US3721886A

US3721886A - Blasting machine with overvoltage and undervoltage protection for the energy storage capacitor

Info

Publication number: US3721886A
Application number: US00201527A
Authority: US
Inventors: E Phinney; I Linkroum
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1971-11-23
Filing date: 1971-11-23
Publication date: 1973-03-20
Anticipated expiration: 1990-03-20
Also published as: IT971104B; GB1366619A; CA951785A; DE2257523A1; FR2163022A5

Abstract

A blasting machine for firing an explosive bridge wire device or the like. The blasting machine includes a storage capacitor that is charged to an energy level within a predetermined range. The upper limit of the energy range is controlled by a two-electrode spark discharge device which operates as an upper voltage control and the lower limit of the energy range is controlled by a twoelectrode spark device which does not permit the capacitor to be discharged until the second device is conducting, which occurs at the desired lower voltage level whereby the energy discharged from the storage capacitor must be within the energy levels established by the two spark discharge devices.

Description

United States Patent [191 Phinney et a1. 5]March 20, 197 3 [5 BLASTING MACHINE WITH 3,417,306 12/1968 Knak ..320/1 OVERVOLTAGE AND UNDERVOLTAGE PROTECTION FOR THE ENERGY STORAGE CAPACITOR Primary Examiner--Bemard Konick Assistant Examiner-Stuart Hecker Attorney-Raymond J. Eifler et a1.

[75] Inventors: Earl M. Phinney, Oneonta; Irving E.

Linkroum, Hancock, both of N.Y. [57] ABSTRACT 73 A Th sslgnee Bend Corporahon Southfield A blasting machine for firing an explosive bridge wire MlCl'l. device or the like. The blasting machine includes a [22] Filed: Nov. 23, 1971 storage capacitor that is charged to an energy level [211 App]; No: 201,527 within a predetermined range. The upper limit of the energy range is controlled by a two-electrode spark discharge device which operates as an upper voltage US. Cl- ..320/1, 3 control and the lower of the energy range is con- [51] Int. Cl. ..H03k 3/30, H02m 3/22 trolled by a two electrode Spark device which does not [58] Field of Search ..320/l; 317/80; 307/108 permit the capacitor to be discharged until the Second 56 device is conducting, which occurs at the desired 1 References C'ted lower voltage level whereby the energy discharged UNITED STATES PATENTS from the storage capacitor must be within the energy levels established by the two spark discharge devices. 3,541,393 11/1970 Diswood ..320/1 X 2,826,693 3/1958 Resnik ..320/l X 2 Claims, 2 Drawing Figures CAPACITOR v CHARGE 8 VOLTAGE D HA s INDICATOR 6 I] 3) FIRING CIRCUIT POWER ENERGY PULSE SUPPLY STORAGE GENERATOR TRIGGER LOAD 2 VOLTAGE m R EG U LATOR PATENTEDMAR20|973 SHEET 20F 2 N MEDQE BLASTING MACHINE WITH OVERVOLTAGE AND UNDERVOLTAGE PROTECTION FOR THE ENERGY STORAGE CAPACITOR BACKGROUND OF THE INVENTION This invention relates to an improved blasting machine for detonating blasting caps or the like. The invention is more particularly related to a battery powered blasting machine of the capacitor discharge type.

Basically, electrical systems for firing explosive devices include a source of power such as a battery, an oscillator, a transformer responsive to the oscillator for stepping up the pulses therefrom, a storage capacitor which is charged by the pulses from the transformer, and a trigger circuit which allows the energy stored in the capacitor to discharge to fire an explosive device. The energy stored in the capacitor is discharged through the explosive device by means of a triggering circuit which may be operated automatically or manually. Examples of such blasting devices may be found in US. Pat. No. 3,417,306 entitled Regulated woltage Capacitor Discharge Circuit to J .'L. Knak, issued Dec. 17, 1968, and US. Pat. No. 3,275,884 entitled Electrical Apparatus for Generating Current Pulses to L. H. Segall et al., issued Sept. 27, 1966.

