Friction Tester Type RPG (2)   Measuring The lower test piece or, in case of a test against metal, the corresponding metal surface is secured onto the measuring slide; a bracket connected via a spring to a force meter, accomodates the second upper piece of foil. A meter cylinder whose characteristics are prescribed by the standard test used generates the necessary surface pressure in the friction coupling. During the measurement process the measuring slide moves at a specific velocity against the resistance of the friction coupling. The force meter available in two forms records the magnitude of the frictional force generated. The standard vesion of the unit contains a low-attenuation, low-inertia lever/spring balance with maximum indicator showing the maximum frictional force (static friction om commencement of the measuring process). The smaller sliding friction must beread off manually during measurement. Here, the electronic version is equipped with a load cell, in-cuircuit amplifier a/d board, RS-232 interface and software. The coefficient of friction µ is the ratio of the frictional force to the pressure applied. To avoid constantly recurring decimals, the coefficient of friction should be utilised as per DIN 53 375: µN = 100 x Fr/Fa. The frictional behavior of plastic foils is a mixture of sliding friction and static friction. The frictional force fluctuates around the sliding friction figure, but reverting constantly to its maximum, the static friction force. The special feature of the tester described is its ability accurately to reflact the variation in frictional force with time which is impossible by other means.