GB2397365A

GB2397365A - R.F.-protected explosive device

Info

Publication number: GB2397365A
Application number: GB7929847A
Authority: GB
Inventors: Norman John Olohan; David Timothy Punshon
Original assignee: EMI Ltd
Current assignee: EMI Ltd
Priority date: 1978-09-01
Filing date: 1979-08-28
Publication date: 2004-07-21
Anticipated expiration: 1999-08-28
Also published as: GB7929847D0; GB2397365B

Abstract

An electrically initiated explosive device comprises a tubular metal body 1 and a central contact 2 coaxial with the body and insulated from the body by dielectric material 34, thus forming transmission path. A bridgewire 5 brIdges the contacts internally of the device and an electrical current is applied to it via external contacts C1 and C2 to initiate an explosion. When handled in the presence of R.F., the transmission path transmits the RF to the wire 5 making the device hazardous. In order to reduce the hazard, a resistive layer 9 is placed across the input X-Y of the path to dissipate RF at the input. A resistance 9 may be placed anywhere across the path.

Description

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1 2397365 R1? PROTECTION DEVICE The pi esent invention relates to electrically initiated e.7osive devices (SIED), and in pa:-ticlar to such a À-eYice incorporating protection against radio-frequency hazard] A 'noun KIT-D is an Ade.n can -which is filled with explosive contain' nJ carbon particles which provide resistance to provide initiating current for firing the cap. The current is applied to external contacts on the cap.

A different form of that type- of LIED co,-r.prises a copper ring contact concentric with a copper disc co-.tac with a thic' 1. f.i^m e;i==o between ther'' on: c.er-:,nic suost ace, Current applied Yin the contacts to the thick-Film resistor fires the ClEV A wire can lee llSeC' l_C, per E..-. the s.rr!* f -.c--on as.

thick-fi'".m resi-.;or an some appl_cci -o-ns. 'i'he cur,erlt it 10;; frequnc.v A^C. or Deck It h.s vein discovered that such CtúD art potent. i'1 -; hazardous in the presence Of radio-f-equenn; (fly') electromagnet_= energy such as its rouaced by À-dar. Tn* ill can be picked up -via the extrnai-connections--to-an-=TwO when it is in the firing position, or hen handled_ Varicus protecti.-meas'-i haYe been proposed, One" proposal is no keep the rc'-u,ni a.;_ o_ the Con breach until required for firing_ Another proposal in to provided a long meandered r.ansiiission 1. ne Waite lousy o.2;ect'-c in the,'.IR.) to connect I'll dirt* r.. ? '-- l'his p7-OOOSEt is CI.linberSC,rile Wind not ?1Y confect Ire, : 2: It is an object of the invention to provide -ln electrically initiated explosive device, Which incorporates protection against IlF' ha-.ards, According to the inverl-tion, there is provided an electrically initiated explosive device comprising a pair of external contacts for receiving an electrical cur rent a pair of i,.ter=.1 contacts connected to the external contacts via resp.ctiYe conduction paths, which are insulated from each other and tone.. t-ansms:ion path capable o-E transmittir,g rado-^requency eiecr3--iacine-lc energy from the external r.ontacts forming the ink + To ine line to the i=cerna1 con- acts and at any point resistances Or;ling the conduction path-,/ across the ransmissicjr path 5 Thor dissic 'nil r..c.-, Are.; enc= energy.

In an rs.bodirn-n' of the TIED, the n+erna1 contacts are bridged Myra 'esis-'ance Bile;-hl_h, in oport on, recei-res a clre.- to initiate she DIED. The re.cisan e rid99;-se xt.ructl con..ecs is pre'^'ably a resistive film.

For a b*-er-understndir.g of th* rse.,t inversion, and to show how ± same Bay o ari-'s into --fc rt;-rence will now be made, by way Of examl:-, to the -ccorso-rlyin3 Wing, in which: Figur" 1 is a crozis-sec,on th ought a typical e;mbodi,nnt of a circularly sysnetricai cop ' an Adze roslad7 according to the inventions F gore '2 is an iui-.len, circuit of the cap, .,sd }'i3r 3 is an.-!-.-= -Y-Ai 'I-' a o.lificl cap :. typical cp of i'gurx 1 cossp:is-; HI t'''ll<r sn*t.1 body 1.-5SI;:: i ic-tiaip act ':'tl I_;,-- nsn,''>r 2 c:o.;:1 wits-l the. \ : :

