In addition to the zero point, the scale is marked at the angles relevant to the test specifications, i.e. 12 and 4, or 6 and 3, or all four angles. At these limits, a photo-sensor is accurately positioned to register swings of the pendulum. The pendulum is cocked with a swinging arm. It is held in its start position by a lock pin, which is released by a flexible cable trigger.
The hardness of any given coating is given by the number of oscillations made by the pendulum within the specified limits of amplitude. The signals from the photo-sensor are registered by an automatic electronic counter, and the result of a test is shown on the digital display. The influence of surface smoothness, film thickness, temperature and relative humidity must all be carefully controlled, therefore, the instrument is housed in a perspex case. |