Hysteresis Error

In this series, we shine a light on terms and specifications often used in measurement technology. In this newsletter, we look at hysteresis error and repeatability error. Both are significant sources of errors in pressure sensors that are often misinterpreted or not considered.

What is hysteresis error?
The term hysteresis comes from the late Greek hystérēsis, which literally means coming up short. The Duden dictionary interprets the word hysteresis as "the lagging behind of an effect behind the variable force causing it." A complicated definition that becomes clearer in the practical application of pressure measurement technology. If one increases the nominal pressure from 0 to 100% when measuring a pressure sensor, the output signal will always be smaller than the real value. If the pressure is subsequently reduced from 100% to 0%, the value displayed will always be slightly too high. The figure below illustrates this process:
 

The maximum difference between the upward and downward characteristic curve is indicated as a hysteresis error. But where does this measurement error come from?

Cause and compensation of the hysteresis error

Hysteresis corresponds to the elastic properties of the sensor element and its design. The inertia of the sensors means that they therefore "lag behind" the actual nominal pressure. The displayed measured value therefore depends not only on static ambient conditions, but also on the values that were measured previously. Technically, this error cannot be compensated. For a metrological evaluation, however, it can. The hysteresis error can be determined by the sequence of several up and down series during the calibration of a test equipment.