In certain blasting operations such as those performed in tunnels and shaft mining, it may be necessary to connect from as few as one blasting cap and as many as 150 blasting caps together in a parallel circuit. Parallel connections are used because such connections permit rapid connection of the blasting caps with minimal possibility of error. To insure that all the blasting caps are fired, the blasting machine must always deliver a given minimum energy each time it is fired, otherwise all of the blasting caps may not be fired. Further, it is also important that the blasting machine does not deliver too much energy to the blasting caps, otherwise malfunction of some of the blasting caps may occur. Therefore, to insure that all blasting caps are fired the blasting machine must always deliver an amount of energy in a predetermined energy range depending upon the number of blasting caps to be fired.

SUMMARY OF THE INVENTION This invention prevents the firing of a blasting machine below and above a predetermined energy range.

The invention is a battery powered blasting machine characterized by an electrical circuit that charges a storage capacitor within a predetermined energy range before it can be discharged. The circuit is further characterized by two, two electrode spark discharge devices, one of which establishes the upper energy level and the other of which establishes the lower energy level.

In one embodiment of the invention, the blasting machine comprises: a capacitor; means for supplying electrical energy to the capacitor; means for producing a plurality of electrical pulses when the capacitor has reached a first predetermined energy level, the pulse means including a second normally nonconductive gaseous conductor which is rendered conductive when a predetermined voltage is applied thereto and a resistor-capacitor circuit in series with the second gaseous conductor so that when the second gaseous con ductor is rendered conductive, the capacitor in series with the resistor lowers the voltage applied to the second gaseous conductor to a voltage below the predetermined value and the second gaseous conductor is rendered nonconductive; switching means for receiving the pulses, the switching means ,operable to permit the discharge of the capacitor only during the presence of the pulses, whereby the capacitor cannot be discharged below the predetermined energy level, the switching means including a first normally nonconductive gaseous conductor in circuit relationship with the pulse means, thefirst gaseous conductor being rendered conductive upon receiving the pulses whereby when pulses from the pulse means are transmitted to the first gaseous conductor, the first gaseous conductor is rendered conductive to permit the capacitor to discharge, and a switch connected between the first gaseous conductor and the pulse means, the switch operable in the ON position to permit the passage of said pulses to the first gaseous conductor whereby the capacitor is discharged only when the switch is in the ON position and when the pulse means is producing pulses; and a third gaseous conductor means for preventing the capacitor from exceeding a second predetermined energy level which is above the first predetermined energy level whereby the capacitor is prevented from reaching energy levels above the second predetermined energy which may cause failure of said means for storing electrical energy.

Accordingly, it is an object of this invention to provide a battery powered explosive ignition system that can deliver energy only in a preselected energy range to fire electrically energized squibs and like firing units such as explosive bridge wire devices.

Another object of this invention is to provide a novel electrical system that prevents applying too little or too much energy to fire explosive bridge wire devices or the like.

The above and other objects and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings and claims which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a blasting machine that utilizes the principles of this invention.

FIG. 2 is a schematic diagram of a preferred embodiment of the circuitry for a blasting machine shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now to the drawings, FIG. 1 illustrates a block diagram of a blasting machine which utilizes the principles of the invention. the basic portion of the system includes a power supply 1, an energy storage device 3, such as a capacitor for storing energy supplied by the power supply I, a pulse generator 5 for generating pulses when the energy in the capacitor has reached a predetermined energy level, and a firing circuit 6 which permits the discharge of the energy in the energy storage device 3 through the load 8 which are the blasting caps or the like, when the trigger portion 7 of the firing circuit 6 receives pulses from the generator 5.

The power supply 1 may be either a a.c. or d.c. and include the necessary electrical components for charging an energy storage device such as a capacitor.

