Post on 31-Mar-2020
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
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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
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M782 MOFA “Time Mode”time line
Fire Det.
Discharge battery T > 200 sec
PD function
Battery InitiationT = 0
Launch Mechanical ArmFuze TimeoutSet
ElectArm
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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
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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.
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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
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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
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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.
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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]
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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
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Problems to Solve (Packaging)
Previous MOFA Det Delay PWA
Det/DelayASIC
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Problems to Solve (Packaging)
Present MOFA Det Delay PWA
EOD Circuitry
Det/DelayASIC
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Trade Studies
• ASIC vs. Discrete Component Solution
• Digital vs. Analog
• Discharge with a Simple Resistive Load or More Complicated Scheme
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Trade Study Digital Approach
VoltageRegulator Divide by N Counter Latch
BATTBattery Discharge
Circuit
DischargeResistor
Power-On Reset
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Trade Study Analog Approach
BATT
RC Timer
-
+
Battery DischargeCircuit
DischargeResistor
Comparator
Regulator
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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
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Fast Acting Fuse Data Sheet
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Fast Acting Fuse Data Sheet
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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
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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
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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%
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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
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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
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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
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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.
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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.