MOFA EOD CircuitNDIA Fuze Conference

April 5–7, 2005

BY: Robert E. Keil

Alliant Techsystems

2

Presentation Outline

• Introduction to MOFA EOD Circuit• EOD Requirements for MOFA• Design Constrains or Problems to

Solve• Trade Studies• Final Circuit Concept• Summary

3

MOFA (M782) Fuze

4

MOFA (M782) Fuze Description

•Multi-Option Fuze for Artillery

•4 Function Modes: Time, Proximity, Point Detonate & Delay

•Work Performed under Contract DAAA21-92-C-0075

5

M782 MOFA “Time Mode”time line

Fire Det.

Discharge battery T > 200 sec

PD function

Battery InitiationT = 0

Launch Mechanical ArmFuze TimeoutSet

ElectArm

6

MOFA (M782) Fuze Level 1 Assembly

Fuze Level II Assembly

Detonator/Delay Assembly

Post-Launch Battery

O Rings

Connector RetainerCollar

Sleeve

Det/Delay Retainer

7

MOFA (M782) Fuze Cutaway

Radome

Inductive Coil

Collar

Transceiver

Connector Retainer

Flex Cable

Control/ProcessorAssembly

Fuze SleeveBattery

Detonator/DelayAssemblyS&A

Booster CupBooster

Crush Switch

8

Detonator/Delay Assembly Location

9

Why the EOD Project?

• Original Calculations Showed that the Battery Bleed Resistor and the Control/Processor Load Could Dissipate the Battery Energy Within 30 Minutes.

• Subsequent Testing Revealed that, Under Special Conditions, the Firing Circuit Could Function in the Absence of the Control/Processor.

• A special EOD Circuit was Therefore Required to Discharge the Battery.

10

What is EOD?

• EOD – Explosive Ordnance Disposal

• Mil-STD 1316 Requires all firing energy to be dissipated in 30 Minutes

• Battlefield Clean-up and Disposal of Explosive Ordnance

11

EOD Circuit Block Diagram

TimingCircuit>200

Seconds

Battery Shorting Circuit

Energy (Battery) Disconnect Circuit

Battery

Fuse 1

Fuse 2

• Initiates its actions after a >200 second Timeout

• Shorts the Battery Input Connections

• Opens Battery Circuit

12

MIL-STD-1316

4.6.4 Electrical firing energy dissipation. For electrically initiated fuze explosive trains, the fuze design shall include a provision to dissipate the firing energy within 30 minutes of the expiration of the fuze arming life, or a fuze failure. The dissipation means shall be designed to prevent common mode failures.

13

EOD Requirements Compliance

Requirement1. Discharge Post Launch Battery

30 minutes after gun launch to < 1.02 Volts.

2. Incorporate a Timer to initiate the discharge circuit independent of the Control Processor.

3. Use external components to control turn-on time and discharge current.

4. Modified circuit shall not reduce the fuze functional reliability below ORD specification.

Implementation1. Opens circuit to the battery and

‘shorts’ the power to the firing circuit.

2. An RC timing circuit and comparator perform this function

3. The RC components determine turn-on time and the base pull-up resistor on Q502 determines the discharge current.

4. Reliability prediction showed little change from previous prediction. [.969 to .966 in Time Mode]

14

Problems to Solve(Battery Discharge)

• Worst Case Discharge takes 212 minutes.

• A simple 1K resistor cannot discharge the battery in < 30 Minutes.

• Multiple Cells Discharge Unevenly and can rebound when load is removed. 0

2

4

6

8

10

12

1 11 21 31 41 51 61 71 81 91 101

111

121

131

141

151

161

171

181

191

201

211

221

231

241

251

261

271

281

291

Time in minutes

Bat

tery

vol

tage

PLBAT414PLBAT535PLBAT379PLBAT487PLBAT371

Graph Supplied by Fred Oliver at ARDEC

15

Problems to Solve (Packaging)

Previous MOFA Det Delay PWA

Det/DelayASIC

16

Problems to Solve (Packaging)

