DIGITAL DELAY UNIT

Abstract: An extended delay detonator assembly (1) provides a pre-selected, electronically controlled delay between an incoming non-electric impulse input signal from, e.g., a shock tube (10) or other input transmission line, and detonation of the output charge (44) the energy from which may be used to set off a blasting charge or to transfer the signal to another signal transmission line such as output shock tube (216). In another embodiment, the delay detonator is disposed in a housing (12) closed at one end and opened at the other end for coupling to the input transmission line (10), the signal from which may be amplified by a booster charge (20) mounted within the housing (12). A piezoelectric generator (30) converts the optionally amplified impulse input signal to electrical output energy. A battery-powered programmable electric delay circuit such as that contained in digital delay module (232) is activated by the electrical output from piezoelectric generator (30), counts the pre-selected delay period, at the end thereof ignites an electrically operable output charge (44).

Description: DIGITAL DELAY UNIT BACKGROUND OF THE INVENTION Field of the Invention This invention relates to detonation devices using electronic delay timing for use with non-electric blasting initiation systems. Background and Related Art Blasting operations normally involve sequentially timed detonations of explosive charges placed within bore¬ holes drilled into the earth, for example, into a rock or ore mass to be fragmented. Generally, one or more trans- mission lines are deployed from a central initiating point to send a signal to detonate the individual blasting charges located within the respective boreholes. These transmission lines may consist of one or more trunklines connected to a plurality of "downlines" leading from the trunklines into the boreholes to transmit the initiating signal to a detonator, sometimes referred to as a blasting cap, which, upon detonation, generates a shock wave that detonates the main explosive charge within the borehole. The timing of sequential detonations within each borehole must be closely controlled to achieve the desired fragmen¬ tation and movement of ore and rock. The time intervals between borehole detonations are on the order of millisec¬ onds to achieve the desired results and are attained by providing a delay between the time the initiating signal is received by the detonator and the detonation of the de¬ tonator. Generally, at least an eight millisecond delay is required between adjacent boreholes, and significantly longer millisecond delays are often used. In non-electric blasting systems the requisite delay periods may be obtained by the use of blasting caps and/or in-line signal transmission caps which contain a pyrotech¬ nic delay composition. As is well-known in the art, these delay compositions provide a length of material within the detonation train of the caps which burn at a controlled rate to provide a preselected delay, e.g., 25, 50, 250 or 500 milliseconds, between the receipt of an incoming deto¬ nation signal and the detonation of the primary charge within the cap to transfer the detonation signal to the main explosive charge in a borehole or to another length of signal transmission line. The provision of such pyro¬ technic delays in blasting caps is illustrated in U.S. Patent 3,987,732 to Spraggs et al, which describes a de- vice utilizing a pair of blasting caps having different delay periods. However, such pyrotechnic delays exhibit inherent variances in burn time and hence, in the desired delay interval. Consequently, the exact delay periods as¬ sociated with a given blasting cap varies within a range which depends on the manufacturing tolerances. This burn time variance, which results from compositional and manu¬ facturing variances which, as a practical matter, are una¬ voidable, leads to time scatter or inaccuracy associated with the delayed ignition of the borehole charges. The variation or scatter of the ignition times can result in poor rock fragmentation and possibly damage outside the blast zone. If the time between sequential detonations is very short, for example, at or near the eight millisecond minimum, the time scatter resulting from burn time varia- tions may approach or even exceed the programmed interval, thus resulting in out-of-sequence detonation of adjacent boreholes. Conventional detonating cords are noisy and have a tendency to throw debris and shrapnel from destroyed con- nectors and the like, which may result in cutting the transmission line ahead of the signal, thereby disrupting the desired blasting pattern. These disadvantages in a transmission line may be overcome by the utilization of known, non-destructive signal transmission lines. One type is commonly referred to as "shock tube" and is illu¬ strated in Thureson et al U.S. Patent 4,607,573. Other non-destructive transmission lines include low velocity signal transmission tubes as illustrated in Thureson et al U.S. Patent 4,757,764. Shock tube and low velocity signal transmission tube ("LVST tube") generally comprise hollow, plastic tubing which is coated on its interior surface with a thin layer of a suitable explosive (shock tube) or deflagrating composition (LVST tube). Upon initiation of the explosive or deflagrating composition within such sig¬ nal transmission tubes, a shock wave, flame front or other such impulse signal is transmitted through the tube. This impulse signal may be utilized to detonate signal trans- mission and blasting caps in order to initiate timed de¬ tonation of the main charges. As indicated above, the use of pyrotechnic delay de¬ vices in signal transmission lines is known in the art. For example, a pyrotechnic delay unit for a signal trans- mission tube is shown in U.S. Patent 4,742,773, issued to Bartholomew et al, on May 10, 1988. This Patent calls for using, in a signal transmission tube, a delay assembly comprising a delay element which contains a shaped pyro¬ technic delay composition having a pre-selected combustion time. As described beginning at column 3, line 49 of the Bartholomew Patent, signal transmission tubes are received in the opposite ends of the delay assembly and connected to opposite ends of the delay element. An incoming im¬ pulse signal from one of the transmission tubes connected to the assembly initiates the timed combustion of the de¬ lay element, starting at one end thereof. The combustion time of the delay element may range from nine milliseconds to ten seconds or longer, depending on the delay composi¬ tion utilized (column 4, lines 11-15). When the combus- tion proceeds from one end to the other end of the delay element, the pre-selected delay period will have elapsed and the burning delay element ignites the other, outgoing signal transmission tube. Consequently, a selected delay in timing of transmission of the signal through the trans- mission tube connected by the delay unit is attained. The pyrotechnic delay assembly of the Bartholomew Patent em¬ ploys transition and delay chemical compositions compris¬ ing various reactive chemical compounds, as explained be- ginning at column 4, line 38. The use of electrically-initiated detonators which contain pyrotechnic delays is, of course, subject to the same problems as described above with respect to non-elec- trically-initiated systems insofar as inherent variances of burn time of the detonator delays is concerned. The use of electrical blast sequencing machines in conjunction with instant detonators or electronically-timed detona¬ tors, while capable of providing accurate borehole-to- borehole time delays, requires an electrical potential of hundreds of volts to reliably ignite all of the large num¬ ber of blasting caps used in such systems, and such volt¬ ages pose sometimes lethal safety hazards to workers in the field. On the other hand, only a relatively small amount of energy is required for the ignition of an indi¬ vidual electric blasting cap so that premature or unin¬ tended detonations can be caused by static electricity, ground currents, currents induced by power lines, radio- frequency or microwave sources or other sources of rela- tively low energy electromagnetic noise. Further, the interconnection of electric blasting caps in large blast patterns can be extremely complex and an error in calcula¬ tions could result in failure of the detonation of one or more detonator caps, resulting in the very hazardous situ- ation of undetonated main explosive charges in the muck pile caused by those charges which did explode. U.S. Patent 5,173,569, dated December 22, 1992 des¬ cribes an electrical delay detonator (blasting cap) for use in non-electric blasting systems which enables the at- tainment of a pre-selected delay in detonation of the de¬ tonator's output charge in response to the arrival of an incoming non-electric signal through the use of an elec¬ tronically timed delay circuit disposed within the deto¬ nator. This Patent details the use of a transducer, e.g., a piezoelectric element which is responsive to a pressure wave generated by detonation of a booster charge which is detonated by an incoming non-electric impulse signal, e.g., from a shock tube, to power an electronic circuit providing a preset, solid state-controlled time delay for detonation of the detonator and thereby of the explosive charges served by the detonator. The disclosure of U.S. 5,173,569, which is hereby incorporated