A Persoz pendulum is a device used for measuring hardness of materials. The instrument consists of a pendulum

Pendulum

A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...

 which is free to swing on two balls resting on a coated test panel. The pendulum hardness test is based on the principle that the amplitude

Amplitude

Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...

 of the pendulum's oscillation

Oscillation

Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...

 will decrease more quickly when supported on a softer surface. The hardness of any given coating is given by the number of oscillations made by the pendulum within the specified limits of amplitude determined by accurately positioned photo sensors. An electronic counter records the number of swings made by the pendulum.

Construction

The pendulum consists of balls which rest on the coating under test and form the fulcrum. The Persoz pendulum is very similar to the Konig pendulum. Both employ the same principle, that is the softer the coating the more the pendulum oscillations are damped and the shorter the time needed for the amplitude of oscillation to be reduced by a specified amount. The two pendulums differ in shape, mass and oscillation time, and there is no general relationship between the results obtained using the two pieces of equipment. In either case, the test simply involves noting the time in seconds for the amplitude of swing to decrease from either 6 to 3 degrees

Degree (angle)

A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...

(Konig pendulum) or 12 to 4 degrees (Persoz pendulum).