AlllOb 178037

NBSIR 84-1698(^9

AN ASSESSMENT OF

ELECTROMAGNETIC INTERFERENCE

(EMI) AND ELECTROMAGNETIC

COMPATIBILITY (EMC) MEASUREMENT

PRACTICES TO MEET U.S. ARMY

AVIATION RESEARCH AND

DEVELOPMENT COMMAND EMI/EMC

REQUIREMENTS

National Bureau of Standards

U.S. Department of Commerce

Boulder, Colorado 80303

January 1984

-Q0

100

,U56

84-1598

1984

£. a

NBSIR 84-1698

AN ASSESSMENT OF ,2,;

ELECTROMAGNETIC INTERFERENCE

(EMI) AND ELECTROMAGNETIC ^

COMPATIBILITY (EMC) MEASUREMENT

PRACTICES TO MEET U.S. ARMY

AVIATION RESEARCH AND

DEVELOPMENT COMMAND EMI/EMC

REQUIREMENTS

Electromagnetic Fields Division

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Boulder, Colorado 80303

January 1984

Prepared for: U.S. Army Aviation Research and Development Command (AVRADCOM)

W. J. Alspach

C. K. S. Miller

G. R. Reeve

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

CONTENTS

Page

I. INTRODUCTION 1

II. CONTRACTOR SELECTION 2

III. CONTRACTORS AND PRINCIPAL PERSONNEL CONTACTED 2

IV. BACKGROUND 4

V. HISTORICAL PERSPECTIVE OF MILITARY SPECIFICATIONS 5

VI. SURVEY INFORMATION BASE 7

VII. EMI/EMC SPECIFICATIONS, STANDARDS, AND PRACTICES..... 7

VIII. EMI/EMC MEASUREMENT PROBLEMS 12

IX. COST OF EMI/EMC ACTIVITIES 16

X. ELECTROMAGNETIC HAZARDS TO PERSONNEL AND EQUIPMENT 18

XI. AN NBS ROLE TO IMPROVE EMI/EMC MEASUREMENTS 18

XII. CONTRACTOR RECOMMENDATIONS FOR EMI/EMC TEST AND SPECIFICATION

CHANGES AND OTHER CHANGES. 19

XIII. CONCLUSIONS 21

XIV. COMMENTS 23

i i i

M Assessment of Electrwagnetic Interference (EMI)

and Electromagnetic Compatibility (EMC) Measurement Practices

to Meet U.S. Army Aviation Research and Development Cornua nd

EMI /EMC Requi reuse nts

W. J. Alspach, C. K. S. Miller, and G. R. Reeve

Electromagnetic Fields Division

National Bureau of Standards

Boulder, Colorado 80303

A survey of selected industrial contractors, airframe

maufacturers, and electronic test and calibration firms was conducted during June - August 1982 by the Electromagnetic Fields

Division, National Bureau of Standards, to assess industrial and

commercial testing and measurement practices used to meet electromagnetic interference/electromagnetic compatibility ( EMI /EMC

)

requirements of the U.S. Army Aviation Research and Development

Command (AVRADCOM). This survey addressed the cost of conducting

EMI /EMC tests; whether or not electronic components, subassemblies, systems, and their testing met specified AVRADCOM EMI/EMC

requirements; and whether the test practices, test equipment, and

EMI/EMC requirements are appropriate. The following conclusions

were reached: (1) Victim-source testing, although limited, is the

only current EMI test that is meaningful for whole system testing. (2) It is questionable whether electronic systems will

perform satisfactori ly in a battlefield electromagnetic environment. (3) There is no correlation in EMI/EMC test practices; it

is possible that electronic systems are overdesigned, overbuilt,

and overtested. (4) Future issues such as high-level field

testing and electromagnetic pulse (EMP) need to be addressed.

Keywords: electromagnetic compatibility (EMC); electromagnetic

interference (EMI).

I. IMTRODUCTI0M

A survey of various industrial contractors, air frame manufacturers, and

electronic test and calibration firms was conducted in the time period June - August 1982 by the Electromagnetic Fields Division, National Bureau of Standards (NBS) to assess industrial and commercial testing and measurement practices used to meet electromagnetic interference/electromagnetic compatibility

(EMI/EMC) requirements of the U.S. Army Aviation Research and Development

Command (AVRADCOM).

1
NBS made this survey under the auspices of an agreement with AVRADCOM to

"provide engineering and measurement assurance services" to the AVRADCOM

Product Assurance Directorate, St. Louis, Missouri.

This survey addressed the following:

• Do electronic components, subassemblies, and systems and the testing

(calibration) of such meet AVRADCOM specified EMI /EMC requirements?

• Are the EMI/EMC requirements appropriate?

• Are the test practices, test equipment, etc. appropriate to meet these

requirements?

• What is the financial cost of conducting such tests?

The survey results consist of voluntary comments and suggestions made by

those surveyed. The aim of the contractors is to improve EMI/EMC measurement

assurance and reduce the costs of such assurance.

MBS does not necessarily approve, endorse, or disagree with these com- ments and suggestions. This document, rather, only reports on the comments

and suggestions made as (1) a representation of the current state of EMI/EMC

measurement practices, and (2) the perceived desire of industry to improve

upon their measurement assurance practices while reducing the costs of such to

their customers--the military and, in particular, AVRADCOM.

II. CONTRACTOR SELECTION

A list of industrial contractors who furnish sophisticated electronics

components and systems (e.g., communications and navigation systems) and the more commonplace (e.g., electrical power generators) equipment for AVRADCOM's

AHIP helicopter and AQUILA remote piloted vehicle programs was given to NBS by

the Product Assurance Directorate. From this list, NBS selected several con- tractors to contact. Additionally, NBS selected certain airframe contractors

(who furnished complete Army aircraft) and commercial test and calibration

firms (who provide specialized EMI/EMC measurement services) for contact.

Personal visits were then made by NBS personnel to the selected contractors. In most cases, excellent cooperation was given by these contractors.

