testing methods and techniques: testing electrical

NASA SP-5943(OI)

*

TESTING METHODS AND TECHNIQUES:

TESTING ELECTRICALAND ELECTRONIC DEVICES

A COMPILATION

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

https://ntrs.nasa.gov/search.jsp?R=19720011865 2018-02-15T20:21:16+00:00Z

ForewordThe National Aeronautics and Space Administration and the Atomic Energy

Commission have established a Technology Utilization Program for the rapiddissemination of information on technological developments which have potentialut i l i ty outside the aerospace and nuclear communities. By encouraging multipleapplication of the results of its research and development, NASA and AECearn for the public an increased return on the public investment in aerospaceand nuclear R&D programs.

The methods, techniques, and devices presented in this compilation areused in testing various electrical and electronic apparatus. The items describedrange from semiconductor package leak detectors to automatic circuit analyzersand antenna simulators for system checkout. In many cases, the approachespresented can result in considerable cost savings, together with improved qualitycontrol.

The compilation is presented in three sections. The first describes the testingof various electronic components, assemblies, and systems; the second treats thetesting of various electrical devices; and the third deals with the testing ofcables and connectors. This compilation is not intended as a complete surveyof the field of electrical and electronic equipment testing. Rather, it presents asampling of many diverse activities for the interest of electrical, electronic, andquality control designers and engineers. Its diversity of content may even lendthis compilation some interest as an introduction to the field, for those unfami l i a rwith the principals and practices of electrical and electronic equipment testing.

Additional technical informat ion on individual devices and techniques canbe requested by circling the appropriate number on the Reader Service Card en-closed in this compilation.

Unless otherwise stated, neither NASA nor AEC contemplate patent actionon the technology described.

We appreciate comment by readers and welcome hearing about the relevanceand uti l i ty of the information in this compilation.

Technology Utilization Of/iceNational Aeronautics and Space Administration

NOTICE • This document was prepared under the sponsorship of the National Aeronautics and SpaceAdministrat ion. Neither the United States Government nor any person acting on behalf of the UnitedStates Government assumes any liability resulting from the use of the information contained in thisdocument, or warrants that such use will be free from privately owned rights.

For sale by the National Technical Information Service, Springfield, Virginia 22151 — Price $1.00

ContentsSECTION!. Testing Electronic Components, Assemblies and Systems Page

Testing Semiconductors Without Disconnecting Themfrom Circuit 1

Semiautomatic Device Tests Componentswith Biaxial Leads 1

Test and Inspection Techniques for MonolithicCircuit Production 2

Component Package Leak Detection 2Heating Stage for Scanning Electron Microscope 3Powdered Styrofoam Substitutes for Potting Material'in Vibration Testing 4

Tooling Compound Used to Encapsulate SmallComponents for Testing 4

Vibration Test Detects Intermittent ElectricalFaults 5

Inspection of Potted Cordwood Modules 5Monopulse-Antenna Simulator 5Cold-Testing Printed Circuit Boards 6Preliminary Isolation Test Protects Low-VoltageCircuits 6

Modified PCB Extender Is Troubleshooting Aid 7Module-Carrier Design Gives Easy Access

with Minimum Wear 7Ventilated Test Enclosure 8Noise-Testing Device Facilitates Data Acquisition

System Calibration 8Testing Power Supply Recovery Time . 9Automatic Telemetry Checkout System ; . . . 9

SECTION 2. Testing Electrical DevicesIdentification of Thermocouple Materials 10Thermocouple Resistance Measured Without

Disconnection from System 10Measuring Battery Charge Leakage 11Measuring Set/Release Pressure and Travel

of a Circuit Breaker 12Torque Meter Aids Study of Hysteresis-Motor Rings 12Recommended Operating Torques for Rotary Controls 13DC Motor Commutating Brushes Tested in Dry ArgonAtmosphere 14

Microphone Calibration at High Sound Pressures 14

SECTIONS. Testing Cables and Connectors page

Moire Pattern Used to Check Flat ConductorCable Spacing 15

Experimental Prediction of Superconducting-CablePerformance 15

Measuring Insulation Mechanical Failure Rates 16Cable Insulation Resistance Tester 16Tester Automatically Checks Insulation

in Multiconductor Cables 17Shielded Cable Tester 17Grid-Plate Adapter for Wire Tester 18Measuring Tensile Loads Induced in Connector Pins

by Cable Bending 18Measuring the Connect/Disconnect Forces ofan Electrical Connector 19

Measuring RF Leakage from Coaxial Connectors 20Fuse-Holder Adapter for Ammeter Probe 21Measuring the Length of Electrical Connector Pins 21Quick-Connect Device for Monitoring Signalon Barrier-Type Terminal Strips 22

Test Device Prevents Weld-Joint Damage on UnpottedModules 22

Section 1. Testing Electronic Components,Assemblies and Systems

TESTING SEMICONDUCTORS WITHOUT DISCONNECTING THEMFROM CIRCUIT

S1

ojooo

o0ooo

TransistorUnderTest S~,'

-4 L

PNP

Oscilloscope

: Horizontal

PNPTransistor

NPN NonlinearTransistor Transistor

GoodDiode

DiodeReversedIn Tester

OpenCircuit

ShortCircuit

An oscilloscope, together with the test cir-cuitry shown in the figure, can be used to check(Semiconductors that are wired into a circuit.For transistors, approximate gain and linearitycan be determined; for diodes, open circuits,short circuits, and reversed polarity are indicatedclearly. The quality and breakdown point oflow-voltage (<10 V) zener diodes can be meas-ured.

The idealized oscilloscope traces show the typesof waveforms to be expected under various cir-cumstances, provided that the impedance of theexternal circuit is much greater than that of

the component under test. If -this is not so,the waveforms obtained will vary, dependingon the external circuit properties. In either case,when an assembly to be tested contains mult ipleidentical circuits, the tester may be employedcomparatively to identify a defective component.

Source: B. C. Allen ofNorth American Rockwell Corp.

under contract toMarshall Space Flight Center

(MFS-1163)

Circle I on Reader Service Card.

