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COTS E3 Risk Assessment Guide |
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For DOD E3 Systems Engineers |
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Final Draft for the DOD E3 |
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May 2011 |
Table of Contents
III. Determining the Electromagnetic Environment (EME) and
EM Requirements
V. Evaluate COTS EM Performance and Conduct Gap Analysis
A. Identify Commercial EMC standards/ Obtain &
Analyze data
B. List MIL-STD-461F Required/Desired Tests
C. Perform Gap Analysis for Each Test
D. Assign Risk Severity to Gaps
A. Criticality (Equipment and/or Platform)
B. Standard Definitions of Likelihood (Probability) and
Severity (Consequence)
VII. MITIGATION OF UNACCEPTABLE RISK Mitigate Risk through Design and/or Retest:
Appendix A – Commercial
EMC Compliance Requirements
Appendix B – Spectrum
Certification Process
Appendix C – Risk
Assessment Analysis Template
e) Impact to Existing Systems –
will have to define
f) Interoperability Impact –
will have to define
Appendix D –
Case Studies - Pending
Appendix G –
Glossary of Terms
B. EM-TARTT
Electromagnetic Test & Requirements Tailoring Tool
C. UEM - Unified Electromagnetic Design
1. Unified EM Design Software Request Form
Figures and Tables
Figure 1 - COTS E3 Risk Assessment Process
Figure 2 - Gap Analysis Process
Figure 3- Effect of Criticality on Risk Assessment
Figure 4- Flowchart for
Evaluating Spectrum Supportability of COTS
Table 1 - EM Threats vs.
Platforms
Table 2 - Shipboard Equipment Category Examples
Table 3 - Equipment Requirements Matrix
Table 4 – Shipboard Example of Criticality vs. EME
Zones
Table 5 - Applicability of MIL-STD-461F Test Methods
Table 6 - Terma Scanter 2001 - Example EMI
Requirements Comparison
Table 7 - Terma Scanter 2001 Example EMI Requirements
Table 8 - EMC Gap Analysis Factors Affecting Test Severity
Table 9 - Guide to Minimum
Acceptable Risk Resulting from EMC Gap Analysis
Table 10 - Assessment of Commercial Standards vs.
MIL-STD-461
Table 11 - Guide to Acceptability of Risk Resulting
from EMC Gap Analysis
Table 12 - Guide to Risk Rating Resulting from EMC Gap
Analysis
Table 13 - Risk Levels (High, Serious, Moderate and
Low)
Table 14 - Levels and Types of Consequence Criteria
Table 15 - Suggested Mishap Probability Levels
Table 16 – Modified 3x3 Risk Reporting Matrix
Table 17 - Example Mishap Risk Assessment Values
Table 18 - Example Mishap Risk Categories and Mishap
Risk Acceptance Levels
The use of commercial items (CI) or commercial-off-the-shelf (COTS) [hereafter
referred to as COTS] equipment presents a dilemma between imposing military E3 standards
and the desire to take advantage of existing commercial systems, and accept the
risk of unknown or undesirable electromagnetic interference (EMI)
characteristics. Regardless of the pros
or cons of using COTS, any procured equipment should meet the operational
performance requirements, including electromagnetic compatibility (
Integration of COTS electrical/electronic equipment on
DOD platforms is an increasingly common practice for a variety of good
reasons. COTS typically offer the latest
technology and can be cheaper and more quickly fielded than military systems
developed from scratch. Unfortunately,
commercial equipment is not designed for the harsh electromagnetic environments
(EME) found in military platforms and theaters of operation.
One of the biggest difficulties with integrating
COTS products into complex military systems is achieving
COTS equipment has typically been designed, tested
and fielded to much less demanding commercial
The use
of Commercial Items and Non-Developmental Items (CI/NDI) or Commercial
Off-the-Shelf (COTS) equipment allows the military to take advantage of
technological advances, cost savings and rapid procurement stemming from the
competitive pressures of the commercial marketplace as well as developments in
other DOD or government agencies. The
use of these items can minimize or eliminate the need for costly,
time-consuming, government-sponsored research and development programs.
