f~t)4517tff 5

a) ~ ROYAL AIRCGRAFT EOTABLI8I1MfNT

EQUIPM W T9$T H3?TW O N FO R W MR ALLY IPROMf CEfl

by

R, A, flibbo

Joly 1987

DTIC

Pvnqiorament Exocutiva, Ministry of Defen~o

Farnrnntovog, Hoonts

S2 20 07.1

ROYAL AIRCRAFT ESTABLISHMENT

RAE TECHNICAL MEMORANDUM FS(F) 457

ISSUE 2

Received for Printing; 25 June 1987

EQUIPMENT TEST METHODS FOREXTERNALLY PRODUCED ELECTROMAGNETIC TRANSIENTS

by

R.A.Hobbs

SUMMARY

This Memorandum is the re ult of the work at the Royal AircrAftEstablishment in assessingacthe effect of electromagnetic pulseand lightning strike produced transients to aircraft systems. Itdetails suitable tests for the simulation of these effects andshould be used to form the basis of any future aircraft projecttransient specification with suitable tailoring to meet specificrequirements with the for 1' approval of the Project Director.

Copyright

Controller HMSO London1987

This Memorandum expresses the opinions of the author and does notnecessarily represent the offical view of the Royal AircraftEstablishment.

CONTENTS

Section/paragraph Subject Page No.

1. INTRODUCTION I

1.1 NEMP environment I1.2 Transient effects produced by

lightning strikes1.2.1 High frequency transients 21.2.2 Resistive/diffusion flux coupling 21.2.3 Aperture flux coupling 21.2.4 Ground voltage spikes 21.3 Validity of testing at equipment level 2

2. EQUIPMENT LAYOUT FOR NEMP AND LEMP 4TEST METHOD

2.1 Ground plane 42.2 Line impedance stabilisation networks 42.3 Equipment layout and lead lengths 52.4 Bonding of equipment under test 52.5 EUT interface loads and test jigs 62.6 Excitation of equipment under test 62.7 Current probes 62.7.1 Injection probes 62.7.2 Monitoring probes 7

2.8 Oscilloscope and probes 7

3. SUSCEPTIBILITY CRITERIA 8

4. TRANSIENT GENERATORS 84.1 NEMP and HF lightning induced transients 84.2 Ground voltage transient generators 8

5. HEALTH AND SAFETY AT WORK 9

6. TEST METHODS 96.1 EMP and lightning HF transients effects 96.1.1 Selection of transient injection

frequencies 106.1.2 Transient injection testing 106.1.3 Test limits for damped sinusoidal testing 11

6.2 Lightning ground voltage injection 126.2.1 Transient testing 136.2.2 Test limits for ground voltage injection 13

Accession ForN-IS GRA&I

_____DTIC TAB

Unannounced 0Justification

Distribution/

Availability 6odesAvail and/or

Dist Special

A:1

7. ACCEPTANCE TESTING OF EQUIPMENT POST TRIAL 15

8. CONCLUSION 15

9. ACKNOWLEDGEMENT 15

TABLE 1 Test frequencies 16

REFERENCES 17

INDEX TO ILLUSTRATIONS 18

ILLUSTRATIONS Figures 1-13

1. INTRODUCTION

This issue of RAE Technical Memorandum FS(F) 457 replaces theoriginal 1982 version (Ref 1) which should no longer be used.Since the publication of that version there have beenconsiderable improvements to the test methods for the effectsof exo-atmospheric nuclear burst (NEMP) and the similartransients produced as a result of lightning strike (LEMP).This Memorandum covers the testing of avionic systems that areto be installed in aircraft and similar vehicles, includingthose of hybrid metallic/composite construction.

1.1 NEMP Environment

The electromagnetic pulses produced by an endo orexo-atmospheric burst have been well accepted in terms of thedefinition of amplitude, rise and fall times, polarization andimpedance. They are defined in QStag 244 as 'The NATO StandardEMP Pulses'. When an aircraft is subjected to a NEMP there arelarge currents induced in the skin and these will exciteresonances in the aircraft structure and wiring looms. Theaircraft can be thought of as a 'tuned receiver' which couplesstrongly in the HF band but only weakly at other frequencies.Hence for aircraft the exoatmospheric EMP is more severe thanthe endoatmospheric EMP. The current flow in the cable loomswill be of a damped sinusoidal nature. Since the aircraft sizeand loom lengths/impedances are mainly resonant in thefrequency range 2 to 30 MHz and the main energy content of theEMP extends up to this frequency bands the test method describedsimulates these currents.

1.2 Transient Effects produced by lightning strikes

A detailed explanation of the three types of lightning inducedtransient that can affect aircraft avionic equipment togetherwith a review of test methods used by some lightning expertsand the rationale for the tests proposed in this document willbe given in an RAE Technical Memorandum (Ref 2), however thethree types of transient are briefly described below. Designcertification and testing requirements for Group I (direct) andGroup II (indirect) effects of lightning which this Memorandumdoes not address will be found in RAE Technical MemorandumFS(F)632 (Ref 3) which will require equipment tests to be madein accordance with this document.