SEMIAUTOMATIC DEVICE TESTS COMPONENTSWITH BIAXIAL LEADS

The device shown in the il lustration is usedfor enviromental testing of electronic componentsequipped with biaxial leads. The components tobe tested are loaded in a slotted clip. A remotely

operated wheel with two notches diametricallyopposed on its perimeter feeds the componentsone at a time into the load station. The loadstation consists of four spring-loaded clips

TESTING METHODS AND TECHNIQUES.

mounted on two dual-sided, copper-clad revolvingdisks. These clips close on the component leadswhen the disks are rotated clockwise to the meas-uring station position. The co'mponent surfacetemperature is measured by the thermocouple.Electrical connection to the component undertest is made through spring-loaded metal brushesriding on the disks.

After the component is tested, the crankis turned clockwise to the release station, whichopens the clips. The component slides downa ramp to a storage compartment.

• ' Source: T. C. Marshall ofNorth American Rockwell Corp.

under contract toManned Spacecraft Center

(MSC-516)

Circle 2 on Reader Service Card.

Test Components

RemotelyOperated Wheel

LedexSwitch

TEST AND INSPECTION TECHNIQUES FOR MONOLITHICCIRCUIT PRODUCTION

Quality assurance procedures have been devel-oped for the mass production of high reliabilitymonolithic integrated circuits at reasonable cost.Many of the suggested controls may be toostringent for engineering prototype work or forsmall quantity production, but may provide abasis for a homogeneous process'in moderateor mass production quantities.

A report detailing the test and inspection pro-cedures covers the following areas:

Configuration ControlBasic Fundamentals of Quality ControlControl ChartsWafer Process EvaluationProcess Evaluation ~"~

Evaluation Score SystemDiffusion EvaluationWafer ScribingBonding OperationTest Controls

Copies of the report, Test and Inspection forProcess Control of Monolithic Circuits, areavailable.

Source: E. Spangenberg ofWestinghouse Electric Corp.


(MFS-13084)


COMPONENT PACKAGE LEAK DETECTION

A simple, reliable, inexpensive method forgross-leak testing of electronic devices is basedon the conventional fine-leak technique. Themethod can detect leaks as small as 10"7 cchelium per sec. As shown in the diagram, thetester includes a sample chamber connected by

a small orifice to a test chamber, a heliummass spectrometer, and a high-vacuum pump.The test chamber is continuously evacuated, elim-inating the necessity of vacuum cycling for eachtest and greatly simplifying the testing pro-cedure.

TESTING ELECTRONIC COMPONENTS, ASSEMBLIES AND SYSTEMS

In summary, the test consists of the followingsteps:1. The devices, housed in open bottles, are placed

in a pressure vessel, with helium at 515 kN/m'2

(60 psig), for at least 2 hours.2. Immediately after pressurization, the bottles

containing the devices are closed.3. The device to be tested is removed from its

bottle and placed in the sample chamber, whichis then immediately closed with the rubberstopper. A high-vacuum pump continuouslyevacuates the test chamber through the heliummass spectrometer. The orifice at the bottomof the sample chamber limits gas flow so thatthe gas pressure within the test chamber re-mains at approximately 0.01 micron, eventhough the pressure within the sample chamberis atmospheric. Helium gas diffuses out of thedevice into the sample chamber. The result-ing helium and air mixture flows through theorifice into the mass spectrometer, where thehelium leak rate is measured.

4. After gross leak testing is completed, thedevice is removed from the sample chamber,which is then purged with nitrogen gas inreadiness for the next gross-leak test.Fine-leak testing of the device should be

done after gross-leak testing. This may beaccomplished by inserting the device into the test

StopperSample IChamber —L

DeviceOrifice

TestChamber High-Vacuum

Pump

Helium MassSpectrometer

chamber, without using a sample chamber. Themouth of the test chamber is then sealed witha cap and the helium leak test is conducted inthe conventional manner. It is not necessaryto repressurize the device with helium, and onlythose devices that do not show gross leaksshould be subjected to the fine-leak test. Becauseof the testing range of the gross-leak test, itmay be sufficient for many applications.

Source: T. L. AltshulerElectronics Research Center

(ERC-10150)


HEATING STAGE FOR SCANNING ELECTRON MICROSCOPE

A heating stage and holder for use in a scan-,ning electron microscope allows examination of apower transistor at various temperatures. Thiscapability is used in quality control testing tocheck for leaks resulting from different coef-ficients of thermal expansion at the plastic/metalinterface of the transistor package.

A heating coil is attached with silicone rubberto a standard specimen holder and is incorporatedin the scanning electron microscope stage, asshown in the sketch. The power transistor isalso attached with silicone rubber to the heat-ing'stage, together'withianembeddedithermocouplethat contacts the bottom of the specimen. Aground wire is connected to the transistor leads

_... „ .. .Power TransistorSHiconeRubber|Specimen

Ground Wire

Shielded ThermocoupleLeads

SpecimenHolder

IncidentElectronBeam

ReflectedElectronBeam

.ThermocoupleJunction

JSS_Ceramic Cementtawr Jacket

PorcelainHeaterCore

HeaterWindings

TESTING METHODS AND TECHNIQUES

to avoid accumulation of charge from the elec-tron beam.

Specimen, heating stage, and holder areplaced in the scanning electron microscope,and a direct current voltage is applied across theheating coil. The power transistor temperature ismonitored with a thermocouple bridge, and thevoltage is adjusted to maintain the requiredtemperature.

Source: G. Jacobs and B. Slaughter ofSperry Rand Corp.

under contract toGoddard Space Flight Center

(GSC-10963)

No further documentation is available.

POWDERED STYROFOAM SUBSTITUTES FOR POTTING MATERIALIN VIBRATION TESTING

A metal box made to contain an electronicmodule and powdered styrofoam potting materialfacilitates testing (particularly failure-analysisvibration testing) of small components thatare normally potted. Monitor wires are fedthrough slots in the top of the box and connectedto the component, which is placed in the boxon a bed of powdered styrofoam. After thebox is overfilled with powdered foam, the coveris clamped down, compressing the foam andessentially duplicating the potted condition for

the purposes of vibration testing. Removing thecomponent for inspection is easily accom-plished by opening the box and pouring outthe powder.

Source: F.B. Squires ofNorth American Rockwell Corp.


(MSC-15473)


TOOLING COMPOUND USED TO ENCAPSULATE SMALL COMPONENTSFOR TESTING

Another temporary substitute for potting com-pound dur ing the dynamic testing of small elec-tronic assemblies is a standard, commerciallyavailable tooling compound. The compound,which has the desirable properties of low meltingpoint (340 K; 150° F), low density (1.4 g/cc;0.05 lb/in3) , high rigidity, and water solubility,is cast around the assembly to be tested, and thecasting is cut to form a standard sized cube.The casting is poured in layers about 1 cm thick,to prevent the development of internal cavitiesdue to temperature gradients and thermal ex-pansion of the compound.