Present MOFA Det Delay PWA

EOD Circuitry

Det/DelayASIC

17

Trade Studies

• ASIC vs. Discrete Component Solution

• Digital vs. Analog

• Discharge with a Simple Resistive Load or More Complicated Scheme

18

Trade Study Digital Approach

VoltageRegulator Divide by N Counter Latch

BATTBattery Discharge

Circuit

DischargeResistor

Power-On Reset

19

Trade Study Analog Approach

BATT

RC Timer

-

+

Battery DischargeCircuit

DischargeResistor

Comparator

Regulator

20

EOD Circuit Schematic

VCC

VEE

U2

R4R6

R5

C6 C7

R8

C9

Q1

Q2

R9

R10

RC

D1

R11

C4

F2250 ma

BATT8

F1750 ma

R3C8

B_Plus

Fuse to openBattery Circuit

Fuse Used asTimeout

Memory Device

21

Fast Acting Fuse Data Sheet

22

Fast Acting Fuse Data Sheet

23

Final Circuit Concept – Normal Battery

VCC

VEE

U2

R4R6

R5

C6 C7

R8

C9

Q1

Q2

R9

R10

RC

D1

R11

C4

F2250 ma

BATT8.0

F1750 ma

R3C8

B_Plus

Current Through¾ A Fuse

Current Through¼ A Fuse

IF1

Tran

3.8

0500Msec0 time

IF2

Tran

2.1

0500 Msec0 time

24

Final Circuit Concept – Low Battery

VCC

VEE

U2

R4R6

R5

C6 C7

R8

C9

Q1

Q2

R9

R10

RC

D1

R11

C4

F2250 ma

BATT

F1750 ma

R3C8

B_Plus

IF2

Tran

0.6

0500 Msec0 time

Current Through¾ A Fuse

Current Through¼ A Fuse

IF1

Tran

10.0

0500 Msec0 time

2.5

25

EOD RC Time Measurement

• Setup of the MOFA Final Functional Tester– 8 volts is applied to B+ (TP 5)– The voltage on RCTIME (TP 4) is

measured after 5.5 seconds.– Limits are .18-.27 volts– Average results are .25+/-0.01 volts

(+/- 4 %) With a Specification Tolerance of +/- 20%

26

RC Time Ambient Production Data

MOFA FFT TIME_RCTIME 12/20 5:47 to 12/21 8:56

Count of data: 874

Volta

ge

TIME_RCTIME

Tester Low Limit

Tester Hi Limit

Dataset - 3 Sigma

Dataset + 3 Sigma

27

RC Time Histogram

MOFA FFT TIME_RCTIME 12/20 5:47 to 12/21 8:56

020406080

100120140160180200

-3.0

sig

ma:

-2.5

sig

ma

:

-2.0

sig

ma

:

-1.5

sig

ma

:

-1.0

sig

ma

:

-.5 s

igm

a :

Mea

n: s

igm

a

.5 s

igm

a:

1.0

sigm

a:

1.5

sigm

a:

2.0

sigm

a:

2.5

sigm

a:

3.0

sigm

a:

Count

28

EOD Tests

• Check Turn-On of Output Transistor Q2• Check Off-State of Output Transistor Q2• Test Turn-On of Comparator and FET Q1• Measure Timer Circuit• Verify Both Fuses are Intact

29

Patent Protection

1. Fuze explosive ordnance disposal circuitAPL 2004-11-25 20040231547/US-A1 NDN- 041-0323-1472-0

INVENTOR(S)- Keil, Robert, E. WI, US

PATENT APPLICATION NUMBER- 441665/10DATE FILED- 2003-05-20

PUBLICATION NUMBER- 20040231547/US-A1PUBLICATION DATE- 2004-11-25

MAILING ADDRESS- 6109 BLUE CIRCLE DRIVE, SUITE 2000; MINNETONKA, MN; 55343-9185; US

ATTORNEY, AGENT, OR FIRM- VIDAS, ARRETT & STEINKRAUS, P.A.U.S. PATENT CLASS- 102206000O

INTERNATIONAL PATENT CLASS- *07; F42C02100

The present invention comprises an electronic Explosive Ordnance Disposal (EOD) circuit which is desirably used with fuzed explosive weapons, such as projectiles

having a nominal mission time. After expiration of the mission time, if the explosive has not detonated, the inventive circuit controls the energy supplied to the fuze

detonation circuit to a level that is less than a threshold level required by the fuze for detonation, thereby preventing subsequent detonation of the explosive.

30

Unique Approach for EOD

• Ensures that all potential sources of Firing Energy are Dissipated within 30 minutes. i.e. Battery and Firing Capacitor.

• Uses a two-pronged approach to remove the battery as a potential source of Firing energy.

• The Over all Reliability Prediction for the MOFA Fuze Changed very little from the Baseline: .969 to .966 in the Time Mode.