Attachment_8_Environmental_Test_Plan_for_Warhead_Arming_Device-MAU191A.pdf

Attachment VIII: ETP for WAD. For Reference Purposes Only i

Environmental Test Plan

For

Warhead Arming Device, MAU-191/A

AGM-86, Air Launched Cruise Missile

Aging & Surveillance Program

December 3, 2008

Prepared By

For

498th MSUG

7339 Sentry Blvd

Tinker AFB, OK 73145

TABLE OF CONTENTS

Section Page

I. ITEM DEFINITION

1.1 Physical

1.2 Theory of Operation

II. AGE SENSITIVITY ITEM ANALYSIS SUMMARY

III. TEST METHODS

3.1 Test Methods for Each ASIA Parameter

3.1.1 Wet Tantalum Capacitor Leakage Current and Capacitance Value

3.1.2 Ceramic Capacitor Failure Due to Manufacturing Defects

3.1.3 Relay Contact Failure

3.1.4 Cracks in Circuit Board and Solder Post Terminals

3.1.5 Cracks in Diode Components

3.1.6 Degradation of Conformal Coating

3.1.7 Thermal Stress of Transistors

3.1.8 Insulation Degradation of Wound Components

3.1.9 Corrosion and Wear on Connectors

3.1.10 Rotary Switch Contact Resistance and Disk Degradation

3.1.11 Motor Brush Contact Area and Brush Holding Spring Force

3.1.12 Armature Fretting and Discoloration

3.1.13 Ball Bearing Contamination

3.1.14 Wear on Rotary Switch Gears

3.1.15 Clutch Wear, Pre-Load, and Reduction of Torque

3.1.16 Clutch Reduction of Torque

3.1.17 O-Ring Embrittlement and Compression Set

3.1.18 Wire Chaffing

3.1.19 Solder Manufacturing Defects

3.1.20 Insulator Pad Degradation

3.2 A&S Test Methods and Environments

3.2.1 Test Methods for WAD Assembly

3.2.1.1 Visual Inspection, External

3.2.1.2 Functional Tests

3.2.1.3 Relay Tests

3.2.1.4 Rotary Switch Tests

3.2.1.5 Motor Tests

3.2.1.6 Wet Tantalum Leakage Current

3.2.1.7 Housing Seal Integrity Test

3.2.2 Test Methods Requiring Removal of WAD Cover

3.2.2.1 Visual Inspection, Cover Removed

3.2.2.2 Measurement of Motor Winding Resistance

IV. TEST EQUIPMENT AND FACILITES REQUIREMENTS

V. AGING & SURVEILLANCE STORAGE ENVIRONMENTS

VI. A&S TEST REQUIREMENTS

6.1 Test Classifications

6.2 Test Types

6.2.1 Baseline “A” Tests

6.2.2 Interval “B” Tests

6.2.3 Comprehensive “C” Tests

6.3 Test Sequence

6.4 Test Data Categorization

VII. MEASUREMENTS LIST

LIST OF TABLES

Tables Page

Table 1. Recommended Parameters for WAD Monitoring Table 2. Random Vibration Levels Table 3. Temperature Test Levels Table 4. Combined Environmental Test Levels Table 5. Relay Functions that can be Tested Through the External WAD Connectors Table 6. Rotary Switch Functions that can be Tested Through External WAD Connectors Table 7. Equipment and Facilities Required for WAD Testing Table 8. Recommended A&S Tests (Cont’d) Table 9. A&S Sample WADs Test Schedule for the First 10 Test Cycles (10 years) Table 10. Measurement List

LIST OF FIGURES

Figures Page

Figure 1. WAD Physical Interface Figure 2. WAD Electrical Interface Figure 3. Temperature Variances for MOB 1 and MOB 2 Figure 4. Humidity Variances for MOB 1 and MOB 2 Figure 5. Recommended Test Sequence and Total Number of Samples Per Test Cycle

I. ITEM DEFINITION

1.1 Physical

The Warhead Arming Device (WAD) is defined on Envelope Drawing 232-30050, The Boeing Company and detailed by Consolidated Controls Corporation (CCC) Drawing 76560. The source for all WADs was Consolidated Controls Corporation (CCC). (Note:

Eaton Industries acquired CCC in 1986, and Eaton Industries was subsequently acquired by VACCO in 2000.)

The WAD is a switching device that provides circuit paths for all warhead arming and fuzing commands and interface status-monitoring circuits. Major WAD subassemblies include the following:

1. three circuit board assemblies

a. general component circuit board (CB1)

b. impact sensor signal conditioner circuit board (CB2)

c. impact sensor trigger circuit board (CB3)

2. a relay assembly composed of 7 different mechanical relays

3. an electromagnetic impulse (EMI) assembly

4. a motor driven arm/disarm switch deck

5. necessary component-to-component internal wiring harnesses

6. three interface connectors for external electrical mating: (J1 to the Inertial Navigation Element (INE), J2 to the Warhead, and J3 to the Impact Sensors)

7. a mechanical safing link

8. a structural housing which provides mounting flanges for a mechanical interface with the ALCM structure

9. an observation window which provides a visual display of a green band with a black “S” when the WAD is safed or a red band with a black “A” when the WAD is armed.

Figures 1 and 2 show the physical and electrical interfaces.

