GB910045A - Improvements in shot exploders - Google Patents

Abstract

910,045. Testing for continuity. MARSTON EXCELSIOR Ltd. Jan. 9, 1961 [Jan. 29, 1960], No. 3250/60. Class 37. A shot exploder has a testing circuit and an external circuit including a number of detonators, the testing circuit including two transistors connected such that when the external circuit resistance is below a predetermined value the emitter to collector conduction of the first transistor is altered causing the second transistor which has its base connected to the collector of the first transistor, to be energized and indicating means connected to the collector of the second transistor to operate. The indicating means may be a lamp which lights to indicate that the circuit is safe for exploding, that is when the total resistance is sufficiently low as to indicate that all of the detonators are connected satisfactorily. The first transistor is preferably of silicon type to reduce the sensitivity of the circuit to temperature changes. As shown in Fig. 1, electric detonators are connected across terminals 1, 2 and a sufficiently low value of firing circuit resistance will cause transistor 10 to be cut-off so that the resulting base current flow through resistor 11 to transistor 12 causes the latter to conduct and the lamp 13 to light. The circuit of Fig. 7 includes three transistors 10, 36, 12 connected so that a sufficiently low value of firing circuit resistance results in transistor 10 being biased off, in transistor 36 conducting and in transistor 12 being biased off so that this latter transistor does not act as a low resistance shunt across the indicating lamp which will consequently be illuminated. In the circuit of Fig. 2 (not shown), the bias to the emitter is obtained from a potential divider and a resistor is connected in parallel with the external circuit. In the circuit of Fig. 4 (not shown), regeneration is provided from the collector of the second transistor to the base electrode of the first. The two transistors may also be of opposite conductivity types, Figs. 5, 6 (not shown).