The control of coating thickness is the key parameter in the process of color coating. There are two contorl methods for coating thickness control: one is adopts pressure sensor, the other is adopts magnetic scale control. GEITGROUP coating machine adopts magnetic scale + pressure sensor technology, Magnetic ruler is used to control among the feeding roller, measuring roller and coating roller and the pressure sensor is used to control between the coating roller and steel strip. The position value between the rollers and the pressure value between the coating roller and the steel strip are displayed on the operating screen, the thickness controlled within 1μm.