Linearity describes the real characteristic curve's maximum deviation from the ideal straight line. The value is given in percent relative to the nominal (rated) force.
Often, no linearity error is specified with reference force transducers (U15, Top Class transducers, etc.) that offer maximum accuracy, because in these cases no sensitivity is used but, instead, a polynomial or interpolation points. In this case, the so-called relative interpolation error is specified, i.e. the maximum deviation from the fitting curve.
Furthermore, specifications for reference force transducers indicate the accuracy the force transducer will at least achieve during a calibration. In general, requirements as specified in the international ISO 376 standard are used, therefore, HBM provides corresponding values in its technical data sheets. Hence, the specified linearity refers to the actual value, i.e. it is relative to the measured value.
Force transducers for use in industrial applications or in experimental mechanics comply with VDI/VDE 2638. Here, linearity refers to the nominal (rated) force.
At 20% of its nominal (rated) force (1000 N), a force transducer has a linearity error of 0.2 N. The linearity error relative to full scale is 0.02%. The deviation relative to the actual value needs to be calculated based on 200 N and is 0.1%. This is five times the original value.
In practical applications, the linearity error can be substantially reduced by competently selecting the transducer's calibration range. If a force transducer with a nominal (rated) force of 100 kN, e.g., is used at 50 kN, it can be calibrated in this range. This halves the error, since computation of the linearity error now can be based on the calibration range.
Benefit from our practical on-line glossary to look up the most important technical terms in the field of force measurement: