patent is to avoid the inconveniences of the discrete devices made up to now making a small portable sensor device without moveable pieces and which by means of optical fibers permits centralized remote control thereof in order to complement the description that is going to be made hereinafter and for the purpose of providing a better understanding of the features of the invention the present specification is accompanied by a set of diagrams in whose figures the most significant details of the invention are represented fig2 it shows a diagram of the sensor head and the relative position of the optical fibers in terms of the same fig3 it shows a theoretical curve of the variation of the reflection coefficient in view of the commented figures and in accordance with the numbering used we can observe how the device of the invention is comprised of a sensor head 1 a light emission 2 and light detection 3 system and an optical fiber system 4 that connects the sensor head with the light emission and light detection systems the sensor head consists of a transparent geometric figure 5 in which one of its surfaces 6 is a cylindric mirror whose axis a is in the plane of the geometric figure upon the flat surface 7 and perpendicular to the cylindric mirror a flat parallel sheet 8 of a transparent material such as glass or plastic similar to that forming the geometric figure 5 and upon which a thin metal layer 9 has been deposited is adhered by means of a refractive index adapter.