The surface color difference of steel sheets, especially of colored galvanized sheets, is one of the most important factors to be measured. The measurement is usually carried out by 'on-line' or 'off-line' visual inspection, or by 'off-line' instrumental one, but it has not been done by 'on-line' instrumental one.
Through a strong request to establish automatic inspection technique for on-line use, a new inspection system has been developed. In this system, two light-sources illuminate a travelling sheet with the intensity of more than 105 lux.A high speed data processor provides the spectral reflective property of the illuminated sheet surface. Remote inspection of the instrument has an advantage that it can be installed in almost any production line. On-line performance tests have proved high reliabilityof the instrument ; the values of the color difference measured by this instrument coincide within ±0.2 with those measured by an 'off-line' sampling test with a spectrophotometer. Applying this instrument to the production line, the color difference of the sheet to its standard color is successfully measured over the whole length of a coil. It is resultantly expected that the control of the color difference in the production line will be realized with this instrument.