COTS equipment
usage forces the need for a balance between imposing the usual military
Electromagnetic Interference (EMI) controls on existing designs, which may have
unknown or undesirable EMI characteristics
Because these systems are often not designed for the military
electromagnetic environments (EMEs), they may malfunction from susceptibility
to the EME or cause other operational EMI problems. COTS are typically designed and tested to EMI
specifications and standards that don’t provide the same protections against
undesired emissions and susceptibilities that military EMI standards requirements
do. Using COTS carries a risk of
fielding equipment with electromagnetic incompatibilities onboard a military
platform. To mitigate the risks, a suitability assessment is required to evaluate
the installation environment and the equipment’s EMI characteristics through a
review of equipment design, existing test or analytical data, or even limited
testing results.
SD-2, Buying Commercial and Non-Developmental Items, An acquisition guidance handbook,
defines Commercial Items (CI) and Non-Developmental Items (NDI) as follows:
A commercial item is any product or service that is
customarily used by the general public or nongovernmental entities and has:
Non-Developmental
Items (NDI), on the other hand, are defined as having been previously developed
and used for Government purposes by another DOD /Federal Agency, State or local
Government, or by a foreign Government that has a mutual defense cooperation
agreement with the US.
Since commercial
items/COTS are already designed and built for a commercial EME, the intended
operational EME and required E3 performance characteristics must be carefully
considered for the desired application during the military acquisition
process. Candidate COTS must then be
assessed against these criteria for acceptability. EMI problems can present a potentially
hazardous situation resulting in unacceptable degradation of mission
performance capability, damage to hardware, or even loss of platforms and
lives. To mitigate the risk, an
assessment should be performed to evaluate the equipment’s immunity characteristics
against the planned EME and ability to meet the desired performance. Factors to be considered in evaluating the suitability
of COTS for military applications include:
After
determination of the intended operational environment, the risk assessment
process starts with obtaining and reviewing existing design criteria
(commercial specs), analysis/test data and
conducting additional EMI testing (if necessary.) If the COTS was designed to a commercial
standard, or to one from another Government agency, there should exist EMI analysis/test
data or a Declaration of Conformity (DoC) (see Appendix A.) That data, if available, should be reviewed to
determine if the item is suitable for the particular application or intended
installation. If data cannot be obtained, or does not allow comparison with the
applicable
While
there are a wide variety of commercial E3 standards available, no single commercial
standard covers the EM environments and requirements of the military. There are E3 related standards developed by
professional societies such as American National Standards Institute (
On the
whole, most COTS equipment has less strict EM requirements (lower immunity levels,
higher allowable unintentional emissions, lax or nonexistent susceptibility
limits) than military equipment and could therefore be more apt to be upset or
damaged when exposed to high level radio frequency (RF) fields or could
interfere with legacy systems. Therefore the use of COTS introduces additional
risk of incompatibility and can result in problems, plus associated extra
costs, in maintaining performance through life and for re-use in other
scenarios. When considering COTS or NDI
in an acquisition, it is important to include E3 requirements and obtain and
review any existing EMI test and/or analytical data.
Figure
1 is a roadmap to systematically evaluate the EMC risk of using a COTS product
for a military application.
Figure 1 - COTS E3 Risk Assessment Process
1 Developed
originally by Pete Dorey, a Senior EMC Consultant at T�V Product Service Ltd for the UK MoD. Used with permission and adapted for US DOD
purposes
The
process above requires the intended EME and actual EM performance requirements
to be defined, and evidence of commercial EMC compliance to be evaluated. That is followed by a detailed analysis of
the “gap” between the actual EMC performance and the required performance. This gap analysis provides the basis for
performing a risk assessment of using a particular COTS item for a particular function/mission
requirement, in combination with the functional criticality of the equipment
and platform as determined by the procuring activity. Finally, the unacceptable risks are to be
mitigated by either carrying out remedial re-design, installation methods (EM barriers),
or replacement, and/or retesting. Each
major block above will be expanded in detail in the following sections.
