrical signal.
Typical spring body types for load cells:
- Double bending beam for small loads
- Shear beam for larger loads
- Column-shaped spring body (pressure beam or hollow cylinder)
- Ring torsion spring body for heavy loads
Load cells have different dynamic properties depending on their spring elements. High dynamics are important, for example, with many filling and sorting systems because there are often only a few fractions of a second available for the weighing process. Older load cells still work by being filled with oil to cushion impacts. Newer systems use a combination of mechanically rigid load cells and electronically matched filters in the downstream measuring device. In static applications, the size and type of load introduction (assembly) plays a crucial role; examples being whether the load cells have to be integrated harmoniously or whether the installation height of a container is fixed or not.
Measuring technology properties
- Nominal load, up to the point at which the load cells are to be operated
Load limit, at which persistent deterioration of the sensor occurs (deformation of the spring element)
- Parameter or output signal at rated load (e.g. 2 mV/V)