Warhead

WAD

UmbilicalAircraft

Rotary Switch

INE

Impact Fuze

Figure 1. WAD Physical Interface

Figure 2. WAD Electrical Interface

E F I S J H R G Q T E

J M N P M L H K P K

S C D F R G A Y B V X W

U T M Q E D R P S B C

H J F I B Z N H K Y R

T S P V X C M L A A K

G J W G D

B F

CD FIRE

CD CLOCK

PAL REGLTR CNTRL

PAL KEY & DATA

PAL UNLCK MON

PAL STATUS MON

CD MONTOR

CD POWER

CD DATA

PAL/CD RETURN

SAF PREARM CMD

SAF SAFE CMD

D2 D1

MONITOR COMMON

SAF SAFE MON

SAF PREARM MON

AF SQUIB OUTPUT

BF SQUIB OUTPUT

AF/BF SQUIB RETURN

AV SQUIB OUTPUT

BV SQUIB OUTPUT

AV/BV SQUIB RETURN

A1 B1 A2 B2 A3 B3

RELAY COMMON

A4 B4

RELAY RETURN

Impact Fuze

CD FIRE

CD CLOCK

PAL REGLTR CNTRL

PAL KEY & DATA

PAL UNLCK MON

PAL STATUS MON

CD MONTOR

CD POWER

CD DATA

PAL/CD RETURN

ESD WORD A

ESD WORD B

A/D SAF CMD

SAF NON EXCITATION

CLASS III MONITOR

SAF PREARM MON

SAF SAFE MON

SAF SIGNAL COMMON

CLASS III CMD A

SAF PREARM CMD

SAF SAFE CMD

ORD ALARM LOOP

ORD ALARM LOOP RTN

CLASS III CMD B

CLASS III ACTIVATE

CONSTANT LOAD BUS RTN

A4/A3 MON RTN

VALUE ACTIVATE

A3 MONITOR

MAIN LOAD BUS

MAIN LOAD BUS RTN

SEP ARM/WHD CMD

(EXCITATION RTN)

ARM ENABLE CMD

ARM 1 CMD

ARM 2 CMD

A4 MONITOR

INTERNAL FUZE CMD

RELAY COMMON

WARHEAD ARMING DEVICE

C on di tio ni ng

C irc ui try

J1 J2

J3

Warhead

1.2 Theory of Operation

The WAD has four modes of operation while installed in a missile: ground alert/handling, captive carry, launch, and free flight. The WAD provides mechanical and electrical lockout features between the main load bus power and the warhead for ground alert/handling and captive carry operations. It also provides the control circuitry to isolate and/or activate the arming and fuzing circuit paths as required during launch and free flight. Each mode is described below.

Ground Alert/Handling. During ground alert/handling and transportation between operating locations and the depot repair facility, the WAD is in the safe state. This condition is verified by retracting a mechanical link. An internal mechanism allows the arm/safe switch to be safed either electrically or manually. Design features of the WAD prevent the device from being manually armed. During periodic testing at the operating location or depot test facilities, the mechanical link is extended so the WAD can be functionally tested. The warhead is physically disconnected from the test loop during all ground testing. The WAD is returned to the safe condition prior to reconnecting the warhead.

Captive Carry. The WAD mechanical link is manually extended after the missile is uploaded to the aircraft. In this mode, the Rotary Switch in the missile prevents main load bus power from reaching the WAD. Therefore, the WAD remains in a safe condition during captive carry. The WAD provides the following functions in the safe state:

a. A motor driven, multiple pole arm/disarm switching deck is set to separate the critical warhead arming and fuzing loads from the inactive main load/power bus. The arm/disarm switch also provides a continuity path for ordnance alarm monitoring during captive carry.

b. A human intent circuit is employed in the WAD. This circuit consists of a relay that is identified as the Class III Select Relay. If the air crew selects the “Class III Command A”, the Select Relay is open and the Class III Activate Relay cannot be closed, thus preempting the arming and fuzing sequence in free flight. The aircrew must select the “Class III Command B” during captive carry to close the Select Relay, which completes a path for the Class III Activate command to close the Class III Activate Relay during free flight. The Class III Select Relay setting is reversible upon command from the aircraft throughout captive carry.

Launch. Power to the WAD is provided via the ALCM Pulse Load Battery during the transition from captive carry to free flight.

Free Flight. The AGM-86, Air Launched Cruise Missile employs three targeting options:

1. Air Burst with Ground Backup

2. Air Burst Only

3. Ground Burst Only

During free flight, the WAD provides a means of controlling the application of main load bus power and critical warhead arming and fuzing commands. The Inertial Navigation Element (INE) issues commands to the WAD relay circuitry. The relays in turn configure the main bus power and return lines to the warhead electrical loads.

Specifications indicate that the main air vehicle bus will supply the WAD main load bus with 26 to 32 volts dc power at the J1 input connector. The worst-case power consumption of the WAD is not specified. Based on the design implementation, the power consumption should not exceed 5 amps. This power consumption includes the maximum transient motor current plus the total relay activation currents.

The motor driven arm/disarm switch deck, in conjunction with the warhead interlock circuitry, comprise the majority of the electronics within the WAD.

The motor driven arm/disarm switch deck contains twenty-two sets of rotary contacts.

Two sets provide D1/D2 circuit path. Four sets are required to provide the current paths and return paths for each of the AF/BF and AV/BV circuits. Eight sets provide the current paths for the warhead arming signals (A1/B1, A2/B2, A3/B3, and A4/B4 ~ Inertial Fuze). One set is dedicated to the Ordnance Alarm Loop. Two sets provide motor control functions (one for selecting the safing field coil, and one for selecting the arming field coil). The 22nd set of contacts completes the A3 and A4 monitor return line.

The WAD warhead interlock circuitry includes eight relays. Two relays provide monitor paths for the warhead safe, SAF safe and warhead pre-arm monitors during captive carry;

one relay isolates the main bus power from the WAD until activated during free flight;

and five isolate the warhead loads from main bus power until activated during free flight.

The WAD also provides the final warhead fuzing signal upon ground impact. An impact fuze signal conditioner circuit provides the fuzing signal for the ground burst option in both the primary and backup targeting mode implementation of the Ground Burst option.

Energy stored in a capacitor bank is discharged through the signal conditioner to the warhead upon missile impact.

