The method of crushing rocks by group explosion of high-explosive (HE) blast-hole charges is often utilized for geological prospecting, for the development of useful ores, and other mining operations.Sometimes, unexploded detonators remain in the medium because of defects in the detonator ignition system or for other reasons, causing great danger for people during subsequent drilling of the rock.Consequently, the problem of developing new methods of detecting unexploded detonators in the bulk of rocks is a quite urgent problem.The electromagnetic field that originates during detonator explosion is studied experimentally and theoretically in this paper.Conditions are studied for detection of signals, their duration and amplitude.The aim of the paper is to show the possibility of separate recording of electromagnetic signals from individual explosions when exploded as a group. The method investigated permits computation of the number of explosions in a series if the intervals between them exceeds 0.i msec.A method of detection of the failure of one or several detonators during a group explosion is thereby given.Detonators of the type EDKZ-PMZ5 with a 25 msec delay of the explosion relative to the ignition were used for the experiments.The explosions were carried out in air and in artificial soil consisting of a paraffin-salt mixture.Both ignition modifications were investigated using both unmagnetized and magnetized detonators as well as with a permanent ferrite magnet of 0.3-0.4 cm 3 volume packed in the explosion borehold.Detonator magnetization was effected using a permanent magnet with annular magnetic flux density of 0.1-0.2 Teslas magnetic induction, with the detonator being installed in the hole in the magnet poles during magnetization.Detonator blasting was effected by two methods: connection in a d.c. 40-50 A electric circuit for detonator ignition and by a short (2-4 msec) current pulse of 200 A peak current developed during discharge of a condenser (around 4.5 J energy) through a thyristor.Recording the signal was accomplished by two methods, by use of a stub antenna or a magnetic coil.Signals were observed on a digital oscilloscope. The stub antenna was a 25 cm long coaxial cable segment from which the braid was removed.A Rs = i0 k~ load resistor was connected to it. The antenna was located at 20 cm to 3 m distance from the site of the explosion, and its orientation could be selected in any of three mutually orthogonal directions.The magnetic field of the explosions was recorded by using a circular frame of 0.4 m diameter on which i00 turns of copper wire were wound.To assure interference-immunity aluminum foil was wound around the frame as an electrostatic shield.The shield was insulated from the turns of the frame.Insulation was also used to prevent short-circuiting by the shield.The coil leads were connected to the coaxial cable and the electrostatic shield was connected to the braid.The block diagram of magnetic coil connection is represented in Fig. i. The coil inductance in this experiment is L = ...
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