PURPOSE: To measure a descaling state of a steel plate surface at each position for the width direction of the steel plate by the photodetected intensity by irradiating light to the steel plate surface at each position for the width direction and photodetecting the reflected light at each position for the width direction of the steel plate.
CONSTITUTION: The light generated from light sources 7, 8 are reflected at the surface of the steel plate 1, the diffused and reflected light is made incident to an optical sensor 15 of each channel of an optical sensor part 9, the light is photodetected by photodiode and the current corresponding to the light intensity is outputted. The output is converted to a voltage signal by an I/V converter 22, the noise is eliminated by a low-pass filter 23, then is inputted to a sample holding circuit 25 through an amplifier 24. In case of driving light sources 12, 13 by AC voltage, the photodetected signal Vd is sampled for every peak of AC voltage waveforms. A comparator 27 compares the sample hold value Vd of the circuit 25 with the reference level Vr set by a level setting device 28, and outputs a signal S indicating the bad descaling state in case of Vd<Vr.
ABE HISATO
FUJII TSUMORU
