INSTRUMENT FOR MEASURING LENGTH OF HOT-ROLLED STEEL

PURPOSE:To quickly measure the length of hot-rolled steel with high accuracy by providing two or more hot slab detectors for detecting the front end of the rolled steel on the downstream sides of rolling rolls and checking the function of a laser Doppler type speedometer. CONSTITUTION:A measurement control section 5 finds the reference length Lo between hot slab detectors 7 and 8 at every rolling in order to discriminate whether or not a laser Doppler speedometer 6 normally operates. Namely, the section 5 calculates the length Lo at every rolling by integrating speed values inputted from the speedometer 6 during the period until the front end of a roller steel pipe 3 reaches the detector 8 after the front end of the pipe 3 passes by the detector 7. When the lengths Lo actually measured at every rolling are within the upper and lower limits of a preset fixed length Lx between the detectors 7 and 8, the section 5 discriminates that the speedometer 6 normally operates and outputs a numerical value obtained by correcting the actually measured value of the speedometer Lx/Lo. When the lengths Lo exceed the upper or lower limit of the fixed length Lx, the section 5 discriminates that setting of the speedometer 6 is erroneous and issues an alarm.