The energy storage device 3 is preferably a capacitor. The voltage regulator 2 may be used in electrical circuit relationship with the energy storage device 3 to assure that the energy stored in the energy storage device 3 does not exceed a predetermined voltage level. The energy storage circuit may include a switch that, in the ON position permits the energy storage device 3 to store energy, and in the OFF position allows the energy storage device 3 to discharge so that no energy remains in the energy storage device 3 when the blasting machine is not in use. The charge and discharge switch 9 may be either a single switch or multiple switches and may also be part of the firing circuit 6. 1

A voltage indicator 4 may be used in combination with the pulse generator 5 to produce either visual or audible signals when the pulse generator 5 is generating pulses.

The firing circuit 6 includes a trigger 7 which allows the energy storage device 3 to discharge into the load 8. The trigger 7 may be a gaseous conductor of the threeelectrode type wherein the trigger electrode upon receiving pulses from the pulse generator 5 allows the remaining two electrodes which are in series with the energy storage device 3 to conduct, thereby allowing the energy stored in the device 3 to discharge into the load 8. If it is desired that the blasting machine not be automatically triggered, a switch may be loacted in series with the pulse generator 5 so that when the voltage indicator 4 gives indication that pulses are present, manually operating the switch to close the contacts will cause the trigger to conduct and discharge the energy into the load.

FIG. 2 is a schematic diagram ofa preferred embodiment of a blasting machine that utilizes a battery and an oscillator to charge the storage capacitor which will be discharged to fire a blasting cap or other explosive bridge wire device or the like. The dotted lines outlining portions of the circuitry indicate the power supply 1, the energy storage device 3, the voltage regulator circuit 2, the voltage indicator 4 associated with the pulse generator, the pulse generator circuit 5, and the firing circuit 6.

The power supply 1 in this embodiment includes a battery 140, a switch 9, a smoothing capacitor 130, and a transistorized oscillator circuit in combination with a step-up transformer 150, the output voltage of which is applied to the energy storage means 3. In operation, the power supply circuit 1 operates as follows:

A solid state switch oscillator is powered by a battery 140 or other direct current source. In one embodiment twelve one and one-half volt batteries were used, which, because of the internal resistance thereof, provided a voltage between 10 to 12 volts. Connected across the battery 140 is a capacitor 130 which, when charged, provides additional current to the oscillator. A transformer 150 has its primary winding 101 connected into the oscillator circuit and its secondary winding 151 connected to a storage capacitor 153 through a diode 152 to store the energy generated by the oscillator. The windings 101 and 151 of transformer 150 are inductively coupled and wound and disposed in the manner indicated by the dots.

The solid state switch oscillator operates to intermittently interrupt current flow from the battery 140 through the primary winding 101 of the transformer 150 and includes a first switching transistor 103, a first voltage divider network (110, 111, 112, 1 13), a second voltage divider network (121, 122, 123), and first diode means (102, 104, 106) connected between the first voltage divider network and the primary winding 101 of the transformer 150 to direct the flow of current to and from the primary winding 101. The oscillator circuit shown is capable of producing oscillations in the range of 800 to 2,000 Hz.

The first voltage divider network includes a diode and a plurality of

resistors

111, 112 and 113 connected together in series across the primary winding 101 of the transformer and the first transistor 103.

The diode means that directs the current from the primary winding 101 includes a first diode 102 connected by its anode terminal to the junction between the primary winding 101 and the first transistor 103. To permit current to flow from the primary winding 101 when transistor 103 is off, diodes 104 and 106 are connected in series with one anode terminal connected to the junction between the primary winding 101 and the first transistor 103 and one cathode terminal connected to the junction between the second transistor 1 l2 and the third transistor 113.

The second voltage divider network includes a transistor 121, a resistor 122, and a resistor 123 connected together in series across the battery 140. The base of the first transistor 121 is connected, for biasing purposes, to the junction between the diode 110 and resistor 111 of the first voltage divider network. The base of the first transistor 103 is connected to the junction between resistors 122 and 123 to supply a current to the base of transistor 103 when the transistor 121 is in the conductive state.

The secondary winding 151 of the transformer 150 is connected to a diode 152 and a capacitor 153. When the battery is l0 to l2 volts, the maximum charge that can be obtained on capacitor 153 is about 7,000 to 8,000 volts. However, voltages of this magnitude are not generally required in battery powered explosive ignition systems, therefore, an additional circuit (not shown) may be added to limit the voltage across the capacitor 153. The energy stored in the capacitor 153 is used for firing an explosive bridge wire device or the like.

