Apparatus for measuring the surface hardness of building materials

An apparatus for measuring surface hardness of materials, comprising a housing with a moveable hammer of a given length arranged therein, a driving spring for driving said hammer, an impact pin with a front end and an opposite rear end, said hammer being driveable by means of said driving spring along a path in said housing for impact against said rear end of said impact pin, said front end of said impact pin being for placement on a surface to be measured, and a measuring device for measuring a rebound height of said hammer after impact, wherein said hammer is provided with an optical pattern over at least part of its length, said optical pattern comprising a plurality of regularly arranged alternating first and second zones, wherein said measuring device comprises an optical detector arranged adjacently of said path of the hammer for detecting the number said first and second zones which pass by said detector at least when the hammer is rebounded, and wherein said measuring device further comprises an evaluation circuit connected to said optical detector to determine, from said detected number, the maximum rebounding height of the hammer, said hammer having a cylindric outer surface defining a cylinder axis parallel to said path of the hammer, wherein said first and second zones are formed by a plurality of successive strips extending around the circumference of said cylindric outer surface an being alternatingly provided with light reflecting and light absorbing surface structures, said optical detector comprising a light emitter and a light sensor focused on said cylindric outer surface of said hammer, and wherein said first zones reflect light from said light emitter into said light sensor and said second zones prevent said reflection, respectively, dependent on the axial position of the hammer on its path and independent of the angular position of the hammer about said cylindric axis.