II. AGE SENSITIVITY ITEM ANALYSIS SUMMARY

The Age Sensitivity Item Analysis (ASIA) on the Air Launched Cruise Missile (ALCM) Warhead Arming Device (WAD) has concluded that the device is age sensitive and that its inclusion in the ALCM A&S program is appropriate. The details concerning all ASIA findings and recommendations are documented in the ALCM Warhead Arming Device ASIA Report, dated 8 October 2008. The WAD is one of three ALCM hardware components included in the Nuclear Weapon Sub-System (NWSS) that provide the electrical interface with the warhead for arming and fuzing control.

The materials analysis found evidence of major aging concerns associated with the electrolytic capacitors, motor driven switch deck, electrical relays, and mechanical interference/design constraints associated with an insulator pad and CB1 within the WAD. Each of these issues is highlighted below.

Four electrolytic (wet tantalum) capacitors on the impact sensor signal conditioning circuit board (CB3) currently have high leakage currents, which will continue to get worse due to metal migration within the components, and eventually may result in a short circuit across the capacitor. Redundancy in this part of the circuit is lost because the same capacitor is used for both paths of the circuit.

There are several aging effects and motor conditions that may, alone or in combination, eventually cause the motor to fail to start. The aging effects include diffusion of copper through the gold plating of the contact switches (resulting in oxidation of the copper and an increase in switch contact resistance); contamination debris in the rotary switch assembly ball bearings (which increases the motor torque requirement to overcome the bearing friction); a surface oxidation and fretting on the motor armature (which may be an additional source of debris that can contaminate bearings) and wear on the motor brushes, increasing the brush contact resistance.

The relays inside the WAD have exhibited some oxidation and contamination on the relay contact surfaces leading to open circuits. This is an aging effect that is likely to become more frequent over time.

An insulator pad is employed in the WAD to separate the CB1 circuit card assembly from the relay assembly. This pad has exhibited deformation, holes and burn marks in many WADs that can lead to potential shorts over time. In addition, some WADs are known to have a manufacturing defect in the soldering process, which has led to solder flows into areas on the underside of CB1 that should be nonconductive. Vibration of the assembly over time, coupled with the insulator pad deterioration and the solder defects, can lead to shorts.

These mechanisms, coupled with other known aging mechanisms in this type hardware, have led to the identification of 40 critical parameters and 5 non-critical parameters for the WAD. The 5 non-critical parameters were dismissed as viable A&S candidates as described in the Warhead Arming Device ASIA Report. All 40 critical parameters were recommended for inclusion in the ETP and TRD development efforts. The delineation between critical and non-critical parameters can be found in the WAD ASIA Report.

Table 1 summarizes the conclusions of the ASIA study and identifies the critical and non-critical aging mechanisms that should be considered for inclusion in the A&S program for this component.

Identifier Name Aging Mechanism Critical Non-Critical

Circuit Board CB1 – General Components

Diodes Cracks due to vibration

Relays, K1 & K2 Contact wear/contamination

Solder Post Terminals Fatigue causes cracks/breaks

Conformal Coating Degradation

Circuit Board CB2 – Impact Sensor Signal Conditioner

Ceramic Capacitors Fatigue of voids and delaminations

Transistors Thermal stress

Diodes Cracks due to vibration

Wound Components Degradation of insulation

Solder Post Terminals Fatigue causes cracks/breaks

Conformal Coating Degradation

Circuit Board CB3 – Trigger Circuit

Wet Tantalum Capacitors Metal migration and electrolyte leakage

Diodes Cracks due to vibration

Solder Post Terminals Fatigue causes cracks/breaks

Conformal Coating Degradation

EMI Filter Assembly

Wet Tantalum Capacitors Metal migration and electrolyte leakage

Feed thru capacitors Fatigue of voids and delaminations

Inductors Degradation of insulation

Capacitors Fatigue of voids and delaminations

Connectors Corrosion, wear

Table 1. Recommended Parameters for WAD Monitoring

Relay Assembly

Relay K3 Contact wear/contamination

Relay K4, K5, K6 Contact wear/contamination

Relay K7, K8, K9 Contact wear/contamination

Motor Components

Armature Degradation of magnet wire insulation and wear/fretting

Brush Plate Assembly Wear and reduced contact area

Ball Bearing, Rear Contamination

Field Windings Degradation of magnet wire insulation

Gear Box and Clutch

Cluster Gear Assembly Wear

Spur Gear Wear

Ball Bearing, Gearbox Contamination

Spring Corrosion or spring fatigue

Clutch Disk Wear

Safing Arm Wear of clutch face

Rotary Switch Deck Components

Contacts Diffusion of copper through gold plating

Bearing, Switch Deck Contamination

Switch Deck Discs Degradation & cracking

Table 1. Recommended Parameters for WAD Monitoring (cont)

Other Electrical Components

Circuit Board Fatigue

Wiring Wire chafing

Connector Assembly Corrosion

Solder Vibration, exposure

Insulator pad Degradation, burns, holes

Housing Components

O-Ring Seal Embrittlement and cracking

Table 1. Recommended Parameters for WAD Monitoring (cont)

Aging & Surveillance testing on the WAD is required to provide the data necessary for analysis and life predictions relative to the noted age sensitivities. The critical aging parameters identified can be grouped into categories based on aging mechanism, which is given below. Methods of testing each of these aging mechanisms are discussed in Section III.

1. Two (2) critical parameters are associated with metal migration in wet tantalum electrolytic capacitors.

2. Three (3) critical parameters are associated with possible failure of ceramic capacitors that may fail due to stressing of manufacturing defects.

3. Four (4) critical parameters are associated with relay contact failure.

4. Four (4) critical parameters are associated with cracks in circuit boards and solder post terminals.

5. Three (3) critical parameters are associated with cracks in diode components.

6. Three (3) critical parameters are associates with degradation of conformal coating allowing shorts due to manufacturing defects.