herein, discloses a device in which the power generated by pressurizing the transducer is the source of a power needed to initiate and operate the delay circuitry as well as to activate, i.e., detonate, the booster charge. The limited amount of ener¬ gy available by pressurization of the transducer necessar- ily limits the duration of the delay which can be attain¬ ed. The device of U.S. 5,173,569 required a booster charge to activate the transducer; the booster charge may be omitted if the input transmission line has sufficient energy to reliably energize the transducer, e.g., if the input transmission line is a low energy detonating cord. SUMMARY OF THE INVENTION Generally, the present invention provides a delay unit containing an output charge, e.g., a delay detonator, adaptable for in-line or downhole use which, in one embod¬ iment, utilizes circuitry which includes an energy source such as battery means which is used to supply power to the delay circuit upon activation by a signal received from the energized transducer. The battery means or the like is designed to provide sufficient energy to power the de¬ lay circuit even for an extended duration of delay, but the energy available from the battery means is limited so that even in the event of a short circuit or other mal¬ function, the energy output of the battery means is insuf- ficient to detonate the output charge. In another embod¬ iment of the invention, the delay unit includes one or more output line retainer means for retaining one or more output transmission lines in proximity to the output charge whereby detonation of the output charge ignites the one or more output transmission lines. Specifically, in accordance with the present inven¬ tion, there is provided an electrical delay unit, e.g., a delay detonator, for use in blasting initiation systems energized by a non-electric impulse signal. The delay unit comprises a housing means, e.g., a tubular, electric¬ ally conductive body, having one end thereof dimensioned and configured to be coupled to an input transmission line. The input transmission line may be, e.g., an input transmission tube such as a shock tube, or it may be a low energy detonating cord. In any case, the input transmis¬ sion line is capable of transmitting an input non-electric impulse signal. The housing means, which may be closed at the end opposite the aforesaid one end, has: (i) a signal conversion means disposed in signal-communicating rela¬ tionship to the transmission line for receiving an impulse signal from the transmission line and converting the im¬ pulse signal to an electrical output signal, and (ii) an electric circuit including delay means having an output conductor means. The electric circuit is connected to the signal conversion means to receive from it the electrical output signal and thereupon start counting a selected time interval. Upon lapse of the time interval, the electrical output signal is transmitted by the electric circuit to the output conductor means. The delay unit of the present invention further comprises (iii) an electrically operable igniter means contained in the housing means and connected to the output conductor means of the electric circuit and to an output charge. The igniter means is energized to detonate the output charge upon receipt of the electrical output signal from the electric circuit. In accordance with one aspect of the present inven¬ tion, the electric circuit includes a battery means con- nected thereto to supply the electric circuit with power for counting the selected time interval upon receipt by the electric circuit of the electrical output signal. Another aspect of the present invention provides that the power output of the battery means is insufficient to energize the igniter element sufficiently to detonate the output charge. In another aspect of the invention, the electric cir¬ cuit comprises an oscillator for generating cycles con- nected to the battery means to receive power therefrom for generating the cycles, a counter connected to the oscilla¬ tor for counting the cycles, and means for preloading the counter with an initial value. There may be a voltage re- gulator connected to the energy storage means. According to still another aspect of the invention, the housing means may comprise one or more output line retainer means for retaining one or more output transmis¬ sion lines in proximity to the output charge whereby deto- nation of the output charge can ignite one or more output transmission lines disposed therein. Yet another aspect of the present invention provides for the inclusion of a booster charge disposed within the housing and positioned to be detonated by the impulse sig- nal received from the input transmission line to amplify the impulse signal received by the signal conversion. Other aspects of the invention provide for the elec¬ tric circuit to comprise means to convert the electrical output signal to a first signal which starts the counting of the time interval and a second signal which energizes the igniter element at the end of the time interval; other aspects of the invention provide for the signal conversion means to comprise (a) a transducer, e.g., a piezoelectric generator, for converting the input impulse signal to electrical energy and (b) an energy storage means, e.g., a storage capacitor, connected to the transducer to receive therefrom and store electrical energy for release from the energy storage means as the electrical output signal. Any of the foregoing embodiments may include an input transmission line, e.g., an input transmission tube, e.g., a shock tube, or a low energy detonating cord coupled thereto. Some embodiments may include programming means carried by the housing. The programming means is effec¬ tive to program the duration of the time interval of the delay circuit. Optionally, the programming means may be accessible from the exterior of the housing and may fur¬ ther include an interface connector connecting the pro¬ gramming means to the delay circuit whereby the duration of the time interval of the delay circuit may be program¬ med. The interface connector may comprise an inductive pick-up means. A method aspect of the present invention provides for interposing a time delay between the application of an in¬ put non-electric impulse signal received from a transmis¬ sion line and the detonation of an output charge. The method comprises the following steps. (a) Converting the input impulse signal to a first electric signal. This step may be carried out by pressurizing a piezoelectric generator with the impulse input signal. The input signal may optionally be amplified by using it to detonate a booster charge which in turn pressurizes the piezoelectric generator. (b) Transmitting the first electric signal to an oscillator. (c) Counting the number of cycles generat¬ ed by the oscillator in response to the first electric signal; the power to carry out this step may optionally be supplied from a battery means. (d) Generating a second electric signal upon the completion of a preprogrammed count of the number of cycles. (e) Transmitting the sec¬ ond electric signal to an electrically operable output charge to detonate the output charge. Optionally, the method may comprise using the energy of the output charge to ignite one or more output transmission lines, to emit one or more output signals. These and other aspects of the present invention, to¬ gether with objects and advantages thereof, will be appar¬ ent in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view partly in cross section showing one embodiment of a delay detonator of the present invention having a shock tube input transmission line coupled thereto; Figure 1A is a view, on a scale which is enlarged re¬ lative to Figure 1, of the isolation cup and booster charge components of the detonator of Figure 1; Figure IB is a partial schematic view partly in cross section showing a second embodiment of a delay detonator of the present invention having a low energy detonating cord input transmission line coupled thereto; Figure 2 is a schematic cross-sectional view showing one embodiment of a delay unit of the present invention including an input transmission line and an output trans¬ mission tube attached thereto; Figure 2A is a view, enlarged relative to Figure 2 , of the low energy booster detonator of the delay unit of Figure 2 and certain connections thereto; Figure 2B is a view, enlarged relative to Figure 2, of the output detonator of the delay unit of Figure 2 and certain connections thereto; Figure 2C is a schematic block diagram representing the structure of the embodiment of Figure 2; Figure 2D is a schematic cross-sectional view corre¬ sponding to that of Figure 2 but with parts broken away, showing another embodiment of the delay unit of the pre¬ sent invention including an input transmission line at¬ tached thereto; Figure 2E is a schematic block diagram of one embodi¬ ment of a delay circuit utilizable in accordance with the present invention, e.g., in the embodiments of Figures 2, 2C and 2D; Figure 3 is a schematic block diagram depicting the major components of the ignition and electronic delay cir¬ cuitry of the present invention; Figure 4 is a schematic block diagram depicting the electronic counting and programming circuitry of a typical embodiment of the present invention; Figure 5 is a schematic block diagram depicting addi¬ tional programming circuitry usable in conjunction with the