The functional principle of all tactile sensors is based on mechanical contact with the measuring object. The electrical signals for further processing are derived from this. A distinction is made between touch trigger and measuring touch probes. With a tactile sensor, the measurement result contains both the geometry (= form and size) of the contact form element (sphere) and the spatial position and geometric shape of the object surface to be measured.

Figure 25 shows that the position of the probing point in tactile scanning cannot be determined from the known coordinates of the centre of the probe sphere without mathematical correction. For an exact correction, the probing mould element must be carefully calibrated (probing sphere correction). It is also necessary to probe several points on the geometric feature to be measured. The error resulting from the omission of this correction depends on the diameter of the probing sphere: the smaller the diameter, the smaller the error. Large stylus diameters can also suppress small structural deviations. This mechanical filtration can either have a favourable effect on the measurement results or lead to their falsification.

Figure 26 shows the principle influence of the number of probe points on the measurement result. For real geometric features with form errors, it is essential to capture a large number of measurement points. This is problematic with switching sensors due to the considerable amount of time involved.

Tactile measurement corresponds well to traditional manual measuring methods (calipers, height gauges) and is largely independent of the surface properties of the objects to be measured. With "star probes" and stylus changes, an object can be measured three-dimensionally from all orientations with relatively little effort. Even in applications that require optical measurement, the additional use of tactile sensors may be essential. Features that cannot be measured optically, such as side surfaces, cylindrical surfaces and undercuts, can be captured with reasonable effort.