7. One (1) critical parameter is associated with thermal stress of transistors.

8. Two (2) critical parameters are associated with insulation degradation of wound components.

9. Two (2) critical parameters are associates with corrosion and wear on connectors.

10. Two (2) critical parameters are associated with rotary switch contact resistance and disk degradation or cracks.

11. One (1) critical parameter is associated with reduced brush contact surface area or reduction of brush force due to spring fatigue.

12. Two (2) critical parameters are associated with fretting and oxidation on the armature shaft thrust shoulder or insulation breakdown of the armature and field windings.

13. Three (3) critical parameters are associated with contamination of ball bearings due to internally generated contaminants.

14. Two (2) critical parameters are associates with wear on gears in the rotary switch assembly.

15. Two (2) critical parameters are associated with clutch disk wear.

16. One (1) critical parameter is associated with reduction of clutch pre-load due to spring fatigue.

17. One (1) critical parameter is associated with failure of O-ring seals in the WAD housing.

18. One (1) critical parameter is associated with wire chafing.

19. One (1) critical parameter is associated with solder manufacturing defects being exposed through conformal coating degradation and vibration.

20. One (1) critical parameter is associated with a breakdown of the insulator pad used in the WAD.

III. TEST METHODS

This report section describes test methods recommended for the A&S program for the WAD. Program constraints limit ALCM A&S testing to non-destructive test types.

Therefore only test methods and test environments that are non-destructive in nature are fully documented for use in the development of the Test Requirements Documents. In Section 3.1, test methods are described which are suitable for characterizing the individual ASIA parameters noted in Section II. In Section 3.2, these test methods are combined into more specific A&S test methods that will be used as the basis for the development of the Test Requirements Document (TRD) in those cases where non-destructive tests can be implemented.

3.1 Test Methods for Each ASIA Parameter

The following paragraphs discuss methods of testing for each of the aging mechanisms identified in the ASIA and noted in the table of Section II. Where applicable, alternative methods of testing are discussed, and recommendations are made.

3.1.1 Wet Tantalum Capacitor Leakage Current and Capacitance Value

There are two types of wet tantalum electrolytic capacitors used in the WAD. Four 110 F wet tantalum electrolytic capacitors are used in the impact sensor signal conditioning circuitry. The ASIA identified high leakage currents in these capacitors, and evidence of metal migration across the glass seals. Two 270 F wet tantalum electrolytic capacitors are used in an EMI filter. Although the ASIA did not find high leakage currents in these components, they are susceptible to aging due to being the wet tantalum type.

Measurement of capacitance and leakage current can be made with the capacitor removed from the circuit, either by completely removing it from the circuit board, or by lifting one leg of the component (note that the circuit board has conformal coating). In both cases, this requires destruction of the potting in order to access the capacitor. The capacitors in the EMI Filter can be tested for value and leakage nondestructively since they can be isolated with an open relay and access is available from the WAD J1 connector. The capacitors in the impact sensor signal conditioning circuit can be tested nondestructively through a special technique using access through the WAD J3 connector. Leakage current can generally be measured by applying a voltage across the capacitor (typically either the in-circuit voltage, or the capacitor’s rated DC voltage) while measuring the power supply output current. The measured leakage current is then compared with the manufacturer’s rated maximum value. Capacitance can be measured by looking at charge time constants.

3.1.2 Ceramic Capacitor Failure Due to Manufacturing Defects

Ceramic capacitor samples studied in the past that are identical to those found in the WAD had manufacturing defects such as voids and delaminations. This included ceramic capacitors on the circuit boards, as well as in one of the EMI filters. Although the manufacturing defects themselves are not a problem (since the capacitor meets its rated electrical specifications), they are a mechanical stress point for fracture of the ceramic material as the capacitor is overstressed or subjected to repeated cycles of stress.

Any defects noted can be traced back to a specific manufacturer and production dates since the components have manufacturer and date codes.

The only way to know whether a ceramic capacitor has an internal void or delamination is to destructively cross section the component and examine it under a microscope. For the A&S program, there may be some benefit gained from inspecting the ceramic capacitors from sample WADs in order to characterize the extent of such defects, and to look for components which may have failed. Note that many of these components are used as “filter capacitors,” which typically cannot be tested adequately in-circuit because their function is often to provide a high-pass filter for electrical noise (bypass to ground).

Environmental stress testing of the WAD is the best way to find these problems outside of destructive testing.

3.1.3 Relay Contact Failure

Relay contact wear can be evaluated by visual inspection using a microscope (approximately 30X magnification). However, this requires that the metal cover on the relay be removed by destructive means. Further, the contacts are more easily examined if the relay is dissected so that the contact pads can be individually exposed for viewing.

The condition of the relay contacts can be judged indirectly by precisely measuring the contact resistance. In most cases, it is possible to do this by connecting test leads at the WAD external connectors.

3.1.4 Cracks in Circuit Board and Solder Post Terminals

Conductor cracks that fail open may be detected during ground testing such as Level I or Service STAR testing. However, it is possible to have fatigue cracks in the conductive paths which close and maintain the electrical connection. Thus, a visual inspection of the circuit board and flex circuit is recommended to look for fatigue-related cracks in the conductors. Also, a functional test when the WAD is in under an applied environment of vibration and temperature extremes should identify such aging problems.

3.1.5 Cracks in Diode Components

Cracks that cause diode failure can be found in functional testing of the WAD. Cracks that will eventually lead to failure may be identified by functional testing when the WAD is under an applied environment of vibration and temperature extremes.

3.1.6 Degradation of Conformal Coating

Visual inspection of the circuit boards in the WAD is the best way to identify problems in the conformal coating. Degradation has already been observed in some WADs and can manifest itself as a failure when contact is made with other parts of the WAD, such as the relay assembly. Outside of visual inspection, such problems will best be observed in a functional test when the WAD is in under an applied environment of vibration and temperature extremes.