After machining, the cubic specimen is mountedon the dynamic testing apparatus, using a rubber-

coated compression plate to damp the naturalresonance of the cube. Acceleration, shock, andvibration testing are then performed.

After testing, the specimen is placed in abeaker atop a hot plate, and sufficient com-pound is melted to release the test part. The restof the compound is washed off with water.

Source: K. O. Campbell ofThe Boeing Co.


(MFS-15161)



VIBRATION TEST DETECTS INTERMITTENT ELECTRICAL FAULTS

A novel, nondestructive test method can detectintermittent discontinuities (faulty crimps on elec-trical connections, cold solder joints, loose pin con-tacts, etc.) in electronic cable harnesses and cir-cuits. The circuit under test is ultrasonically vi-brated, and the resultant noise signal due toany intermittent discontinuity is observed on anoscilloscope. This test method employs readilyavailable commercial equipment and is particularlyuseful for detecting faulty electrical connections ininaccessible or hidden portions of electronic;har,-n'ess assemblies and connectors.

Acoustic power is applied across an air gapto the circuit under test. The power is generatedby a 250 W loudspeaker horn positioned about5 cm from the test circuit terminal board. Noise

levels developed in the test specimen are meas-ured across a shielded 100 kfi wire-wound re-sistor and read on an oscilloscope. A directcurrent of 60 MA (maximum) is supplied from a6 V battery to leads clipped to terminal pointson the test specimen.

A permanent record of the test signal tracescan be made by using a logic plug-in unit toprint frame numbers and a frequency plug-inunit with a response to 50 kHz.

Source: D. E. Roberts and S. M. Grieve ofNorth American Rockwell Corp.


(MSC-15158)


INSPECTION OF POTTED CORDWOOD MODULES

X-ray superimposition techniques improve theinspection reliability of potted electronic modules,while greatly reducing the time, effort, and costrequired for the inspection.

The components in small, precision cordwoodmodules are usually interconnected by means ofnumerous small (0.5 x 0.25 mm) rectangularribbons spot welded to the component leads.These ribbons frequently break during potting.Conventionally, potted modules are inspected forsuch defects by X-raying the completed module,projecting the magnified negative, and then visu-ally tracing each ribbon to detect separation.This process is tedious, time-consuming, andcostly.

The inspection is greatly simplified by X-ray-ing the module before potting. An X-ray positive isthen printed from the negative. After potting andcuring, the conventional X-ray is made, and thenegative is overlayed on the previously madepositive. Any physical movement of the ribbons isindicative of a break and will show up im-mediately as a white area on an otherwiseuniformly dark image. This method allowsinspection with nearly 100% reliability.

Source: W. C. Johnson ofNorth American Rockwell, Inc.


(MFS-18090)


MONOPULSE-ANTENNA SIMULATOR

A simple, easily controlled monopulse antennasimulator is used in a shielded environment for theevaluation checkout of various electronic sub-assemblies, corporate feeds, \ monopulse ' sum-and-difference networks, etc., prior to system

checkout on an antenna-pattern range. It canalso be used for system checkout in place ofactual phase-sensing, amplitude-sensing, or hybridantennas. The simulator consists of four types ofcomponents: square hybrids, phase delays, load


terminations, and variable phase shifters. Threeweighting circuits are used; each has one variableparameter (phase shift).

In the simulation of a pure phase-sensing an-tenna, the phase shifts are set to produce equal-amplitude signals. The phases of these signalsare then adjusted according to the interferometricequations. To simulate a pure amplitude-sensingantenna, the phase shifts are set so that the derived

voltage ratios of field strength are obtained atthe output terminals. When used as a hybrid-antenna simulator, the phase shifts are set toprovide the desired amplitudes, and phase ad-justment is used to simulate the phase relation-ships among the received signals.

Source: R. F. Schmidt and A. D. EliaGoddard Space Flight Center

(GSC-522)


COLD-TESTING PRINTED CIRCUIT BOARDS

In cold-environment testing of printed circuitboards (PCB) and board holders, the deviceshown in the illustration prevents the formationof frost on components during the test. Whereprevious methods required the use of a dry boxinstalled over the cold chamber and pressurizedwith dried gas, the new method uses a barrierlayer of freon vapor. The vapor is evaporatedfrom the tank of liquid freon used to cool thepart being tested.

Source: R. E. McNeill and D. A. Cross ofThe Boeing Co.


(MFS-15115)Circle 7 on Reader Service Card.

Connectors & Leads toTest Equipment

Printed Circuit Card

Freon Vapor

Liquid Freon

Sheet Metal Adapter to/Retain Freon Vapors

Cold Chamber

PRELIMINARY ISOLATION TEST PROTECTS LOW-VOLTAGE CIRCUITS

A simple test that supplements the checkout ofelectronic systems with automatic circuit analyzerscan detect inadequate insulation between high andlow voltage circuits. Correction of such a condi-tion before the high voltage circuits are ener-gized can prevent damage to low voltage com-ponents.

Automatic circuit analyzers enable the insula-tion resistance and continuity of the hundreds ofcircuits in complex electronic systems to bechecked quickly. After connection to the system,usually by several test cables, the analyzer firsttests the high voltage insulation. A "short bus"

internally connects all test terminals in theanalyzer. The analyzer's program disconnects thecircuits to be checked from the bus, applies highvoltage (over 100 Vdc) to these circuits, and meas-ures the leakage current on the short bus. Aproblem arises when a defect shorts the highvoltage to a low voltage line. Even the small(3 mA) maximum current from the testercan damage some low voltage components. Suchdamage can be prevented by first performing thenew test.

Since standard circuit analyzers are not ar-ranged to permit disconnecting low voltage


circuits from the short bus as a group, anexternal connection scheme is required. Each ofthe cables that carry low voltage lines is dis-connected from the analyzer, and connectedinstead to a special plug, which is wired toconnect all low voltage lines to one commonlead and all high voltage lines to another lead.These two leads are then connected across a

standard megohmmeter, to check for adequateinsulation resistance between them.

Source: W. Hufeld ofNorth American Rockwell Corp.