circuitry of Figure 4; Figure 6 is a schematic partial view generally cor¬ responding to that of Figure 1 but showing a schematic structural rendition of piezoelectric generator 30 instead of the schematic box rendition of Figure 1; Figure 7 is a schematic exploded view of the compo¬ nents of Figure 6 on a scale enlarged relative to Figure 6, with the piezoelectric generator component thereof shown in a more detailed, schematic rendition; and Figure 8 is a view on a scale enlarged with respect to Figure 7 of a more detailed schematic view of the piez¬ oelectric generator of Figures 6 and 7. DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF The accuracy of the timing of initiation of individu¬ al explosive charges in a multiple-charge blasting system must be closely controlled to achieve the desired fragmen- tation of ore and rock, and to reduce the influence of the blast on structures outside the blast zone. The accuracy of timing of the initiation of individual charges controls the effectiveness of the blast by providing the required distribution of blast induced Shockwaves. The present in- vention provides delay detonators that can be used for closely controlling the timing of the transmission of de¬ tonation signals through signal transmission lines and the initiation of individual explosive charges in non-electric multiple-explosive charge blast operations. Referring now to Figure 1 there is shown one embodi¬ ment of an extended range digital delay detonator 1 of the present invention for use in detonating a downhole charge. In the illustrated embodiment, the delay detonator is coupled to a suitable input transmission line which com- prises, in the illustrated case, a shock tube 10. It is to be understood, however, that other nonelectric signal transmission means such as a detonating cord, low energy detonating cord, low velocity shock tube and the like may be used. Generally, any suitable nonelectric, impulse signal transmission means may be employed. As is well- known to those skilled in the art, shock tube 10 comprises hollow plastic tubing, the inside wall of which is coated with an explosive material so that, upon ignition, a low energy shock wave is propagated through the tube. See, for example, Thureson et al, U.S. Patent 4,607,573. Shock tube 10 is fitted to a suitable housing 12 by means of an adapter bushing 14 about which housing 12 is crimped at crimps 16, 16a to secure shock tube 10 and form an envi¬ ronmentally protective seal between adapter bushing 14 and the outer surface of shock tube 10. Housing 12 has an open end 12a which receives bushing 14 and shock tube 10, and an opposite, closed end 12b. Housing 12 is made of an electrically conductive material, usually aluminum, and is preferably the size and shape of conventional blasting caps, i.e., detonators. A segment 10a of shock tube 10 extends within housing 12 and terminates at end 10b in close proximity to, or in abutting contact with, an anti- static isolation cup 18. Isolation cup 18, as best seen in Figure 1A, is of a type well-known in the art and is made of a semiconductive material, e.g., a carbon-filled polymeric material, so that it forms a path to ground so as to dissipate any static electricity which may travel along the interior of shock tube 10. For example, see Gladden U.S. Patent 3,981,240. A low energy booster charge 20 is positioned adjacent to anti-static isolation cup 18. As best seen in Figure 1A, anti-static isolation cup 18 comprises, as is well-known in the art, a generally cylindrical body (which is usually in the form of a truncated cone, with the larg¬ er diameter positioned closer to the open end 12a of hous¬ ing 12) which is divided by a thin, rupturable membrane 18b into an entry chamber 18a and an exit chamber 18c. The end 10b of shock tube 10 (Figure 1) is received within entry chamber 18a (shock tube 10 is not shown in Figure 1A for clarity of illustration) . Exit chamber 18c provides an air space or stand-off between the end 10b of shock tube 10 and booster charge 20. In operation, the shock wave traveling through shock tube 10 will rupture membrane 18b and traverse the stand-off provided by exit chamber 18c and impinge upon and detonate booster charge 20. Booster charge 20 itself comprises a booster charge shell 22 of cup-like configuration within which is pressed a small quantity of primary explosive 24, such as lead azide, which is closed by a first cushion element 26. First cushion element 26, which is located between isola- tion cup 18 and primary explosive 24, protects primary explosive 24 from pressure imposed upon it during manufac¬ ture. A non-conductive buffer 28, which is typically 0.030 inches thick, is located between booster charge 20 and a piezoelectric generator 30 to electrically isolate piezo¬ electric generator 30 from booster charge 20. Adapter bushing 14, isolation cup 18, first cushion element 26, and booster charge 20 may conveniently be fit¬ ted into a booster shell 32 as shown in Figure 1A. The outer surface of isolation cup 18 is in conductive contact with the inner surface of booster shell 32 which in turn is in conductive contact with housing 12 to provide an electrical current path for any static electricity dis¬ charged from shock tube 10. Generally, booster shell 32 is inserted into housing 12 and housing 12 is crimped to retain booster shell 32 therein as well as to protect the contents of housing 12 from the environment. Referring again to Figure 1, a capacitor 34 is con¬ nected to piezoelectric generator 30 to receive electrical output from generator 30 for storage. Capacitor 34 may be a 10 micro-farad unit rated at 35 volts. Its series re¬ sistance is preferably low to accommodate the fast rise- time of the 1 to 2 microsecond-long pulses it will receive from piezoelectric generator 30. A battery means 36 is positioned next to capacitor 34 and adjacent to battery means 36 is a timing module 38 next to which is located an electrically activated igniter means 40. A second cushion element 42, which is similar to first cushion element 26, is interposed between output charge 44 and an electrically activated igniter means 40 for the same purpose as first cushion element 26. Output charge 44 comprises a primary explosive 44a and a second¬ ary explosive 44b, which has sufficient shock power to detonate cast booster explosives, dynamite, etc., the det¬ onation of which is the usual purpose to which such deto¬ nators are put. Igniter means 40, which is connected to the output of timing module 38, when energized, detonates primary explosive 44a, which in turn detonates secondary explosive 44b, i.e., igniter means 40 serves to detonate output charge 44. Igniter means 40 is positioned within a preferably non-conductive bushing (not shown) which serves to prevent inadvertent detonation of output charge 44 by igniter means 40 by virtue of the relatively low resis¬ tivity of the bushing and its contact with housing 12. The components contained within housing 12 are suit¬ ably encased within potting compounds to protect the com¬ ponents, and minimize the chances of detonation or damage by mechanical impact or electrical signals. The fact that housing 12 is made of aluminum or other electrically con¬ ductive material, also helps to shield the internal compo¬ nents against both electrical signals and mechanical shocks that could inadvertently activate booster charge 20 or output charge 44. The electrically conductive housing 12 provides a high degree of attenuation of potentially damaging electrical fields by forming a Faraday cage around the electrically sensitive components. The size and configuration of the housing 12 is, as noted above, preferably selected to duplicate industry standard detona¬ tor sizes currently in use. In operation, the digital delay detonator 1 of Figure 1 receives a pressure input pulse via shock tube 10 which detonates booster charge 20, the explosive output of which is thus an amplification of the pressure input pulse de¬ livered by shock tube 10. Piezoelectric generator 30 is subjected to the energy delivered by the explosion of booster charge 20 and converts the energy into electrical energy. This electrical energy is stored in storage capa- citor 34 and a part of it is used to activate the timing circuit of timing module 38 and, after lapse of a pre-se¬ lected interval, to energize igniter means 40 to detonate output charge 44. Battery means 36 is used to supply the necessary power to operate the delay timing circuitry of timing module 38. Upon completion of its timing cycle, the stored energy from capacitor 34 is applied to electri¬ cally activated igniter means 40, thereby detonating pri- mary explosive 44a and secondary explosive 44b. The delay detonator 1 may thus be employed to provide a very accu¬ rately controlled delay in the initiation of an explosive charge as may be required in blasting patterns in which a large number of charges are to be detonated in a predeter- mined timing pattern. The electric circuit control of the delay permits much more accurate delays than those which are attainable by conventional pyrotechnic delays, and the battery-powered timing means permits the selection of much longer delays than would be attainable if the piezoelec- trie generator 30 had to supply the power for both power¬ ing the timing circuits and energizing the igniter means 40. Referring now to Figure IB, in which parts identical to those of the Figure 1 embodiment are identically num- bered except