The tests described apply to items of avionics such as enginecontrol systems etc, but not to the high voltage insulationtesting that is performed on items such as the Pitot tubeheater supply or to aircraft antennas.

1.2.1 High frequency transients

The energy contained in the rapid rate of change of E and Hfields at the instant of lightning current attachment to theaircraft will excite electrical resonances in the structure andwiring looms that will respond in the same way as for NEMPdescribed above. As such, the testing for this effect issimilar to NEMP.

1.2.2 Resistive/diffusion flux coupling

A cable voltage will be produced which is approximatelyproportional to the lightning current, due to resistivecoupling (for example, the voltage gradient on the inside of anaircraft skin), or to inductive coupling where the magneticflux has diffused through a high resistivity skin (such ascarbon-fibre composite) and in doing so has effectivelyundergone an integrating process.

1.2.3 Aperture Flux Coupling

A cable voltage will be produced which is proportional to thederivative (slope) of the lightning current, due to direct(aperture flux) magnetic coupling. The voltage will then beproportional to the maximum rate of rise of the lightningcurrent, taken to be 100 kA/us for a severe stroke.

1.2.4 Ground Voltage Spikes

The resistive/diffusion and aperture flux coupling describedabove will give rise to large current flow in cables andvoltage stresses to filter components etc where equipments arein different parts of the aircraft but connected by wiringlooms. These effects are simulated by tests described in thisMemorandum; the resistive/diffusion coupling by the 1/15Ouswaveform test and aperture flux coupling by the 0.05/2uswaveform test.

Note:For an equipment operating within an airframe of metallicconstruction the effects of aperture flux coupling andresistive diffusion flux coupling may be of less significancecompared with the high frequency transients. This may not bethe case for equipments that are to be installed in aircraftwhere large areas, such as wings, are of compositeconstruction.

1.3 Validity of testing at equipment level

As with EMC test methods it must be realised that the testhouse environment and equipment layout are inevitably not asfound in an aircraft or any other vehicle's actualinstallation. The test methods for equipment level testing aredevised such that as realistic an environmemt as possible iscreated. Divergence from the actual installation willnecessitate simulation of loads or cable types and thus therewill exist the possibility of introducing non-representativefailures/upsets. These aspects should be considered and if

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appropriate discussed in the trial report at the conclusion oftesting. Experience gained in the development of EMC testfeetnods shows that good correlation is normally obtainedbetween failures found by current injection test methods andthose obtained as a function of the on-board environment.

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2. EQUIPMENT LAYOUT FOR NEMP AND LEMP TEST METHOD

The equipment layout for this test method shall be the same asis specified in RAE Technical Memorandum FS(F) 510 (Ref 4),Recommended Test Specification For The ElectromagneticCompatibility of Aircraft Equipment, section 6. This is defineasuch that the equipment under test is operated in asrepresentative manner as possible and that repeatabilitybetween test houses for the testing may be obtained.

2.1 Ground Plane

In order to provide a reference plane, the equipment under test(EUT) shall normally be mounted on a solid-plate metallicground plane having a minimum thickness of 0.25 nm for coppper,U.5 mm for aluminium (non-preferred because of oxidisation) and0.63 mm for brass, with a minimum area of 2.25 m and minimumside of 0.7 m. The ground plane shall be bonded to the screenedroom walls, solid sheet bonds being preferred, the bonds beingnot more than 0.9 m apart. The dc resistance between the groundplane and the walls shall not exceed 2.5 milliohms.

For large equipment mounted in a metal rack or cabinet, themetal rack or cabinet shall be considered a part of the groundplane for testing purposes and shall be bonded to the groundplane by the normal rack or cabinet bonding arrangements.

2.2 Line Impedance Stabilising Networks (LISN)

In order to eliminate possible differences in power supplyimpedance at the different EMC Test Houses, and to provide adefined impedance that is based on typical aircraft bus-barimpedances, a LISN shall be included in all power supply leadsto the EUT.

The circuit diagram of the LISNs shall be as shown in Figure 1,further design details are given in RAE Technical MemorandumFS(F) 613 (Ref 5).

The characteristics for the LISN shall be as shown in Figure 2when loaded with a 50 ohm termination at the measuring setterminal and with the supply or load terminal shorted to thecase.

The measuring set terminal shall be terminated by a 50 ohmlow-reactance load.

A 10 uF feedthrough capacitor shall be connected on the supplyside of the LISN, being bonded to ground.

When used on dc power supplies an additional 30,000 uFcapacitor shall be connected between positive and negative inthe power supply side of the LISN to improve its low frequencyperformance. Figure 3 shows protection circuitry which may benecessary to reduce switch-on surges. For safety reasons ableed resistor (1000 ohms, 1 watt) should be connected acrossthe capacitor.

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2.3 Equipment layout and lead lengths

Figure 4 shows d typical EUT set-up on a ground plane. Aphotograph or detailed sketch of the test layout shall oeincluded in the Test Report.

The EUT's power leads dnd interconnecting cableforms shallwhenever possible be of the length, type and layoutrepresentative of the aircraft, an installation as similar aspossible to that of aircraft should be used. Interconnectingcables shall be supported above the ground plane on 50 niminsulated stand-offs (e.g. Styrofoam). The purpose of this isto simulate the ground loop area of a typical installationwhere wiring runs cannot always be clamped directly to thevehicle structure over the whole of the cable lc.ngth.