(MSC-15669)


MODIFIED PCB EXTENDER IS TROUBLESHOOTING AID

A modified PCB extender provides contactpoints for troubleshooting protectively coatedPCB's without damaging the coating. The modifi-cation consists of two additional connector bars,wired in parallel with the bar into which thePCB is inserted. Brass sockets, sized to accept amale test probe, are then placed in each slot of theadded connectors.

Source: R. L. Durham ofThe Boeing Co.

under contract toKennedy Space Center

(KSC-10285)

No further documentation i.s available.

MODULE-CARRIER DESIGN GIVES EASY ACCESS WITH MINIMUM WEAR

A novel chassis design for an assembly oflogic modules or other microelectronic componentsmounted in a tray provides easy access to the un-

derside of the modules and minimizes the degreeof bending to which electrical cables connectedto the chassis are subjected. The two essential


features of this design are (1) the module as-sembly is not attached directly to the framebut rather to two rotatable carriers, and (2)the connector panel in the rear, also attached tothe rotatable carrier, is inclined at about ?r/4 rad(45°) to the vertical. The mounting of themodule assembly allows it to be tilted into avertical position, providing easy access to theunderside of the assembly for modification ormaintenance. At the same time, the inclinationof the connector panel minimizes flexure andeliminates any possibility of stretching the elec-trical cables.

This design would be most useful when in-corporated into custom test apparatus, proto-type assemblies, and specialized equipment, wherefrequent modifications are expected.

Source: D. F. Smith ofLockheed Electronics Co.


(MSC-13488)


VENTILATED TEST ENCLOSURE

Figure 1

The illustrations show a transparent en-closure useful for testing electronic subassembliesthat are prone to overheat unless adequatelyventilated. The enclosure approximates the en-vironment of the subassemblies when rackmounted for use, including forced ventilationwhich is supplied by the fan mounted on topof the enclosure.

Figure 2

Source: J. E. Edwards and D. W. deCarle ofNorth American Rockwell Corp.


(MFS-16955)


NOISE-TESTING DEVICE FACILITATES DATAACQUISITION SYSTEM CALIBRATION

An automatic testing device measures the noisecontent of analog inputs to a data acquisitionsystem and determines whether the electroniccalibration units (EC) on the data channels areoperating properly. The two checks were pre-

viously accomplished manually, using a digitalto analog converter and a storage-type oscil-loscope. Since anywhere from 50 to 400 indi-vidual channels had to be checked, this methodrequired several operators, was very time con-


suming, and called for a good deal of judgmenton the part of the operators.

The automatic digital noise checker has thefollowing characteristics: (l),Operates on-line usingreal-time data, or off-line using prerecorded checkdata; (2) uses digital data rather than recon-structed analog data; (3) sequences automaticallythrough all system channels; (4) prints out thechannel, noise content, and a representativedata value occurring in a number of noisecheck samples; and (5) prints out the channelcalibration within a predetermined EC range.

The noise checker consists of four digitallogic chassis, a control panel, a printer, and powersupplies. The unit has four operating modes.Modes 1 and 4 provide automatic noise checks,mode 2 provides the EC check, and mode 3provides a multiplexer pattern-sorting capabilityfor the data acquisition system.

Source: J. L. Harrold and C. F. WeegmannLewis Research Center

(LEW-10173)


TESTING POWER SUPPLY RECOVERY TIME

An electronic switching circuit enables meas-uring the full-load recovery time of solid statepower supplies. Because of the high current and

Approx.75H r*

+ 1origger 5

T 1/7 V

^ 1 r-GateSwitch

0 O T5

(.

C

yjV.

Test

— O

Ext.

Switch forOutside 6 VPower Source

O- CInt.

I °J Connection forAlternate Outside6 V Power

short time element (recovery times of 1000 //sor less are not uncommon), this parameter hasnot been easy to 'measure for large ; powersupplies. No mechanical switch combines suffi-cient current handling capability with high enoughspeed.

The illustrated circuit, on the other hand, usesa high-current silicon controlled rectifier, hasswitching times on the order of 1 MS, and canhandle currents up to 35 A. As shown, the cir-cuit is mounted in a small metal box which alsoserves as a heat sink for the rectifier.

Source: G. S. Sosack ofNorth American Rockwell Corp.


(MFS-16371)


AUTOMATIC TELEMETRY CHECKOUT SYSTEM

A telemetry checkout station automaticallyperforms many measurements on a telemetrylink. Its unique features include reaj-time digitiz-ing and computer controlled station setup, dataprocessing, and self-check.

Telemetry checkout was previously performedmanually, but, with the increasing number ofmeasurements that must be made on more

sophisticated equipment, automation became'nec-essary.

Standard telemetry equipment is used to receive,demodulate, and process the various signals.Continuous and time-multiplexed signals fromdiscriminators are automatically digitized andassembled into a predetermined time slot. Eachword of the constructed wavetrain is scaled

10 TESTING METHODS AND TECHNIQUES

and calibrated using stored calibration values.These data are then forwarded to a computerfor evaluation.

The checkout system can be made to performa wide variety of automatic tests by supply-ing the appropriate computer programs.

Source: W. V. George ofThe Boeing Co.


(MFS-12580)

Circle. 11 on Reader Service Card.

Section 2. Testing Electrical DevicesIDENTIFICATION OF THERMOCOUPLE MATERIALS

Materials used in the fabrication of thermo-couple junctions can be positively identified by

Lead made from same materialas probe (ribbon, wire, etc.)

Cold Junction \ Heated Probe

Hot Junctionwhen hot probe tipis contacted withmaterial in question

.Material

Cold JunctionAny number of additionalcold junctions are allowed.

comparison with a standard set of probes madefrom representative thermocouple materials.A probe made of a known material is heated byany convenient means and placed in contact

with the material to be identified, forming a hotthermocouple junction at the probe tip. If theprobe and test materials are the same, no thermo-electric voltage will be measured, regardlessof the temperature of the hot junction. If thetest material is not identical to the probe material,a thermoelectric voltage will be generated, andthis voltage will be a function of the probe-object-junction temperature, the cold-junctiontemperature, and the Seebeck coefficients of thetwo materials.

Source: J. J. Vrolyk and R. F. Nelson ofNorth American Rockwell Corp.