for the addition of a prime indicator, an alternative embodiment of the present invention comprises a detonator 1', only a portion of which is shown in Figure IB. In this embodiment, shock tube 10 of the Figure 1 em¬ bodiment is replaced by a transmission line comprising a low energy detonating cord 46 which is mounted within adapter bushing 14' located at open end 12a' of housing 12' so that a portion 46a thereof is sealed within housing 12' by crimps 16', 16a' cooperating with bushing 14' and detonating cord 46. The energy output of detonating cord 46 is selected to be low enough not to destroy components of delay detonator 1' so as to prevent it from function¬ ing, but high enough to cause the input impulse signal provided by the explosive output of low energy detonating cord 46 to act, without need for amplification, directly on piezoelectric generator 30'. Generator 30' responds to the shock wave from low energy detonating cord 46 to gen¬ erate electrical energy that is transmitted for storage in storage capacitor 34'. Consequently, booster charge 20 of the Figure 1 embodiment is omitted from the embodiment of Figure IB, as is isolation cup 18, for which there is no need in the embodiment of Figure IB. Otherwise, the other parts of the Figure IB embodiment, their arrangement and operation are the same as those discussed in conjunction with the embodiment of Figure 1 and it is therefore not necessary to repeat the illustration and description thereof. Generally, in the Figure IB embodiment, the energy necessary to energize piezoelectric generator 30' is derived directly from the shock wave coming from low energy detonating cord 46. Figure 2 shows another embodiment of the present in¬ vention as an in-line delay unit 210. In this embodiment, housing 212 may be made of any suitable dielectric mater- ial such as a synthetic organic polymer (plastic), for ex¬ ample, polyethylene or other thermoplastic material, and it contains the other components of the in-line delay unit in suitable cavities formed therein. Housing 212 also serves to receive and connect the input and output trans- mission lines, i.e., input shock tube 214 and output shock tube 216. A suitable inlet bore (unnumbered) is formed in housing 212 and receives and securely retains the input shock tube 214, as described in more detail below. Input shock tube 214 comprises a hollow plastic tube, the inner surface of which is coated by an explosive powder layer, 214a (Figure 2A) . Input shock tube 214 terminates within housing 212 adjacent to a booster charge 226. ' Low energy booster detonator 218 (Figures 2 and 2A) comprises a detonator shell 220, within which are disposed an anti-static cup 222, a first cushion element 224, and a booster charge 226. A transducer which, in the illustrat¬ ed embodiment, comprises a piezoelectric generator 228, and a first conductor means which, in the illustrated em¬ bodiment, comprises a pair of leads 230a, 230b are mounted within housing 212 adjacent to low energy booster detona¬ tor 218. Detonator shell 220 is crimped around a bushing 231 within which input shock tube 214 is received to help retain the end of the shock tube securely in place within low energy booster detonator 218. In addition, the one hundred eighty-degree return bend configuration of the in¬ let bore (Figure 2) which receives input shock tube 214 provides a strain relief which helps to hold input shock tube 214 firmly in place within housing 212. This em¬ placement of input shock tube 214 within housing 212, which is usually carried out in factory assembly of the device, resists the tendency of mechanical forces to dis¬ lodge input shock tube 214 from housing 212. As best seen in Figure 2A, booster charge 226 is sep¬ arated from anti-static cup 222 by first cushion element 224, the function of which is to distribute, during fac¬ tory assembly of booster detonator 218, the pressure of a steel pin used to insert booster charge 226 into detonator shell 220. This distribution of pressure reduces the chance of detonation of booster charge 226 during the man¬ ufacturing process. First cushion element 224 has a cen¬ tral aperture 224a formed therein and closed by a thin, rupturable membrane (unnumbered) to seal booster charge 226. Central aperture 224a provides a low-resistance path to booster charge 226 for the impulse signal delivered by input shock tube 214. Anti-static cup 222 is in the shape of a truncated cone with a thin, rupturable membrane 222a extending across its midsection and against which the end of input shock tube 214 is seated, providing an air-gap "stand-off" between the end of input shock tube 214 and booster charge 226. Anti-static cup 222 contacts the sides of detonator shell 220 and serves to ground any electrostatic discharge traveling through input shock tube 214 against shell 220 to reduce the possibility of an electrostatic charge pre¬ maturely detonating booster charge 226. A buffer 225 is provided between the booster detona¬ tor shell 220 and piezoelectric generator 228. Buffer 225 is a dielectric material and serves to electrically iso¬ late piezoelectric generator 228 from detonator shell 220. Piezoelectric generator 228 is thus located in close proximity to booster charge 226 with only shell 220 and buffer 225 intervening between them. Piezoelectric gener¬ ator 228 comprises multiple alternating layers of a con¬ ductor and a piezoelectric ceramic wherein the metal lay¬ ers are interconnected in parallel to form the output ter- minals (not shown) of piezoelectric generator 228. Leads 230a, 230b connect the output terminals of piezoelectric generator 228 to a delay module provided in the illustrat¬ ed embodiment by digital delay module 232 (Figures 2 and 2C). Referring to Figure 2C, digital delay module 232 in- eludes an energy storage capacitor 234, a trigger circuit 236, a delay circuit 238, and a programming interface means 242 mounted thereon. Energy storage capacitor 234 is,, in the illustrated embodiment, about a 3 micro-farad unit rated at 35 volts. Its series impedance is prefer- ably low to accommodate the fast rise time of the 1 to 2 microsecond pulses generated by piezoelectric generator 228. Referring to Figures 2 and 2B, the output of digital delay module 232 is electrically connected by second con- ductor means to igniter element 246 of output detonator 248. In the illustrated embodiment (Figures 2 and 2B), the second conductor means comprise a pair of leads 244a, 244b, the ends of which are connected by a bridge wire 245 embedded within an igniter element 246 (Figure 2B). As best seen in Figure 2B, output detonator 248 comprises the igniter element 246 contained within an igniter cup 247 positioned within output detonator shell 250 in close proximity to an output charge 254. Leads 244a, 244b are retained within output detonator shell 250 by a bushing 251 held in place by the necked-down portion (unnumbered) of shell 250. A second cushion element 252 identical to first cushion element 224 abuts and separates igniter ele¬ ment 246 from output charge 254. Second cushion element 252 contains a central aperture 252a which serves the same function as central aperture 224a of first cushion element 224 and is similarly closed with a thin, rupturable mem¬ brane (unnumbered) to seal output charge 254. The end of housing 212 adjacent to output detonator 248 is configured to provide a plurality of output line retainer means for retaining one or more output transmis¬ sion lines in proximity to output detonator 248. In the illustrated embodiment, these output line retainer means are provided by a combination of output line bores 256 and cleats 258. Output line bores 256 have entry mouths 256a and exit mouths 256b. Cleats 258 are generally hook-shap¬ ed, terminate in flexible lips 258a, and are located adja¬ cent to and aligned with the exit mouths 256b of output line bores 256. Output line bores 256 and cleats 258 thus cooperate to provide the output line retainer means in the illustrated embodiment. Although only two such output line retainer means are illustrated in Figure 2, it will be appreciated that more than two such output line retain- er means could be provided. For example, in the illus¬ trated embodiment, four or even six such output line re¬ tainer means could be evenly spaced about the periphery of housing 212. Output shock tube 216 has a terminal end 216a which is closed and sealed against the environment by seal 216b which flattens and seals shock tube 216. A suitable deto¬ nator cap (not shown) is crimped onto the remote end (not shown) of shock tube 216 and may be emplaced within an ex¬ plosive charge or may be utilized as a signal amplifying and transmission cap to ignite another signal transmission tube to which it is connected. Obviously, any suitable length of output shock tube 216 may be employed and delay unit 210 may remain on the surface whether output shock tube 216 comprises a surface transmission line or a down- hole line. Alternatively, delay unit 210 may be placed within a borehole, e.g., when it is used in conjunction with an instantaneous blasting cap to provide an accurate delay period for a downhole blasting cap. A period tag 216c is attached near the terminal end 216a of shock tube 216 to indicate the delay period of the detonator cap (not shown) attached to the remote end (not shown) of shock tube 216. In the illustrated embodiment, the legend "Per¬ iod Zero" on period tag 216c indicates that the detonator cap attached to the