When the aircraft cableform length is not known, control andsignal cable lengths shall be 2m :L 0.1m. Primary power linesshall always be Im ± 0.lm.

When the length of an interconnecting cableform is greater than2m, the leads must be deployed in a defined manner. Thecableform shall be arranged as in Figure 4 with the excesslength zig-zagged at the back of the test bench on 50 mmsupports. This method is preferred to that of coiling the cableas coiling could increase the cable inductance by as much asten times for a very long cableform. Some installations requirevery long cable runs and these cannot be accommodated on thetest bench; therefore the maximum length of the interconnectingcableform for these tests shall not exceed 15m. Duplication ofan actual installation cableform shall be considered the idealrepresentation. The lengths of the cableforms must be recordedin the equipment test report.

2.4 Bonding of Equipment Under Test

The provisions included in the design of the EUT and specifiedin the installation instruction shall be used:

(a) to bond the EUT items together, such as equipment case andmount, and/or

(b) to bond the EUT to the ground plane.

When used, bonding jumpers and routing shall be as close aspossible to those specified for the installation including themethod of connection and type of bonding lead.

Equipments intended to be grounded through a third wire shouldbe grounded via that method unless a special installationrequires otherwise. When this method is used the EUT shall beplaced on an insulating mat.

When EUTs are secured to mounting bases having shock orvibration isolators, bonding straps when furnished withmounting bases, shall be connected to the ground plane. Ifbonding straps are not specified none shall be fitted.

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Portable equipment shall not be bonded to the ground planeduring testing unless this is required by the installationspecification. Portable equipment that is grounded through thepower cable shall not be bonded to the ground plane but shallbe mounted on insulating material 50 mm above the groundplane.

When an external terminal lug, stud or connector pin isavailable for a ground connection on the EUT, it shall be usedif normal installation so indicates. When the installation isunknown, the ground terminal or pin shall not be used.

2.5 EUT Interface Loads and Test Jigs

Ideally the transient test should be performed on a completesystem or sub-system.

EUTs interfdcing with other units, which for practical reasonsare not part of the EUT, shall be suitably loaded. The loadsmay be electrical, electronic, and/or mechanical, asapplicable. Electrical/electronic loads should simulate theimpedance of the actual load as far as is practical. Careshould be taken to ensure that any active loads do notcontribute to the susceptibility of the EUT. This may beachieved by filtering the load inputs or outputs,

2.6 Excitation of Equipment Under Test

In addition to the requirements of 2.5 above the followingconsideration shall be made.

An EMC/EMP Test Plan shall be produced by the manufacturerwhich defines the mode(s) of operation of the equipment to beused for the tests and the various criteria for performanceverification. The test plan shall define the standard of theequipment under test together with details of the interface tosupport equipment if appropriate.

When practically possible the EUT shall be exercised by thesame means as in the actual installation. For example, if asolenoid or a relay is switched by a thyristor or similarsemiconductor device do not use a mechanical switch to operatethe solenoid or relay. Voltage and/or current regulators whichfunction intermittently shall be exercised during the test, asdescribed in the EMC Test Plan, to simulate real lifeconditions.

2.7 Current Probes

2.7.1 Injection Probes

The injection probe to be used for the injection of the dampedsinusoidal test waveform shall be as described in RAE TechnicalMemorandum FS(F) 588 (Ref 6), in which design details andperformance requirements are specified.

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2.7.2 Monitoring Probes

The current probes to be used for the measuremen t of theinduced transient must be capable of accurately recording thetransient without saturation either by the primary current flowin the loom under test or when combined with the level ofinjected transient. The transfer characteristic of the probefrom the lower -3dB point to the upper -3dB point over thefrequency range 0.1 to 50 MHz shall nave a uniform flatcharacteristic such that the correct waveshape is recorded. Theprobe winding should be electrostatically shielded and theconnecting instrumentation cables shall be double screened orsuperscreened', or similar in order to prevent signal

breakthrough.

2.8 Oscilloscope and Probes

The oscilloscope shall be such that it records the levels andwaveforms of both fast and slow transients as required Dy thetest limits. The use of a fast digitising oscilloscope orsimilar instrument is recommended.

The oscilloscope shall have a 3dB bandwidtn of dc to at least50 MHz for single shot events with facilities for externaltriggering of the timebase. A suitable means of termination(50 ohm feedtnrough or 50 ohm input impedance) shall beprovided for the current probes where appropriate. A means ofrecording the oscilloscope trace shall be provided such thatrepresentative waveforms may be included in the test report.For the voltage measurements to be made a suitable high voltageprobe or high impedance, high voltage divider will be requiredthat has a frequency response as defined for the oscilloscope.It should be noted that as the duration of the transients isshort the voltage rating of the probe may be higher than the dcrating.

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3. SUSCEPTIBILITY CRITERIA

The Equipment Test Plan shall specify the criteria formalfunction or degradation of performance such that the testengineer may readily determine whether or not the EUT hasfailed during test, Whilst not every possible failure mode canbe predicted none the less the normal operating requirements ofthe EUT should be clearly described. The threshold of.susceptibility is the minimum level of interfering signal atwhich a specified malfunction or degradation takes place andshould be noted.

