US3022446A - Detonator device - Google Patents

Description

1962 c. s. IRISH, JR

DETONATOR DEVICE Filed Sept. 22, 1958 FIG. 3

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INVENTOR. CHARLES G. IRISH, JR.

VOLTAGE- CURRENT CURVE OF I N90 GERMANlUM DIODE United States Patent 3,022,446 DETONATOR DEVICE Charles G. Irish, In, Cheshire, Conm, assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Sept. 22, 1958, Ser. No. 762,409 1 Claim. (Cl. 317-80) The present invention relates to electric detonators, blasting caps or similar devices and deals inparticular with a means for rendering the devices responsive to a given level of electrical energy while being non-responsive to a lower energy level.

It is a particular feature of the invention to provide an electrical detonator which functions at normal current levels but which requires high voltage for firing.

The range of normal current is intended to extend from .1 amp. to 20 amps. while the language high voltage includes a range of from about 25 volts to about 300 volts.

By virtue of the range of voltage levels at which the firing of devices of the present invention are responsive or non-responsive, it is possible to achieve selective detonation of a string or group of detonators by merely wiring a plurality of detonators together where each is actuated by a difierent voltage.

Thus, selective firing can be achieved by means of a variable voltage power supply and appropriate time delays can be incorporated in such a firing plan readily.

A further feature of the invention is that the electrical detonator has an exceedingly low probability of being fired by unwanted signals such as electrostatic voltages or induced currents from electromagnetic fields.

Another feature of the invention is the provision of an electrical detonator whose electrical continuity may be tested safely by relatively high voltages prior to activating the detonator. These test voltages may range from to 50 volts less than the firing voltage depending upon the value or magnitude of the desired firing voltage.

An electrical detonator embracing certain features of the present invention may comprise a housing or shell, an ignition assembly disposed within the shell comprising a pair of lead wires connected at their terminals to a bridge wire and at least two germanium diodes in circuit with the lead wires.

Other features and advantages of the present invention will become more apparent from the succeeding specification when read in conjunction with the appended drawings in which:

FIG. 1 is a perspective view of a detonator embracing the principles of the invention with certain portions of the housing broken away for clarity;

FIGS. 2 and 3 show preferred circuit arrangements, and,

FIG. 4 shows a typical voltage-current curve of a 1N9O germanium diode.

Referring now in detail to the drawings there is shown a detonator indicated generally by the reference numeral 10 including a tubular housing 11 enclosing at one end an appropriate priming charge 12 within which there is disposed a bridge wire 13 connecting the terminals of a pair of leads 14 and 16. The end of the housing from which the lead wires 14 and 16 protrude is appropriately sealed with waterproofing compound such as asphalt, wax, epoxy resin or the like, as indicated by the reference numetal 21.

Disposed within the sealed end of the tubular housing 11 is a small board or plate 17 formed of insulating material and snugly engaging the interior diameter of the tube. Mounted upon the board 17 are two germanium diodes 18 and 19. The diodes are electrically connected to the leads .14 and .16 in accordance with the wiring diagram of FIG. 3 so that the diode 18 is in series with the lead 14 while the diode 19- is in series with the lead 16.

It is intended that these diodes possess a reasonably high value of initial resistance, for example, 67,000 ohms, with a corresponding decrease in resistance, an inverse voltage characteristic, upon dissipation of power in the diode. Diodes having the necessary inverse voltagecharacteristics include germanium gold-bonded diodes and point contact diodes. For example, point-contact diode 1 N has been found satisfactory.

An alternative scheme for arranging the circuit of the detonator is shown in FIG. 2 wherein two diodes are shown wired in series with the lead 14.

FIG. 4 shows in graphic form the electrical characteristics of a diode utilized in the present invention. Note the inverse voltage characteristic wherein, initially, the current increases slightly with an increase in voltage; thereafter the voltage drops as current continues to increase.

Thus, the present invention affords a means for convetting any standard electric primer, detonator, match, squib blasting cap, etc. into an ignition device which requires high firing voltages. Although the current requirements remain normal, the power requirements are higher because of the higher voltages. The high voltage and power requirements for firing make it very difficult to fire by unwanted signals such as electrostatic discharges or induced currents from electromagnetic fields.

As stated previously, a preferred form of the invention would embrace a standard blasting cap with two 1N90 diodes back to back incorporated into the leads as shown in FIGS. 2 and 3. The blasting cap modified in this manner can be checked for continuity with voltages up to 50 volts with no danger of firing because current remains low as apparent in FIG. 4. In prior art devices, any voltage source used to check continuity must have a current limiting resistor.

In the detonator of the present invention the current at 50 volts will not exceed 750 microamperes, while the current required to fire the ordinary detonator is in excess of times as great.

A typical arrangement for operating my blasting cap involves connecting the leads to a variable transformer which is, in turn, connected to volts A.C. As the voltage is slowly raised, the current increases very little until the inverse voltage rating of the diode is approached (50 to 60 volts for the 1N90). As the voltage exceeds this value the current increases because the power rating of the diode is exceeded. Eventually the dynamic resistance (represented by slope of curve of FIG. 4) of the diode goes to zero and the diode then enters a negative resistance region wherein the voltage across the diode drops and sizable currents flow actuating the ignition device. The large currents usually destroy the two diodes by changing the conductivity of the germanium and by melting the fine contact wire.

Two diode types have been found to be satisfactory. These are the point contact diode and the gold bonded diode. There are many diodes of both types of structure with different characteristics. By selection of proper diode, insensitivity to voltages ranging from 30 volts to 250 volts can be obtained. The 1N90 has been selected because it provides adequate protection and is reasonably priced.

The variety of electrical characteristics available facilitates the design of a series of blasting caps which will fire at different voltage levels--50, 75 and 100 volts, for example. In blasting operations this feature affords a decided advantage in that multiple banks of charges could set off at any desired time interval.

Obviously, a variety of modifications and arrangements of the detonator of the present invention can be devised without departing from the spirit and scope thereof.

diode; whereby said test voltage level is of the order of 15 to 50 volts lower than the firing voltage level, and the test current is about 750 microamperes.

References Cited in the file of thispatent i a UNITED STATES PATENTS 2,514,434 iWindes July 11, 1950 2,828,692 Webster Apr. 1, i958 2,909,122 Shoemaker et al Oct. 20, 1959 FOREIGN PATENTS 320,243 Switzerland u--- May 15, 1957

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