remote end of shock tube 216 has no delay period, i.e., it is a zero period or instantaneous detonating cap. Obviously, depending on the design of a particular blasting pattern, the detonator cap at the re- mote end of shock tube 216 may, if desired, have an elec¬ tronically controlled time delay period and such would be reflected in period tag 216c. A digital delay detonator cap of the type described in U.S. Patent 5,173,569 would provide an accurate cap delay period. Shock tube 216 is easily and securely attached to housing 212 by bending the tube back on itself a short distance away from terminal end 216a so as to form a loop or bight in shock tube 216, and forcing the bight of the tube upwardly into entry mouth 256a of bore 256 and out through exit mouth 256b to protrude beyond mouth 256b. The bight is advanced to protrude a distance sufficient to enable folding over of the shock tube to bring the bight thereof beneath the associated cleat 258 in the vicinity of the lip 258a thereof. The overlapping lengths of the shock tube are then pulled downwardly in the direction of the unnumbered arrow in Figure 2, to pull the bight of the tube upwardly past flexible lip 258a and thus seat the looped shock tube 216 firmly within cleat 258 as shown in Figure 2. Additional output transmission tubes may be secured to the other output line retainer mean(s) of hous¬ ing 212 in the same manner. The proximity of shock tube 216 (and of any other output transmission lines similarly attached to housing 212) to output detonator 248 assures that the detonation of output detonator 248 will initiate an output signal in the connected output transmission lines. The combination of output detonator 248 and ignit¬ er element 246 provides an electrically detonatable output charge. A programming interface means 242, which may comprise any suitable electrical, optical or other programming in¬ terface means is programmable from exteriorly of housing 212 and may be connected to digital delay module 232 by any suitable means represented by interface connector 262. A programming window 268 is formed in housing 212 against which a suitable programming interface means 242 (not shown), such as a hand-held programmer, may be placed to carry out programming of delay unit 210 to provide a se- lected delay period for it. A guide-ridge 268a is formed about the periphery of programming window 268 to guide placement and retention of the programming interface means 242 in proper alignment with programming window 268. Interface connector 262 may comprise any suitable connector means, e.g., soldered electrical wires, which, in the illustrated embodiment, serve to connect program¬ ming interface means 242 to digital delay module 232 to enable the entry of a specific time delay into delay mod¬ ule 232. The power necessary to perform this function and the programming signal can be transferred by induction in a pick-up coil comprising part of programming interface means 242, in a well-known manner. In this way, program¬ ming interface means 242 need not have any external pins or metallic conductive means requiring one or more physi- cal openings in housing 212. This helps to assure the in¬ tegrity of housing 212 and the contents thereof against environmental and stray electric field effects. If the programming of digital delay module 232 is to be performed via an optical path, a small battery having a long shelf life, such as a lithium battery, is provided to supply the power necessary for performing the programming function. The voltage and capacity of the battery is cho¬ sen to ensure that the energy available from the battery is not sufficient to trigger igniter element 246 in case of a malfunction. In a typical embodiment, housing 212 is made of a non-conductive polymer that shields the internal compo¬ nents against both electrical signals and mechanical shocks that could inadvertently activate low energy boost- er detonator 218 or output detonator 248. To increase shielding effectiveness against electrical disturbances, conductive members (not shown) may be encased within the walls of housing 212 to provide a high degree of attenua- tion of magnetic or electrical fields thereby protecting the internal circuitry, including the programming cir¬ cuits, by forming a Faraday cage around the electrically sensitive components. Alternatively, housing 212 may co - prise a semi-conductive material to provide shielding for the circuitry components. Assembly of the components may be carried out by en¬ capsulating the components with potting compound within suitable recesses formed in housing 212, which may be gen- erally cylindrical in configuration. Preferably, the in¬ put transmission line such as shock tube 214 will be fac¬ tory-installed and sealed within housing 212. The delay unit of the present invention may thus be provided with only a suitable length of shock tube 214 (or other suita- ble input transmission line) attached thereto. In such case, the connections to output transmission tubes, such as illustrated output shock tube 216, may be made in the field as required. Alternatively, both input and output transmission lines may be factory-installed or field-as- sembled. A cover (not shown in the drawings) may be provided for housing 212 to cover and seal the installed compo¬ nents. As a final step in the assembly of housing 212, the cover may be secured in place by integral clips, ul- trasonic welding, solvent bonding, ultrasonic staking, or an adhesive in order to provide a moisture-tight enclosure protected from the environment. The operation of the delay unit 210 of Figures 2 and 2C is described with reference to Figures 2 , 2C and 2E, the latter Figure showing details of one embodiment of the circuitry of delay module 232. Ignition of the input shock tube 214 delivers an impulse signal to low energy booster detonator 218, where it ruptures the membrane of anti-static cup 222 and first cushion element 224 to im- pact upon booster charge 226 and detonate it. Piezoelec¬ tric generator 228 converts the shock energy delivered to it by the detonation of booster charge 226 into electrical energy which is delivered to digital delay module 232 via leads 230a, 230b. Digital delay module 232 stores the electrical energy delivered to it from piezoelectric gen¬ erator 228 in capacitor 234. In the illustrated embodi¬ ment, piezoelectric generator 228 and energy storage ca- pacitor 234, respectively, comprise the transducer and en¬ ergy storage means which together comprise the signal con¬ version means of the present invention. The electrical energy stored in capacitor 234 is used in one embodiment for two purposes: the powering of the electronic timing of the digital delay module 232 and, after the preset time delay, the ignition of igniter element 246. More specifi¬ cally, when the voltage of the electrical energy stored in capacitor 234 is above a selected threshhold, the logic and timer portion of the delay module 232 (Figure 2C) is energized. Referring to Figure 2E, the first electric signal generated by piezoelectric generator 228 is transmitted through steering diode 266 to capacitor 234, which stores the electrical energy. When a predetermined minimum volt- age is reached on capacitor 234, voltage regulator 277 is activated to apply a portion only of the power generated by piezoelectric generator 228 to the timing circuits of oscillator 278, counter 280, and power-on reset circuit 282. A silicon controlled rectifier ("SCR") 284 is acti- vated by counter 280 at the conclusion of the timing in¬ terval, thereby supplying the remaining energy in capac¬ itor 234 to the second conductor means provided, in the illustrated embodiment, by leads 244a, 244b. During operation of the circuit of Figure 2E, the power-on reset circuit 282 preloads the counter 280 with count information from interface connector 262 (Figures 2 and 2C) or, in an embodiment of the invention (not illus¬ trated) which does not include a programming interface means such as programming interface means 242, preloads the counter with an initial preset count value. This pre¬ loading occurs at the time capacitor 234 receives the electrical signal from piezoelectric generator 228. Concurrently, oscillator 278 starts generating pulses (or cycles) that are counted by counter 280. As the counter 280, activated by the pulses from oscillator 278, reaches a pre-selected count as, for example, 1, the preprogrammed delay period expires and an activation signal is sent to SCR 284. The activation signal puts SCR 284 in a conduct¬ ing state which allows it to conduct the electrical energy in capacitor 234 to leads 244a, 244b and bridge wire 245 which, in the illustrated embodiment, provide the second conductor means which serve to detonate igniter element 246 and thereby detonate output charge 254 (Figure 2B) which, in turn, ignites the shock tube(s) 216 retained in proximity to detonator 248. The arrival at SCR 284 from capacitor 234 of the en¬ ergy needed to detonate output charge 254 is seen to be delayed by an interval essentially equal to the time re¬ quired for the counter 280 to count the pulses from oscil¬ lator 278 from the initially preset amount from power-on reset circuit 282, to some value, for example, 1. In other embodiments of the invention, a battery may be included in the circuit to supply energy for program¬ ming the time delay. In yet another embodiment, the bat¬ tery energy may also be used not only for programming the time delay, but