4. TRANSIENT GENERATORS

4.1 NEMP and HF Lightning induced Transients

The transient generator for this test method shall provide adamped sinusoidal waveform, the resonant frequency of whichshall be tuneable anywhere in the frequency range 2 to 30 MHz.The injection probe shall be an ERA Type 36 or 45. The use ofthe ERA Type 36 probe is preferred where space on the loompermits. The damping of the waveform shall be such that theamplitude of the eighth half cycle shall be at least 25 percent but not more than 75 per cent that of the second halfcycle as shown in Figure 5. The damping of the waveform shallbe verified by injecting Into a calibration jig terminated ateach end in a 50 ohm load resistance. The damping of thewaveform shall comply with the requirements specified above forall transients above 50 volts. The probe calibration Jig shallbe as shown in Figure 6.

It should be noted that the damping is specified when injectinginto an effective loop impedance of 100 ohms. When applying thetransient to a cable loom the damping may vary considerablyfrom the calibration value. This is normal and is a function ofthe response of the loom under test. Additional information onthe design of the pulse generator may be found in RAE TechnicalMemorandum FS(F) 550 (Ref 7)

4.2 Ground Voltage Transient Generators

The pulse generator for this test method shall produce aunipolar pulse of both positive and negative polarities,selectable by the test engineer during the test. The waveformsshall be as shown in Figures 7 and 8 and shall be verified forboth open circuit output and for a load resistance of 1 ohm.The waveform shall be as specified for all transient voltagesabove 50 volts, with a time accuracy of ± 20 per cent.

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***********WARNING *******

S. HEALTH AND SAFETY AT WORK.

IT MUST BE NOTED BY ALL OPERATORS AND TRIALS ENGINEERS THATBOTH THE PULSE GENERATORS DESCRIBED ABOVE CONTAIN AND WILLPRODUCE LETHAL VOLTAGES. IT IS ESSENTIAL THAT GREAT CARE ISEXERCISED IN THE USE OF THESE GENERATORS AND THAT THE NECESSARYSAFETY PROCEDURES ARE USED.

*** * WARNING *

6. TEST METHODS

6.1 ENP and HF Lightning Effects

If cw bulk current injection testing is to be performedaccording to the test methods described in RAE TechnicalMemorandum FS(F)510 this shall be undertaken prior to thetransient test method to be described here. This is in order todetermine if the EUT has any susceptibilities in the frequencyrange 2 to 30 MHz. If any susceptibilities are found they shallbe recorded for use in this test.

Before transients are applied to the cable looms of the EUT itwill be necessary to measure the bulk rf impedance of the loomsover the frequency range 2 to 30 MHz at the entry points to theEUT boxes. These measurements will determine whether there arefrequencies where the cable looms have maximum and minimumimpedances (i.e. maximum voltage and current coupling to thecable). These cable loom resonances could have a significanteffect on the apparent equipment susceptibility and hence needto be determined.

The test has two main sections: (a) the selection of transientinjection frequencies from cable impedance measurements and thecw current injection testing if it has been performed. (b) thetransient injection testing and monitoring the EUT forsusceptibility. For both of these tests it will be necessary tomeasure the induced cable current and the induced cable loopvoltage. The current induced in the cable shall be measured bya suitable current probe as defined in section 2.7.2. A smallsingle turn monitor loop is fitted around the injection probefor monitoring the voltage. This shall be connected to themeasuring instrument such that the load impedance on the outputof this loop is not greater than 20 pF or less than 4000 ohms,thus ensuring that the coil Is neither loaded nor hasresonances induced. Figure 9 shows such a loop.

For primary power lines the test shall be made at the EUTconnector end of the cable. For other cables the test shall beapplied at each end of the cable where the cable under test islinking two or more EUT boxes. A spacing of 50 mm shall bemaintained between the EUT connector shell or any extension of

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that shell and the faces of the current monitoring probe and

the injection probe. This is shown in Figure 10.

6.1.1 Selection of transient Injection Frequencies

To measure the cable loom impedance, low level swept cw signalsshall be injected into the interconnecting cableforms orpowerlines under test over the frequency range 2 to 30 MHz,using the ERA 45 injection probe. The ratio of the injectedcable voltage to injected cable current is a measure of themodulus of the cable's bulk rf impedance.

Prior to the measurement of the loom impedance the measurementsystem shall be calibrated such that any aberrations in thesystem may be removed. This is performed by the use of thesetup shown in Figure 11. The use of a network analyser orsimilar is required. Approximately 1mW of power is applied toan ERA45 probe sweeping the frequency range 2 to 30 MHz. Ashort turn of wire is placed around the probe as shown suchthat the induced driving voltage around the loop may bemeasured. The use of a loop as defined in section 6.1 above isadvised. The ERA45 probe is placed on a short loop of wire thatis terminated in a known value of resistance, typically 100ohms. The resulting induced current in this loop is monitoredwith a measurement probe as defined in section 2.7.2 above. Thenetwork analyser is set to display the voltage divided bycurrent against frequency hence impedance is obtained. Thedisplay should at this stage have no major aberrations.Normalisation may be used to obtain a flat amplitude responseat this stage. The terminating resistor may be changed to adifferent value, that is for example 20dB higher and then 20dBlower, in order to demonstrate that the measurement system isfunctioning correctly.