body 1. The mernbcer 2 is insulated from the body 1 by insulating washers 3 and lo The body 1 Loran.; Etn external electrical contact 11 and the member has at central limb forming another external contact 6 extending through the washer 4, which is annular, into Etn opening 7 in the end of the body 1. This enables electrical contact to be made, via the member 2 and the body 1, to a bridge wire 5 of for example 0.5Q resistance which bridges the member 2 and body 1 within the cap between an in-termcil contact torte 8 on the head of the member and internal contact area on the body. A resistive film 9 of for example 05 resistance is provided on the st' face of the washer bridging the contact 5 and the tubule. body:', The film 9 Ray be only in tr.e opening 7 bribing th" contac, and bad;- 1, or nay extend over the entire 7ur.52ce ox.' he washer as shown in Figure 1.

The eq_.linc circuit c>f tine cap is shown it: Figure 2, _, - The body 11 centr.tl mealier 2, and w-tsrle= 3 and l from a trCtHsOlis'-; ior.

path 10 with the À-il-n resistor across its input XY and the bridge wire 5 across its output.

In operation, electr7ca', contacts C' and C2 are brou5'nt 1-co contact Pith the body i.-und she ev.._.-nal contact 6 and a D.C, or low frfequenc=^.C. current is app'iea --rho, The current applied to the? bridge wired 5 d;etonate.s the round of Unit tiC?n, the current being split -evenly (in -shim example be?-?en _t --.d the resistive film 9, T' Gina'. pO..';?r in incident on "he Cap Ah* film resistor 9 -dissipte?.Y--70-of it, i;- exam '-.pvtio.3 being clepenclerlt on the Ethos elf. ch<aract*7istica am.l - f3qtl-?ncy c>f LYE? r.f. cat tile input to L-.E? traD.miSior 2=-?,? ;l' - A. S D-C poller is split evenly b- tY?en the re;i=.tors 5 and A, It has been fowl in practice that cllthc>il, i3 low:. in:i iris-; 3r;.-i..iV;t:y:i'; plocl;ct:^rl the? 1 power : ll: incident on resistor 5 nay be reduced by very much more, e.g. as much as 35dB in some circumstances, The embodiment of' Figure 1 uses El bridge wire resistor 5, -which is advantageous as i' responds slowly, e,g, in 30ms, to pulsed FLY and hence in general responds to mean rather than pulsed r,f_ A thick film resistor could be used to bridge -the head 8 and body 1; the response of this to pulsed Pi7, woul d depend on the thickness of the film, In order to produce the resistive filin 9 in the opening it 0 may be silk screen printed over the end lace of the cap and rubbed - off the metal boa,; 1 anti to-.- motif coitac-- limb 0 leaving a decos- i_ only or. ibe eoo:3el part of t}-le wah* 4 in _h opening between;; e limo 6 and the boar.1. Alternatively a hic'c layer may be al)plie i -to th* end lace of he ca? and rl;bb.?d off to expose the me.1 of the body- 1 and limb 6 and until the protective esis-tance is -the desired - value. A, another alternative, a ring of resistive materi=.1 r.ay be inserted in -the gap 7 - rid g Lund in Toni Lion by a conduct-ire glue. The washers 3 an-:4 heir be o:t cardboard and contribute to the dissi<, atioi3;-o th--energ,r at micro-are Ireque=.cies_ an ne-Isregoin example the resistor 9 was equal -in resistance to The resistor 5, g -fling a 3dB loss in sensitivity -oO d.c, but a much larger loss in se.si-.i-y to:RF, However, the resistance Do the.? resistor co.'l= b-? made much larger or milch smeller-th.-n that of the -si-;t<,r, Reducing the? resistance of resi3t,r 9 increases t.e dis;--io-t of OF btit reduce tier? c.

sensitivity, :i.e. require... . I.:r-.-,-- d.c. current to ini-ti.at th.? rotund, tr.cr<eu;2n<; t'-e,.-;i;-;-.;;...- of t'n- c.si.tor 9 r<luc;s It'd . dissipation of RF but increases the d.c. sensitivity liken the resistor 5 has a resistance of 0 5Q, the resistance of the resistor may be typically in the range O,l to lOQ.