In this embodiment, when a constant current source having an output voltage of about 10 volts is used in lieu of the battery 140 and the capacitor 153 is a 100 microfarad capacitor, the capacitor 153 can be charged to 200 joules within [0 seconds and to 400 joules within 20 seconds. Since batteries deteriorate with use, they are capable of achieving the initial charged energy previously stated, but tests reveal that when they are used to charge the capacitor 153 to 400 joules three times a day for 21 days, it would take a maximum of 71 seconds of charge time to obtain 400 joules of energy at the capacitor 153. The minimum charge time at the end of this period to obtain 400 joules of energy at the capacitor 153 would be 49 seconds.

The energy storage means 3 includes a blocking diode 152 and storage capacitor 153 in circuit relationship with the secondary winding 151 of the transformer 150. The discharge resistor 154 allows the energy storage in capacitor 153 to be discharged when the switch 9 in the power supply 1 is in the OFF position.

The voltage regulator 2 which prevents the voltage on the capacitor 153 from exceeding a predetermined value includes a two-electrode spark gap 160, a resistor 163, a capacitor 165, and a resistor 167. The function of the regulator circuit is to drain excessive energy off the storage capacitor 153 to prevent the storage capacitor from exceeding a predetermined upper energy limit. The spark gap 160 is a normally nonconducting device that conducts when the voltage across the device has reached a predetermined voltage. In this instance, the breakdown voltage of the spark discharge device 160 is chosen to be the predetermined upper voltage limit desired across storage capacitor 153. In operation, the voltage across the storage capacitor 153 appears across the spark gap 160. As the storage capacitor 153 is charged, the voltage across the spark gap 1160 increases until the breakdown voltage of the device is reached. The spark gap 160 then breaks down and conducts current to charge capacitor 165. The current through the spark device 160 decreases as capacitor 165 becomes more fully charged. Eventually the current through the spark device 160 decreases to the point where it no longer will support an arc in the discharge device 160. The are extinguishes and spark gap 160 ceases conduction. The charge on the capacitor 165 is then discharged through resistor 167. As capacitor 165 discharges, the voltage across the spark gap device 160 therefore increases, and if the voltage across the storage capacitor 153 is still greater than the breakdown voltage of the spark gap discharge device 160, the discharge device 160 again conducts and the cycle is repeated again. If desired, a neon indicator light could be used in combination with this circuit to give an indication when the voltage regulator is operating. The suggested method with respect to a voltage indicating device would be to place a neon indicator light and resistor across capacitor 165 which is responsive to the charging and discharging of capacitor 165.

The pulse generator circuit 5 includes a two-electrode spark discharge device 1711, resistor 171, capacitor 177, resistor 173, and resistor 175. The voltage indicator light 4, such as a neon bulb, is in circuit relationship with

resistor

173 and 175 and is responsive to the charging and discharging of capacitor 177. In operation, the two-electrode spark discharge device 170 will remain in a nonconducting state as long as the voltage on the storage capacitor 153 is less than the breakdown voltage of the spark discharge device 170. When the voltage on the storage capacitor 153 exceeds the breakdown voltage of the discharge device 170, the device conducts allowing current to pass through resistor 171 to charge capacitor 177. As the voltage on the capacitor 177 increases, the voltage across the spark device decreases until the spark device 170 returns to the original nonconducting state. At this time, capacitor 177 then discharges through

resistors

173 and 175 which further applies a voltage to the neon light 4 which gives an indication that this circuit is in operation. When the voltage across the spark discharge device 170 again rises to the breakdown potential of this device, conduction begins again and the cycle repeats itself. Each time capacitor 177 is charged, voltage is applied to neon indicator light 4 through the

resistor divider network

173, 175. The neon indicator light 4 stays lit until the voltage across the light drops below the minimum sustaining voltage of the light 4. By this means, each time capacitor 177 is charged, there is a visible light pulse to signal the operator that the minimum voltage has been reached and the blasting machine may be fired. With this circuit, when the minimum voltage across the capacitor 153 is reached and pulses are being generated by the pulse generator, pressing the firing switch 181 in the firing circuit 6 will cause the pulses to be transmitted to the firing circuit.

