IEEE Transactions on Nuclear Science, Vol. NS-29, No. 6, December 1982

ADVANCED RAPID ATTENUATION MEASUREMENT SYSTEM (ARAMS)

Y. B. YuAutonetics Strategic Systems Division

Rockwell International Corporation3370 Miraloma AvenueAnaheim, CA 92803

ABSTRACT

An advanced cable shielding acceptance testsystem, Advanced Rapid Measurement System (ARAMS),for production end items is proposed, evaluated,and analyzed. In this method, the requirement ofshielding against external electromagnetic fieldsis translated into transfer impedance requirementsfor cable overbraids and connectors within a cableset. These transfer impedance requirements areshown to be met by conducting tests using theARAMS.

INTRODUCTION

The ARAMS flat plate concept is an extensionof the trough concept (ref 1, 2 and 5) used in theRapid Attenuation Measurement System (RAMS). RAMSis an established method used at Rockwell Interna-tional for cable shielding acceptance testing ofproduction end item configurations. It has beenshown in previous programs to be adequate and costeffective. However, for complex cables the RAMSconfiguration is too difficult and costly to imple-ment. Hence, these restrictions have led to thedevelopment of the ARAMS flat plate configuration.

Interconnections are essential for all elec-tronic and electrical systems. Common elements forinterconnection are cables and connectors thattransmit signals or energy from one part of a sys-tem to another. Electronic systems are oftenrequired to meet certain external environments. Toattenuate the external environments such as anelectromagnetic field, overbraid shielding of thetable becomes necessary. The following steps areneeded to define this type and amount of overbraidshielding:

(1) define the open circuit voltage and/or shortcircuit current at the interfaces such thatinterface circuits will operate,

(2) calculate the cable shield and connectortransfer impedances such that the externalenvironment is attenuated to meet theseinterface requirements,

(3) use these corresponding transfer impedances to

calculate the equivalent current attenuationratio needed in an ARAMS test configuration,and then

(4) measure the current attenuation ratio in theARAMS and accept those samples which meet orexceed the calculated ratio.

THE RAPID ATTENUATION MEASUREMENT SYSTEM

The RAMS configuration is shown in Figure 1for a cable with one branch. The cable set isplaced in a pair of metallic troughs with the innerand outer troughs forming one transmission line andthe cable shield and the inner trough forming theother. Terminating resistors are chosen to match

This work has been supported by the USAF underContract F04704-78-C-0021.

these formed transmission lines. The spacings be-tween the cable shield and troughs are chosen suchthat the signal source drives a matched load.

This configuration results in a uniform cur-rent along each cable branch without any reflectionat the termination. The shield current penetratesthrough the cable shield to cause current flowingin the inner core conductor(s) of the cable. TheCurrent Attenuation Ratio (CAR) is defined as thetotal shield current, Io, at the driven end rela-tive to the core current, ILo at the same end ofthe cable in decibels as:

ICAR = 20 log1o o dB

IL

The current attenuation ratio is known asshielding effectiveness in ref 1, 2, and 3. Thereason CAR is used is to differentiate it from thecommon usage of shielding effectiveness for elec-tromagnetic field attenuation in enclosures.

Figure 1. RAMS

THE ADVANCED RAPID ATTENUATION MEASUREMENT SYSTEM

The RAMS configuration is excellent when acable is structurally simple. For a complex cable,the configuration needs to be modified. The flatplate configuration was developed to fulfill thisneed. As shown in Figure 2, the ARAMS configura-tion involves folding down the sides of bothtroughs to form two parallel flat plates. The lay-out of a typical cable on the upper plate is shownin Figure 3. To test the whole cable, it is desir-able to obtain an equally weighted uniform currentflow in all end branches for the entire frequencyrange of measurement. In order to accomplish this,one varies the height of the branches to vary thecharacteristic impedances of the transmission lineformed by the cable branches and the upper plateuntil a matched condition is reached. The

0018-9499/82/1200-1930$00.75© 1982 IEEE1930

electronic equipment and the definition of currentattenuation ratio are the same as for RAMS.

