FIELD: well logging. SUBSTANCE: when drilling holes, magnetic marks are automatically made on steel string at certain distance from point of drilling. These marks are registered after perforation and compared with background magnetic properties of string noted before perforation. Device for perforation interval control has surface control panel connected by means of logging cable to downhole instrument. The latter has separating block located between perforation block and inductor. Additionally connected to output of surface control panel containing control unit and power source is switching block whose inputs are connected to power source and control unit. EFFECT: higher reliability of control of deformation interval and higher efficiency of perforation. 2 cl, 2 dwg
