Relative reversibility error
The relative reversibility error is the difference of the output signals when measuring the same torque applied in increasing and decreasing steps (see Fig. 4). The specified value is the maximum deviation (according to absolute value) in the measuring range. It is specified as a percentage of the sensitivity C.
The relative reversibility error is a measure of hysteresis, that is, the difference between the characteristic curves determined with increasing and decreasing torque. For determining the relative reversibility error, a load cycle from zero torque through nominal torque and back is recorded. The practical calculation is based on measurements at a number of predefined points in the load cycle (e.g. 0 %, 50 %, 100 % of Mnom).
Hysteresis describes the dependency of the measuring signal on the transducer’s loading history. It is of particular importance if a transducer is used for a wide measuring range and no unloading takes place between acquiring two relevant measurement points. The most extreme case is the use from zero torque up to nominal torque. The effect of hysteresis occurring during a partial load cycle is usually significantly smaller than the hysteresis during a load cycle covering the entire nominal torque range.
Fig. 4: Determination of the relative reversibility error dhy from a load-relieve cycle (here based on the load steps 0 %, 50 %, 100 % Mnom). The value to be specified is the maximum reversibility error of the given load steps (here dhy,0 and dhy,50)