1. Composition LD-EMD5A Electromagnetic Defectoscope is mainly composed of upper and lower electronic assemblies. 2. Function LD-EMD5A Electromagnetic Defectoscope is a downhole logging instrument which adopts the electromagnetic method. It can be used to detect various damages such as corrosion, deformation, crack, fracture, holes in the downhole pipe string, and both the inner and outer metal loss of the string, to determine the thickness of downhole pipe string, and can correctly reflect the well sketch and the position of the downhole tools (collar, casing shoes, packers and valves, etc).LD-EMD5A Electromagnetic Defectoscope can be connected with LANDAU Cased Hole Logging Surface System to constitute a Cased Hole Imaging Logging System. The Electromagnetic Defectoscope sends the acquired measurement data to the surface system for decoding via the mono-cable. The decoded data is then processed by the surface software to generate the pipe wall thickness curve and the related 3D image, which will intuitively demonstrate the damage details of the downhole pipe string and the position of the downhole tools.