also for powering the delay circuits. However, in all embodiments of the invention, ignition of the output charge (item 254 in the embodiment illustrated in Figure 2B) is powered by energy emitted from the trans¬ ducer (piezoelectric generator 228 in the embodiment illu¬ strated in Figure 2A) and not by battery or other stored energy sources. The battery or other stored energy source utilized is of insufficient power to detonate the output charge. This provides a safety factor because the piezo¬ electric generator is designed to be actuated substantial¬ ly only by the impulse signal imposed upon it by detona¬ tion of the booster charge (item 226 in the embodiment il- lustrated in Figure 2A) or the detonating cord, described below in connection with the embodiment of Figure 2D. Thus, the transducer (e.g., the piezoelectric generator 228) is of sufficiently low sensitivity that mechanical shocks or vibration imposed upon it by rough handling, be¬ ing dropped or impacted in normal or rough usage, or by nearby explosions, e.g., in an adjacent borehole, will not cause the transducer to be activated. Thus, the transduc- er will generate electric power sufficient to ignite the igniter element (item 246 in the embodiment illustrated in Figure 2B) and thereby ignite the output charge (item 254 in the embodiment of Figure 2B) to generate the outgoing signal substantially only by the input impulse signal or the amplification thereof by the booster charge (item 226 in the embodiment of Figure 2A) . Thus, in cases where a battery or other suitable stored energy source is provided, instead of using the power derived from the piezoelectric generator, e.g., piezoelectric generator 228 of the illustrated embodi¬ ments, for both the timing and ignition of the output charge (output charge 254 in the illustrated embodiments) the delay circuits are powered by a source, e.g., a bat¬ tery, connected therethrough through a silicon controlled rectifier (SCR) switch which is activated by a signal de¬ rived from the energy output of the piezoelectric genera¬ tor. An embodiment of the invention illustrating the utilization of battery power for both programming the time delay and powering the delay circuits is illustrated in Figure 3. The utilization of battery power enables the provision of a much longer delay period than that which could be attained if the piezoelectric generator were the sole source of power. Further details of the operation of the present in- vention are illustrated in Figure 2C which diagrammatical- ly shows input shock tube 214 for delivering a pressure input pulse to low energy booster detonator 218 which de¬ tonates to provide the amplified signal used to generate a pressure pulse on piezoelectric generator 228. Energy storage capacitor 234, trigger circuit 236 and delay cir¬ cuit 238 are part of digital delay module 232. Piezoelec¬ tric generator 228 generates the first electric signal pulse in response to the pressure imposed on it from low energy booster detonator 218. This first electric signal is stored in an energy storage capacitor 234 to be subse¬ quently used by trigger circuit 236 and delay circuit 238. Delay circuit 238 activates trigger circuit 236 after the time interval programmed into delay circuit 238 has elaps¬ ed. Trigger circuit 236 allows electrical energy stored in energy storage capacitor 234 to flow as a second elec¬ trical signal to igniter element 246, thereby triggering output charge 254 to generate a pressure output pulse large enough to initiate one or more output transmission lines such as shock tube(s) 216 which are retained in close proximity to output charge 254. Optionally, delay circuit 238 communicates through interface connector 262 and programming interface means 242 with any suitable external means (not shown) placed against programming window 268 and oriented thereagainst by guide-ridge 268a (Figures 2 and 2C). The signals from the external programmer means are encoded by any suitable well-known techniques to both power and pass delay infor- mation to delay circuit 238 via interface means 242 and interface connector 262. By way of illustration, an in¬ fra-red emitter 260a and receiver 260b are shown in Figure 2 as the means to provide communication between the exter¬ nal programmer means and interface means 242. Figure 2D shows another embodiment of the present in¬ vention in which items similar to those of the embodiment of Figures 2 and 2C are identically numbered to those of Figure 2 but with the addition of a prime indicator. Identical components are identically numbered. In the em- bodiment of Figure 2D, the input transmission line con¬ nected to delay unit 210' is provided by a low energy de¬ tonating cord 214', which is used in lieu of input shock tube 214 and booster charge 226 of the embodiment of Fig¬ ures 2 and 2C. In the illustrated embodiment of Figure 2D, detonating cord 214' is mounted in housing 212 in the same manner as shock tube 214 of the Figure 2 embodiment, but terminates in opposite-facing proximity to piezoelec¬ tric generator 228 within a chamber 215 defined by detona- tor shell 220'. The impulse input signal required to ac¬ tivate the piezoelectric generator is provided in this em¬ bodiment directly by low energy detonating cord 214'. The low energy detonating cord has a solid explosive core 214a' of sufficiently low explosive power to ensure the preservation of the integrity of the housing 212 of the in-line delay unit 210'. Nonetheless, detonating cord 214' has sufficient explosive power to directly excite the piezoelectric generator 228 to produce electrical energy sufficient to generate the electric signal needed to deto¬ nate the output charge (not shown in Figure 2D). Piezo¬ electric generator 228 responds to the input impulse sig¬ nal provided by the explosion shock wave generated by detonation of low energy detonating cord 214' by generat- ing electrical energy that is stored in energy storage capacitor 234 (not shown in Figure 2D) . All the compo¬ nents of the embodiment of Figure 2D other than as specif¬ ically set forth above, are identical to those illustrated in Figure 2 and function in exactly the same manner. Therefore, it is not necessary to illustrate them in Fig¬ ure 2D or to repeat the description of their function. It will be appreciated that the above-described em¬ bodiment of the present invention thus provides an accu¬ rate time delay between an impulse input signal (flame front, pressure wave, explosion, etc.), i.e., a non-elec¬ tric signal, carried by an input transmission line and an output impulse signal transmitted by one or more output transmission lines to, e.g., each borehole in a group of multiple boreholes. In addition, the signal line connect- or embodiment described above provides for a field pro¬ grammable delay detonator, adjustable in small time incre¬ ments, thereby requiring only a single type of in-line de¬ lay unit to be kept in stock and used for the implementa¬ tion of different in-line delays at a blasting site. Figure 3 details schematically an example of an elec¬ tric timing circuit suitable for use in timing module 38 of the embodiment of Figure 1 or digital delay module 232 of the embodiment of Figure 2, with which the optional in- terface connector 262 may be employed, as described above. Elements of Figure 3 which are also illustrated in Figure 1 are identically numbered in both Figures, although it will be understood that corresponding elements can also generally be found in the embodiment of Figures 2-2D. Piezoelectric generator 30 generates electrical current when it is pressurized as described above, e.g., by deto¬ nation of booster charge 20 (Figure 1) or low energy deto¬ nating cord 46 (Figure IB). The output energy from gener- ator 30 passes through steering diode 48 and is stored in storage capacitor 34. The voltage reached by capacitor 34 is divided by resistors 52 and 54 to activate silicon con¬ trolled rectifier ("SCR") 56. Once activated, SCR 56 causes the power from battery means 36 to be applied to the timing circuits comprising oscillator 60, programmable counter 62, and power-on reset ("POR") circuit 64. At the conclusion of the preset timing interval, SCR 66 is acti¬ vated by programmable counter 62 thereby releasing the electrical energy stored in capacitor 34 to flow to igni- ter means 40. During operation of the timing circuit of Figure 3, the POR circuit 64 preloads the programmable counter 62 with count information, setting the counter 62 with an in¬ itial preset count value. This preloading occurs upon the activation of SCR 56, i.e., at the time capacitor 34 re¬ ceives the electrical input from piezoelectric generator 30. Concurrently, oscillator 60 starts generating pulses (or cycles) that are counted by counter 62. As the count¬ er 62, activated by the pulses from oscillator 60, reaches a preselected count, as for example 1, the preprogrammed delay period expires and an activation signal is sent to SCR 66. The activation signal puts SCR 66 in a conducting state which allows SCR 66 to conduct the electrical energy in capacitor 34 to igniter means 40 via lead 40a, bridge wire 41, and lead 40b, thereby detonating output charge 44. (Output charge 44 is not shown in Figure 3 but is shown in Figure 1. ) The arrival of the energy from storage capacitor 34 at igniter means 40 and the consequent detonation of out¬ put charge 44 is therefore delayed by an interval essen¬ tially equal to the time required for the programmable