(MFS-18540)


THERMOCOUPLE RESISTANCE MEASURED WITHOUT DISCONNECTIONFROM SYSTEM

To monitor the electrical resistance ofmultiple thermocouple installations without dis-connecting them, a test circuit is connected acrossthe input of the telemetry data system. The con-stant current test circuit shown in the figure con-sists of a battery, a potentiometer, and twoswitches connected across the output of thecommutator. The test circuit output is adjustedso that the voltage across a known resistance,which^is greater than the resistances to be meas-ured, equals the full scale range of the data sys-

tem. Each thermocouple loop is sampled by thecommutator, and the voltage measured acrossthe loop is proportional to the thermocouple re-sistance. A readout is taken first with the batterydisconnected (SI open), to confirm the ab-sence of tare voltages. A readout with SI closedthen directly reflects the thermocouple totalresistance. Placing S2 in the A or B positionprovides a measurement of the resistance of aleg in the thermocouple circuit.

A shorted thermocouple gives a zero or

TESTING ELECTRICAL DEVICES 11

very low reading, depending on where the shortoccurs. An open circuit gives a ful l scalereading on the data system. In many cases, themeasurements give sufficient indication of the

S2

f BITest Circuit « Q

: Disconnect

ThermocoupleJunction

Output

Commutator

LowLevelAmp.

nature and location of the defects to simplifythe repair operation.

Typical resistances in the system used rangedfrom 20 to 400 0. The test circuit was set for0.1 mA, so that the 50 mV range of the systemrepresented 500 Q. fu l l scale.

Though a pulse duration modulation (PDM)system was used in the test case, the techniqueshould be applicable to pulse amplitude modula-tion (PAM) or other modulation systems.

Source: O. Rosenes and W. Altemouse ofRepublic Aviation Corp.

under contract toLangley Research Center

(LA R-182)


MEASURING BATTERY CHARGE LEAKAGE

A technique for safely and accurately deter-mining the leakage resistance in an activatedbattery is shown in the illustration. A low-im-pedance voltmeter is grounded to the battery case

-4—V1

Battery B

and connected alternately to the two batteryterminals. Given the parameters,

R = leakage resistance between one battery celland the battery box

E = open circuit battery output voltage (ter-minal voltage)

r = measuring resistor with a value « Rn = cell number (counting from the negative

terminal)N = total number of battery cells

Vi <= absolute value of the voltage measured be-tween the positive battery terminal and thebattery case

V2 = absolute value of the voltage measured be-tween the negative battery terminal and thecase,

the leakage resistance R, and its position, n, with-in the battery can be computed from the equa-tions:,,

r ER =

Vl + V2and n =

N V2

Vl + V;2

Prior methods for measuring leakage resistanceused microammeters, high-impedance voltmeters,or ohmmeters. Since the high values of leakage re-sistance are accompanied by minute currents andvoltages, the meters used had to be extremelysensitive. Such meters, however, were also highlysusceptible to ambient electromagnetic fields,which could cause incorrect meter readings.

Source: G. Hano and H. G. Solewin ofIBM Corp.


(MFS-14689)



MEASURING SET/RELEASE PRESSURE AND TRAVELOF A CIRCUIT BREAKER

Circuit BreakerUnder Test

\

Support' Bracket Direct Reading

js^Spring Scale

Lathe X-YRotary Head Adjustment &

Locking Bolts

Scale Support Bracket

Base

HandCrank

MeasureReset orReleaseDistance

A test device for measuring circuit breakerplunger travel and actuation pressure uses a direct-reading gage to record the forces necessary to setor release the circuit breaker. The apparatus (seefig.) is assembled in two sections. The first isa standard lathe X-Y rotary head, onto whichthe circuit breaker is mounted via an L-bracket.The other is a direct-reading spring scale mountedon a supporting bracket at the same height asthe circuit breaker's pushbutton. Locking boltsclamp the scale against the pushbutton, and the

Adjusting Slot

hand crank is used to press the button againstthe scale. Actuation pressure is read from thespring scale, and travel distance is read from ascale at the crank.

Source: J. N. Jenkins ofNorth American Rockwell Corp.


(MSC-15630)


TORQUE METER AIDS STUDY OF HYSTERESIS-MOTOR RINGS

The illustrated hysteresis torque meter simulatesthe operation of a high-speed hysteresis motor.This allows the performance characteristics ofcandidate rotor-ring materials to be analyzed,without actually building and testing a hysteresismotor. The meter determines the motor torque,monitors the actual stress in the ring, aidsin the study of asymmetries or defects in rotorrings, and measures rotational hysteresis. In theslowly rotating magnetic field made possiblewith this instrument, the dependence of torqueon the position of the field relative to the ring

can be examined, and the effect of discontinuitiesor directional properties can be measured.

The hysteresis torque meter is based on theprinciple that the torque exerted on the rotorring of a hysteresis motor is very small when itis operating near synchronous speed. Such amotor may be spinning at 25,000 rpm, but theapplied field will be rotating relative to the ringand at only a few rpm out of synchronism. There-fore, the meter simulates motor operation byslowly rotating a magnetic field around a ringheld stationary by an elastic suspension.

TESTING ELECTRICAL DEVICES 13

Perspex Tube

Window-

Magnetic Alloy

1Suspension Wire

Mirror

Oil Damping

HelmholtzMagnetic Coil

Hg Contact Troughs

In the meter shown, a rotor ring is held ina brass clamp. The clamp, hung from a fixedpost on a tungsten wire, has a mirror cemented onthe top. The whole suspension is inside a Perspex

tube, immersed in a damping oil. A pair ofHelmholtz magnetic coils, 11.5 cm in diameter,is capable of generating a field of 6,050 A/m(76 oersteds). Contact to the coils is made throughmercury-filled troughs, and the coil platform isrotated by a belt-drive from a 5 rpm motor.

The rotor ring is held horizontally at the centerof the magnetic field while the Helmholtz coilsrotate at 1 to 10 rpm. The torque exerted onthe specimen is measured by the angular de-flection of a light beam reflected from the mirroron the suspension wire. The light beam is 200 cmlong, giving a deflection of 200 mm for 124 dyne-cm of torque. When the torque measurements atvarious speeds are extrapolated to zero speed, thesynchronous torque of the motor can be measuredand the ring properties can be assessed.

Source: M. Cole ofMetals Research Ltd.


(MFS-12219)


RECOMMENDED OPERATING TORQUES FOR ROTARY CONTROLS

Maximum and min imum operating torquestandards for rotary selector switches and controlknobs have been compiled. Tests were conductedwith various sized hands, both bare and gloved,on recessed rotary selector-bar knobs and onnon-recessed cylindrical knobs, both smooth-sur-faced and knurled.