The measurement system is now ready to measure the bulk rfimpedance of the interconnecting cable looms. If thenormalisation has been applied then the resonances that may bepresent in the impedance of the loom will have the correctrelative amplitudes. The test set up for these measurements isshown in Figure 10. A plot of the cable loom impedance shall beincluded in the test report.

6.1.2 Transient Injection Testing

Having measured the cable loom impedances the transientinjection shall take place. Transients shall be injected at thefrequencies listed in the following three sections:-

(a) The most susceptible frequencies in the range 2 to 30 MHzfound from the cw bulk current injection test (assuming thatthis test hds been performed and that any susceptibilities werefound).

(b) The frequencies at which maxima and minima cableimpedances occurred (found from the method of section, 6.1.1).

(c) Over the frequency range 2 to 30 MHz inclusive not lessthan 50 frequencies such that any resonances in the EUT

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internal circuitry are excited so subjecting any active orpassive devices to maximum voltage or current threat. Thesefrequencies shall be spaced evenly with a logarithmicincrement. The frequency of each injection is obtained by theuse of the following equation:

Test frequency (MHz) = 10 r (0.301 + 0.024 * K)

for K = 0,1,2,3 to 49 for 50 increments.

NB. There are 50 test frequencies. Table 1 gives thefrequencies obtained with this formula for 50 increments

The requirement is for a minimum of 50 frequencies and theselection of individual frequencies as definc-i above is suchthat an even distribution is obtained. Ootaining exactfrequencies is not critical, it is more important that thefrequency range be covered adequately. It may be found that thetuning arrangement on the pulse generator used, will lenditself to a higher number of injection frequencies with greaterease of use, this is acceptable.

The transients shall be injected using the test configurationshown in Figure 12. The frequency of the generator shall befinely tuned for (a) above. The frequency shall also be finelytuned for (b) above such that maximum induced voltage for highimpedance or maximum induced current for low impedance isproduced. It should be noted that the resonant frequency of thedamped sinusoid varies slightly during the transient as aresult of coupling effects with loom resonances. The frequencymeasurement should thus be obtained from an average overseveral zero crossings of the waveform.

6.1.3 Test Limits for Damped Sinusoidal Testing

The EUT shall not exhibit any malfunction, degradation ofperformance, damage or deviation from the equipment'sindividual specification when subjected to pulses up to andincluding the following test limits and conditions. Thetransient induced cable current shall be measured with thecurrent probe and the transient voltage shall be measured bymeans of the loop around the injection probe.

At least 5 transients shall be injected at each frequency andat maximum amplitude as defined below whilst the EUT ismonitored for degradation or malfunction. The time intervalbetween transients shall be a minimum of 2 seconds in order toensure that the generator gives the required output for eachpulse. It should be noted that with digital systems if theEMP/lightning pulse coincides with clocking pulses or otherdata transfer actions data corruption couldoccur. It may benecessary to inject more pulses in order to achieve confidenceof required error rates. This latter situation should beidentified in the test plan. If a susceptibility occurs thetransient level shall be reduced to obtain the threshold ofmalfunction. The test report shall contain details of theinduced transient current and probe loop voltage in addition tothe frequencies selected for test. The loom current at each

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frequency is to be recorded graphically together with daindication of where failure has occurred during this test.

Suggested levels for the naximum induced current, the maximuriprobe ioop vol tage and the maximum vol t-amp product of thecurrent and voltage are:

20 amperes peak current2000 volts peak voltage10 kilo volt-amperes.

The test limit will have been reached when any one of the abovecriteria has been met. For low impedance cables the currentlimit will usually be reached first, for high impedance cablesthe voltage limit will be reached first and for others thevolt-amp product. The volt-amp product is tridt obtained bytaking the product of the maximum induced current value andthe maximum probe voltage taking no account of the relativetime at which the maxima occur or of their sign. Using thisapproach gives a reasonably simple method of ensuring that thetest takes account of variations of cable impedance and hencereduces the possibility of an overtest.

The above test limits are based upon the estimated currentinduced into equipment cables in the fuselage of an attack typemilitary aircraft. For any project application, test levelsshould be the subject of an assessment taking account of theaircraft size, fuselage screening and degree of overtestrequired to meet hardness assurance requirements. The valuesgiven above should only be used as guidelines.

6.2 Lightning Ground Voltage Injection

For this test method the effects of variations in the "groundpotential" of the grounding point of the EUT during a lightningstrike are assessed. Where equipments are mounted within 0.5 inof each other with ground bonding within 0.5 m to the same partof the aircraft structure then such equipments shall be treatedas one for this test. If the equipments are close together butwith connections or bonds to different parts of the structure,such as equipments mounted on an engine casing connecting withan equipment mounted within the engine nacelle, then suchequipments shall be treated as separate devices.

