Method of automatically measuring the thread density per unit length of a moving band of material

PURPOSE: To measure a string density per unit length of a band-shaped object to be moved automatically by detecting light through the band-shaped object using a number of sensor elements arranged on a plane and converting it to a digital signal for calculation. CONSTITUTION: A band-shaped object 1 is transmitted through light by a flash source 1 and the transmission light is detected by a number of sensor elements arranged on a plane and are converted to digital signals 4. The digital signals are stored at an image memory 5 and are displayed 7 by a computer 6. A calculated image is inspected in terms of brightness by the computer 6 and is properly applied to the exposure time of the flash source 2 at the time of exposure shortage or exposure excess. Then, the result is displayed by the computer 6 and the string density per unit length of the band-shaped object 1 to be moved is automatically measured.