British Pendulum Tester (BPT)
British Pendulum Tester (BPT) Ready for Testing (Click to Zoom)
The British Pendulum Tester (BPT) is a friction device used to measure the skid resistance of a surface for new construction and in-service evaluations. Originally developed for evaluating flooring surfaces, it was updated for use with pavements. The skid resistance is evaluated using a swinging pendulum and measuring the energy lost to friction when the pendulum contacts the surface at the base of its swing.
The system consists of a frame, a swinging pendulum arm, rubber sliders, an interface box, and an on-board computer for data collection and storage. The pendulum attaches to the center of the frame such that the rubber slider mounted on the pendulum head just contacts the test surface at the base of its swing. One side of the frame has a clamp to hold the pendulum arm before it is released, while the other side has a scale to measure the pendulum test value (PTV). The PTV measures the skid resistance based on the energy lost to friction when the rubber slider contacts the surface.
If allowed to swing freely without touching the test surface, the pendulum arm should swing to its mirror position on the other side of the frame, corresponding to a PTV of 0. This is due to the fact that no energy is lost to friction from contacting the surface. During testing, the rubber slider will contact the surface at the base of the swing and the pendulum will lose energy to this resistance. The pendulum will swing partially up the other side, but not to the mirror of its start position. The distance below the 0 PTV mark that the pendulum reaches is proportional to the energy lost to friction. The lower the height reached by the pendulum, the higher the value of the surface friction.
BPT Disassembled in its Carrying Case (Click to Zoom)
The BPT is a small, portable device that is simple to operate. For each test location, the BPT must be leveled and calibrated before testing and five measurements should be taken, wetting the surface prior to each measurement. The system can be used in the field or laboratory test beds, but the PTV data should not be compared to other measurements of surface friction.
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