US 3171063 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Feb. 23, 1965 J. 5. HUTCHISON ETAL 3,171,063
REMoTE TRIGGER ARRANGEMENT FOR BLASTER Filed July 20, 1962 WILLIAM J. STARK JOHN S. HUTCHISON INVENTORS A T TORNE Y United States Patent 6 3,171,063 REMOTE TRIGGER ARRANGEMENT FOR BLASTER John S. Hutchison and William J. Stark, Tulsa, Okla,
assiguors to Jersey Production Research Company, a
corporation of Delaware Filed July 20, 1962, Ser. No. 211,267 9 Claims. (Cl. 317--80) This invention relates to a remote trigger arrangement for blasting. More particularly, the invention relates to a system for firing a blasting cap or explosive initiators as used in geophysical prospecting including means whereby the system is substantially insensitive to varying lengths of cable extending from the point of firing control to the point of firing the blasting cap. Still more particularly, theinvention relates to an improved circuit arrangement providing a high impedance circuit for remote firing of a blasting cap wherein the current in the firing conductors of a cable extending from the point of firing control to the point of firing of the blasting cap is maintained at a low level so that the time interval between initiation of the firing control and the firing of the blasting cap is substantially insensitive to varying lengths of cable, and in an arrangement whereby the firing circuit and firing conductors are isolated and balanced to prevent feed-over to other conductors in the cable.
In the well known art of geophysical prospecting, a shock is generated at or below the surface of the earth to initiate a wave of seismic energy which is detected and recorded as the seismic wave is reflected from subterranean formations. The most frequently used method of initiating the shock is to set otf an explosive. Most ge11- erally the explosive is initiated by applying a voltage across a blasting cap.
The firing of the blasting cap must be accurately controlled in relation to the mechanisms employed to detect and record the reflected energy. In present day seismograph equipment, blasting is usually controlled at a point of firing control by automatic initiation of firing by the recording mechanisms. When the point of firing control is close (within at least a few hundred feet) to the actual point of firing the explosive charge, there is no particular difiiculty encountered in the timed initiation of the blasting cap. When such relatively short distances are involved, it is only necessary for the recording mechanism to trip a switch applying a voltage directly to the blasting cap, or in the alternative, to apply a voltage to control a relay switch which in turn applies voltage to the blasting cap.
When relatively long distances exist between the point of firing control and the point at which a blasting cap is fired, necessitating the use of a relatively long cable between these points, a difiiculty is interposed in that there is a considerable time interval between the initiation of firing at the point of firing control, and the actual firing of the blasting cap. Varying cable lengths vary the time interval in that when a voltage is introduced on a relatively long pair of conductors in a cable, the inductive efiect of the conductors and cable retards voltage buildup at distances along the cable.
The capability of seismograph records to convey information as to the disposition of substrata formations is based on the ability of seismic equipment used to accurately measure the time relationships between bits of recorded information with respect to the time of firing of the blasting cap. Otherwise, the necessary critical time relationships between recorded events are not accurately obtained. For this reason, it is important in seismic work to provide, as this invention accomplishes, a means of accurate time control between the initiation of firing and the actual firing of a blasting cap which is relatively inde- 3,171,063 Patented Feb. 23, 1965 ice pendent of the length of cable used to convey the blasting signal.
Ordinarily the conductors used to initiate blasting consist of a separate pair of conductors run independently of signal carrying conductors. In some methods of geophysical prospecting it is desirable to place the blasting conductors in the same cable with other conductors used to convey signals picked up by geophones back to the central recording point. When a high current is required to initiate a firing blast, there is a great amount of current feed-over to the other conductors in the cable. This gives false signals on the seismograph record which are naturally highly undesirable.
It is therefore an object of this invention to provide a remote trigger arrangement for blasters wherein the time interval between the initiation of firing control and the firing of a blasting cap is substantially independent of the length of cable extending between the point of firing control and the blasting cap.
Another object of this invention is to provide a remote trigger arrangement for blasting which uses a high im pedance signal coupling means. The signal coupling means includes a cable extending between a point of firing control and the point of actual firingwhereby only a relatively small current is used, and voltage feed-over to other conductors in the cable paralleling the conductors carrying the firing control voltage is materially reduced.