The recommendations are useful as humanengineering requirements in designing controlpanels where visibility at low sight angles is im-portant.

The results indicate that: (1) maximum torquetransmission capability increases monotonicallywith diameter for controls of any given configura-tion; (2) for recessed bar knobs, torque trans-mission is significantly better for the 4.45 cm(1.75 in.) size than for the 3.81 cm (1.50 in.)

size; (3) for knobs up to about 5 cm (2 in.) indiameter, knurled cylindrical knobs show thehighest torque capability; (4) for larger diameters,recessed bar knobs show the greatest torqueability;(5) the maximum torque exerted on smooth-sur-faced cylindrical knobs is greater for the glovedhand than for the bare hand; (6) the recom-mended operating torque for recessed barknobs is approximately one-half the maximumtorque capability.

Source: J. A. Roebuck, Jr., ofNorth American Rockwell, Inc.


(MSC-90566& 90569)



DC MOTOR COMMUTATING BRUSHES TESTEDIN DRY ARGON ATMOSPHERE

Tests to determine the most suitable materialfor use as commutator brushes for special pur-pose manipulator drive motors were performedby operating the motors in an enclosure con--taining an atmosphere of high-purity argon.A gas-purification system was used to control themoisture and oxygen contents of the enclosure.Brushes were supplied by three vendors onthe basis of their brush-grade recommendationsfor use in dry atmospheres.

The tests resulted in the selection of a brushmaterial that is being used successfully in man-ipulator-drive motors. Similar brushes havealso been installed in other dc motors usedin processing equipment undergoing test in argonatmospheres. The same material has been em-ployed in universal motors used in vacuumcleaners and hand-drill units working in argonatmospheres; here, the material has greatlyincreased the life of motors with high commuta-tor peripheral speeds.

One such vacuum-cleaner motor ran for onlyabout 15 min in a dry argon atmosphere on thebrushes provided with the unit; the brushes hadthen worn completely down and caused short-circuiting of the armature commutator. How-ever, an identical motor with brushes madefrom the new material, has now been in heavy usefor about 1 year in a similar atmosphere. Thenew brushes still wear faster than in normal-humidity atmospheres, but at a reasonable ratethat can be tolerated. Limited tests show promisefor other grades of brushes in low-impurity at-mospheres.

Source: M. A. Slawecki, G. J. Bernstein,and L. F. Coleman

Argonne National Laboratory(ARC-10243)


MICROPHONE CALIBRATION AT HIGH SOUND PRESSURES

A coupling device for accurately calibratingmicrophones at high sound intensities employs aliquid as the coupling medium. Air is not a suit-able medium because of its inherent nonlinearityat high sound intensities. With the liquid couplingdevice, microphones can be calibrated at soundintensities from 110 to 175 dB (referred to apressure of 2 x 10"4 dyne/cm2) in the frequencyrange from 16 Hz to 10 kHz.

The device incorporates a small liquid-filledcavity driven at one end by a cylindrical stackof electrically excited piezoelectric disks and apiston with an effective diameter of 3.8 cm. Thecavity, in the shape of a rectangular prism at oneend and a conical f rustum at the other, has anoverall volume of approximately 19.6 cc. An acvoltage applied across the faces of each disksets the composite piston into mechanical vibra-tion over a displacement amplitude required to

produce the desired sound level. Motion of thesealed piston against a diaphragm tends to com-press the liquid in the cavity, thereby producingrelatively high calibration pressures for smalldisplacements. These pressures vary proportionallyto the displacement of the piston. Needle valvesin the device isolate the flow of liquid to andfrom the cavity and also to and from a pres-sure gage, which is used to set the sound level.The needle valves have a built-in safety adjust-ment which protects the microphones from ex-cessive pressures.

Source: A. Gillen ofGulton Industries, Inc.


(MFS-11980)


TESTING CABLES AND CONNECTORS 15

Section 3. Testing Cables and Connectors

MOIRE PATTERN USED TO CHECK FLAT CONDUCTORCABLE SPACING

The moire tester shown in the drawing canquickly detect small variations in flat conductor

Test Cable

Negative of FlatConductor Cable

Test CablePlacementAdjusters

Light Box

cable (FCC) spacing by comparing the cable tobe tested with the negative of a very precise

standard cable. The standard negative is mountedon top of a box containing a light source anda diffuser plate for uniform illumination. The testcable is aligned in parallel with the standard cablenegative so that the conductors cover the openingsof the standard negative; no light should bevisible. Any imperfection in conductor widthor spacing will form small cracks between thenegative and the test cable lines.

A moire pattern can be formed by placing thetest cable on a slight angle to the standard nega-tive. This pattern consists of alternate light anddark bands, the irregularities in which can beinterpreted to reveal errors in spacing. A cableangle of one degree will amplify the spacingerror 114 times.

Source: W. AngeleMarshall Space Flight Center

(MFS-20426)


EXPERIMENTAL PREDICTION OF SUPERCONDUCTING-CABLEPERFORMANCE

A "broken superconductor" method of short-sample testing can be used to predict the per-formance of well-cooled, stabilized, supercon-ducting cable coils. It yields a field-versus-currentcurve for a short sample of cable with a lengthof superconductor removed from its middle.

The broken-superconductor method of testingpermits separating the performance charac-teristics of the superconductor and copper con-stituents of a stabilized cable. The break in thesuperconductor isjin effect, an artificially inducedsteady-state normal region that forces completetransfer of current into the stabilizing copperin the region of the break. Potential taps

are placed at the ends of a superconductingsection of cable and, as current through the sam-ple is increased, a potential appears across thesetaps. The current observed is the maximumsuperconducting current at a given field.

As current through the sample is increasedfurther, current is shared between the supercon-ductor and the stabilized copper. At sufficientlyhigh current, the heat generated in the copperis greater than that which can be carried awayby nucleate boiling of a helium bath, so thatthe heat-transfer characteristic changes from nu-cleate boiling to film boiling, and the temperaturedifference between the copper and the helium


changes from about 0.3 K to about 5 K.. Thisrise in temperature causes all the current totransfer from the superconductor into the copper,and thermal runaway results. The characteristicsof the copper are obtained by plotting thethermal-runaway point as a function of fieldstrength.

