Displacement sensors

A displacement can be defined as the variation, as a function of time, of a position. A mechanical system has six degrees of freedom: three in translation and three in rotation. Displacement transducers can therefore be grouped into two families: linear displacement transducers and angular displacement transducers.

The scope of this article is limited to the measurement of relative displacements (i.e. in relation to a frame of reference linked to a reference solid considered as fixed). The sensors presented here therefore generally comprise a fixed part linked to the reference solid and a moving part linked to the solid whose displacement is the measurand. Some transducers, however, escape this rule, such as some capacitive transducers (e.g. those operating by charge induction on the target whose displacement is to be measured).

The sensors presented in the rest of this article are classified according to the physical principle used:

• variable electrical impedance sensors ;

• sensors with variable inductive coupling ;

• optical digital sensors.

The presentation of the physical principles required to describe the operation of sensors is deliberately limited so as not to weigh down the article.

A final section presents the sources of uncertainty linked to sensor positioning.