There are several areas of concern for thisflat plate configuration; these are: (1) theradiation loss must be small for current propa-gating down a long cable, (2) the circumferentialcurrent distribution must be acceptable, even forlarge diameter cables, and (3) any fault detectioncapability should be comparable to RAMS. A recentARAMS measurement on a long cable set shows nonotable loss of shield current caused by radiation.The measurement of the circumferential currentdistribution agrees very well with the theoreticalpredicted values as shown in Appendix A. The cir-cumferential current variation is within the ac-ceptable range.

Since RAMS was an established method it isdesirable to verify that ARAMS has a comparablefault detection capability. Therefore, cabledamage comparison tests for double overbraid cableswith axial and circumferential shield damage inRAMS and ARAMS configurations were carried out, andthe data showed that their fault detection cap-abilities were comparable. A description of thistest is given in Appendix B.

The following steps are used to obtain thecable acceptance test criteria: (1) set up the testconfiguration such that there are adequate andreasonably uniform currents in all branches, (2)measure the shield current in each branch acrossthe frequency band with sweep frequencymeasurement, (3) measure the internalcharacteristic impedances of all branches by theTime Domain Reflectometry (TDR) method, (4) processthe shield current measurement data and add theproper phase to the current amplitude estimatedfrom measured data, and (5) use the shieldcurrents, internal characteristic impedances ofbranches, and the transfer impedances of theoverbraid and connectors as input data to the MBCCcomputer code to produce a current attenuationratio vs frequency curve as the acceptance testcriteria.

The acceptance test criteria will act as thestandards for ARAMS measurements at the factorylevel for the corresponding cable sets. If the ac-tual ARAMS measurement data are equal to or exceedthe corresponding acceptance test criterion, thecable set passes the test and will be accepted.Otherwise, the cable set will not pass the test andwill be rejected.

CABLEBRANCH

DIELETRICSPACERS

a. RAMSTROUGH FIXTURE b. ARAMS FLAT PLATE FIXTURE

Figure 2. Comparison of RAMS and ARAMS

SHIELD

FLAT PLATE CONDUCTIVETERMINATING TRANSITIONRESISTORS

DISCUSSION

There are two more questions concerning thefault detection capability of the ARAMS configura-tion. Because current divides as it goes downbranches, CAR is less sensitive to degradations onthe end branches. While this is a deficiency forARAMS, it is the same deficiency for RAMS. Neitherone or any known method is superior. When thecable lays closely to the plate, the circumferen-tial current variation is near 12 dB as shown inFigure A2. While this is not desirable, it posesno major problem to the ARAMS. Since the maintrunk at the driving end lays closest to the plate,it also carries most of the current. The faultdetection insensitivity for a fault facing up isthus compensated by higher fault detection sensi-tivity which is caused by a larger total current inthe trunk. Since the end branches are high enoughabove the plate, nearly uniform circumferentialcurrent distribution is expected.

CONCLUSION

According to the above evaluation and themeasurement setup for the cable development test,ARAMS is a valid concept for screening cables anddetecting cable shield faults.

Figure 3. Typical ARAMS Configuration

ACCEPTANCE TEST CRITERIA

The ARAMS test for cable rf shielding measure-ments is unique in that a Go/No-Go result can beobtained under factory production line conditions.To obtain the Go/No-Go qualitative acceptance lev-els for cable sets, one needs to go through thesteps outlined in the previous section. To handlethis, a Multi-Branch Cable Code (MBCC) was devel-oped. It is a computer code that is capable ofcalculating the ARAMS test criteria for the multi-cqnductor/multi-branch cable sets.

APPENDIX A. CIRCUMFERENTIAL CURRENT DISTRIBUTION

In this appendix, the method of measuring thecircumferential current distribution of a cable inan ARAMS configuration is presented. The measureddata are then compared with the theoretical predic-tion for various heights of the cable above theupper flat plate.