3.1.7 Thermal Stress of Transistors

Transistors are used in the A4/B4 trigger circuit. This circuit is prone to problems due to thermal stress. Environmental stress testing is the best way to observe aging problems due to thermal stress by carefully monitoring the A4/B4 trigger circuit.

3.1.8 Insulation Degradation of Wound Components

Problems due to insulation degradation of wound components can be found during functional testing of the WAD, and aging degradation can be brought out through environmental stress testing. This applies to the testing of filter inductors, as well as the motor windings.

3.1.9 Corrosion and Wear on Connectors

Visual inspection, functional testing and special resistance measurements can be used to identify corrosion and wear on the WAD connectors.

3.1.10 Rotary Switch Contact Resistance and Disk Degradation

The diffusion of copper through the gold plating on the rotary switch contacts can be characterized by metallurgical examination. A cross-sectioned sample can be examined by means of SEM and X-ray energy dispersive spectroscopy (EDS) line scan in order to identify the metals near the surface of the sample. The diffusion of copper into the gold plating layer can thus be characterized. In advanced aging cases, copper oxide (black in appearance) may be seen on the gold plating during a visual inspection under a microscope. Destructive disassembly of the WAD is required in order to gain access to the contacts for inspection. Resistance testing of the rotary switch contacts can be performed during functional testing and resistance values can be monitored over time to characterize aging.

3.1.11 Motor Brush Contact Area and Brush Holding Spring Force

It has been observed that the motor brushes typically do not make full contact with the commutator. This increases the electrical resistance of the path. Visual inspection will allow characterization of the brush contact area, although this requires that each brush be removed from the motor for inspection. Direct measurement of contact resistance is not considered a viable approach for characterization of aging since the resistance would be expected to change significantly as the motor shaft is moved to a new rotational position.

Measurement of motor current may indirectly aid characterization of brush contact resistance.

The brush contact force is applied by a metal torsion spring that is assembled into the spring holder. The brush contact pressure (the spring force, divided by the brush contact area) affects the electrical resistance of the brush and commutator interface. The spring force can be measured using a force transducer and instrumentation. Also, the brush springs and brush holders should be visually inspected for misalignment or other manufacturing damage.

3.1.12 Armature Fretting and Discoloration

The ASIA identified a wear pattern on the thrust face of the armature shaft, which had resulted from metal-to-metal rubbing. Further, there was an unidentified brown deposit at this contact area. These two phenomena can generate contaminants that can find their way into the ball bearings. The armature thrust face could be visually inspected with the aid of a microscope (approximately 30X magnification). Motor current and minimum voltage drive testing can indirectly find and characterize aging problems due to these factors.

3.1.13 Ball Bearing Contamination

There are multiple ball bearings in the WAD rotary switch assembly. The bearings are lightly-oiled for lubrication, which makes them susceptible to contamination from any debris that is generated inside the motor, gearbox, clutch, or switch deck.

A quick test for bearing contamination is to rotate the bearing by hand to feel for any roughness and to listen for any unusual noise. Another technique for relative comparison is to spin the outer race while the inner race is held stationary, then remove the applied torque causing it to spin, then time how long it takes for the bearing to stop spinning.

The second technique can be automated. Without disassembling a WAD, motor current testing, switch time testing, and minimum voltage drive testing can indirectly find and characterize aging problems due to bearing contamination.

3.1.14 Wear on Rotary Switch Gears

Visual inspection is the primary method for detecting gear wear. However, motor current testing, switch time testing, and minimum voltage drive testing can indirectly find and characterize aging problems due to wear on the rotary switch gears.

3.1.15 Clutch Wear, Pre-Load, and Reduction of Torque

The purpose of the clutch is to allow manual disarming of the WAD, i.e., the clutch allows the shaft in the rotary switch deck to slip during manual disarming. If the clutch slips while the motor is driving it, it is possible that the rotary switch deck may not actuate properly. These problems can be characterized in functional testing by measuring rotary switch activation time, motor current and the minimum voltage required to drive the rotary switch deck assembly.

3.1.16 Clutch Reduction of Torque

A test can be devised to measure the torque at which the clutch slips. If the torque should be too low, further investigation would be necessary to determine the cause. This would require disassembly of the unit and measurement of individual components.

3.1.17 O-Ring Embrittlement and Compression Set

O-rings seal the cover and each of the externally accessible fasteners. The integrity of the housing seal can be checked by developing a pressure test. One of the externally accessible fasteners can be removed so that a special pneumatic fitting can be installed.

Then, a helium / nitrogen mix can be used to pressurize the container so that a leak test can be performed.

Additional evaluation of the O-rings will require that they be removed from the housing.

The cover O-ring may be the most convenient to use because of its size. An elongation test can be used to check for embrittlement of the material. A durometer (hardness) test can be performed on the O-ring, although the test may need to be repeated several times in order to get meaningful results (the small material volume can affect the test). A visual inspection of the O-ring should also be performed to look for cracking and changes in cross section due to compression set.

3.1.18 Wire Chaffing

Wire chaffing can best be identified by functional testing of the WAD under environmental thermal and vibration stress.

3.1.19 Solder Manufacturing Defects

Some WADs have exhibited solder manufacturing defects due to the assembly process.

This represents a severe problem in the WAD that can best be identified by visual inspection, but may also be found by testing the WAD under thermal and vibration stress.

3.1.20 Insulator Pad Degradation

The WAD uses an insulator pad between a circuit board and the relay assembly which is usually found to have holes and is somewhat degraded. This problem combined with the solder defects and conformal coating degradation can lead to failures due to shorts in the WAD. Visual inspection and environmental stress testing are the best methods of characterizing these problems.