The firing circuit 6 includes a three-electrode spark gap discharge device, a step-up transformer for raising the voltage of the pulses received from the pulse generator 5 and applying them to the trigger electrode of the spark discharge device 180, and a firing switch 181 which permits the trigger pulses from the pulse generator 5 to be transmitted to the primary winding 185 of the step-up transformer. For further details concerning the particular type of three-electrode spark gap discharge device required for this circuit see U.S. Pats. Nos. 3,187,215 entitled Spark Gap Device to I. E. Linkroum issued June 1, 1965, and 3,229,146 entitled Spark Gap Device with a Control Electrode Intermediate the Main Electrodes to I. E. Linkroum issued Jan. 11, 1966. In operation, when the firing switch 181 is in the OFF position, no pulses are being supplied to the spark discharge gap thereby preventing the firing of any blasting caps attached to the output terminals 190. Further, the firing switch 131 in the OFF position is yet in combination with the power switch 9 in the OFF position to place the discharge resistor 154 across the storage capacitor 153 to drain any charge thereon. When the firing switch 181 is placed in the ON position, the storage capacitor 153 will discharge if trigger pulses are present. Therefore, to discharge the energy in capacitor 153 to blasting caps attached to the output terminals 190, it is necessary that the pulse generator 5 is generating pulses and that the firing switch 181 is in the ON position. When these two conditions are met, the output pulses of the pulse generator 5 are transmitted to the primary winding 185 of the step-up transformer where the pulses are stepped up to a higher voltage and applied to the trigger electrode of the spark gap discharge device through resistor 183 thereby causing ionization within the spark gap discharge device and permitting current to flow through the two main electrodes which allows the energy storage capacitor 153 to discharge through the blasting caps connected to the output terminals 190. If it is desired to eliminate manual firing of the blasting caps and to have the blasting machine discharge the energy in the capacitor 153 automatically when it has reached a predetermined energy level, the firing switch 181 may be eliminated completely. In this instance, as soon as voltage pulses are available from the pulse generator 5, the three-electrode spark discharge device would be triggered to discharge the energy in the capacitor 153 through the blasting caps (not shown) connected to the terminals 190.

OPERATION Referring now to FIG. 2, the circuit operates as follows: When switch 9 is in the OFF position, resistor 154 removes the energy stored in capacitor 153. When switch 9 is closed, resistor 154 is removed from the eircuit and current flows from the battery 140 through capacitor 130 and through transistor 121, resistor 122 and resistor 123. Accordingly, a voltage is applied across the voltage divider network containing transistor 121 and the voltage dividing network containing diode 110. Since there is a positive voltage applied across the emitter base circuit of the transistor 121, the transistor 121 conducts permitting a current to flow through resistors 122 and 123 and through lead 124 to the base of transistor 103 which is in the nonconducting state. When the current to the base of transistor 103 is sufficient, transistor 103 conducts (ON). When the transistor 103 conducts, current flows through the transformer primary winding 101 and transistor 103. With current flowing to ground through the primary winding 101, transistor 121 begins to return to the nonconductive (OFF) state as the base to emitter current of that transistor begins to decrease. Eventually transistor 121 becomes nonconductive, removing the necessary base current to transistor 103 which also becomes nonconductive (OFF). Once the transistor 131 turns OFF, the electrical energy stored in the primary winding 101 during the ON or conduction period of transistor 131 is removed as current leaves the primary winding 131 and flows through

