CU:NON-CU VOLUME RATIO. The Cu:non-Cu ratio can be measured on a polished cross section of strand. The boundary between Copper and non-Copper area is identified by grey scale contrast (using optical microscope) or by atomic number (scanning electron microscope): the marked areas are digitally scanned and the ratio of the number of pixels for each area determines the Cu:non-Cu ratio. Reproducibility of the measurements can be estimated within ± 10%. Planimetric analysis of magnified cross section pictures can also be used by specially trained operators: the absolute reproducibility must be better than 5%. On line, non-destructive measurements of the Cu:non-Cu ratio can be obtained (on bronze method Nb3sn strand) by carefully measuring the strand resistance between two fixed points, as it is usually done for NbTi strands. To the extent it is applicable to the considered type of strand, the IEC61788-12 standard shall be considered.