The form of the resistance 9 also affects the protection against RF because heat dissipated in the resistance 9 it trans- ferred via the central member 2 to the resistor 5 limiting the protection achievable against RF. For instance iI the resistor 9 is in the form of resistive stripes as shown in Figure 3, each bridging the contact 6 and 'e body 7, such heat transfer is reduced compared to *he case whee-=he resistor 9 covers the whole of the washer i-n bye cozening 7. Such Ae.t Lranser may also be reduced by,.ne arrangement acttal7 shown in:3aure l where the resistor 9 covets Ohs Close =11.'4aCe of the iasi:er 'I; in this cave he.--- transfer to the bode- ' is improved. . Although the resistance 9 is sho.m in the Figures bridging the input XY, it may be placed a+ any point across t'.e transmission path although it may be less effective than at the input. The resistance 9 must not be placed so near to the bridgetrire as to transfer a substant it 1 amount of heat to the wire 5. For instance the resistanc.e 9 may be placed at that side of the rasher 3 remote from the \'ire 5, in which case its would be for example an e.nn.lus of resistive material contacting or connected by conductive material to t.le outer periphery of the face of the central member 2 facing the rasher 3 and contacting or connected by conductive material to the inner surface of the body 1. : 6:

Claims

T.rat À.,F] Claim is 1. An electrically i.n;.ti,ated eYn?osve devlcP

copri,sin.>, a ?al r of ext,ernal contacts for reeeiv.ing an e]ectri.cal c,Arrent, a palr of interna3 contacts connecter) r,o r.he external cont-.?cts via respective con,?uction paths, T,h;.ch are nsulated fro. each other ard form a tYansmisslor ath capable of transmltt ntr', adio-fTreGuenc-l electrom?rnet;.c energy rom the external contact.s rormln.T the in?'ut to the li.ne to the internal contacts, and a resistance, bri.rli'.nT, the con.luction paths at; any point across th.e t.-ansmiss:i.on path, .or liss;.P,^tinT rarli.o req''enc,; ener,,Tv.

?. A rievi.ce a,.ccorr.?i.nP, to rlaim 1, Therei.n f,he saic2 resi.st?r. ce bri,?S t,he exter,.l.-al contac,.s ?CrOS'i t,he inp.t to tle tans?iss1.on.

pat.h to dssinatr rad4.o 'reqnPncy enr..r,Ty at tt. i.n?ut 3. device accordi.n,-, to Cla;.m 1 or T;herein the nterr.a.l contacts are bri.i.Ted by a resistance v!ire rh:ich, in operation, rece,.vs t'e c'rrent to initiate the rievice.

. dev.ce accordin,, to C]aim wherein the Dair of extenal contacts co,?r;; se a t?oular netal borT,- and a c',,Ti.ndrical. cPnt,ral coaxi-il.Ti.th the body, .and wTrre.n the said resls.tance bridT,in,r, the external cont, act,s ls,i res;.stive laer on an,ann,.'2..?r w-asher held betveen the hody and the central C;,t.lCt.

5. A d?v-ce 1ccorinT to rl?. or Z' TTherei.n the resistan.ce ^-ir?!T'n!-=, t,he e;rternal cont?.ccomorl.sPs a resistnce film.

[!. (?r\'[iCF, !CCC!r(?i.n 0 rl,i!t c wh.n anp'=?n.!'<.? to!' i''< -a-: n t.he res.lc:tannce ?:-i -lin=. t?e e,ter.a.1 contact,s conr)r; S-?S a r. . ? ! -. l; t, . N' . ? .,-? t F' re, ; s,. P.!?C f- " t: I' . pf ',, : 7: 7. An eler.tr,call'! initiated explosive device substantially as herein before ^.escribed with reference to Figures 1 and. or with reference to i, Fures 1 and. as codified by T,4 inure of the aceo.r,an,v.ing clr.aT,;ns.

PA m-,thod of protecting from OF ha,,a-.'s an electrically lritia.ted explosive device comprlsir, a pair of external contacts for receiving, an electrical current,, a pal.r of internal. contacts connected to the external contacts by respective conduction paths w'nich are insulat.ed from each other and form a transmission line caDab.le of transmlLted radi. o-freQuency electromanetlc energy from the external contacts fo,-ml.r., the Spelt. to the line to the internal contacts, the method corl-,risin,, the step of ri:,i-!,n the external contacts across the i nest, to the transmission line with electri.na].].y res.st;.ve matr?,ri.nl to d;, ssipate the ra!.':',o-frennncy energy at the input.