It is necessary to insulate the case of the EUT from the groundplane with an insulation material capable of withstanding 1600volts. Any ground bonding straps to the EUT shall be removedtogether with any connections to ground as described above.

A connection between the output of the pulse generator and theEUT case bonding location, or if this is not provided then asuitably cleaned attachment point, shall be made. Anyelectrical wiring as described above shall also be connected tothe pulse generator output. Figure 13 shows a typical testarrangement. These connections shall be both short and of aslow an impedance as possible.

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The pulse generator shall be earthed to the gruund pl1ne oitn ashort, low inductance bonding strap, the impedance to groundbeing less than 10 milliohms at dc.

The output voltage and current of the pulse generator shall bemeasured with a storage oscilloscope with the input terminatedby a suitable 50 ohm feedthrough. The pulse generator describedin RAE Technical Memorandum FS(F)550 incorporates outputs forboth current and voltage measurements by an oscilloscope with a50 ohm input impedance.

6.2.1 Transient Testing

The EUT shall be set up as detailed in sections 2 and 6.2 thenoperated in accordance with the Test Plan. Two test waveformsare to be applied, the first has a rise time of approximately2us and fall time of 150us, whilst the second has a 5Ons risetime and 2us fall time. At least 1U transients of each typeshall be applied at the amplitudes listed in section 6.2.2within a period of one minute. The ainplitude should beincreased gradually to these levels whilst the EUT is monitoredfor malfunction or degradation.

6.2.2 Test Limits For Ground Voltage Injection

The test limit will be deemed to have been met when either thevoltage or the current limits tabled below have been reached.If a degradation in performance or malfunction occurs then theoutput level of the pulse generator shall be adjusted todetermine the threshold of malfunction. The current and voltagelevels at the threshold of malfunction shall be recorded. Thetest report shall record the currents and voltages whether ornot a susceptibilty occurs, if a susceptibility has occurredthen the nature of that shall also be recorded.

The levels of voltage and current to be applied are based onthose levels recommended in the SAE AE4L committee report: TestWaveforms and Techniques for Assessing the Effects ofLightning-Induced Transients dated 15th December 1981. Thelevel to be applied is based on the type of equipment andposition within the aircraft. To be consistent with the SAEdocument the same level classifications are used. These are:

Level 1. Not considered appropriate for militaryequipments.

Level 2. Intended for equipment which will be installed inenvironments where lightning induced transients would becontrolled to a level which is consistent with thatrepresented by FS(F)510 or DEF STAN 59-41 or similarstandards. This level is considered to be consistent withgood engineering practice for such equipment and should havea relatively minor impact on the associated designpractices.

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Level 3. Is representative of the more intense transientswhich may be experienced during norm:ial operations.

Level 4. Is representative of severe transients ,ahich nayappear on power lines. The power associated with this levelis relatively severe and its impact on equipment designpractices will probably be significdnt.

Level 5. This is an upper limit on transients to whichsubsystem equipment should be exposed. Transients whichlightning could induce in long and/or exposed wiring shouldbe controlled to be consistent with this test level. Thepower level associated with this level represents a severethreat to most electronic circuits and the impact onequipment design will be significant. The voltage levelswill in addition stress insulation material, of items suchas connectors and transformers.

These levels have the following voltage and current limits:

Level Voltage Limit Current Limit

Volts Amperes

2 125 25

3 300 6u

4 750 150

5 1600 320

The Equipment Test Plan shall indicate which of the test levelsshall apply to each EUT, or indeed another level which is seenas realistically representing the stress to an equipment in aparticular application. Both polarities of pulse shall beapplied to the appropriate limit as specified above.

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7. ACCEPTANCE TESTING OF EQUIPMENT POST TRIAL

The transients described in this Memorandum may have damagingeffects on the EUT which nay not preclude apparently normalfunctioning of the EUT. Such effects may be the destruction offilter components etc. In order to verify that this has notoccurred a full acceptance test of the EUT shall be made at theend of the trials. Details of any such damage must be includedin the Test Report.

8. CONCLUSION

The test methods described in this Memorand,11 are based onextensive application at the Royal Aircraft EstDlishment andhave been modified to make them more easily used. The pulsegenerators to perform the tests are avai - able and alsodescribed in the documents referenced.

It is emphasised that the test levels given are for guidanceonly and the levels to be used need to be defined for aparticular project and application.

The test methods and limits may well be changed in the futureto reflect better knowledge of the problems and changes inequipment designs. It is intended to produce modified testdocuments in the future as further issues of this Memorandum.

Whilst the test levels may at first seem high, they have beenused on avionic equipments. In general if adequate EMChardening has been applied equipments should pass the EMP testwith little or no modification.

9. ACKNOWLEDGEMENTS

The author is grateful for the help and guidance of Dr J.Bishop, Supt. of FS(F)5 Division, in the development of the EMPtest method in this Memorandum.

