Proceedings CEEM'2009/Xi'an

Pulse Sensitivity of EED

YAO Hongzhi'f FENG Qingmei l2- ZHAO Tuan l2 Jl Xiangfei'f

(lNational defence key laboratory for SRTP, shaanxi xi 'an 710061

2 Shaanxi Applied Physics-Chemistry Research Institute , shaanxi xi'an 710061)

Abstract:In this paper, it describes the thermal response ofpulse effect ofbridgewire electroexplosive device according to heat balance equation . Sencondly ,

it provides the measurement procedure ofpulse sensitivity of electroexplosive device . At last, it point out the Vital status of function time in assess the effect

ofpulses or EMC analysis .

Key word: pulse seositivity ; EED ; EMC

Solve the equation (3), we get

During cooling, the temperature decreases according toequation (2) only without the part of electric energy. It can

describe as equation (3)

aTCat = -A(T - To) (3)

1'. is the initial temperature of EED(OC).

T is the thermal time constant(s), T is the quotient of

Cand A.The (2) and (4) are the principle during heating and

cooling for pulse effect ofEED , the pulse wave is described as

Fig.! .

(4)

time

Fig.! Square wave

=

o

'""0:s............-CIl

This form is useful to determine the power and hence the

current needed to fire an EED within a specified time. Forexcitation caused by a sequence of either periodic or aperiodicpulses[2I. where the cooling time between pulses is of the same

order as the thermal time constant, a combination of (2) and (3)may be used to determine cumulative temperature rise[3I,

commonly known as stacking. This is illustrated in Fig.2.

1 InstructionElectroexplosive devices are used in a wide variety of

applications. Hot-bridgewire electroexplosive device (EED) is

an initiator that sets offa little part ofprimary explosive by

joule heating due to electrical current flowing in its bridgewire.

When the primary explosive reaches its critical temperature, it

explodes and detonates a secondary explosive charge. Recent

concern with pulsed electromagnetic interference and the

nuclear electromagnetic pulse indicate the lack ofmethodology

for assessing EED vulnerability.

2 Pulse response of EEDWhen the EED locates in the electromagnetic

environment, the electromagnetic environment that may

induce stray currents in the lead wire ofan EED is usual1y

poorly known. The theory how energy may be transferred from

this environment by unintended antennas (any electrical

conductor) is also poorly understood. These two relevant topics

are not within the scope of this paper, they must be considered

in any comprehensive EMC analysis.In this part, the relevant thermodynamic concepts are for

identifying thermodynamic parameters relevant to EED

characterizations. The methodology introduced in this section

is based on physical principles.Pulse effect of EED is a process of energy conversion, and

it must be different from the DC and continuous wave effect .

But it also fol1ow basic heat flow equations similar to those

used in determining temperature distribution around a shortwire.

The heat balance equation is[t]

peaT =-AV2T+P(t)+pqZe-EIRTm (1)at

It is so difficult for us to solve equation (l) that we try

to simple it . Initial1y , in the moment of bridge-wire

heating , the respond speed of medicament is very srnal1 and

it release little heat . Before the explosive detonate , we

ignore chemic energy release from the response of

medicament and the equation (I) can simple to

(2)aTc- = -A(T - T ) + pet)at 0

Where, T is the temperature as a function of time (OC),

t is function time as the time after application ofcurrent

(s),

P(t) is the power due to joule heating(w),

To is the ambient temperaturet''C),

A is the coefficient ofheat emit(J/oC'cm2),

C is the thermal capacity of the EED wire andexplosive-binder mixture (J/0C) .

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Proceedings CEEM'2009/Xi'an

Fig.4 Tests of function time

3kW 1

1.5kW 1

0.75kW 1

0.38kW 1

0.19kW 0

0.29kW 1

0.24kW 0

0.27kW 1

0.26kW 1

O.l3kW 1

0.07kW 0

O.lkW 0

0.18kW 1

0.14kW 0

Peak: power Statement

X 1=3WX2=1.5W

X3=0.75W

X4=O.38W

X s=O.19W

X6=O.29W

X7=0.24W

Xs=O.27WX9=O.26W

X lO=O.l3W

X ll=O.07W

X12=O.lW

X13=O.l8W

X14=O.l4W

Average

power

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Number

Note:I---fire O---no-fireAccording to GJB377A and data from table I , we get the

50% fire power as 0.187W(average power) .The pulse sensitivity test which acquires the sensitivity

about EED in the situation of pulse injection help the designerof EED to understand the pulse effect of EED , and assesselectromagnetic compatibility of EED .4 Function time

In pulse sensitivity test , it's very important to understandthe concept of function time . The time from the input ofstimulus to detonation of EED is called function time (5).