MEASUREMENT

A solid copper pipe was used to simulate thebraid. The coaxial conductor inside the pipe wasterminated with the transmission line characteris-tic impedance of 50 Q. Three small holes of ade-quate separation were drilled through the pipe toprovide the inductive coupling to the inner conduc-

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tor. The ARAMS set-up and the pipe parameters areshown in Figure Al. The pipe was measured at twoheight positions corresponding to 50 and 100 ncharacteristic impedances of the transmission lineformed by the pipe and the upper flat plate. Ateach height position, the pipe was rotated from 00for holes facing up to 1800 for holes facing downin 30° steps. The current attenuation ratios fromthe corresponding measurement are shown in the up-per graphs of Figures A2 and A3.

CONNECTED TOARAMS INSTRUMENTS

/ ~~~~~SUPPORT BLOCK

g>COPPER PIPE //

TERMINATION RESISTOR

PARALLEL COPPER PLATES

PIPE DIAMETER 7/8" NUMBER OF HOLES 3PIPE THICKNESS 1/16" HOLE DIAMETER 1/8"

HOLE SEPARATION 3"

Figure Al. Circumferential Current DistributionCopper Pipe Measurement

(a) MEASUREMENT

NOTE: DASHED LINES ARE THE CALIBRATION LINES.

wherea + Rxcosf a + R2cosf

)R2 + a-2 + 2aR cos R2 + a2 + 2aR2cosf

R= h + /h2 - a2

R2 h - /h2 - aa2

and J is a constant. The meaning of the notations0

are as follows;

a - radius of the copper pipe

h - distance from the axis of the pipe to the flatplate

* angle measured from the upper part of the pipe

(a) MEASUREMENT

a

I-z0

SHIM HEIGHT 1.52 CM tTERMINATION RESISTOR 50 Q=1

(b) THEORETICAL

o

z

FREQUENCY (MHz)

(b) THEORETICAL

z

0 110p

z120

FREQUENCY (MHz)

Figure A2. Comparison of the Copper PipeMeasurement Data to TheoreticalPrediction for Shim Height 1.52 cmCorresponding to 50 Q

THEORETICAL CALCULATION

For a TEM wave the theoretical circumferential

current distribution, J( ), is given by the follow-ing expression,

J(W) = JO F( )

FREQUENCY (MHz)

Figure A3. Comparison of the Copper PipeMeasurement Data to TheoreticalPrediction for Shim Height 3.14 cm

Corresponding to 100 Q

The TEM electric and magentic fields generatedby this surface current at the shield surface willpenetrate the holes and act as voltage and current

sources to excite the internal line. According toref 3, the equivalent voltage and current sources

for a hole located at position x from the drivenend are

Ve= jw lo aImJ ( e-y'2,ffa -yx

Ieq = jw J ( ) e2 waZc

y _ julv

v _ velocity of propagation

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a

z2

z

tU

.o0o

w _ 21r (frequency)

am = magnetic polarizability of the hole

ae = electric polarizability of the hole

Z = characteristic impedance of the cable

Let x be the distance from the driven end tothe nearest hole, then the current in the core con-ductor at the driven end is

= (w n)J )2yXo 1 - e 6dyIcr = - (ae - a )J(f)e L -dcore 4irfaZ 1 ~e 2dyc

where d is the hole separation. The shield current(copper pipe current) at the driven end is

I = fi J(+)dX = Jo f F(+)dX0 0

According to ref 4, the magnetic and electricpolarizabilities are as follows,

Am= 1.-12r 3 e.841T/rQm0

ae = -0.55 r3 e- 2405T/re 0

where T is the wall thickness and r is the radiusof the hole. The Current Attenuation Ratios (CAR)were calculated according to the formula

ICAR = 20 log10 I dB

core

The calculated curves for the correspondingtest configuration were shown in the lower graphsof Figures A2 and A3.

As shown in Figures A2 and A3, the theoreticalcalculations and measurements closely agree.

