JPS646702A - Pinhole detector for magnetic disc - Google Patents

Abstract

PURPOSE:To perform a non-destructive detection of the presence of a pinhole while recording the location thereof, by utilizing that electrostatic capacitance reduces at a position where any pinhole exists, when the pinhole is detected as existing in a plated layer of a magnetic disc. CONSTITUTION:A spindle M3 is rotated by a rotating means M4 to turn a magnetic disk M1 having a plated layer mounted on the spindle M3 and a displacement of the rotation is detected by a detection means M5, an output of which is inputted into an electrode position calculating means M8. A measuring electrode M2 is arranged on the disc M1 at an interval, is moved by an electrode driving means M6 from the center to the perimeter thereof M1 using an electrode holding/moving means M6 and a capacitance signal obtained with the electrode M2 is detected by a movement detection means M7 connected to the means M6. An output of the means M7 is also inputted into the means M8, an output of which 8 is then, sent to a pinhole decision means M9, where an electrostatic capacitance varying between the disc M1 and the electrode M2 is judged to detect a pinhole while the location thereof is recorded.