In addition to the commercial contractors, NBS personnel also visited

Army personnel at Fort Monmouth, New Jersey, who are concerned with EMI/EMC

measurements and requirements.

III. CONTRACTORS AND PRINCIPAL PERSONNEL CONTACTED

The following is a list of all industrial contractors and their principal

personnel visited for this EMI/EMC survey. Army personnel at Fort Monmouth

are also listed.

2
1. Sperry Flight Systems - Albuquerque, New Mexico

A1 Farquer - AH 64 Program Mgr.

2. Rockwell International/Collins - Cedar Rapids, Iowa

Merrill Ludvigson - Prog. Mgr., Govt. Avionics

Wilbur Evarts - Mgr., Evaluation Engineering/Product Assurance

Larry Mulbrook - Mgr., Communications & Navigation

3. Lear Siegler - Maple Heights, Ohio

Robert Feucht - Vice-President, Engineering

Laszlo Hormat - Sr. Project Engineer

Kenneth Arner - Chief Test Engineer

4. Westi nghouse Defense & Electronic Systems - Baltimore, Maryland

Andrew Lavoie - Mgr., Product Qualifications Lab

Alwyn Roberts - EMC Engineering

Tony Cesko - EMC Engineering

5. Fort Monmouth - New Jersey

Jerome Blackman - Actg. Dir. Center for Communications Systems

Warren Kesselman - Center for Communications Systems

Colin MacDonnell - Deputy Director, Logistics Engineering Directorate

George Kopecky - Logistics Engineering Directorate

6. AEL Service Corporation - Farmingdale, New Jersey

Margaretta Stone - EMI /EMC Section Head

Gene Barber - EMI/EMC Engineer

William Wild - Facility Mgr.

7. Kearfott Division, Singer Co. - Wayne, New Jersey

Gus Stavis - Mgr., Advanced Development Dept.

Edgar Freud - Senior Engineer

Bud Jaeger - EMC Test Engineer

8. RCA/Government and Commercial Systems - Burlington, Massachusetts

A. Amato - Mgr., Products Engineering

Stan Patrakis - Mgr., Products Design

Russ Williamson - EMI Engineer

9. Detroit Diesel Allison - Indianapolis, Indiana

Eugene Ervin - Supervisor, Electrical/Electronic Design

Gail Hill - Sr. Experimental Engineer

Robert Nelson - Development Engineer

10. McDonnell Douglas Astronautics Co. - Huntington Beach, California

Kenneth A. Francis, Vice President, Engineering

W. E. Bounds, Chief Electronics Engineer

Robert Obelman, Avionics, Control & Information Systems

3
11. Northrup Co. - Anaheim, California

Harlen Beck, Manager, Support Services Engineering

John Hornung, Manager, Systems Design

William B. Gaumer, Process Engineering Specialist

12. Litton Guidance and Control Systems - Woodland Hills, California

John M. Leonis, Director, Systems and Software

Fred R. Hotter, Manager, EMC Engineering

13. Hughes Helicopters - Culver City, California

Gerald A. Booth, Chief, Electrical Systems

14. Lockheed Missiles and Space Co. - Sunnyvale, California

Ivan Beck, EMC Engineering

Paul E. Bolande, Program Office

15. Elite Electronic Engineering Co. - Downers Grove, Illinois

Donald E. Schmit, EMI Engineer

16. Bell Helicopter Textron - Fort Worth, Texas

Richard C. Henschel, Manager of Avionics & Electrical Systems

John G. Mast, Group Engineer, Avionics Design

Jack G. Dillard, Group Engineer, Standards & Electronics Lab

Phil Smith, Group Engineer, Electronic Systems Lab

IV. BACKGROUND

The Institute of Electrical and Electronics Engineers (IEEE), in their

IEEE Standard Dictionary of Electrical and Electronics Terms (IEEE STD 100-

1977), defines EMI and EMC as:

eleetronagraetic interference. Impairment of a wanted electromagnetic signal by an electromagnetic disturbance.

and

electroiwgnetic compatibility. The capability of electronic

equipments or systems to be operated in the intended operational

electromagnetic environment at designed levels of efficiency.

Thus, in the context of Army aircraft, EMI can (and, unfortunately, too

often does) adversely affect the performance of electronic equipment and systems. This EMI can take the form of a radiated or a conducted signal and can

cause, for example, garbled communications, a false alarm from a radar threat

receiver, or erroneous navigation.

Further, an electromagnetic signal, whether intentional or inadvertent

(interference), may adversely affect human health and well being.

4
Still further, an electromagnetic signal, given the correct circumstances

of frequency and power, may adversely affect military ordnance. For example,

the electromagnetic explosive device (EED) used in ordnance may cause its

detonation if the EED is exposed to certain electromagnetic signals for too

long. To guard against detonation, great pains are often taken to shield the

EED against such signals.

This points up the fact that Army aircraft, be they sophisticated electronic surveillance systems, well-armed helicopter gunships, or simple remotepiloted vehicles, with on board electronic systems may suffer performance

degradation (even malfunction and crash) if such systems are not "properly

designed" and tested for electromagnetic threats.

To ensure that the electronic systems are "properly designed," certain

testing specifications have been generated by the military and industry.

These specifications are, for the most part, imposed upon industry (the

component manufacturers as well as the system integrators and the airframe

contractors) by Department of Defense (DOD) contract requi rements. These

contract requirements call for the exposure of components to certain electromagnetic environments to determine that component performance is not degraded

beyond certain limits. This exposure is frequently referred to as "electromagnetic susceptibility" or electromagnetic compatibility testing. Components

are also tested to determine the electromagnetic radiation emitted by the

component (one "black box's" EM emission can be another box's EM interference). This is referred to as "electromagnetic emission" testing.