Another object of this invention is to provide a remote trigger arrangement for blasting including a balanced pair of conductors extending between the point of firing control and the point of firing a blasting cap to reduce feed-over of the firing voltage pulse to other conductors paralleling the firing conductors.
Another object of this invention is to provide a pulse detector circuit adaptable to receive a low voltage pulse from a pair of conductors and to actuate a firing relay upon receipt of the voltage pulse.
Another object of this invention is to provide a pulse detecting circuit adaptable to actuate a relay to fire a blasting cap upon the receipt of a voltage pulse, and including automatic circuit means for resetting the circuit after the circuit has been actuated to fire a blasting cap.
These and other objects and a better understanding of the invention may be had from the following description and claims taken in conjunction with the accompanying single drawing which is a schematic diagram of the circuit arrangement of this invention.
Generally speaking, this invention concerns a seismic initiation circuit utilized to remotely fire a blasting cap. A firing relay used to energize the blasting cap is placed in series with a voltage controlled impedance means with a voltage placed across the seriesed impedance and relay. A pulse detector connected to the cable functions to supply the control voltage to the control voltage impedance means and to alter the control voltage upon receipt of a pulse voltage along the cable initiated from the operator control point. The receipt of a voltage pulse by the pulse detector circuit alters the control voltage on the voltage controlled impedance means which reduces the impedance thereof, energizing the firing relay to fire the blasting cap. Accordingly a relatively small current flow along the cable is utilized which minimizes voltage feed-over to the adjacent conductors in .the cable.
Referring now to the drawing the circuit of this invention may be said to consist of three portions, that is, a pulse generating circuit indicated generally by the numeral 10, a cable indicated generally by the numeral 12, and a firing circuit indicated generally by the numeral 14. Cable 12 includes two conductors 16A and 16B which are one pair of conductors included in a multi-conductor cable -the other conductors of the cable are normally utilized for transmitting geophone created voltages to geophysical recording equipment, not shown.
A system of geophysical prospecting in use at the present time frequently requires the operator control point, recording equipment, etc., to be located at a substantial distance from the shot point at which seismic waves are initiated. The pulse generating circuit 18 of the drawing will be normally a part of recording equipment. The recording equipment is usually mounted in a truck and serves to record energy received from a multiplicity of planted geophones. The firing circuit 14, on the other hand, is located near the point where the blast is to occur. Thus, the pulse generating circuit and the firing circuit 14 of the drawing may be located one-half mile or even a much further distance apart. This invention concerns a system whereby a voltage pulse initiated in the pulse generating circuit 10 is used to trigger firing circuit 14 which in turn fires a blasting cap 18.
Pulse generating circuit This invention uses a short duration, high voltage, low current pulse communicated to conductors 16A and 168 to fire the blasting cap 18. Conventional methods of firing a blasting cap from a remote location use a relay adjacent to the blasting cap 18 which is closed by applying a voltage at the control point to a pair of conductors extending from the point of firing control to the relay. When cable portion 12 is long, the inherent inductance of the parallel conductors, such as conductors 16A and 1613, means that, subsequent to the application of a voltage, the voltage builds up to a point sufficient to energize the relay to fire blasting cap 18. Varying lengths of cable 12 will result in varying time lapses after applying such voltage until the closure of a relay to fire cap 18. In addition, such methods of energizing a relay over a long length of cable requires fairly high currents which feed over to the other conductors making up the cable.
These inherent disadvantages of conventional methods are overcome by the system of this invention wherein only a low current, short duration pulse is used to fire blasting cap 18.
Pulse generating circuit 10 consists of a battery 20 in series with a first winding 22 of a pulse generating transformer 24. In series with battery 20 and winding 22 is a switch 26. Second winding 28 of pulse generating transformer 24 is connected to conductors 16A and 16B.
When switch 26 is closed, battery 20 causes a current flow through first winding 22 of transformer 24. This tends to induce a voltage pulse in secondary Winding 28 which is applied to conductors 16A and 16B. This voltage pulse generated on closure of switch 26 may be used to fire blasting cap 18; however, the preferred embodiment of this invention uses the fly back pulse induced on conductors 16A and 16B when switch 26 is opened. The fly back pulse is of a greater magnitude than the voltage pulse created by the closing of switch 26 and is of an even duration and of a consistent shape. Thus, in the preferred embodiment of the invention the voltage pulse used to fire blasting cap 18 is created by the pulse generating circuit 10 upon opening switch 26.