3.2 A&S Test Methods and Environments

This section provides recommended A&S test methods based on the testing requirements identified in Section 3.1 above. A limited amount of testing can be performed on the WAD assembly by making measurements through the external electrical connectors.

Additional A&S testing will require various degrees of disassembly of the WAD. Even with the housing cover removed, access to the circuit board and motor/gearbox/switch components is limited, so further “destructive” disassembly would be necessary to view or probe components. In some cases, the component itself may need to be destructively examined. However, since there are a limited number of WADs available for the A&S program the WADs cannot be allowed to be destroyed for A&S purposes. Thus, described below are non-destructive tests that can be performed at the WAD assembly-level, and also after removal of the top cover of the WAD.

3.2.1 Test Methods for WAD Assembly

The following test methods will not damage the WAD, nor will they require any disassembly of the WAD, potentially allowing it to be placed back into service. The recommended vibration and temperature environments are taken from the WAD Acceptance Test Procedure used for individual acceptance of the units. The recommended non-destructive tests may provide indications of possible aging effects of internal components, and thus may be beneficial for screening of samples to select candidates for disassembly and more detailed inspection.

The testing described below is intended to gather specific data to be recorded and tracked by the A&S program for the purpose of monitoring aging effects. The tests do not include functional checks performed by Service STAR, which may provide additional data to be collected for the A&S program.

3.2.1.1 Visual Inspection, External

The WAD assembly should be inspected for the following types of aging and damage:

Corrosion of the housing

Bent connector pins

Evidence of moisture around observation window

Handling damage

Loose fasteners

Any visible evidence of aging-related or handling damage should be photographed for documentation purposes. If there is moisture inside the WAD, it may be visible on the observation window (cooling of the WAD and/or window may cause moisture to condense on the glass). Any bent connector pins should be noted before electrical tests are attempted. Loose fasteners may indicate loss of housing seal integrity. Fastener loosening might be judged by observing the condition of the paint around the fastener (i.e., if the paint around the fastener is cracked, the fastener may have loosened). Do not attempt to judge fastener torque by tightening the fastener (which could damage the corrosion-protection paint, strip the fastener, or even break the fastener).

3.2.1.2 Functional Tests

A functional test capability is recommended such that the WAD can be tested independent of the missile and can be tested under environmental conditions. It will be necessary to confirm periodically that dedicated A&S samples still provide basic functionality, in addition to the recommended tests to collect A&S monitoring data.

Also, certain aging effects (e.g., failures due to component and solder defects, loss of housing seal integrity, etc.) may become apparent during a functional test, particularly if the test is performed while the WAD is under thermal and vibration environments.

The functional test can be developed based on the WAD Depot Level Test Procedure for individual unit acceptance after depot repairs (232-12129), but modified to correct known test deficiencies.

For testing under environment, the WAD Requirements Specification (232-30050) specifies random vibration test levels for each of the three axes as follows:

Frequency Spectrum Level

10 Hz to 34 Hz 0.0015 g2/Hz

34 Hz to 100 Hz Ramp 0.0015 g2/Hz to 0.015 g2/Hz

100 Hz to 2000 Hz 0.015 g2/Hz

Table 2. Random Vibration Levels

The recommendation for A&S testing, based on the WAD Requirement Specification and the goals of the A&S program, is for performing vibration for each axis at temperature for the duration of one functional test (about 10 minutes at each axis).

For testing under environment, the WAD Requirements Specification (232-30050) specifies the following temperatures and durations:

Temperature Duration Ambient (72F) 2 Hrs 40 minutes

-65F 2 Hrs 40 minutes +160F 2 Hrs 40 minutes

Table 3. Temperature Test Levels

To provide a functional test under environments for the A&S program these temperature and vibration levels can be combined with functional testing at each axis as follows:

Temperature Soak Duration Vibration Duration Axis

+160F 120 minutes 10 minutes X

Ambient (72F) 120 minutes 10 minutes Y

-65F 120 minutes 10 minutes Z

Table 4. Combined Environmental Test Levels

Notes: 1. Temperature ramping shall not exceed 5F per minute.

2. Functional Testing of the WAD occurs during the 10 minute vibration period at the end of the temperature soak.

3.2.1.3 Relay Tests

The closed contact resistance measurement can be used to characterize aging effects associated with arcing, pitting, and general wear of the contacts. In addition, gross failure of the electrical connections through the external connector, circuit board, and internal soldered connections can be detected by means of measurements at the electrical connections to the WAD.

The following table identifies the relay functions that can be tested through the external WAD connectors. It will be necessary to reference the electrical schematic drawing 76561 to aid interpretation of the table. When a switch contact is closed, the measured resistance should be near zero. A high accuracy ohmmeter with a 4-wire test lead (to eliminate effects of the test lead) should be used to make this measurement, since the measured resistance will be very low. Limits will need to be established for the acceptable resistance of the contact and associated connections. Initially, a 1.0 ohm (1000 milliohm) value can be assumed as an acceptable limit, until sufficient A&S data has been collected to establish more precise limits. (The WAD specification states that monitor signals, which are generally relay contacts, shall have a resistance of less than one ohm when active.)

In some cases, it is necessary to power the relay contact before the switch resistance can be measured. The relay pull-in and drop-out voltages should also be recorded and tracked for the A&S program, which can be performed by monitoring for continuity through any relay contact while the applied coil voltage is ramped up or down. The nominal relay coil voltage is 28 VDC. The WAD specification states that the maximum actuation current for each of relays K3, K4, K5, K6, K7, K8, and K9 is 250 milliamperes.

There specification of maximum actuation current for relays K1 and K2 is 100 milliamperes.

Relay Identifier

Stimulus (S)

Measure (M)

Units Data Format

Actuate Relay Across Pins Closed

Contacts Across Pins

Stimulus or Measurement

Measurement Limits + -

K1 S VDC XX.XX J1-c J2-r actuate K1 M VDC XX.XX pull-in voltage K1 record for A&S monitoring M mΩ XXXX J1-A J1-a contact resistance 1000 mΩ max.