Even with these testing specifications, electromagnetic interference and

electromagnetic compatibility are difficult to determine because the measurement processes associated with such are imprecise or impractical. EMI is

difficult to measure; therefore, interference is difficult to isolate as a specific or distinct problem. In some cases, the testing specification

requirements are considered ambiguous and misleading. Additionally, testing

methods called for in the specifications can be inadequate or inappropriate to

such a degree that testing repeatabil i ty and measurement accuracy are seriously compromised. Individual component testing under these specifications is no assurance that the final end product (i.e., the electronic systems in the

host vehicle) will "pass" system EMI/EMC testi ng--"the sum of the parts does

not necessarily equal that of the whole system."

Unfortunately, this failure or shortcoming of testing and measuring under

imposed specifications can, and does in the opinion of many industrial con- tractors, result in the overdesign of many components and systems. The

contractors believe that they cannot afford EMI/EMC failures, so they overdesign. Such overdesign has its price--it costs DOD dearly in larger contract

prices paid to system contractors and their suppliers.

V. HISTORICAL PERSPECTIVE OF MILITARY SPECIFICATIONS

Military specifications concerning EMI/EMC have been in existence for

quite some time; thus, the rationale for and circumstances of these specifications becomes more obscure with the passing years. Accordingly, representatives from NBS visited Fort Monmouth, New Jersey for discussions with Army

personnel who have been associated with EMI/EMC concerns for a number of

years. These Army personnel were involved in, or were closely related to, the

5
generation and evolution of EMI/EMC specifications. The following presents an historical perspective of these specifications and represents the memory and

viewpoint of the Army EMI personnel visited.

Of the three military services, the Navy has responsibility for the

"coordi nation" of military specifications. For example, the preparation of

specifications is the work of many from both industry and the military, but

the gathering together of i nputs and the final draft of specifications and

their eventual issuance is a Navy function.

The primary military specifications concerning EMI/EMC, issued in about

1967, are MIL STD 461 and MIL STD 462. These were generated at the behest, if

not insistence, of industry; who, for the lack of such specifications,

apparently often found themselves at odds with the military and with each

other in defining and determining (measuring) electromagnetic interference and

compatibility. The lack of measurement consistency resulted in chaos. MIL

STD 461 established performance limits, e.g., what electromagnetic environments should not cause electronic equipment degradation, or how much degradation is permissible. On the other hand, MIL STD 462 outlined the measurement

practices, including recommended equipments, to be used for making such determinations. MIL STDS 461 and 462 probably represented the best available

thought and technology of their day, about 1967.

When MIL STDS 461 and 462 were agreed upon and issued, they were intended

to serve only as gui del i nes--not as mandatory requirements. That is, they were to be regarded as interpretive and subjective guidelines and not to be

rigid rules and regulations (specifications). Apparently, little time passed

before MIL STDS 461 and 462 assumed a position of specifications in DOD

contracts.

At the time MIL STDS 461 and 462 were being generated, or shortly thereafter, it was determined by the EMI/EMC community that still another standard

was needed: MIL STD 464. This standard was intended to serve as an electronic systems (as opposed to MIL STDS 461 and 462 serving as components test

documents) test document and the Air Force was assigned responsibility for

generating such. No MIL STD 464 came into being. The reason for this is now

unknown.

Army EMI personnel at Fort Monmouth state that the Army does not have a "hard nosed approach" or attitude towards MIL STD 462, the test methods specification, even if such is called for in Army contracts. Instead, a contractor's EMI/EMC test plan is reviewed and, if the contractor proposes a "better"

test plan than is the case with MIL STD 462, the Army will "listen to and

consider such." Comments from the industrial firms contacted for this survey

indicate that this "listen to and consider such" is an inconsistent practice

of the many Army personnel involved in the total acquisition and program monitor process.

Present practice of the Army appears to be to use MIL STD 461, the performance limits specification, and appropriate Notices in its contracting

requirements. These Notices are, essentially, "modifications" of MIL STD 461.

6
Meanwhile, MIL STD 461B, an updated version of MIL STD 461, has been

issued and is apparently used by the other services. The Army does not use

the B version, apparently because a determination has been made by appropriate

Army personnel that there is a "lack of sufficient measurement techniques" to

meet B version requirements.

There appears to be considerable dissatisfaction with MIL STDS 461 and

462, including updated versions, amongst the military and their contractors.

This dissatisfaction is a reason why the Society of Automotive Engineers AE-4

Committees (a voluntary standards organization) offered to "rewrite MIL STDS

461 and 462." Apparently this offer is now about 15 years old and no "rewritten" specifications have as yet appeared from the committee.

VI. SURVEY INFORMATION BASE

Early on in the survey, it was quickly and easily determined that the

various industrial contacts' comments and suggestions could be categorized in

the following subject areas:

- EMI/EMC specifications, standards, and practices

- EMI/EMC measurement problems

- Cost of EMI/EMC activities

- Electromagnetic hazards to personnel and equipment

- An NBS role to improve EMI/EMC measurements

- Contractor recommendations for EMI/EMC testing and specification

changes.

Accordingly, all contractor comments, suggestions, etc. have been grouped

into these subject categories. Some comments are "favorable" while some are almost like a cry of despair. This grouping constitutes the data base, i.e.,

the information base for this report, and essentially consists of a multitude

of informational "bullets" that express the contractor's thoughts, ideas,

wishes, etc. This data base is somewhat voluminous and is considered as private information since nearly all of the contacts were particularly frank

and honest in their discussions, opinions, etc. The National Bureau of

Standards respects all of the contacts for their openess and candidness and is

grateful for such.

VII- EMI/EMC SPECIFICATIONS, STANDARDS, AND PRACTICES

Survey Information

Contractor Comments :

MIL STD 461 environment curves (requirements) do not necessarily cor- respond to the real world, not combat related with electromagnetic

warfare ( EW ) considerations.

MIL STD 461 requires measurements at own on-channel signals; this is

ridiculous, especially for receivers.

7
Specifications are seldom met completely, hence we go to the Army for

waivers.

Specifications are designed for electrical power users, not for power

generators, yet the same specs apply to both.

Conducted emissions tests are a real problem; there is no correlation

between labs of test results and, further, the conducted emissions

tests are not necessarily related to host vehicle requirements anyway.

