How do you calculate a PTV value?
A rig is set up above a test surface that holds the pendulum arm parallel to the test surface. This arm is at a length so that it comes into contact with the surface when it is perpendicular.
Let's quickly jump back to school to help with this. If you release the pendulum at 90 degrees to the floor without coming into contact with anything, then the laws of conservation of energy say it will end its swing at 90 degrees with the floor. Therefore, we can be sure that any different outcome is because of outside interference.
When the pendulum comes into contact with the test tile, it loses some of its kinetic energy to friction. This loss will mean the swing will not finish at 90 degrees to the surface, and we can measure the change in final height. This is the coefficient of friction (CoF) and it gives us our PTV value.
The slippier the surface loses less energy to friction, meaning the pendulum will swing higher. You can apply the same principles to the grippier surface, generating a higher value.
There are several testing conditions; slider 96 and Slider 55, and wet and dry.
Slider 96/55 - You place rubber sliders on the end of the pendulum.
Slider 96 is a harder rubber, so you use it to emulate the effect of shod pedestrians (people with shoes on).
Slider 55 is a softer rubber, often used to mimic walking with bare feet.
Wet and dry - ...the definition for this is not going to revolutionise the way you think, but it is always good to set it out in writing so that no one jumps to the wrong conclusions. Lying water on the flooring surface will add a low friction layer on top of the finish making the sample being tested slippier. When these tests are conducted, the tests are often done in wet and dry conditions to fully understand the range of slippiness.