M VDC XX.XX drop-out voltage K1 record for A&S monitoring

K2 S VDC XX.XX J1-c J2-G actuate K2 M VDC XX.XX pull-in voltage K2 record for A&S monitoring M mΩ XXXX J1-L J1-a contact resistance 1000 mΩ max.

M VDC XX.XX drop-out voltage K2 record for A&S monitoring

K3 S VDC XX.XX J1-K J1-B actuate K3-DN M VDC XX.XX pull-in voltage K3-DN record for A&S monitoring M mΩ XXXX J1-M J1-a contact resistance 1000 mΩ max.

S VDC XX.XX J1-f J1-B actuate K3-UP record for A&S monitoring M VDC XXXX pull-in voltage K3-UP record for A&S monitoring

K4 M mΩ XXXX J2-A J2-Y multiple contacts 1500 mΩ max.

M mΩ XXXX J2-B J2-Y multiple contacts 1500 mΩ max.

K5 M mΩ XXXX J2-V J2-X multiple contacts 1500 mΩ max.

M mΩ XXXX J2-W J2-X multiple contacts 1500 mΩ max.

K4, K5 S VDC XX.XX J1-f J1-B actuate K3-UP S VDC XX.XX J1-i J1-D actuate K4 M VDC XX.XX pull-in voltage K4 record for A&S monitoring S VDC XX.XX J1-N J1-D actuate K5 M VDC XX.XX pull-in voltage K5 record for A&S monitoring M mΩ XXXX J2-Y J2-X multiple contacts 1000 mΩ max.

M VDC XX.XX drop-out voltage K4 record for A&S monitoring M VDC XX.XX drop-out voltage K5 record for A&S monitoring

Table 5. Relay Functions that can be Tested Through the External WAD Connectors

Relay Identifier

Stimulus (S)

Measure (M)

Units Data Format

Actuate Relay Across Pins Closed

Contacts Across Pins

Stimulus or Measurement

Measurement Limits + -

K6 S VDC XX.XX J1-R J1-D actuate K6 M VDC XX.XX pull-in voltage K6 record for A&S monitoring

M mΩ XXXX J1-Y J1-Z contact+EMI resistance 1000 mΩ max.

M VDC XX.XX drop-out voltage K6 record for A&S monitoring K7 S VDC XX.XX J1-G J1-D actuate K7

M VDC XX.XX pull-in voltage K7 record for A&S monitoring M mΩ XXXX J2-N J2-J contact resistance 1000 mΩ max.

M mΩ XXXX J2-P J2-m contact resistance 1000 mΩ max.

M VDC XX.XX drop-out voltage K7 record for A&S monitoring

K8 S VDC XX.XX J1-J J1-D actuate K8 M VDC XX.XX pull-in voltage K8 record for A&S monitoring M mΩ XXXX J2-M J2-J contact resistance 1000 mΩ max.

M mΩ XXXX J2-L J2-m contact resistance 1000 mΩ max.

M VDC XX.XX drop-out voltage K8 record for A&S monitoring

K9 S VDC XX.XX J1-g J1-D actuate K9 M VDC XX.XX pull-in voltage K9 record for A&S monitoring M VDC XX.XX drop-out voltage K9 record for A&S monitoring

Table 5. Relay Functions that can be Tested Through the External WAD Connectors (Contd)

3.2.1.4 Rotary Switch Tests

The closed contact resistance measurement can be used to characterize aging effects associated with wear and oxidation (resulting from copper diffusion through the gold plating) of the switch contacts. In addition, gross failure of the electrical connections through the external connector, flex circuit, circuit board, and internal soldered connections can be detected by means of measurements at the electrical connections to the WAD.

The following table identifies the rotary switch functions that can be tested through the external WAD connectors. It will be necessary to reference the electrical schematic drawing 82075 to aid interpretation of the table. It is important to note that the switch contacts through which the motor current conducts are not included in the table because they cannot be isolated through the external connectors. When a switch contact is closed, the measured resistance should be near zero. A high accuracy ohmmeter with a 4-wire test lead (to eliminate effects of the test lead) should be used to make this measurement, since the measured resistance will be very low. Limits will need to be established for the acceptable resistance of the contact and associated connections. Initially, a 1.0 ohm (1000 m) value can be assumed as an acceptable limit, until sufficient A&S data has been collected to establish more precise limits. (The specification states that the D1 and D2 outputs, which are switched through contacts “u” and “t”, shall have a resistance of less than 200 milliohms.)

The rotary switch has two positions (SAFE/ARM). Assuming that the A&S WADs samples will normally be acquired in the SAFE state, it is important that all SAFE position contact resistance measurements be done first, since motion of the rotary switch provides some cleaning of the contacts. All other contact resistance measurements must be made with the switch in the ARM position. The following procedure can be used to drive the motor:

Apply motor power (24-32 VDC) across pins J1-k and J1-Y

Actuate relay K6 (nominal 28 VDC) across pins J1-R and J1-D

After the rotary switch has been driven to the desired position, motor power should be removed while measuring the switch contact resistance. Power to relay K6 must be left on so that resistance measurements through the K6 relay can be made.

Switch Contact Identifier

Stimulus (S)

Measure (M)

Units Data Format

Switch Position

Closed Contacts

Across Pins Measurement Measurement

Limits s M mΩ XXXX SAFE J1-h J1-j contact resistance 1000 mΩ max.

R M mΩ XXXX SAFE J2-K J2-F 2 contacts + EMI 1000 mΩ max.

A,B M mΩ XXXX SAFE J2-A J2-Y 2 contacts 1000 mΩ max.

