Strain gauge based force transducers always comprise a spring element to which force is applied. This force results in minimal deformation of the spring element. Strain gauges installed at appropriate points are extended and therefore show a change in resistance. A minimum of four strain gauges are connected into a Wheatstone bridge circuit. When voltage is fed to this measuring bridge, the resulting output voltage is proportional to the applied force.
Piezoelectric sensors comprise two crystal disks with an electrode foil mounted in between. When applying force, this results in an electrical charge that can be measured using a charge amplifier. The charge is proportional to the applied force.
Some strain gauge based transducers provide an IP68 degree of protection (S9M, U10M with cable option). Hermetically sealed enclosures protect the sensitive strain gauges. This permits use of these transducers in unfavorable environments. Charge cables for piezoelectric transducers are available that use a special seal to ensure that the connection to the sensor housing is hermetically sealed and thus guarantee high operational safety. (KAB145-3)
Modern force transducers achieve very high accuracy; this refers, in particular, to strain gauge based transducers that provide excellent individual errors of 200 ppm.This applies for industrial standard products; force transducers for calibration tasks (e.g. HBM TOP-Transfe) consistently achieve smaller individual errors. Piezoelectric sensors have a slightly higher linearity error, in general 0.5% relative to full scale. They are also limited by their high drift. Calibration in the force range in which measurements are to be taken later on enables significantly higher accuracy to be achieved.
Piezoelectric force sensors can be very compact - e.g. the CLP series with heights of less than 4 mm. Such sensors are the optimal solution when integration in existing systems is required. Compromises have to be made in terms of the precision that can be achieved, however, the requirement for very small dimensions is paramount in many applications.