Source: J. R. Purcell and J. M. BrooksArgonne National Laboratory

(ARG-10215)


MEASURING INSULATION MECHANICAL FAILURE RATES

A novel cut-through tester can accurately meas-ure the failure rate of various wire and cableinsulating materials as funct ions of time andcutting pressure. The tester consists of the follow-ing bench mounted components: a counterweightedbeam on which the penetrator is mounted; anelapsed-time indicator; a mercury reservoir con-nected by valved tubing to a receiver that rideson the outboard end of the beam; and associatedelectronics.

During operation, an insulated sample is placedbeneath the penetrator and the valve in the mercuryline is opened. As the mercury flows into thereceiver, the beam pivots, bringing the penetrator

into contact with the insulation under testand starting the timer. When the penetrator cutsthrough, the associated electronic circuitry simul-taneously stops the timer and closes the mercuryvalve. The weight of mercury in the receiver,related to the elapsed time, indicates the resis-tance of the specific tested insulation to sharpobjects.

Source: E. U. Baker ofDouglas Aircraft Co.


(MFS-12506)


CABLE INSULATION RESISTANCE TESTER

A switching uni t can greatly simplify the jobof checking the insulation resistance between in-dividual leads in a multiconductor cable. Thecircuit contains an array of double-throw,spring-return switches, whose movable contactsare wired to individual pins in the cable con-nector, and whose fixed contacts are wired inparallel for connection to a megohmmeter. Intheir normal position, all switches connect thenegative megohmmeter lead to the cable con-ductors. When a switch is operated, the positivemegohmmeter lead is applied to a single cable con-ductor, and the meter registers the total (parallel)

insulation resistance between that conductor andall others in the cable. Use of the switching unitgreatly speeds the job of checking insulation re-sistance, particularly in large cables, and avertspossible damage to the cable connector due toinsertion of meter leads directly into the con-nector.

Source: G. W. Waite ofNorth American Rockwell Corp.

under contract toMarshall Space-Flight Center

(MFS-16951)



TESTER AUTOMATICALLY CHECKS INSULATIONIN MULTICONDUCTOR CABLES

An automatic cable insulation tester can quicklycheck the insulation of each conductor in a mul-tiple-strand cable containing up to 200 con-ductors. The tester consists of two relay matrices,a combination megohm and low-alarm comparator,and associated readout and control systems. Thecomparator contains a regulated power supply withoutputs of 10, 50, and 500 Vdc, a decade set ofprecision resistors, and a transistorized meteramplifier. An optical meter relay performs thefunctions of resistance value readout and alarm.

The tester operates by sequentially measuring theresistance between each pin and all other pins,which are grounded. If the measured resistance

falls below a preset value, the sequence is stoppedby the comparator at the alarm point, a lampin the check switch is lighted, and the pointidentification indicator displays the pin numberin question. When the start switch is depressed,the comparison sequence continues.

Source: M. Vuckovich and J. Shaw ofWestinghouse Astronuclear Laboratory

under contract toSpace Nuclear Systems Office

(NUC-10068)

Circle IS on Reader Service Card.

SHIELDED CABLE TESTER

An ac signal generator and an ac ammeterrapidly verify the wiring of multiconductor,shielded-group cables. The generator is connectedto one conductor and grounded to a shield. Theammeter is connected from ground to anotherconductor, to measure the leakage current. Thiscurrent is caused mainly by capacitive couplingof the two leads and of each lead with theshield. Because the interlead capacitance is sig-nif icant when both are in the same shield group,

and negligible when one lead is outside thegroup, the measured current will be greater whenboth leads are wi th in the same shield.

Source: G. Dibbs and K. E. Priestman ofGeneral Electric Co.

under contract toNASA Headquarters

(HQN-10102)


18 TESTING METHODS AND TECHNIQUES.

GRID PLATE ADAPTER FOR WIRE TESTER

A modification to a standard impluse testerionization chamber used for verifying electricwire insulation lessens degradation of the wireinsulation by using shorter exposure time and alower test voltage.

Standard impulse testers with seven gridplates are designed for use in high-speed wiremanufacturing runs. Under such conditions, thewire is pulled through the ionization chamberwith sufficient tension to maintain concentricity,and with sufficient speed to keep the high voltageexposure time for each length of wire relativelylow.

However, wire is often tested by the userat a much slower speed, with frequent stops formarking and cutting operations. During suchstops, the wire in the insulation chamber isexposed to high voltages for overly long periods.

The modified grid plate chamber shown in thefigure reduces the incidence of insulation failuredue to stoppages during testing and to lossof concentricity between the grid plates andthe wire. First, the large orifice of the standardtester (about 1.25 cm) has been reduced to lessthan 0.5 cm. Second, the number of plates hasbeen reduced from seven to three. Finally, be-cause of the smaller orifice, a lower test voltageis used.

Grid Plates

Impulse TesterIonization Chamber

SouYce: M. A. Vanasse ofNorth American Rockwell Corp.


(MSC-15198)


MEASURING TENSILE LOADS INDUCED IN CONNECTOR PINSBY CABLE BENDING

Another electrical connector test is performedby the illustrated test f ixture, which measures thelongitudinal tensile loads induced in electrical con-nector pins by wire or cable bending. The es-sential parts of the fixture, and their associatedfunctions, are as follows:1. Tensile load sensing elements (strain gages),

mounted between each connector pin and thedevice structure, to measure the induced loadin each pin.

2. A mobile cable loading assembly, attached tothe movable end of the test specimen, to

apply a known constant load along the longi-tudinal axis of the cable.

3. A mandrel, to govern the cable bend radius.4. A cam, around which the mobile loading

element traverses, to bend the cable around themandrel.

5. A connector insert simulator, to accommodatethe required connector pin spacing and pre-vent lateral movement of the pins duringspecimen bending.The cable is mounted in the device with its

longitudinal axis perpendicular to the mandrel


axis and its surface tangent to the mandrel.The wires to which connector pins have beenattached are inserted into the connector insertsimulator, and each pin is then attached to oneend of a strain gage. The other end of the gageis connected to the device structure. A clamp isattached to the free end of the cable and con-nected to the loading assembly by means of apin joint. After a specified axial load is appliedto the specimen, the loading assembly and thefree end of the specimen are moved in an arcaround the cam, thus bending the specimenaround the mandrel. While the specimen is beingbent, forces induced in the strain gages are con-tinuously monitored, and plots of induced tensileload versus degree of bend are made.