C,D M mΩ XXXX SAFE J2-B J2-Y 2 contacts 1000 mΩ max E,F M mΩ XXXX SAFE J2-V J2-X 2 contacts 1000 mΩ max G,H M mΩ XXXX SAFE J2-W J2-X 2 contacts 1000 mΩ max u M mΩ XXXX ARM J1-S J2-c contact resistance 1000 mΩ max.

t M mΩ XXXX ARM J1-P J2-d contact resistance 1000 mΩ max.

I M mΩ XXXX ARM J1-k J2-J contact resistance 1000 mΩ max.

J M mΩ XXXX ARM J1-k J2-m contact resistance 1000 mΩ max.

R M mΩ XXXX ARM J2-K J3-F contact resistance 1000 mΩ max.

Table 6. Rotary Switch Functions that can be Tested Through External WAD Connectors

3.2.1.5 Motor Tests

Tests can be performed to measure motor current and response time for the changing the rotary switch position. Criteria for acceptable performance will need to be established as part of the A&S program. This test can indicate problems associated with the motor drive circuit (brush wear, improper brush contact, brush holder damage, brush debris in commutator slots) as well as problems associated with motor torque (winding damage, armature thrust face fretting, ball bearing contamination, gear wear, clutch slipping, friction in the rotary switch deck).

The following procedure can be used to drive the motor:

Apply motor power (24-32 VDC) across pins J1-k and J1-Y

Actuate relay K6 (nominal 28 VDC) across pins J1-R and J1-D

The test consists of turning on the motor and then measuring the time required to switch from SAFE to ARM, and then from ARM to SAFE. Switch “u” is convenient for use to detect when ARM position is reached (pins J1-S and J2-c). Switch “R” is convenient for use to detect when the SAFE position is reached (pins J2-F and J2-K).

As the motor is operating, the motor current profile should be recorded using a digital storage oscilloscope or data acquisition system. The motor current will vary as the starting torque is overcome, particularly because of the series windings. For A&S analysis, it may be sufficient to determine peak current and final running current;

however, it is recommended that the complete current profile during the moves be recorded and archived for A&S purposes. The safing circuit requirement (current to drive the motor to the SAFE position using pin J1-V referenced to pin J1-X) is specified to be no more than 2.4 amperes for 1.66 seconds maximum.

3.2.1.6 Wet Tantalum Leakage Current

It is possible to characterize the combined leakage currents of the four 100 F wet tantalum capacitors C1, C2, C3, C4 by measuring the current draw of the impact sensor signal conditioning circuit. Instead of having an impact sensor connected across pins J3- B and J3-D, a shorting circuit can be used which will allow measurement of the current through this path. This impact sensor current can thus be subtracted from the overall current consumption of the circuit. The current draw of the circuit can then be primarily attributed to capacitor leakage current across the four capacitors, since the transistors are biased “off.”

In addition, wet tantalum capacitors C10 and C12 in the EMI Filter can be tested for leakage current (combined) using external pins J1-k and J1-Y, by applying 32 VDC and measuring the combined leakage current.

3.2.1.7 Housing Seal Integrity Test

The integrity of the housing seal can be checked by means of a helium leak test. A pressure decay leak test could also be considered as an alternative approach. Either test can indicate embrittlement or compression set of O-ring seals, or identify gross failure (cracks) in the housing components.

The WAD specification (232-30050) includes purging of the WAD (prior to sealing) with a mixture of nitrogen and helium, of which 4.75% to 5.25% shall be helium. The helium is used as a tracer gas that can be detected with standard leak detection equipment. The WAD specification notes a maximum leakage rate of 1 x 10-6 standard atmosphere cubic centimeters per second. This test is applicable only if the WAD housing is evacuated and re-charged, i.e., the test cannot detect whether helium has already leaked from a used WAD. However, it is useful for A&S purposes to develop a test method that will capture the gases in the housing and analyze them for helium concentration in order to characterize leakage over the life of the WAD. The depot leak test procedure is provided in TO 11N-C5036-3, where the procedure and limits are described in detail.

3.2.2 Test Methods Requiring Removal of WAD Cover

The following test methods will require that the WAD housing cover be removed. This is not considered to be “destructive” to the WAD, but it will be necessary to replace the O-ring seals before putting the WAD back into service. Also, the purge and leak test procedures will need to be performed after the seals and cover are replaced to prevent moisture from being trapped in the housing (e.g., by purging with a dry, inert gas before sealing). Other touch up procedures may be required in accordance with the existing depot repair procedures.

3.2.2.1 Visual Inspection, Cover Removed

With the WAD cover removed, the internal components should be inspected for the following types of aging and damage:

Corrosion: Inspect all visible surfaces of the aluminum and steel components for evidence of corrosion (including the inside surface of the cover). Also, inspect the accessible circuit board solder joints. Discoloration or the presence of surface deposits may indicate corrosion. If corrosion is suspected, it may be possible to examine the area in more detail with the aid of a microscope (approximately 30X). Any evidence of corrosion should be photographed for documentation purposes.

Moisture: Inspect all visible surfaces for moisture or evidence of possible moisture (e.g., mineral deposits, discoloration) inside the WAD. In particular, examine the area around the observation window and the mechanical safing mechanism, and along the O-ring seal in the cover. Any evidence of possible moisture ingress should be photographed for documentation purposes, and this area should be noted for future inspection of corrosion on all WAD’s.

O-ring Seal: Inspect the cover O-ring for hardening, cracking, compression set, or installation damage. Any cracks should be photographed for documentation purposes.

If O-ring cracking is noted, the WAD is susceptible to corrosion resulting from moisture ingress.

Circuit Board: Inspect the accessible surfaces of the circuit board and components for any evidence of aging-related deterioration. In particular, note the condition of the conformal coating on the circuit board and any evidence of degradation (e.g., cracking, peeling, cloudiness). Also examine wiring to solder post terminals for chaffing or strand breaks.