MIL STDS 461 and 462 (testing to such) are expensive to conduct and

are not totally reliable for host vehicle testing; whole system

testing is the one that really counts.

In some cases where EMI failures occur, (some contractors) will obtain

a waiver for such rather than fix the problem.

Someone really needs to determine, "What are military requirements for

EMI?"

The Army (and others) needs a production type EMI test method to assure that production items are the same as the original development

model as far as EMI and EMC are concerned.

In some cases, EMI standards are strictly enforced; whereas in other

cases, exceptions (waivers) are sought and granted.

Wo modern field survey information on EM tactical environments is

avail able.

At least 50% of test samples submitted for EMI testing fail to meet

specification limits.

Using MIL STD 461 B with MIL STD 462 is a problem. An update of MIL

STD 462 is needed.

Equations for radiated emissions testing are horrible to use.

Have to stop test procedures to make calculations.

In helicopters, most EM interference is caused by onboard transmitting

antennas.

It is difficult to obtain approval for use of alternative test

methods.

With present specifications and test methods, there is no assurance

that electronic components and systems will operate correctly in the

final host vehicle. Sometimes, the systems integrators themselves

cause EMI problems because of cabling, bonding, batteries, etc.

There are problems with MIL STD 461B, e.g., power line testing.

8
The standard concerning "broad band" and "narrow band" testing is not

clear and, consequently, leads to differing interpretations.

The helicopter is a bad electrical environment:

• power generators are "noisy"

• austere electronic engineering is required

• the power bus has a lot of current flow at 28 V dc instead of an aircraft 400 Hz ac

• ground return is through a sparse structure.

Present EMI specifications are essentially radio oriented and, thus,

are antiquated because they do not reflect a true electromagnetic

situation; for example, an EW environment.

The Army's Notice 4 (for use with MIL STD 461) covering conducted

emissions is not compatible with Air Force and Navy requirements.

(We) do not have problems in obtaining approvals for use of

alternative equipments, e.g., use of a spectrum analyzer for narrow

band measurements.

(We) perform EMI qualification testing only--no production sample

testi ng.

(We) have problems with EMI/EMC requirements being realistic.

When test results are "out of spec," waivers are negotiated--general ly

successful ly

.

MIL STD 461B transients are out! andi sh--cal 1 for suppression of 100 V power spikes. (We) question reality of a 100 V power spike.

Radiated emission levels are far lower (60 to 70 dB) than susceptibility levels. Meeting such emission levels is very costly.

Specifications call for absorbing a 20 V, peak-to-peak , on-the-powerline bus, but yet cannot put more than 3 pV on the bus. Cannot understand rationale for this, either.

(We) cannot rely on military specifications (MIL SPECS) to define the

EM environment. Design experience and testing assessment are much

more meaningful than are specs.

There is adequate regard for EMI in the early stages of a project;

however, such regard steadily declines as time goes on.

Contractor bids are high because the request for proposals (RFP's) ask

for too many EMI requirements that are not relevant--! iteral ly, a barrage of such requirements.

We test to MIL STDS 461 and 462 which are, generally, more stringent

than needed.

9
We impose MIL STDS 461 and 462 on our suppliers even though we are aware that the components from our suppliers, when meeting these

requirements, can still cause system ES'dI /EMC problems.

We bend MIL STDS 461 and 462 to fit the system.

(We) now have 200 V/m exposure requirements. Handbook 235 (Navy test

document), however, requires 5000 V/m tests.

Occasionally , customers do not have sufficient EMI consciousness.

NASA is best for such; whereas the Army is more lax in this than are

the Air Force and the Navy until a crisis arises, then it overreacts.

The mast-mounted sight for Army helicopters will not be subject to

(our) configuration controls and will have to rely on Army controls

for such. A modified MIL STD 461 applies to this sight; it is felt

that this specification does not reflect the battlefield EM

environment in which the sight is to operate.

In the case of the mast-mounted sight, the helicopter onboard

equipment is probably the worst EMI threat--particul arly the high

frequency (HF) communications gear.

(We) do not presently have sufficient inhouse expertise for all EMI

testing problems; (we) hire an outside consultant for EMI analysis

work.

There is questionable validity of MIL STDS 461 and 462 values in

relation to the real world environment. (We) are not sure if we overdesign equipment or not to meet these values.

We maintain a form of configuration control for EMI/EMC; however, once

our products leave our plant we lose such control . We do, however,

state our external wiring requirements to the system integrator to

attempt to achieve total configuration control. Certain integrators

do get us into trouble because they don't follow our requi rements for

control

.

We impose EMI requirements on our vendors who, in turn, use commercial

test houses. Sometimes these test houses do not follow test plans.

We do not have many problems when our black boxes are installed in the

host vehicle; we conclude by this that our equipment is

"overdesigned.

We have a couple of peeves regarding EMI/EMC: 1) the downgrading of

EMC board activity at the integrator under the direction (control) of

customer. 2) It's a joke to require field levels of 100's of V/m at

frequencies above 1 GHz because such doesn't cause problems here; it

will, however, cause problems at lower frequencies.

Obtaining waivers for EMI/EMC compliance is not a normal order of

business with us. Some of our competitors, however, are of the buildtest-obtain waiver school.

10
In some cases (electronic countermeasures) , the EM emissions limits

are not severe enough.

The Army's Notice 4 is a good attempt at more real isti cal ly defining

EMI requirements.

(The) military regards specifications as sacred documents. We are lenient with our suppliers for specification deviations. The military

is inconsistent with specification derivations; they readily give

waivers for weapons which they understand, but not for electronic

systems which they do not understand.

MIL STD 461 with Notice 3 is a pretty good document. Notice 4 (the

Army document) is a confusing document.

There is no test requirement to validate vehicle performance in a battlefield EM environment. Further, no vehicle (EM) emissions signature measurements are required.

Some helicopters use a fair amount of composite materials that are poor for EM shielding purposes.