Source: F. M. Torre ofNorth American Rockwell Corp.


(MFS-14577)


MEASURING THE CONNECT/DISCONNECT FORCESOF AN ELECTRICAL CONNECTOR

StationaryPortion ofElectricalConnector

Moveable Portionof Electrical Connector

Uniform Force'Balance Ring, with Strain Gages

Low FrictionBall-Bear ingReel

Sliding Assembly withTwo Cylindrical GuidePosts. (Proper LubricationApplied to Lower Coefficientof Friction)

AluminumMounting Body

A test fixture easily and conveniently measuresthe forces needed to mate or separate electricalconnectors, and verifies acceptable maximum

Dead WeightReference Usedfor System Calibration-

and minimum force levels. It may be used inquality assurance programs wherever connectormating forces may be critical.


The fixture shown in the illustration is as-sembled on a rectangular base. It consists of asolid aluminum block, on one end of which ismounted a connector and strain gage supportbracket. On the opposite end, a large diam-eter reel is mounted to a low friction bearingand a reel support stand. A flexible steel cableis joined to the strain gage ring with a standardweight suspended from the reel on the oppositeend. The weight establishes a strain on the gage,which is part of an electrical bridge circuit.Any unbalance in the bridge creates an error

signal which may be recorded and inter-preted as a deflection proportional to weight.Thus, a means is established for recording thedynamic forces applied to the connectors duringengagement and disengagement.

Source: R. D. Clemente ofNorth American Rockwell, Inc.


(MFS-13163)


MEASURING RF LEAKAGE FROM COAXIAL CONNECTORS'

A new technique for quantitatively measuringthe electromagnetic radiation from RF coaxialconnectors is more accurate than the previouslyused coaxial cylinder or untuned cavity techniques.Further, it allows connectors to be tested undervarying environmental conditions. The techniqueconsists of placing the connector in a glassenclosure made from annealed borosilicate glassand sealed at both ends to allow evacuation. (Aspecial enclosure made to contain right angle con-nectors appears in the illustration.) RF power

is supplied to the connector through shieldedcoaxial cables and is monitored by means ofa directional coupler. The actual radiated poweris measured with conventional apparatus.

Source: P. W. Edwards ofNorth American Rockwell Corp.


(MSC-11170)



FUSE-HOLDER ADAPTER FOR AMMETER PROBE

The illustration shows an adapter, made to fitconventional electronic fuse holders, that allowscurrent readings to be made without disconnect-ing wiring and without losing the protection pro-vided by the fuse. The adapter is essentially afuse extender, i.e., a fuse holder equipped withjacks for the insertion of meter leads and fittedwith an insulated connecting rod the same lengthas the fuse.

For use, the fuse is removed from the holderand the adapter inserted. Then the fuse is insertedinto the adapter and the ammeter leads connectedas shown to complete the circuit.

Source: R. L. Riley ofThe Boeing Co.

under contract toKennedy Space Center

(KSC-10187)


Banana JackReceptacle

Spring LoadedPlunger

Twist Lock

Insulating Material

Conducting Rod

Fuse Holder

Ammeter

Banana Jack

VAmmeter Probe

MEASURING THE LENGTH OF ELECTRICAL CONNECTOR PINS

A simple modification to the measuring probeof a micrometer gage allows the length and in-sertion depth of electrical connector pins to be

AnvilRemoved

\

Connect or~^-Body

IndicatingMicrometer

\Press Fit orAdhesive Bond

Typical Connector Pin

Note:Clear Plasticor Soft Brass forGold Plated Pins

accurately measured. As shown in the illustra-tion, the modified instrument has a thin-walled,small-diameter, cylindrical tube attached to the in-strument body in place of the anvil that normallylimits thet gage's travel. The tube's internal diam-eter is someVhat larger than that of a standardconnector pin, while the wall thickness is lessthan the spacing between pins. A small-diameterpin is attached to the micrometer shaft andpassed through the tube. The pin is long enoughthat its end lies at the end of the tube when themicrometer registers zero. The tube may then beplaced over a connector pin and the height ofthe pin above the connector base measured.

Source: A. W. Patterson andD. G. Rohrdanz, Jr., of

North American Rockwell Corp.under contract to

Manned Spacecraft Center(MSC-17068)



QUICK-CONNECT DEVICE FOR MONITORING SIGNALON BARRIER-TYPE TERMINAL STRIPS

The illustration shows a modified barrier-typeterminal-strip to which monitor leads may beeasily attached. Holes are bored in the center ofeach strip midway between the screws, and testleads are terminated with tapered pins. Theseare then press fit into the holes with sufficientforce to hold the test leads securely while meas-urements are made.

Source: R. J. UngerofNorth American Rockwell Corp.

Marshall Space Flight Center(MFS-18349)


Terminal P

Holein Terminal Bar

Recess toAccept Wire

Set Screw

Knurled Surface

TEST DEVICE PREVENTS WELD-JOINT DAMAGEON UNPOTTED MODULES

Gold PlatedSpring Contacts

Module PositioningReaction Plate

A device for testing unpotted electronic moduleswhile preventing weld joint damage makes elec-trical connections to pins on unpotted moduleswithout introducing any axial or displacementforces on the pins. The pins are spaced in a pot-

ting header, but are free to slide in and outexcept for the restraint from welded wire joints.The device consists of a box frame, a carriagewith gold-plated, phosphor-bronze contact springs,a module-positioning reaction plate, a carriage


drive, stops, wiring, and miscellaneous hardware.The carriage holds the contact springs in a

matrix identical to the module pin matrix and thepositioning plate matrix. With the carriage in theretracted position, the springs are completelyclear of the positioning plate holes. The holesare slightly larger than the unpotted modulepins; thus, the pins may enter without force.

Advancing the carriage with the drive screwbrings the springs into contact with the pinsimmediately below the positioning plate, prevent-ing the module pins from moving away. Amechanical stop prevents carriage overtravel and

allows a controlled spring pressure to beexerted on the module pins. The position ofthe contact springs allows testing of unpottedmodules with pins extending only 0.65 cm (0.25in.) or modules with pins up to 2.54 cm (1.0 in.)in length.

Source: R. E. Cree ofGeneral Dynamics/Convair

under contract toLewis Research Center

(LEW-10201)


NASA-Langley, 1972

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testing methods and techniques: testing electrical

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