Ame'dments to the claims have teen fled as follows p: r:-, :; ., , , . , :: . . . . i - . , , , , t. C. _. r. . -1 -,!,,' !ti. ;,o, ^; ,ro '>. r: '- ;,r, , if-! 7!'-'.,.;- .:,; ,, -,, i, ?-OsG<, .,i, . r.-r! - .i,. r7 7'i1.C!-.;' i -;; ; i: !..= .)7,;r t't '>< t ': :,*7.;,e-, ;- ':;: ,, r es2s,.:i-;e mars vii.- ::i: .'= -;,-ice:-id,,,',, !-,::7,",,-, i-,,_t -.

n,,r -,fi cor^'^.-..l-.e;.=rnb=. for a.'..,a'-.; '-.:= de:,'e i.'.! resoQSA. '...

an electrical cu.rren;.; t'ne bo;-ly and '-ie me;-nb*r Dro-fidiQ, -.,t*rna] elec.rlcal coni;acivs for receivin3 the curo.nt and. providinc' respective conduction pths fo-r supplyi..; the cu:-en,, to the;irs' resistive neans; and second, substarnviall y non-ir,cuive res.lstive means within the body bridgi ng the body and the ernber betwen the e- ternal contacts and t.he first resistive rreans t.o dissipate red io- frequency electccmagnetic e;ler.

A devi ce accordi'.lg, to Cla n' 1, wherein ''ne first resistive means coriprise.s a resi sti ve wire.

3. A device according to Clai.,n. 17 herein t'.^e fit st resistive !neans comprises a t:Lck-film resistor.

4. h device according vo Clalr 1, 2 or 3 w7herein the second resistive means colprises an annular insJlative S?port on which is a resist-ive f inn.

5. A device according to Cl.airn. 4, . herelr. t'ne reslstlve film is in the fo-rm of an anr.u'us brlUging.be 23od-y an ',;he said rre!n.ber.

6. , de-.Ti ce accor6!ing' tc, clai-tr! ; v;h?rcir the f i' in is in the f-'3r n of a plural, by of rsis ance s',ri,pes b--- dgrin the Dody and the said nember.

7. A de-vice accord:ing to Clairr. 1, 2 or 3 -.hereln the second resistiv means compr:Lses zn an-ul,.:s of resi stive,naterial coupled to the body and to t.'.e sai member, o l "-7i >f-i 7; ,,j r'?; . 7.i lo! '! ! - .ch ^ i '-! -the.=,-Z:il I.:-, -.

"7?''*f4,' i;h ':-J-,:7, 7.,i? Go,.^;? ,,-! I -t:=r:!',J - - 0,/ Cfnfll_,, ^ ;i,* "'\.;;?.2 Hi.

-? {At id-= V i.:.' ' '.''":'' 'pi. 'so.-7 ry.-: ,, !..7in ^;h=.rii: 7. t? , -. 2 Jan' rsi.,':i7:e rl=.ns bridges t7.7.e 7f.,ody.:-!d Is -,,.7.id. ?mber i'. ,;h--Z. -.i-i of 'r,he said men bet r-!7lo'e frown the" first resistive c7.ean3.

1n. A d-a ao^o:-dig..y-[J1 - 3= 1 a:i-73 1 to 8 wb.srein Ann _6ecotler1 ado; Fit i or an- . 7c7-- an -ho amid womb at ',t

_

0,. A device according to any preceding- claim wherein the resistance of the second resistive means is of the same order of magnitude as that of the First resistive means.

41. *a. A device according to Claim 11, wherein the resistance of' the second resistive means is in the range of 0.1 to 1'' ohms.

(a 3. An electrically initiated explos He device s.bstantlally as herelnbefore described with reference to Figures 1 and optionally as modified by Figure 3 of' the accompanying 'prawns.

t3 Hi. A method of protecting from R.F. hazards an ^-2.ectrically initiated explosive device comprising a tubular conductive body; a conductive.emher zxiall-y disposed within Ache body; means insulating the body from the member; and a first resistive means brlUginS the body and the said member -thin the Aevlce For ar'uati-g it in response to 'ala ele-7ica' cur-e-!i ' he body and the member provlAinO external co-'-.acts,o, r receivln the current and providing respective current pates for su-, clvin_ the current to the first resistive means; the met'.od comprising the steps of bridging the external contacts with a second substantially non-inductive ennui e body resistive meanst to dissipate,-adi.o-requency electromagnetic ener Or.