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TABLE 1. TEST FREQUENCIES GIVEN BY EQUATION 6.1.2(c)

Test number 11Hz Test number MHHz

1 2.0 26 8.02 2.1 27 8.33 2.2 28 8.84 2.4 29 9.35 2.5 30 9.6

6 2.6 31 10.57 2.8 32 11.18 2.9 33 11.79 3.1 34 12.4

10 3.3 35 13.1

11 3.5 36 13.812 3.7 37 14.613 3.9 38 15.514 4.1 39 16.315 4.3 40 17.3

16 4.6 41 18.217 4.8 42 19.318 5.1 43 20.419 5.4 44 21.520 5.7 45 22.8

21 6.0 46 24.022 6.4 41 25.423 6.7 48 26.924 7.1 49 28.425 7.5 50 30.0

As stated previously in section 6.1.2 the requirement isthat the frequency range be covered evenly on a logarithmicbasis. Thus the individual frequency accuracy is lessimportant than the need to cover the frequency range.

-16-

L. ,,~ m im m m

REFERENCES

No. Author Title, etc

1. R. Penny An EMP hardness control plan for avionicsystems. RAE Technical MemorandumFS(F)457 (1982)

2. G A Odam Lightning transients that affectaircraft avionic euipment; a review ofwaveforms, levels and test methods. RAETechnical Memorandum (in preparation)

3. G A Odam Lightning protection requirements foraerospace vehicles. RAE TechnicalMemorandum FS(F)632 (in preparation)

4. N J Carter Recommended test specification for theelectromagnetic compatibility ofaircraft equipment. RAE TechnicalMemorandum FS(F)510 (1986)

5. R A Hobbs Design and construction of lineimpedance stabilising networks. RAETechnical Memorandum FS(F)613

6. G D Barber The design, performance and calibration

of probes 36A, 37A, 4UA, 43A, 45A and50A for bulk current susceptibilitytests. RAE Technical Memorandum FS(F)588(in preparation)

7. R A Hobbs The design and construction of pulsegenerators to comply with therequirements of RAE TechnicalMemoranda FS(F)457 issue 2 andFS(F)510 (in preparation)

-17-

INDEX TO FIGURES

Figure 1. Details of line impedance stabilisation network(LISN)

Figure 2. Impedance chdracteristics of LISN

Figure 3. Modification to dc supplies to limit surgecurrent

Figure 4. Typical test layout on ground plane

Figure 5. Damped sinusoidal waveform requirements

Figure 6. Calibration jig and monitoring for verificationof waveform

Figure 7. Waveform for long ground voltage transient

Figure 8. Waveform for short ground voltage transient

Figure 9. Voltage measurement loop on injection probe

Figure 10. Test set up for loom impedance measurements

Figure 11. Calibration of impedance measurement system

Figure 12. Test set up for sinusoid injection

Figure 13. Test set up for ground voltage injection

L

UH

E e.r >

0 t0o0.'0• I I") 0

3 0 I• - :J Cc LUo -. , ci\ ° .

I--0-

3. 1 L X : .AO L N C ' 0 M M -01.- 0 Ua tU C 0L N u C U0- M

Cn 'a 0 (XN 0 30

C N -M 1U a CU - -If I C *L 0 a.5Wa

* Lhr,0 " CU - D U)

IS L L L +.. 0

V, 0 OL L H- EO. M)0ccU 4. 10OH0 H CP ! W N3C

I I-

U U U M f- -

ID£a~aa~,.a • • -.

J C EN-r'-

(LISN)

.- m mmU

C.) - -n in IA nIN~ U 13

0 4U)l CM)

.C L

C)M

0

Figure 1. Details of line impedance stabilisation network(1 I SN)

-i J(zI- - -- - 1 - ~ - -.-.

N

zz

-LA

5--

(SWLIO)SP 3D)NuadWI

Figure 2. Impedance characteristics of LISN

.C -

IM 0)

o 0

0~

I,-- a•j,:: •.

L3 L•b.,

z 4

'-4t

I

OLr

4--J

:) LJ-L

0Lj

4)4,)

04UCD

E 0

+ L0 C I

(30-

Figure 3. Modification to dc supplies to limit surge

current

Ci

0• l• mm l ll mm m i | II i Ii

V 0 66

*0 * -

CL 4.0 C

QA. 0~ N 0 5- ; a L, . - :6C

(TO '. U 0 -

M L C J2C~ 50.5. 06 >0

ON 0 a. 01i

0 6 U Lim * *m C U60a V h 0 C .0 g

U U LU U * .C -C0%

aQ. (120 0 Co L

C , Cg Oo ON 0 0 -1 )1> 04, 0~ C' 3 0 a C

Li Li 0 C O0 S

0C :5 LM L 00 C2(L m

fo 0 .C0 C.2- 0. ZL0 C 0 60- Cg L

MV U M0 V L . LCLn - L1 1 4.5a~ 40, .5 3 Ci 0

0+0 CN U. Q.**O .

C~~ ~~ Lf L 1

LiCý -q

LU -.0 U 0L. c-

C .

L CL inL

01 0' LA C

01 C .54 Ci

L 0 60

.5 C -3 C ..5 a CLU0. C

CL U0 3 a

ED ~~~L& C a MC

ON, -O 4, 0, 3 0 cOIL 0 C 0 0C .o

5 . 0 C+C '00. 0

C '0. 1- C m i

Nfj 1- U) CD ti!

