MARKED LINE TRACKING OF COLORED SAMPLE FOR TENSION TEST AND SAMPLE

PURPOSE:To enables employing marked lines of white even when white color fails to contrast sufficiently against the fundamental color of a test piece, by applying the marked lines of white on a test piece having white-based fundamental color. CONSTITUTION:Marked lines 2 of while are applied on a test piece 1 having white- based fundamental color and markings as black based color bands 3 and 4 are applied on the top and bottom sides of both the marked lines separately. Then, the test piece 1 is grasped between an upper clamp 13 and a lower clamp 16 and a marked line tracking device 8 is set as opposed to each of the marked lines 2. Here, an irradiation light R1 from a light source 9 is reflected on the white marked lines 2 and the reflected light R2 thereof is projected on a light receiving block 10 through a clearance L between shielding plates 5 and 6. As the clamp 16 moves in the direction of the arrow H, the test piece 1 is pulled in the direction of the arrow D, which causes the marked lines 2 to move from the initial position being extended along the length thereof. So, the rate of changes in the marked lines is detected with the block 10, an output signal of which is sent to a motor to always catch an image being extended along the length thereof by opening the shielding plates 5 and 6. This enables measurement of a distance between the upper and lower marked lines.