The circuit arrangement of the pulse generating circuit 10 of the invention is extremely simple and it is obvious that many other means of generating a pulse on conductors 16A and 16B will be readily suggested. The embodiment shown is preferred because of its simplicity.
Firing circuit Firing circuit 14 may be broken down into basic portions consisting of a blasting circuit 30, and a pulse detecting circuit 32.
Blasting circuit 30 comprises firing relay 34 in series with voltage controlled impedance 36 placed across a voltage source, such as battery 38. Voltage controlled impedance 36 may, by way of example, consist of a silicon controlled rectifier such as a number C36A as manufac- 4 tured by the General Electric Company. The silicon controlled rectifier 36 is normally biased to a non-conductive state such that there is relatively no current flow through firing relay 34. Hence, contacts 40 of firing relay 34 are normally opened. I
Contacts 40 form part of a blasting cap firing circuit which, by way of example, may in addition consist of a firing battery 42 and a disarming switch 44 all in series with blasting cap 18. When disarming switch 44 is closed and, upon the energization of firing relay 34 closing contacts 40, a voltage is applied to blasting cap 18 to set off an explosive charge to create the desired seismic waves.
Pulse detecting circuit 32 consists of a pulse utput transformer 46 having a first winding 48 connected to a transistor circuit and having a second winding 50 connected to conductors 16A and 16B of cable 12. The firing voltage pulse, created when switch 26 is opened, is communicated from the pulse generator circuit 12 by way of pulse generating transformer 24, cable 12 and pulse output transformer 46 to a control transistor 52. Control transistor 52 is normally biased to a cut off condition by a voltage applied to the emitter from a voltage divider consisting of resistors 54A and 54B. The collector of transistor S2 is connected directly to the gate electrode of voltage controlled impedance 36. When a pulse of proper polarity is applied to the base of control transistor 52, the control transistor 52 is momentarily biased to conductivity, which in turn, by way of the transistor collector circuit connected directly to the gate of the silicon controlled rectifier 36, fires the silicon controlled rectifier 36. When the silicon controlled rectifier 36 fires or becomes highly conductive, the voltage drop across it diminishes immediately to a point where sufficient current flows through firing relay 34', closing firing contacts 40.
In order for the voltage pulse communicated to control transistor 52, by way of conductors 16A and 16B, to bias it into conductivity, the pulse must be of proper polarity. The polarity requirement is insured. by the arrangement of pulse generating circuit such that the pulse created when switch 26 is opened, that is, the fly back pulse, is of the right polarity and magnitude to forwardly bias control transistor 52 and thereby silicon controlled rectifier 36 to conductivity.
The voltage pulse transmitted by cable 12 may be, and ideally will be, of relatively short duration. In order to make certain that the firing relay 34 is energized a sulficient length of time to fully close contacts 40 and thereby fire blasting cap 18, a voltage sustaining circuit, generally indicated by the numeral 56, is provided to extend the effective length of the voltage pulse across firing relay 34. Such a voltage sustaining circui-tmay consist of a capacitor 58 and a series resistor 60 in parallel with the silicon controlled rectifier 36. In the normal, non-conductive state of silicon controlled rectifier 36, the capacitor 58 will charge, and when the silicon controlled rectifier 36 fires, capacitor 58 will discharge through resistor 60 providing supplemental and extended current flow to insure proper and full energization of firing relay 34.
Control transistor 52 may typically be of the commercially available type 2N215 as manufactured by the Radio Corporation of America.
An indicating light 62 may be placed in parallel with firing relay 34 to indicate to the operator that the firing relay 34 is energized, and that therefore the firing contacts. 40 are closed. This serves as a warning that the circuit is completed for firing of blasting cap 18.
Silicon controlled rectifier 36 functions in the manner of the well known vacuum tube thyratron, that is, afterit has been biased to firing condition, it will continue to conduct until voltage is removed from across the oath-- ode and anode. After a voltage pulse is received and silicon controlled rectifier 36 is fired, it may be restored to. normal (non-conducting) condition by breaking the volt-- age circuit across it.