Figure 4. Typical test layout on ground'plane

V 0 I-G0-0 c LU0- Di

U C'. 0 .-%4 U)

U0 w CO

.U UC C

.4... U. C M

+4 6j .c 0) L0 C

4-4- c l0 j &#. 4j S 0M

Iv ULV) N

CAU C c.C

-- C ) LO

LUJ

L.JI

Laii0.0

r-

Figure 5. Damped sinusoidal waveform requirements

0o

U)-0

Siz

LL

0.

4.,

0E 0IV

LU

zLE

o ~(.

w0z

LU-m0

41I

z

o 0

-oIA Li..

0

o H-

L

C -

0, CL C

,io

000

0 CEU C

00

Figure 6. Calibration Jig and monitoring for verificationof waveform

LU)

S E:Da.

o• o

+1 N 0

0 Z 0

+ C

c 00~

-- F--4

o 'i -- -

o diL)

43 o __

U

-c r- £0 (

-JJ

.D -D '. I-

- - 0

J3 ja3

0"0

e tr

.. 2

I W

NZ00*) -

Figue 7 Waefor fo log grundvolage ranien

.I .. .. .. 4.

00 0x_.- Qo

E

0

'7-. (.c

+ cf" z4-' 0

*0 -0 W

c t- W0 ) U3

U U) I

A,, 0 -0 -c

~o -o 0 Z~ C)

-C -C >

w '7 .-- IZI

E 1 2

5 7 0

Ow 0 0'

cn U

U-j

mnI

Figure 8. Waveform for short ground voltage transient

0

0

U (0W a-> -0

o r=. 0a. LLi

a) U 0

00 U CLL 0> z

C C

0 - 0

'-J

o zEc~ 0-

CL0

9-J

00

Figue 9 Volagemeasremnt oop n ijecton rob

,0 0 a. -

> U

1/

L. -

U-L3) 0 .L

.0 0 c V~

In 4J 4.) > .-c :3 W

0s L o p0 U4JJ

N U VL a

:3

(Y) CiL

0L4.,3

NU

Figue1. Ts e pfrlo me emaueet

L £-00

E - w

C -Z

L d

LAJOe

LLn

CT

c >Z

QU)

0 0

0 z

u 0cu rL rT

0-

Uww

IU

F r CLs

FigreII Cliratonofimednc mesuemntsy te

,, • i i - - -- l.- - I "| 1 ii i Ci -

4-,

F-L 0

4+) L 0) LC o ~ a. IV 0

+J CD -0a U-0 D C: 0 m W

S L 0 0 L 0 ID 00 0) 41 -

(D C 0 4-'CO 0 -CL 0)- C0 -'0 0Lt

F- L3 0

L 0

Figure 12 Tes se0pfrSnsi neto

w C'4.V

00LLJ

LD

X _J

zo - 0l

4J LU

I o S. - I-;:

SL '- '-,,

a CL

Si 07L

.• U

,j Li

o .S

a.nC.

FeC

CL

JI1

Figur 13. Tetstu0o run otg neto

l1l'.'()1 I IXCtJNIIAN I A I ION IIA(',I.

A~ ldi t 1 i% 11,0w c 1111ý plase %holild (411111 intn111skfe tItJ~iftl .'llflto j1Utiýar II to c hosv~I ilmttd Wifoiirtiat,',i, IlIII boxa.ltni- mo iit heinarkcd it) ittditiit the elaiflcttton, v g. lHud~tit cd, in(CIIlif r e

I I)0C Rercewf2 r4i~~rsleteiice wII 1, Al~vncy 4,rit lts :Iaiifak~s(ltu be aidded hý, lRIC) Rfel i c (

S,)DRIC Ctxd, oro Originator 6. Originator ((orpordtc Ant Ior) Name aný [.cutiorm4

7673000W Royal Air~ratft Establinlhment, Farnborough, Illntw, UK

S'o. nimoring Agency's Code 6w. Sponsoring Agoticy (Contract Atithority) Name and ~o'cation

7. Tilk Equipment test rnothods for exrernnlly produced electromagnetic tranxientsi

7a, (For Translations) Title in Foreign Language

7b. (loirConference l'upcrs) Title, Place and Date of Conference

8.Authior 1. Surname, Initials 9a. Author 2 9b. Autihors 3, 4 .... 10, Date Pages rif.Hobs, .A.July IlHbs .. 1987 34 7

1l1. Contract Nim hcr 12. Period 13, Project 14. Othcr Rcfrencc Nos.

Is. listributiontstilcment(a) Controlled by -

(b) special limitations (If any)-If it is Intended tliat a copy of this document shall be released overseas refer to RAE Leaflet No.3 to Supplement 6 ofMOD Manual 4. ________________________

16, Descriptors (Keywords) (Descriptors marke d arc selected from TEST)

17. AbstroctThis Memorandum is the result of the work at the Royal Aircraft Establishment

irl assessing the effect of electromagnetic pulse and lightning strike producedtransients to aircraft systems. It details suitable tests for the simulation ofthese effects and should be used to form the basis of any future aircraft projecttransient specifications with suitable tailoring to meet specific requirementswith the formal approval of the Project Director.

RAFi Form A 143 (roylsed O',tober 1960)