counter 62 to count the pulses from oscillator 60 from the initial preset amount established by POR circuit 64 to some value, such as, for example, 1. This arrangement provides an accurate time delay means for a non-electric, pressure-type signal, i.e., an impulse input signal pro¬ vided to the delay detonator of the present invention by a suitable transmission line such as shock tube 10 (Figure 1) or detonating cord 46 (Figure IB). The programmed de¬ lay will have an exceedingly small unit-to-unit variance. Consequently, the variance in time delay detonation of each borehole in a group of multiple boreholes will corre- spondingly be exceedingly small. The programmability of the circuitry allows a single type or model of delay deto¬ nator in accordance with the present invention to be used for the implementation of different delays. Thus, a sin¬ gle stock item may be used to provide an entire series of highly accurate detonators of selected delay periods. Figure 4 is a more detailed version of the circuitry of Figure 3, in which some details of typical circuitry suitable for oscillator 60, programmable counter 62 and POR circuit 64 are shown. Elements of Figure 4 which are illustrated in Figure 3 are identically numbered in both Figures. As described above in connection with Figure 3, upon activation of the piezoelectric generator 30, current flows through the steering diode 48 to charge the storage capacitor 34 and the voltage divider formed by resistor 52 and resistor 54 provides a trigger signal to SCR 56, which causes the power from battery means 36 to be applied to the timing circuitry. Referring to Figure 4, programmable counter 62 is seen to comprise a first counter 62a, and a second counter 62b, both of which typically may be well- known monolithic counters such as an industry standard part number 40193. Figure 4 shows standard nomenclature to indicate various parts and connectors, viz., VDD = power and VSS = ground. The POR circuit 64 includes re¬ sistor 110, capacitor 111, Sch idtt-Trigger buffer 133, and inverter 112. Alternatively, an oscillator circuit could be made up of a crystal oscillator, as is well-known in the art. In any case, upon application of input volt¬ age to it, POR circuit 64 preloads first counter 62a. Once the voltage from the battery means 36 has increased beyond a threshold setting, first counter 62a begins de¬ crementing with each input pulse from the oscillator 60. As the counter decrements past zero, the output to SCR 66 is activated and the energy in storage capacitor 34 is ap¬ plied to the igniter means 40. There are many known methods of accomplishing the de¬ lay aspect of the operation and Figure 4 shows one exem- plary circuit which will accomplish the timing task. The circuit of Figure 4 may be comprised of commercially available components and the specific embodiment of the invention illustrated incorporates items such as counters 62a and 62b, and the components numbered 107 through 133 onto a single complementary metal oxide semiconductor in¬ tegrated circuit ("I.C.") 106. The circuit of oscillator 60 is comprised of timing resistor 107, timing capacitor 108, and a commercially available LM 555 timer 109. The programming circuitry utilizes steering diodes 114-117, and 123-126, as well as fuses 118-121 and 127-130. Once SCR 56 is triggered on as described above, power is applied to the delay circuitry from battery means 36. Capacitor 111 of POR circuit 64 is slowly charged through resistor 110 by the voltage apparent at node 135. Once the voltage at capacitor 111 has attained a level of two- thirds of the voltage of node 135, buffer 133 switches the signal of node 137 from a low to a high state. While node 137 is held low, the preset inputs to the counters are ac- tive, causing the signals apparent at the respective sets of inputs PI to P4 to be loaded into the counters 62a and 62b. At this point, the inhibit signal node 138 is held high to prevent the oscillator 60 from functioning. Once node 137 switches from low to high, both the oscillator 60 and counters 62a, 62b are enabled and begin functioning. The output of the oscillator 60 at node 139 directly decrements counter 62a from its preset value. As counter 62a decrements past zero, node 140 is pulsed low and trig¬ gers second counter 62b to decrement one count. Operation continues in this manner until counter 62b decrements past zero. At this time, the borrow output from counter 62b is switched low, gets inverted to a high by inverter 131 at node 141, and activates SCR 66, causing the energy in storage capacitor 34 to be applied to igniter means 40 as described above. Programming of the circuit illustrated in Figure 4 is accomplished by applying a voltage to pins 6 to 13. This voltage application produces a current flow through fuses 118-121 and 127-130. Pin 3 connected to node 139 is pro¬ vided to allow measurement of the actual oscillator fre¬ quency. Through the use of this measurement, it is possi¬ ble to program extremely precise delay intervals without the complications of precision trimming the oscillator 60 to a specific frequency. Generally, fuses 118-121 program first counter 62a to divide by an integer up to 16, as is well-known in the art. Similarly, fuses 127-130 program second counter 62b. In this configuration, first counter 62a will output a signal after a number of cycles have been received from the LM 555 timer 109 of oscillator 60, i.e., a signal will be output when the counter has counted down by the number of preprogrammed cycles or pulses received from oscillator 60. Second counter 62b receives its input from the output of first counter 62a. The input to second counter 62b will be essentially divided as programmed by fuses 118- 121. The state of these fuses determines the counting program of counters 62a and 62b, as is well-known in the art. During counter operation, the output pulses from os¬ cillator 60 will be divided by both first counter 62a and second counter 62b as programmed by fuses 118-121 and 127-130. For example, if first counter 62a is programmed to count down (or divide) from 6, and second counter 62b is programmed to count down from 8, then SCR 66 will be activated after 48 pulses have been generated by oscilla- tor 60 and counted down by both counters. While a two-stage counter circuit (counter 62a and 62b) is shown in Figure 4, additional stages may be cas¬ caded as is well-known in the art for longer time delays or improved programming resolution. The programming section of Figure 4 is simple in that parallel connections are used and the fuses are all burned at the same time. While this produces no difficulties for factory programming of the units, the number of external connections required makes programming in the field pro- hibitive. If field programmability of the delay detonator is desired, additional programming circuitry may be uti¬ lized to reduce the number of external connections to a point where programming in a field environment is feasi¬ ble. An example of such additional circuitry is schemati- cally illustrated in Figure 5, wherein a dual, four-stage static shift register, standard part number 4015, is illu¬ strated and standard nomenclature is shown to indicate various parts and connectors, viz., VDD = power, VSS = ground, CKA and CKB = clocks for segments A and B respec- tively, DA and DB - data for segments A and B respective¬ ly, and Q1A-Q4A and 1B-Q4B = data outputs for segments A and B respectively. The illustrated SCRs 202 through 209 are used to select the appropriate fuses (shown in Figure 4) for programming. Activation of these SCRs is performed by loading the required data lines serially into shift re¬ gister 201. A commercially available 4015 shift register is shown schematically in Figure 5 but a preferred embodi¬ ment would include these functions on the I.C. 85 of Fig¬ ure 4. Once the required programming SCRs are active, a high signal is applied to SCR 210. This high signal ap¬ plies the programming voltage through the selected SCRs (202-209) and burns out the associated fuse illustrated in Figure 4. By utilizing the circuit of Figure 5, the re- quired number of pins for programming is made independent of the number of stages used for the counter. While any suitable transducer may be employed in the practice of the present invention, an effective type of piezoelectric generator is schematically illustrated in Figures 6, 7 and 8, in which elements which are also shown in Figures 1 and 1A are numbered identically in both sets of Figures. The piezoelectric generator 30 comprises a piezocera- mic material stack 50 comprised of a stack of multiple layers 51 of thin piezoceramic material. The stack 50 is supported on a suitable plastic (synthetic organic poly¬ meric material) housing 53, through which terminals 68A and 68b (Figure 7) extend. The output energy from the booster charge 20 impinges substantially directly upon a load distributing disc 70 (not shown in Figures 1 or 1A) , which in turn evenly transmits the energy from the booster charge 20 to the multiple layers 51 of suitable thin piez¬ oceramic material which comprise one embodiment of the stack 50 of piezoelectric generator 30. As best seen in the schematic representation of Figure 8, the piezoceramic material layers 51 are stacked in vertical layers with op¬ posite faces of each layer connected in parallel through the use of electrode layers 72a and 72b interposed between each layer or element 51. In one embodiment, the piezo¬ electric generator of the present invention uses 84 active layers, each approximately 20 microns thick, with discrete positive and negative electrodes as marked on Figure 8 formed from the inner connections. This construction pro- vides output energy levels much greater than those which can be obtained from an otherwise comparable monolithic piezoceramic structure. Referring to Figures 6, 7 and 8 jointly, the plastic housing 53 and load distributing disc 70 contribute, in a preferred structure of the present invention, to obtaining the maximum benefit from the output shock wave of the booster charge 20 and the physical pressure attendant thereto. The stack 50 of piezoelectric generator 30 is mounted to a smooth, flat and hard surface 53a of plastic housing 53 (Figure 7). Surface 53a is substantially par¬ allel to the shock wave front generated by detonation of booster charge 20 and perpendicular to the direction of shock wave travel. To further obtain maxium benefit from the output shock wave of the booster charge 20, the load distributing disc 70 is disposed substantially parallel to and between the output end of the booster charge 20 and the input face of the piezoelectric generator 30 to evenly transmit and distribute the output shock wave energy of the booster charge 20 to the piezoelectric generator 30. This arrangement also helps to prevent premature shatter¬ ing of the piezoelectric generator 30 which would render it inoperable. Terminals 68a and 68b are electrically connected to electrode layers 72a and 72b to establish the desired electrical connection to the timing module 38. Plastic housing 53 and load distributing disc 70 also serve to insulate piezoelectric generator 30 against un¬ intended and random mechanical forces, any electrical charges, etc., and serves to help maintain the piezoelec¬ tric generator in the desired position. Although the present invention has been shown and de¬ scribed with respect to preferred embodiments, various changes and other modifications which are obvious to per- sons skilled in the art to which the invention pertains are deemed to lie within the spirit and scope of the in¬ vention. For example, the input pressure signal need not be limited to shock tubes but can be derived from other non-electric, pressure transmission devices such as low energy detonating cord, or low velocity shock tube, or any other source of shock energy that can be made to reach the piezoelectric generator to produce the input pressure needed to output the required electrical signal. Further¬ more, the timing circuit described can also comprise other ways of timing an interval as is well-known in the art. While the invention has been described in detail with respect to preferred embodiments thereof, it is to be un- derstood that upon a reading of the foregoing description, variations to the specific embodiments disclosed may occur to those skilled in the art and it is intended to include such variations within the scope of the appended claims.

Claims: H3 cq M I O tn I H 3 CΛ 4. The delay unit of claim 1 wherein the electric circuit comprises means to convert the electrical output signal to a first signal which starts the counting of the time interval and a second signal which energizes the igniter means at the end of the time interval. 5. The delay unit of claim 1 or claim 2 including an input transmission line coupled thereto. 6. The delay unit of claim 1 or claim 2 wherein the electric circuit comprises an oscillator for generating cycles connected to the battery means to receive power therefrom for generating cycles, a counter connected to the oscillator for counting the cycles, and means for pre¬ loading the counter with an initial value. 7. The delay unit of claim 1 or claim 2 wherein the signal conversion means comprises (a) a transducer for converting the impulse input signal to electrical energy and (b) an energy storage means connected to the transduc¬ er to receive therefrom and store electrical energy for release from the energy storage means as the electrical output signal and the electric circuit comprises (c) an oscillator for generating cycles connected to the battery means to receive power therefrom for counting the cycles, (d) a counter connected to the oscillator, and (e) means for preloading the counter with an initial value. 8. The delay unit of claim 1 or claim 2 comprising a delay detonator and wherein the housing means comprises a tubular, electrically conductive body closed at the end thereof opposite the one end and wherein items (i), (ϋ) and (iii) of claim 1 are enclosed within the housing. 9. The delay unit of claim 1 or claim 2 including a booster charge disposed within the housing and positioned to be detonated by the impulse input signal received from the input transmission line to amplify the impulse input signal received by the signal conversion means. 10. The delay unit of claim 1 or claim 2 wherein the signal conversion means comprises (a) a transducer for converting the impulse input signal to electrical energy and (b) an energy storage means connected to the transduc¬ er to receive therefrom and store electrical energy for release from the energy storage means as the electrical output signal. 11. The delay unit of claim 10 wherein the transducer comprises a piezoelectric generator and the energy storage means comprises a storage capacitor. 12. The delay unit of claim 10 including an input transmission line coupled thereto. 13. The delay unit of claim 12 wherein the input transmission line comprises an input transmission tube. 14. The delay unit of claim 12 wherein the input transmission tube comprises a shock tube. 15. The delay unit of claim 12 wherein the input transmission line comprises a low energy detonating cord. 16. The delay unit of claim 1 or claim 2 wherein the housing means comprises one or more output line retainer means for retaining one or more output transmission lines in proximity to the output charge whereby detonation of the output charge can ignite one or more output transmis¬ sion lines disposed therein. 17. The delay detonator of claim 16 including a boos¬ ter charge disposed within the housing means and position¬ ed to be detonated by the impulse input signal received from the input transmission line to amplify the impulse input signal received by the signal conversion means. 18. The delay unit of claim 16 wherein the delay cir¬ cuit comprises a voltage regulator connected to the energy storage means to receive power therefrom, an oscillator for generating cycles connected to the voltage regulator to receive power therefrom, a counter connected to the os¬ cillator for counting the cycles, and means for preloading the counter with an initial value. 19. The delay unit of claim 16 further including pro¬ gramming means carried by the housing means and effective to program the duration of the time interval of the delay circuit. 20. The delay unit of claim 19 wherein the program¬ ming means is accessible from the exterior of the housing and further including an interface connector connecting the programming means to the delay circuit whereby the duration of the time interval of the delay circuit may be programmed. 21. The delay unit of claim 20 wherein the interface connector comprises an inductive pick-up means. 22. The delay unit of claim 20 wherein the interface connector comprises an optical coupling means. 23. The delay unit of claim 16 including an input transmission line retained by the input line retainer means. -39- 24. The delay unit of claim 23 further including one or more output transmission lines retained by the output line retainer means. 25. The delay unit of claim 23 wherein the one or more output transmission lines comprise an output trans¬ mission tube. 26. The delay unit of claim 25 wherein the transmis¬ sion tubes comprise shock tubes. 27. A method for interposing a time delay between the application of a non-electric impulse input signal re¬ ceived from an input transmission line and the detonation of an output charge, comprising the steps of: (a) converting the input impulse signal to a first electric signal; (b) transmitting the first electric signal to an oscillator; (c) counting the number of cycles generated by the oscillator in response to the first electric signal employing an electronic timer; (d) generating a second electric signal upon the completion of a preprogrammed count of the number of cy¬ cles; and (e) transmitting the second electric signal to an electrically operable output charge to detonate the output charge. 28. The method of claim 27 wherein the electronic timer is powered by a battery means. 29. The method of claim 27 or claim 28 further com¬ prising igniting one or more output transmission lines with the energy generated by the output charge to emit one or more output signals. 30. The method of claim 27 or claim 28 including car¬ rying out step (a) by pressurizing a piezoelectric gener¬ ator with the impulse input signal. 31. The method of claim 27 or claim 28 including am¬ plifying the impulse input signal transmitted to the pi¬ ezoelectric generator by using it to detonate a booster charge which pressurizes the piezoelectric generator.

Inventors: DORMAN MARK D, MICHNA RICHARD J, PALLANCK ROBERT G, RODE KENNETH A, DORMAN, MARK, D., MICHNA, RICHARD, J., PALLANCK, ROBERT, G., RODE, KENNETH, A.
Applicants: ENSIGN BICKFORD CO, THE ENSIGN-BICKFORD COMPANY
Application year: 1993
Main classification: F42C11
IPC codes: F42B3, F42C11, F42D1