Sometimes, customer will permit "tailoring" of MIL STDS 461 limits.

In most cases, however, Army and Navy will not permit deviations

unless time allows for redesign.

In the lower frequency bands, 20 Hz to 15 kHz, the limits (MIL STD

461) are too loose; whereas, in the band 20 MHz to 200 MHz, the limits

are too tight.

Whenever large variations in test results occur, resolution of the

problem is between the customer and (our) program office. Time is

important in such decision making. If time is tight, the decision is

"liberal."

The Army and Air Force say they will not use MIL STD 461B, a Navy

generated specification. MIL STD 462A lacks the test methods required

by 461B. Further, the Air Force and the Army do not like each others

"changes" which are now incorporated into 461 B.

EMI specifications are too loose--too nebulous for practical matters,

not definitive.

We have to "negotiate" each and every contract involving EMI measurements.

Presently, (our) test facilities have a 200 V/m capability in the 10

kHz to 18 GHz range. The Navy talks of new specifications calling for

pulsed levels to 10,000 V/m at 33 GHz (We) are not considering

offering test capabilities at levels greater than 200 V/m.

(We) question the technical knowledge of Army EMI personnel and their

ability to make proper technical decisions.

11
EMI knowledge varies with the services. Air Force is more technically

astute, whereas Army is conscious of the problem but its knowledgeable

people are spread pretty thin.

In the last 10 to 15 years, (we) have had to resort to specification

waivers only a few times; this was for system testing. In the light

of this, (we) suspect overdesign of equipment.

Component testing does not guarantee a system passing specification

requirements. However, as a general rule, component testing is OK.

(We) claim repeatabil ity of measurements in a screen room to within a couple of dB. (We) take special care in keeping test set ups as identical as possible, as close to end use in aircraft.

(We) are performing more and more host vehicle cabling "hot mockup"

testing because cabling is becoming more of a concern.

(We) have no problems using a spectrum analyzer in place of a receiver. Such is OK with AVRADCOM, Air Force, and Wavy.

(We) do not use outside EMI consultants or test 1 aboratories. (We)

have a concern, however, for the quality of such test laboratories.

VIII. EMI /EMC MEASUREMENT PROBLEMS

Survey Information

Contractor Comments :

MIL STDS permit no use of alternative test methods; waivers for such,

however, are sometimes obtained. This points out inconsistency in the

test methodology.

In some cases where "failures" occur, the test is rerun with a different test configuration and then the item "passes."

There appears to be little correlation between component testing and

system testing results. The sum of the parts is not always equal to

the whole.

At least 50% of test items submitted to an independent test facility

fail EMI/EMC tests.

(We) always have troubles with high frequency EMI testing on host

vehicles because of resonance phenomena.

MIL STD 461 probably requires overdesign (and cost) but the degree of

such overdesign is unknown.

Screen room testing is a joke!

12
(The) repeatability of cabling is a major problem to system

integrators.

Cross coupling of cables (routing within a bundle) is another source

of EMI difficulty.

Interaction between individual black boxes is a most serious problem.

Overdesign of equipment is necessary to pass EMI/EMC tests; there is no opportunity to optimize design for a cost/performance trade off.

(We) like victim-source test for whole system testing. However, (we)

have never heard of any system meeting all of MIL STD 461

requirements; waivers for "failures" are used.

There is no correlation between laboratories for radiated emission and

susceptibility testing. In fact, there is a lack of repeatability in

the test methods themselves. We, ourselves, suffer from a lack of

inhouse repeatability of test results.

Twenty dB or more variations (repeatability) have been noted in

testi ng.

A commercial power supply after rework now fails EMI tests. Rework

had removed critical parts. However, even with replacement of these

parts the unit still fails test. This indicates lack of EMI knowledge

and training plus a lack of configuration control and sample testing

to prevent such.

Test methods for EM susceptibility are not realistic and levels are antiquated.

Screen room testing is nonsense:

• no repeat! bil ity

• specified antennas are inadequate

• customers,- however, require such testing

• have noted test variations as high as 60 dB (1000 to 1).

There is a lack of EMI consciousness on the part of all parties concerned.

Test equipment used for EMI testing is itself susceptible to EMI

unless particular care is taken to prevent such.

Bi conical antenna used for radiated susceptibility testing is

inadequate for purpose intended.

Antenna factor for biconical antennas is meaningless.

Radiated susceptibility measurements above 30 MHz cause problems.

(We) use some antiquated equipment for making these measurements.

13
(We) question the relationship between subsystem and whole system

testi ng.

(We) have repeatability problems with screen rooms--repeatabil i ty is worse at high field levels.

Most of our EMI /EMC problems are with components meeting MIL STD 461

and 462 requirements rather than with system problems.

MIL STD 461 does not address the 28 V power supply system for

susceptibility requirements. MASA has a better specification for

such.

There are lots of things wrong with the test methods defined for

radiated susceptibility testi ng--screen room variations!

Screen rooms are OK for conducted emissions testing but pose problems

for radiated emissions measurements. (We) have had 12 dB, easily,

variations (repeatability) in our screen room measurements.

We can test at exposures up to 200 V/m but no higher--where some new requirements are appearing.

A helicopter environment is a difficult EM environment because:

• electrostatic discharge

• lightning

• no shiel di ng-~they are flying panels.

(We) have had problems in calibrating probes and to use such for test

leveling purposes. NASA approves such use readily. New measurement

techniques are adequately reviewed and approved by NASA; DOD organizations, however, do not really read measurement test plans.

There is some question as to whether or not the EM emissions

requirements of MIL STD 461 are realistic.

EMI testing uses archaic methods:

• doesn't mention use of spectrum analyzer

• no mention of TEM cell

• test methods are out of date, i.e., transient response requirement.

MIL STDS 461 and 462 do not acknowledge or allow the latest in testing

equipment capabilities, e.g., does not respond to computer technology

as applied to aerospace problems.

Victim-source testing for system testing is not always a reliable EMI

system test. We do not know of any integrator who runs a real system

test on the whole vehicle.

