What Does
Pencil-type Pull-off Gauge Mean?
A pencil-type pull-off gauge is a measuring device used to determine the dry film thickness (DFT) of a coating as measured above the substrate. The measurement may consist of a single layer or multiple layers. The thickness of a coating is often directly proportional to the degree of protection against corrosion the metal experiences.
Corrosionpedia Explains Pencil-type Pull-off Gauge
A pencil-type pull-off gauge consists of a permanent magnet, a calibrated spring and a graduated scale. The attraction between the magnet and the steel pulls the two objects together. As the coating thickness that separates the two increases, it becomes easier to pull the magnet away. The coating's thickness is determined by measuring the pull-off force that is experienced.
Measurement of film thickness can be performed with many different instruments. The criteria that determine which method is best for a given application includes the type of coating, the substrate material, the thickness range and the location/accessibility of the coated object. Beyond the pencil-type pull-off gauge, the commonly used measuring techniques include non-destructive dry film methods such as eddy current, ultrasonic or micrometer measurements.