diodes

104, 106, 110 and resistors 111 and 112. This action also operates to back bias transistor 121 so that it remains in the nonconductive state. Further, since during this time the rate of change of current with respect to time (di/dt) becomes sharply negative the voltage induced across the secondary winding 151 for this period also reverses and the secondary winding 151 becomes a current source. Therefore, during the time di/dt is negative, most of the energy stored in the primary winding of the transformer is transferred to the secondary winding 151 in a manner that allows the diode 152 to conduct and to supply energy to the capacitor 153 and to supply energy to the capacitor 153 and to a load (not shown). Thus, electrical energy which is fed to the primary winding during the conducting period of transistor 103 is transferred to the capacitor 153 during the nonconducting period of transistor 103. The entire action is cyclic for as the energy is removed from the transformer 150 the reverse bias on transistor 121 is removed allowing transistors 121 and 103 to turn ON and repeat the entire operation again. (About 800 to 2,000 112.)

As the energy stored in the capacitor reaches a predetermined level, the pulse generating circuit begins generating trigger pulses. This occurs when the spark gap discharge device 170 reaches its breakdown potential. To assure that the energy stored in the capacitor is above the predetermined energy level but not in excess of a second and higher energy level, a voltage regulator circuit 2 is utilized. This eliminates excessive energy levels that cause adverse operation of the blasting machine.

Once the trigger pulses are present and the energy stored in the capacitor is within a preferred range depressing the firing switch 181 applies trigger pulses to transformers 182 which causes spark gap device 180 to conduct, thereby allowing the energy in capacitor 153 to discharge into the blasting caps (not shown) attached to the outputs 190 and detonate explosives.

3300 microfarad, 30 Volts d.c.

0.45 to 0.61 microfarad 3KV 0.008 to 0.012 microfarad,

400 microfarad 2.5KV

0.025 to 0.03 microfarad 3KV Capacitor Capacitor Capacitor 177 Capacitor 153 Capacitor 187 Resistor 122 6.2 ohms, 11W

Resistor 123 33 ohms AW Resistor 111 100 ohms 2W Resistor 112 1000 ohms, AW

Resistor 113 10K ohms AW Resistor 154 SR ohms 10W Resistor 167 20K ohms 20W (2 in series) Resistor 163 2 ohms 20W (2 in parallel) Resistor 175 0.33 megohms 2W Resistor 173 1.36 megohms 4W (2 in series) Resistor 171 500 ohms 10W Resistor 186 20 megohms 1W Resistor 183 1K ohms 5W Resistor 189 10K ohms 10W Transistor 121 Type MJE 341 Transistor 103 Type 2N3055 Beta 20-35

Diodes

110, 102, 104, 106 GE A14F Diode 152 Motorola MR 995A 2200 volts d.c. (breakdown)- Bendix Corp. Sidney, N.Y. Part no. 10-374105-21 2000 volts d.c. (breakdown)- Bendix Corp. Sidney, N.Y. Part no.10-374121-14 Discharge Device 160 Discharge Device Transformer 150 Transformer 182

Switch

9 and 181 While a preferred embodiment of the invention has been disclosed, it will be apparent to those skilled in the art that changes may be made to the invention as set forth in the appended claims, and in some cases, certain features of the invention may be used to advantage without corresponding use of other features. For example, different types of semi-conductors, or solid state control devices may be substituted for the types illustrated. Accordingly, it is intended that the illustrative and descriptive materials herein be used to illustrate the principles of the invention and not to limit the scope thereof.

Having described the invention what is claimed is:

1. A blasting machine for initiating electro-explosive devices which comprises:

means for storing electrical energy, said storage means having two output terminals;

means for supplying electrical energy to said energy storage means;

means for producing a plurality of electrical pulses when said energy storage means has reached a first predetermined energy level, said means for producing electrical pulses including a second normally nonconductive gaseous conductor which is rendered conductive when a predetermined voltage is applied thereto and a resistor-capacitor circuit in series with said second gaseous conductor so that when said second gaseous conductor is rendered conductive, said capacitor lowers the voltage applied to said second gaseous conductor to a voltage below said predetermined value and said second gaseous conductor is rendered nonconductive;