We obtain 6 to 10 dB repeatability in our screen rooms.

14
Our biggest problem is with the standing waves in a screen room.

Photos are vital for test set up repeatability; that is, they are necessary to replicate the test set up.

If high fields exposure and EMP requirements become real, we will have

serious testing problems.

It would be nice if there was one source to deal with EMI issues as opposed to the present system.

CS02 (Conducted Susceptibility) is a problem test area. Power leads

"exercising" components themselves "pick up" EMI.

The upper limit (frequency) of radiated susceptibility is also a problem area. Screen rooms are not a good means for making such

measurements.

(We) have no screen room for high level testing, e.g., a customer

requirement for 265 V/m test. (We) will, instead, use. inhouse an- echoic chamber for this test.

Most testing difficulties with components are at the higher

frequencies.

(Our) small screen rooms have experienced resonance problems, a 6 dB

variability in radiated susceptibility measurements and a 20-30 dB

variability in radiated emissions measurements.

The lack of EMC knowledge by vendors prevents the use of better

testing methods.

We have experienced 25 to 30 dB variations when doing component testing in screen rooms. In screen room testing it is important to

"duplicate" test set ups to ensure repeatibil i ty.

MIL STD 461 does not differentiate between signal and power lines. We

require our vendors to identify critical lines and their upset values.

Screen rooms are difficult to work with because of multiple reflections. Some customers will not "buy" radiated susceptibility testing

in screen (shielded) rooms.

We have difficulties in specifying accurately what field levels are present in shielded rooms.

The Army does not "buy" spectrum analyzers, isotropic probes, etc. for

testing purposes, "nothing new since 1967."

Specifications are so ambiguous that the government has its own interpretation while a vendor has another.

For conducted susceptibility measurements, the Army requirement of -30

dB/m is difficult to do because current and voltage measurements must

be made at the same time. We need better current probes to do such.

15
EMI testing, antenna factors, etc. is a big con job and we don‘t know

how to solve such with a specification.

(We) do not advise "tailoring" of specifications, particularly for

general purpose equipment.

We have had some troubles with MIL STD 461B, CS06 (Conducted Susceptibility) test requi rements; the specification requirements for pulse

width are too short.

New digital systems will cause a significant impact on EMI testing.

Existing specifications do not relate to digital systems.

System measurement problems, as noted by victim-source testing:

• when the components are near their specification limit

• broad band interference to communications receivers in the 100 kHz

to UHF frequency band from own onboard generated interference

occurs.

Emissions problems are, in general, where there is a clock in the component.

IX. COST OF EMI /EMC ACTIVITIES

The survey of contractors furnishing electronic components and systems to

AVRADCOM revealed the following estimated costs incurred by industry for their

EMI /EMC activities. Contractor names are coded for confidentiality.

Electronic Component Contractors

Contractor A:

Contractor B: Contractor C:

Contractor D: Contractor E

:

Contractor F

:

Contractor G:

Contractor H:

Contractor I:

2% to 6% of total product development cost, 0.5%

to 10% of product production cost

4% of total development cost

0.5% to 1.5% of total contract cost

3% to 10% of product development cost

3% to 7% of total development cost

5% of total development cost

10% of total work effort

10% to 20% of total environmental testing costs

1% of total program development cost.

Ai rframe Contractors

Contractor J :

Contractor K:

for components, 5% to 10% of total qualification

testing cost

20% to 25% of total environmental testing costs.

16
These costs are "ball -park" estimates; hence, their accuracy cannot be

assessed. One contractor. Contractor A, performed some cost analysis work on their EMI/EMC activities. Accordingly, the estimate for Contractor A was given with no hesitation or qualification; it is probably fairly accurate.

In addition to the above costing information, the following remarks were

made

EMI testing is easily more than $100, 000/vehicle.

EMI testing is 3 times more costly than all other environmental

(tests) together.

Recently, $150,000 was spent to make 3 (black) boxes EMI compatible.

MIL STD 461 testing is too expensive for more than qualification

testing--not suitable for production sampling.

An inhouse EMI test capability is too expensive; it would cost (us)

$250,000 just to update test equipment and this does not include the

cost of a screen room.

EMI test costs average $15,000 for each EMI test.

EMI testing is done only at item qualification test level --not done

with production items due to high costs.

A screen room has been modified to have one wall covered with ferrite

absorber material at a cost of $100/sq ft.

EMI testing represents 1/3 of total environmental testing costs.

Outside test costs: $400/day at one facility

$600 - $800/day at another facility.

(Our) typical costing is $650 to $800/day. (We) spend "a lot of time"

at a test house. Outside EMI services cost $80/hour.

(We) have had a major retrofit job on an engine with EMI problems that

required 2 years of engineering effort at a cost of $500,000.

Field levels above 60 V/m are very costly—costi ng is not linearily

related to field levels. High fields are very expensive.

(Our) consultant cost is approximately $500/day.

EMI testing is very expensive.

(Our) EMI testing is approximately $70/hour.

Commercial and military systems require about 1000 hours of direct

engineering labor for 6051 system testing. The amount of shop time

for such, however, is unknown.

17
Four months of solid test time were required for 6051 system testing

of a modified aircraft.

X. ELECTROMAGNETIC HAZARDS TO PERSONNEL AND EQUIPMENT

The potential personnel hazards due to exposure to electromagnetic radiation are well known. So-called "safe exposure levels" have been established

and the enforcement of these safeguards is handled, typically, by state and

federal agencies.

Since there is a recognition of this potential hazard to personnel and

equipment, several industrial contacts briefly discussed this matter during

the course of the survey. Their comments follow.

Some contractors have EM safety committees to monitor potential test

hazards.

New requirements for high field strengths, e.g., 200 V/m and 976 V/m

pose definite safety hazards at test facilities.

Operational EM levels appear to be, in many cases, unknown.

f We) have a safety committee that is concerned with high level

fields. Our facility only goes to 50 V/m; for higher level fields we

will use outside facilities. (We are) unaware of a new 976 V/m field

requi rement.

