Product Information for:
DeFelsko PosiTest® FM/GM Coating Thickness Gauge
The PosiTest® FM/GM Coating Thickness Gauge is a magnetic pull-off thickness gauge for the Non-destructive measurement of non-magnetic coatings (paint, enamel, plastic, galvanizing, metalizing, plating, etc.) on STEEL.
Magnetic pull-off gauges use a permanent magnet, a calibrated spring, and a graduated scale. The attraction between the magnet and magnetic steel pulls the two together. As the coating thickness separating the two increases, it becomes easier to pull the magnet away. Coating thickness is determined by measuring this pull-off force. Thinner coatings will have stronger magnetic attraction while thicker films will have comparatively less magnetic attraction. Testing with magnetic gauges is sensitive to surface roughness, curvature, substrate thickness, and the make up of the metal alloy.
Magnetic pull-off gauges are rugged, simple, inexpensive, portable, and usually do not require any calibration adjustment. They are a good, low-cost alternative in situations where quality goals require only a few readings during production.
Pull-off gauges are typically pencil-type or rollback dial models. Pencil-type models (PosiPen shown right) use a magnet that is mounted to a helical spring that works perpendicularly to the coated surface. Most pencil-type pull-off gauges have large magnets and are designed to work in only one or two positions, which partially compensate for gravity. A more accurate version is available, which has a tiny, precise magnet to measure on small, hot, or hard-to-reach surfaces. A triple indicator ensures accurate measurements when the gauge is pointed down, up, or horizontally with a tolerance of ± 10%.
Rollback dial models (PosiTest® shown left) are the most common form of magnetic pull-off gauge. A magnet is attached to one end of a pivoting balanced arm and connected to a calibrated hairspring. By rotating the dial with a finger, the spring increases the force on the magnet and pulls it from the surface. These gauges are easy to use and have a balanced arm that allows them to work in any position, independent of gravity. They are safe in explosive environments and are commonly used by painting contractors and small powder coating operations. Typical tolerance is ± 5%.