Breaking of the voltage circuit across rectifier 36 may be done manually by means of a simple switch (not shown) in this circuit. However, as an additional improvement to the blasting circuit 30 of the firing circuit 14, an automatic reset circuit may be provided as generally indicated by the numeral 66. The automatic reset circuit consists of: A reset relay 68 connected in series with a resistor 70; a capacitor 72 connected in parallel with reset relay 68; and a normally closed contact 74 of reset relay 68 connected in series with firing relay 34. The operation of automatic reset circuit 66 is as follows: When silicon controlled rectifier 36 fires, by the effect of a voltage pulse received on control transistor 52 from cable 12, the impedance of the silicon controlled rectifier 36 is diminished to the point whereby substantially the full voltage of battery 38 is applied across reset relay 68 and seriesed resistor 70. Simultaneously through contacts 74 the voltage is applied across firing relay 34. This increased voltage energizes firing relay 34, closing firing contacts 40 to fire the blasting cap 18. Reset relay 68, however, is not immediately energized because of capacitor 72 which must first be charged to the energization voltage of relay 68 through resistor 70 so that a time delay is imposed by the effect of capacitor 72 and resistor 70. The delay time of energization of reset relay 68 need only be a sufiicient length of time to permit firing relay 34 to fully and completely close firing contacts 40. It is also apparent that this time delay be of a duration greater than the duration of the voltage pulse induced on cable 12. It has been determined that in test conditions a delay of approximately 200 milliseconds is sufficient.
After capacitor 72 is charged sufficiently, reset relay 68 energizes, opening normally closed contact 74 which breaks the circuit of current flow through firing relay 34. With contacts 74 open, the only path of current flow through silicon controlled rectifier 36 is through resistor 70 and reset relay 68. Resistor 70 is of such resistance value that, coupled with the resistance of reset relay 68 and coupled with the fact that after termination of the voltage pulse the gate of silicon controlled rectifier 36 is biased to a non-conductive condition, the silicon controlled rectifier 36 reverts back to its normal non-conductive state. This imposes sufficient impedance to deenergize reset relay 68, allowing contacts 74 to close and place the circuit in condition for firing another blasting cap 18.
As has been previously stated, geophysical prospecting using seismic waves depends upon accurately determining the timed relationship of recorded events. An important bit of information which needs to be recorded is the time of firing of blasting cap 18. This is accomplished by sending back along cable 12 a voltage pulse induced by energizing blasting cap 18. To provide such a pulse a low value resistor 76 is placed in series with blasting cap 18. Placed in parallel with resistor 76 is the primary winding 78 of a blasting pulse transformer 80. The secondary winding 82 of transformer 80 is connected with conductors 84, which form a part of cable 12. A voltage pulse appearing across resistor 76 is thus transmitted back to the recording mechanism to deliver a firing pulse at posts 86. Posts 86 are input terminals to a time-break amplifier for tape or equivalent recording.
When blasting relay contact 40 closes, current, by voltages of battery 42, flows through resistor 76 and blasting cap 18 to fire the blasting cap. This current flow, by voltage drop across resistor 76, is transferred as a voltage pulse by transformer 80 to conductors 84 to deliver a recordable voltage pulse accurately identifying as a time reference the firing of blasting cap 18. When a long cable 12 is utilized, as is sometimes necessary, it can be seen that there is a tendency for the firing voltage pulse on conductors 16A and 16B to feed-over to conductors 84. Any such feed-over would produce an erroneous firing time indication. By the principles of this invention, however, only a very low current firing pulse is induced on conductors 16A and 16B, thereby eliminating voltage feed-over and also erroneous firing time indications on conductors 84.
This invention has been described in a certain degree of particularity for purposes of setting forth an operative embodiment of the principles of the invention. The circuit of the drawing and the accompanying description are illustrative only. Other equivalents may be apparent to those skilled ni the art without departing from the spirit and scope of this invention. For instance, the silicon controlled rectifier 36 is used in this disclosure as an illustrative embodiment of a voltage controlled impedance; and any suitable circuit arrangement providing means for actuating a voltage controlled impedance in series with firing relay 34 upon receipt from cable 12 of a low current voltage pulse would be within the purview of this invention. The use of a silicon controlled rectifier 36 is however considered the preferred embodiment.
The pulse detecting circuit 32 of firing circuit 14 is also merely exemplary as other circuit arrangements will be suggested to detect a voltage pulse on cable 12 and to convert such detected voltage pulse to a control voltage to in turn trigger blasting circuit 39 of the invention. However, it will again be understood that use of the control transistor 52 and its circuit components is the preferred embodiment of the invention.
