All methods of COF measurement involve preparing a sample into two flat pieces, the samples are placed together and a constant weight is applied to represent the normal force. One piece is fixed, and a gradually increasing force is applied to the second sample until the samples begin to slip against one another (Fd Max).
Horizontal Plane (flatbed) Friction Testing
To measure Static and Dynamic coefficients of friction it is necessary to use a fixed bed instrument. These instruments use a motor to pull a sled across the sample, using a load cell to measure the forces.
Original instruments were converted tensile testers that used a cord to pull the sample, the use of a cord has now been removed from many friction measurement standards due to the uncertainty added by its own elasticity and problems with sample positioning.
The Universal Friction Tester uses mechanical linkages to apply the force and uses automatic sled placement for very accurate sample positioning with variable dwell time before testing.