APPENDIX B. CABLE DAMAGE COMPARISON MEASUREMENT INRAMS AND ARAMS CONFIGURATIONS

Two pieces of commercially available doubleoverbraid coaxial cables 103 cm long and 3/4 inchdiameter were used in the test. They were thestripped-down version of the RG-177 cable. Eachwas numbered in sequence as 1 and 2. Cables 1 and2 were subsequently implanted with circumferentialand axial damages, respectively. The inner coreconductor was terminated with the cable character-istic impedance.

For both specimens, baseline measurements wereperformed in RAMS and ARAMS configurations for shimheights of 1/32, 5/32, 3/4, 5-3/8 inches, respec-tively, corresponding to 27, 51, 100, and 200 a ofcharacteristic impedance for the transmission lineformed by the braid and the upper plate. After thebaseline measurements, cable 1 was circumferential-ly damaged with a 1800 cut in the outer braid andfour carriers of the inner braid severed, and cable2 was axially damaged with 10 picks of the outerbraid severed and 6 picks of the inner braidsevered.

In the RAMS test, one measurement was takenfor each configuration. In the ARAMS test, mea-surements were taken at 00, 900, 1800 and some at2700 by rotating the cable at each shim height.The fault facing up was designated as the 00 posi-tion.

Figures Bi and B2 show the results of the mea-surements on cables 1 and 2. In Figures Bi and B2,for brevity, only the 51 n ARAMS configuration isshown. A summary of the measurements at frequen-cies 60 and 100 MHz is given in Table Bi.

90

- 100

z0

D 110z

120

130

20 40 60FREQUENCY IMH2)

80 100

Figure Bl. Measurement Results on Cable 1

z

:2z0

z

Figure B2. Measurement Results on Cable 2

CABLE 1 CABLE 2

TSS NO DAMAGE ClERENTIA NO DAMAG E DAMAG e

MHz M Hz MHz MHz

60 100 60 _0 60 100 6 0RAMS 105 108 90 88 110 106 91 89ARAMS27 Q ill 106 99 94 112 ill 95 95

106 101 83 77 108 106 82 n751 Q 108 110 97 94 1 10 110 94 93

104 1 16 85 80 107 107 84 82100 Q 106 lo! 92 92 110 108 fl2 92

104 104 86 85 107 104 86 86200 Q 103 106 90 90 108 108 90 90

103 103 88 87 105 104 87 87

NOTE: ALL UNITS ARE IN dB.

Table Bl. Summary of the AttenuationMeasurements in VariousConfigurations at 60 and 100 MHz

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1800

/ *.. 90

./ :-.-.-.--.-.-,^---

RAMS (BASELINE)---RAMS (CIRCUMFERENTIALLY DAMAGED)

ARAMS (BASELINE, 51 OHMS)*-ARAMS (Cl RCUMFERENTIALLY

DAMAGED)

80,

11

REFERENCES

1. E. D. Knowles and L. W. Olson, "Cable ShieldingEffectiveness Testing," IEEE Trans. Electromagn.Compat., Vol. EMC-16, pp. 16-23, Feb. 1974.

2. E. D. Knowles and J. C. Brossier, "MeasuringConnector Shielding Effectiveness During Vibra-tion," IEEE Trans. Electromagn. Compat., Vol.EMC-16, pp. 24-29, Feb. 1974.

3. E.F. Vance, "Shielding Effectiveness of Braided-Wire Shields," IEEE Trans. of ElectromagneticCompatibility, Vol. EMC-17, pp. 71-77, May 1975.

4. Noel A. McDonald, "Electric and Magnetic Coup-ling Through Small Apertures in Shield Walls ofAny Thickness," IEEE Trans. Microwave TheoryTech., Vol. MTT-20, No. 10, Oct. 1972.

5. P. J. Madle, "Cable and Connector ShieldingAttenuation and Transfer Impedance MeasurementsUsing Quadraxial and Quintaxial Test Methods,"1975 IEEE EMC Symposium Record, pp 4BIbl-4BIb5.

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