We are concerned with the issue of EM hazards to personnel.

We check for leakage of our screen rooms on a random basis. (We have)

no formal inhouse safety program for EM hazards.

(We) do not make leakage tests of screen rooms.

(We are) concerned with the susceptibility of ordnance to the onboard

and external EM environments. Such hazards are now receiving some emphasi s.

(We have) no special health and safety considerations for EM testing.

[NOTE: From these contacts, and to the best of our knowledge, it is not

apparent where any "high fields" test facilities are or will be found for the

high fields testing of future systems.]

XI. m UBS ROLE TO IMPROSfE EMI /EMC f€ASUREf€NTS

Many of the contractors surveyed suggested a role for MBS so that

improved EMI /EMC test methods and standards would become available.

Representative contractor comments relating to this are:

(MBS should) develop a reasonable, reliable specification with well

defined testing methods.

18
A measurement tool to determine the cross coupling of cables (in the

aircraft) is needed for cabling guidelines.

(We) need more objective testing techniques.

(There is) a need for a better multiple isotropic probe sensor system

to determine (measure) the fields radiated at equipment under test--a

system to cover the 14 kHz to 18 GHz frequency range with a 1 V/m

sensi tivi ty.

(NBS should) develop a reliable test method for emission and susceptibility testing using presently available shielded rooms.

(We) need a high-field strength test method for whole system testing.

(NBS should) develop a transportable reference antenna for checking of

antenna ranges.

NBS should come up with EMI measurement techniques, standards, etc.

(NBS should) develop better equipment for generating known EM fields,

e.g. , a TEM cel 1

.

(NBS should) develop a replacement for the conical spiral antenna for

generating EM fields.

(NBS should) develop means to improve the repeatabil i ty of test

methods.

XII. CONTRACTOR RECOMMENDATIONS FOR EMI /EMC TEST

AND SPECIFICATION CHANGES AND OTHER CHANGES

Practically all of the contractors contacted for this EMI/EMC survey had

suggestions or recommendations to offer concerning the improvement of presently available specifications, standards, and test methodology. These

suggestions and recommendations, in large measure, result from the current

problems the contractors are experiencing in meeting contract-imposed EMI/EMC

requirements. Some contractor suggestions and recommendations are as follows:

Get rid of screen rooms.

Tailor (EMI/EMC) requirements to the host vehicle.

Raise EMI consciousness of all parties concerned.

System integrators, especially, need to be EMI conscious and make sure that the final installation is the same as the test configuration.

MIL STD 462 needs revision to better define test methods and test

rel iabil ity.

19
Definition of quantities in MIL STD 461 is inadequate and should be

revi sed. • Specifications should allow for use of a good spectrum analyzer.

Remove the parallel plate test "jazz."

Update the list of acceptable (test) equipment.

(In the specifications) include alternative test methods such as use

of a TEM cel 1

.

An anechoic chamber would be far better than present screen room

testi ng.

There is a need to standardize the parameters for test receivers:

bandwidth, detector, etc.

MIL STDS are ambiguous on defining "power line" for conducted (EMI)

susceptibility and emissions testing--the physics of the item under

test are (now) ignored. Accordingly, an update of the MIL STDS, e.g.,

units, terms, definitions, is needed.

Criteria for susceptibility levels should be negotiated for the

equipment by the user and contractor rather than using a general

specification.

Signal input and output port characteristics should be specified

separately from MIL STD 461.

A mission profile for EMI should be specified rather than using a general specification. A military expert, not a procurement specialist, should specify the EMI mission profile.

Change the present procedure which calls for a bidder to agree to do

all EMI testing to one of a "tailored" specification. Some con- tractors do not include total EMI test costs in their bid in the

knowledge that waivers for such are available.

Test equipment and operating equipment should also be shielded (put in

a separate shielded room) during testing.

(There is a) need for more tailoring of specifications to suit end

applications, not less.

For EMI/EMC testing (we) would like to see a large, government

operated or owned EM test facility in the Southern California area to

which all contractors would have access.

The conducted emissions on signal lines is a requirement that could be

tailored rather than to the present fixed level.

There is a need for a standard format for EMI control plans.

20
Notice 4 (Army document) for MIL STD 461 is a confusing document and

ought to be thrown away.

Tailored specifications would be more reasonable for host vehicle

appl i cations.

Clarify and quantify language, i.e., "narrowband" and "broadband."

Update the (test) equipment list which dates back to 1964.

MIL STDS 461 and 462:

• need better organization

• need clarification (more readable)

• the transient injection test is subject to interpretation

• there is too much testing of power lines, not enough of signal

1 i nes

• need standard signals for injection

• need tailoring

• need standard test procedure for threshold testing.

(We) would like to see specifications written around antenna factors,

using manufacturer' s figures for such.

Chattering relay test procedure would be good for inclusion in

military specifications as a means to test cabling.

Measurement needs include:

• a method of measuring fields inside a vehicle, in the cabin, in the

avionics bay, etc. without disturbing the field

• detecting the effects on electroexplosive devices from all EM

sources (radiated and conducted)

• since vendors sometimes take screen room liberties, there is a need

to eliminate loopholes in specifications--language needs

improvement to eliminate different interpretations

• a need to better define test methods and test set ups.

XIII. CONCLUSIONS

The contributions to this survey, made by many people in industry and

government, were voluntary and offered in good faith. In the authors' opinion

these contributions were aimed particularly at improving industrial EMI/EMC

measurement assurance and at reducing the presently high costs of such assurance. The authors perceive that industry has a sincere desire to do a better

job, to reduce costs and, further, is looking for help to do so. Accordingly,

the following conclusions have been reached:

21
A. Victim-source testing is the only current EMI test that is meaningful for

whole system testing, but even it has its limits.

• Only one piece of equipment (black box) on the vehicle is tested at

a time; such is not a true system test.

• Electronic system sample testing is inconsistent.

