The conventional mechanical sensors mentioned above all have one thing in common: the signal is transmitted from the probing element through a rigid shaft to the actual sensor (for example, a switch or piezoelectric element). Since each deflection of the shaft affects the measured result, the aim is to use shafts of maximum rigidity. In connection with the sensor technology applied, this leads to relatively high dimensions and probing forces. Practically speaking, the minimum diameter of the probing sphere is several tenths of a millimeter. Such probing systems are thus suitable for measuring small geometric features only under certain conditions.

With the Werth Fiber Probe, these disadvantages are circumvented by using the stylus shaft only in order to position the stylus sphere. The actual measurement of the position is performed by an image processing sensor integrated into the system (Fig. 22). The deflection of the shaft is therefore not included in the measured result. While the fiber probe itself is designed according to a two-dimensional principle, it may also be used to perform three-dimensional measurements, provided that the object surfaces to be probed and the axis of the fiber probe form a sufficiently small angle. The position of the probing sphere in the direction of the fiber axis can also be determined by integrating a second viewing direction of the image processing sensor (second camera or mirror) into the design of the fiber probe.