switching means for receiving said pulses, said switching means operable to permit the discharge of said energy storage means only during the presence of said pulses, whereby said energy storage means cannot be discharged below said predetermined energy level, said switching means including a first normally nonconductive gaseous conductor having one electrode connected to one output terminalof said energy storage means, a second electrode, and a trigger electrode connected through said switching means to said pulse means, said first gaseous conductor being rendered conductive upon receiving said pulses at said trigger electrode when said switching means is closed whereby when pulses from said pulse means are transmitted to said first gaseous conductor, said first gaseous conductor is rendered conductive to permit said storage means to discharge, and a switch connected between said first gaseous conductor and said pulse means, said switch operable in the ON position to permit the passage of said pulses to said first gaseous conductor whereby said energystorage means is discharged only when said switch is in the ON position and when said pulse means is producing pulses;

means for preventing said means forstoring electrical energy from exceeding a second predetermined energy level which is above said first predetermined energy level whereby said energy storage means is prevented from reaching energy levels above said second predetermined energy level; and

means for connecting the second electrode of said first gaseous conductor, and the other output terminal of said storage means to a circuit containing an electro-explosive device whereby said electroexplosive device is exploded upon conduction of said first gaseous conductor and the closing of said switching meanswhich permits the discharge of said energy storage means.

2. The blasting machine as described in claim 1 wherein said means for preventing said means for storing electrical energy from exceeding a second predetermined voltage level includes an electrical circuit which comprises:

a third gaseous conductor connected in series to a resistor and a capacitor, said capacitor connected in parallel with a second resistor, said electrical circuit connected across said means for storing electrical energy whereby when said means for storing electrical energy reaches said second predetermined energy level said third gaseous conductor conducts to prevent said means for storing electrical energy from exceeding said second predetermined energy level.

Claims

1. A blasting machine for initiating electro-explosive devices which comprises: means for storing electrical energy, said storage means Having two output terminals; means for supplying electrical energy to said energy storage means; means for producing a plurality of electrical pulses when said energy storage means has reached a first predetermined energy level, said means for producing electrical pulses including a second normally nonconductive gaseous conductor which is rendered conductive when a predetermined voltage is applied thereto and a resistor-capacitor circuit in series with said second gaseous conductor so that when said second gaseous conductor is rendered conductive, said capacitor lowers the voltage applied to said second gaseous conductor to a voltage below said predetermined value and said second gaseous conductor is rendered nonconductive; switching means for receiving said pulses, said switching means operable to permit the discharge of said energy storage means only during the presence of said pulses, whereby said energy storage means cannot be discharged below said predetermined energy level, said switching means including a first normally nonconductive gaseous conductor having one electrode connected to one output terminal of said energy storage means, a second electrode, and a trigger electrode connected through said switching means to said pulse means, said first gaseous conductor being rendered conductive upon receiving said pulses at said trigger electrode when said switching means is closed whereby when pulses from said pulse means are transmitted to said first gaseous conductor, said first gaseous conductor is rendered conductive to permit said storage means to discharge, and a switch connected between said first gaseous conductor and said pulse means, said switch operable in the ON position to permit the passage of said pulses to said first gaseous conductor whereby said energy storage means is discharged only when said switch is in the ON position and when said pulse means is producing pulses; means for preventing said means for storing electrical energy from exceeding a second predetermined energy level which is above said first predetermined energy level whereby said energy storage means is prevented from reaching energy levels above said second predetermined energy level; and means for connecting the second electrode of said first gaseous conductor and the other output terminal of said storage means to a circuit containing an electro-explosive device whereby said electro-explosive device is exploded upon conduction of said first gaseous conductor and the closing of said switching means which permits the discharge of said energy storage means.

2. The blasting machine as described in claim 1 wherein said means for preventing said means for storing electrical energy from exceeding a second predetermined voltage level includes an electrical circuit which comprises: a third gaseous conductor connected in series to a resistor and a capacitor, said capacitor connected in parallel with a second resistor, said electrical circuit connected across said means for storing electrical energy whereby when said means for storing electrical energy reaches said second predetermined energy level said third gaseous conductor conducts to prevent said means for storing electrical energy from exceeding said second predetermined energy level.