Function time of EED has great difference with in each otherabout type and application , generally in the range of Icf to 10-6seconds. Function time of EED relates with many factors, suchas the radius of EED , the current flow through bridge-wire ,the material ofbridge-wire ,and the medicament ofEED .

There are several methods to test the function time ofEED , such as methods of probe , high-speed photograph andso on .

The measurement method of function time can describe inFigA.

parameter we can measure exactly is power (6). we can easilyassess the compatibility of EED in pulse electromagnetic fieldbefore finding the method for measuring the electromagnetic

(statistical method for sensitivity tests) method 101-langliemethod , and set the minimum stimulate level as OWand themaximum as 6W (average power).

Table 1 Ten centimeter pulse sensitivity of 12# electricblasting caps

Fig.2 Effect process of periodic and aperiodic pulse forEED

Fig.3 Pulse sensitivity of EED

First , we choose ten centimeter pulse source as the sourceof pulse sensitivity , as its center wavelength equal tencentimeter and corresponding frequency between 3.07GHz andpulse duty is I:1000 , pulse width is Ius , maximum peakpoweris IOkW .

Second , the adjustment of the match device is veryimportant . In the military standard of China , we can see theRF sensitivity test method of EED which give us the processfor the test of EED under sine wave . But in the case of pulse ,there must be some difference especially in the adjustment ofmatch device. Get the frequency from frequency meter .Then ,adjust the match device under sine wave for EED at the samefrequency with pulse source . And then , hold the state ofmatchdevice, test according to GJB 5309.I3 (4).

And then, start the test in accordance with GJB377A

3 Sensitivity TestPulse sensitivity test is complied the principle in Fig.3 .

5 AnalysisIn the case of RF , microwave and radar pulse , the only

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Proceedings

energy that absorb of EED .Pulse effect of EED is a complex problem to analysis . In

the course of pulse respond of EED , there are two cases to be

analysed and it's different from each other.

(1) function time less than pulse widthIn the case, it only adhere to equation (2) .

Reducing pulse width or increasing pulse altitude which

will make the time consuming electric energy less than the

thermal time constant , and then the loss of heat will decrease

and use electric energy more effective. In this case , we can

easily fire the EEDs .(2) function time more than pulse width

It's a procedure combing equation (2) and (4) and can

describe as fig.2 .

Because of function time more than pulse width , the heatloss is in the green tree, videlicet the electric energy is not

enough to fire the EED . Equation (4) describes how the hot

wire temperature returns to ambient after a pulse is turned off

6 SummaryIn this paper , it bring forward the test method of pulse

sensitivity . According to the heat balance equation to assess

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CEEM'2009/Xi'an

the pulse effect of EED . It describe the important character offunction time in the pulse effect analysis . Those which makeus know much about pulse response of EED and they are very

important in EMC analysis ofEED.

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university publish company .August 1997.(in chinese)

[2] John W.Adams,Dennis S.Friday.Measurement Procedures for

Electromagnetic Compatibility Assessment of Electroexplosive

Devices.IEEE transctions on electromagnetic compatibility, Vol 30,

NO.4,November 1988.

[3] Wang Kaimin, Wen Yuquan. Design of Initiators and Pyrotechnics

for Weapon System. National Defense Industry Press. May

2005 .(in chinese)

[4] Industrial Technique committee of defence science. Test ofRF

sensitivity. Gffi53 09.13-2004, 2004 .

[5] Li Gu-xin,Cheng, Guo Yuan, Jiao Qingjie. Experiment and test

technology of Initiators and Pyrotechnics. Beijing institute of

technology press. June 2007 .(in chinese)

[6] Yao Hongzhi, Feng Qingmei, Zhao Tuan, Ji Xiangfei. RF safety of

EED . Explosive Materials. February 2008 .(in chinese)