The pulse input transformer 24 and pulse output transformer 46 are preferably matched transformers applicable to reflect a high impedance whereby the voltage pulse on conductors 16A and 16B will be of a low current characteristic. Conductors 16A and 16B are preferably isolated from ground so that conductors 16A and 16B form a balanced line to reduce feed-over of the voltage pulse to other conductors (not shown) making up cable 12.
Other portions of the circuits of the remote trigger arrangement for blasting of this invention are set forth as exemplary; and it is understood that changes may be made in the details and arrangement of components without departing from the spirit and scope of the appended claims.
What is claimed is:
l. A triggering apparatus connected to a multi-conductor cable for applying an electric firing force on a seismic wave initiator blasting cap comprising:
a low current high voltage pulsing circuit connected .by a first transformer to a pair of conductors of said multiple cable;
a pulse detecting means connected to said pair of conductors by a second transformer and adapted, upon detecting a pulse, to apply an output voltage pulse;
a firing circuit connected to said pulse detecting circuit;
a voltage pulse controlled switching means in said firing circuit; and
a firing relay means, within said firing circuit, and connected in series with said switching means such that upon occurrence of said voltage pulse on said pair of conductors said pulse detecting means supplies a voltage pulse to activate said switching means and said firing relay to enable an impression of an electric firing force on said blasting cap without feed-over to adjacent conductors in said cable.
2. A remote triggering apparatus according to claim 1 including a voltage sustaining circuit in communication with said firing relay means whereby the energization of said firing relay means is independent of the duration of said pulse.
3. A remote triggering apparatus according to claim 1 wherein said voltage controlled switching means comprises a voltage controlled silicon rectifier means.
4. A remote triggering apparatus according to claim 1 wherein said pulse detecting means includes transistor means maintained in the normal state substantially at cut off, said transistor means biased to conductivity by said voltage pulse on said cable.
5. A remote triggering apparatus according to claim 1 including automatic reset means, said automatic reset means comprising;
a resistor and a reset relay in series, said reset relay and resistor in parallel with said firing relay means;
and a capacitor in parallel with said reset relay whereby increased voltage across said reset relay charges said capacitor, said reset relay having a reset contact switch in series with said firing relay means and said voltage controlled switching means whereby, upon the energization of said firing relay means and upon the subsequent charging of said capacitor, said reset relay is energized, opening said reset contact to remove said voltage across said voltage controlled switching means, permitting said voltage controlled switching means to return to its non-conducting state. 6. A remote trigger system for firing a seismic charge blasting cap or the like comprising in combination;
a pair of conductors extending from a point of firing control to a point of firing said blasting cap;
voltage pulse generating means at said point of firing control, said voltage pulse generating means communicating with said conductors adaptable, upon actuation, to impose a voltage pulse on said conductors;
firing circuit means at said point of firing said blasting cap connected to said blasting cap and adaptable, upon energization, to fire said blasting cap;
and pulse detecting means at said point of firing said blasting cap communicating with said conductors and said firing circuit, said pulse detecting means adaptable to detect said voltage pulse on said conductors and upon detection of said pulse to energize said firing circuit.
7. A remote trigger system according to claim 6 wherein said voltage pulse generating means andsaid pulse detecting means communicating with said pair of conductors reflect high impedance to said pair of conductors whereby said voltage pulse is maintained at a low current level.
8. A remote trigger system according to claim 6 including first transformer means for communicating said voltage pulse generating means to said conductors and second transformer means for communicating said pulse detecting means to said conductors, said first and second transformer means of substantially identical impedance reflecting characteristics whereby said conductors are balanced, and wherein said conductors and transformer means communicating therewith are isolated.
9. A remote trigger system according to claim 6 wherein said voltage pulse generating means includes;
a transformer having a first and a second winding, said first winding communicating with said conductors;
a voltage source in series with said second transformer winding;
and switch means in series with said voltage source and said second transformer winding.
References Cited by the Examiner UNITED STATES PATENTS 2,892,128 6/59- Wolf 3l780 2,976,485 3/61 Bartz 317 -80 X 3,028,528 4/62 Ghiselin 317- -80,
RICHARD M. WOOD, Primary Examiner.