• Electronic component sample testing is almost nil.

• EMC Contnpl Boards are not always implemented.

• There is a nonuniform configuration control between component

contractors and system integrators.

9 There is inadequate configuration control at Army depots.

B. There is no proof that electronic systems will perform satisfactorily in

a battlefield electromagnetic environment.

• There is no evidence of a knowledge of such an electromagnetic

envi ronment.

• The electromagnetic environment in equipment bays is unknown.

• In some cases performance waivers are granted liberally.

• There are no means to create such an environment for effective

whole system testing.

C. There is no correlation in test practices; thus, electronic systems over- design, overtest, and excessive costs are possible.

• It is quite possible that component specifications are much too severe.

• Component test does not ensure system testing requirements.

• Component specifications are confusing, ambiguous, inadequate, too

general, and are out of date.

• Component specifications are applied too rigorously; they could be

tailored.

• Screen rooms are poor test measurement means.

• EMI consciousness and expertise declines as the product moves from

the design stage to the production stage.

• There is inconsistency in permitting the use of alternate test

procedures.

• There is inconsistency in the granting of specification noncom- pliance waivers.

[NOTE: It would appear that the "management hierarchy" of the vital

electronic systems and subsystems should at least participate in the

waiver granting process rather than continue with the present process.

As mentioned by one contractor, "When we fully understand the system,

such as a gun system, we are much more knowledgeable in deciding on or in

granting waivers." This could be applied to electronic systems.]

22
D. Future i ssues--new EMI /EMC requirements and issues.

• There will be requirements for high-level (greater than 200 V/m

testi ng)

.

• Nuclear EMP test requirements are likely to be imposed.

• There is a need for "EM effects" with composite materials test

information base.

• The increased use of digital systems will impose new EMI /EMC

requi rements.

XIV. COMMENTS

This survey revealed a wide variety of responses from the individuals

contacted. Some responses even contradict each other, e.g., "The Army's

Notice 4 is a good attempt at more realistically defining EMI requi rements" as opposed to "Notice 4 (the Army document) is a confusing document." The

variety of comments illustrates the sometimes narrow viewpoints of certain

personnel involved with EMI/EMC requirements and testing; their own interests

and degree of EMI consciousness all play a significant role in establishing

these particular viewpoints.

It is the authors' considered opinion that if the EMI consciousness of

all parties concerned (engineering designers, managers, DOD personnel, etc.) was raised, better decisions regarding equipment design, system integration

(e.g., cable control), component and system testing, performance waivers, etc.

would be made; further, many of the EMI/EMC related problems would be

significantly reduced. This is particularly appropriate in the light of the

anticipated high fields exposure requirements for future systems.

Also, it appears that in many cases electronic warfare (EW) considerations may not be given sufficient attention. Since there is already much

evidence that EW plays a significant role in weapon systems performance, and

many predictions that it will play an even greater role in the future, it is our opinion that contractors (new and old alike) and users need to make a more concerted effort to properly consider EW and its relationship to electronics

system performance.

The authors have also noted from this survey that aircraft for tri -service end use are often required to meet different EMI/EMC specifications and EM

environments. It is not clear (to us as well as to some of the contractors)

why this is the case. It would seem that a tri-service (i.e., DOD) group

knowledgeable in EMI and EMC, and representing users, could develop appropriate specifications to consolidate the different designs and test activities,

thereby reducing total costs.

Another observation the authors made from this survey is that present

test practices call for single-frequency testing only for EMI/EMC, i.e., one frequency at a time across a frequency band. Since systems, particularly in a battlefield environment, would be in a "swamp of frequencies," it would appear

that testing should incorporate multiple frequencies in the near future. Some

of these frequencies are already known or suspected to be present in an operational environment. As before, it would seem that these frequencies and their

appropriate power levels, etc. could best be determined and implemented by a tri -service group.

23
NBS-114A (REV. 2-80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 84-1698

2. Performing Organ. Report No 3. Publ ication Date January 1984

4. TITLE AND SUBTITLE

An Assessment of Electromagnetic Interference (EMI) and Electromagnetic Compatibility

(EMC) Measurement Practices to Meet U.S. Army Aviation Research and Development

Command EMI/EMC Requirements

5. AUTHOR(S)

W. J. Alspach, C. K. S. Miller, G. R. Reeve

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struction s) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City . State, ZIP)

U.S. Army Aviation Research and Development Command (AVRADCOM)

10.

SUPPLEMENTARY NOTES

J Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most si gnifi cant information. If document includes a si gn i fi cant bibliography or literature survey, mention it here) A survey of selected industrial contractors, airframe manufacturers , and electronic

test and calibration firms was conducted during June - August 1982 by the Electromagnet

Fields Division, National Bureau of Standards, to assess industrial and commercial

testing and measurement practices used to meet electromagnetic interference/el ectromagnetic compatibility (EMI/EMC) requirements of the U.S. Army Aviation Research and

Development Command (AVRADCOM). This survey addressed the cost of conducting EM I / EMC

tests; whether or not electronic components, subassemblies, systems, and their testing

met specified AVRADCOM EMI/EMC requirements ; and whether the test practices, test

equipment, and EMI/EMC requirements are appropriate. The following conclusions were

reached: (1) Victim-source testing, although limited, is the only current EMI test

that is meaningful for whole system testing. (2) It is questionable whether electronic

systems will perform satisfactorily in a battlefield electromagnetic environment.

(3) There is no correlation in EMI/EMC test practices; it is possible that electronic

systems are overdesigned, overbuilt, and overtested. (4) Future issues such as highlevel field testing and electromagnetic pulse (EMP) need to be addressed.

12.

KEY WORDS (Six to twelve entries ; alphabetical order; capitalize only proper names; and separate key words by semicolons)

electromagnetic compatibility (EMC); electromagnetic interference (EMI)

13.

AVAILABILITY

Unl imited [J^For Official Distribution. Do Not Release to NTIS

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

[~^j Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

15. Price

USCOMM-DC 6043-P80