Define Environment: In order to evaluate the
acceptability of the COTS EMC performance, it is necessary to define the EME in
which the equipment will operate. For
existing platforms the EME may already be defined or may be represented by specifying
the requirements documented in standards such as MIL-STD-464. This environment may include geographical aspects
regarding the area in which the equipment may be operated, such as operational
restrictions of US Part 15 & 18 devices in the United States and radiated
susceptibility requirements of European Union /MIL-STD-461.
Evaluate EMC Specification and
Compliance Evidence:
This process or gap analysis identifies the shortfalls of the existing EMC
performance of the COTS equipment. In order to achieve this, the EMC standards,
test methods and limits applied to the COTS equipment must be identified and
compared to the equivalent EMI tests required (like MIL-STD-461). All available E3 specifications and test data
should be obtained when procuring COTS equipment. That will allow a comparison of the
commercial EMI test results to the desired military EMI requirements, such as
MIL-STD-461.
Once the gaps and missing tests have been
identified they can be assigned a risk rating of Low, Medium or High depending
on the extent of the deviation from acceptable EM performance
requirement. When test reports are not available, the PM may have to
conduct E3 testing to determine the acceptability of using the COTS in the
acquisition. Risk Ratings will be discussed in more detail later, but the
assignment of a quantitative risk is a collaborative effort between the
acquiring office and the E3 Engineer. The program office is obviously
responsible for defining, assigning and accepting risks on his program.
But the nature of the technical expertise necessary to conduct an E3 risk
assessment on a COTS item will require that program office relies on E3
engineers for assistance in quantifying and assigning the risks in a meaningful
manner to a given procurement.
When the
COTS is a piece of spectrum dependent (S-D) equipment, there is also the
requirement that it be capable of getting equipment spectrum certification
(ESC); this is the PM’s responsibility.
Assess Risk against Functional
Criticality: The
identified gaps must now be compared to the criticality of the COTS equipment (with
consideration of the platform criticality as well) to perform its function/mission
in the operational EME in which the COTS equipment will be operated. Nil to Low
risk will generally be acceptable. In some non-critical situations Low to
Medium risk may be acceptable. In all cases a High risk is unacceptable and
must be addressed.
Mitigate Risk, Design or Test
There
are basically two options if a particular piece of equipment is to be used:
Spectrum
supportability (SS) is another issue in the militarization of COTS that must be
considered. A chapter in this document is
devoted to the management of COTS supportability issues. Modifications which alter the radio
characteristics of COTS can create coordination difficulty in trying to obtain
ESC and, later, frequency assignments.
In many cases, the systems are limited to a non-interference basis and
may face severe restrictions.
To
summarize, COTS aren’t designed with the harsh military operational EME in mind. S-D equipment is designed for use in
commercial, not DOD, bands. Commercial
EMI control, design and test requirements documents that do exist aren’t
typically stringent enough for military purposes, from either an emissions or a
susceptibility perspective. Thus, using
COTS equipment can introduce performance risk that must be managed and can
actually cause more harm than good if their characteristics are incorrectly
assessed. This document provides
guidance on how to assess these risks.
Defining
ALL the EMEs and EMC requirements is the most critical step in conducting a
risk assessment/analysis. The deployed operational
EME is often the only environments considered; storage, transportation, and
repair are examples of environments that are forgotten or not considered. They will be covered later on in this
section.
While
this document concentrates on EMI requirements, comparisons and gap analyses,
understanding the application of EMI requirements can assist with the
determination of adequate EM protection in other areas, such as applying E3 transient
tests to help determine resistance to lightning damage or EMP.
The
simplest EME definition for a COTS E3 Risk Assessment would be to use tables
from MIL-STD-464 for the appropriate platform type in which the COTS will
operate. But to properly define and
tailor an overall EME definition for the COTS application, many other factors
should be considered.
Systems
will generally be intended for use in a number of operational scenarios with
differing EMEs but there are likely to be only a limited number of scenarios
that are significantly different. It is convenient to categorize the systems by
platform so that its overall EME can be determined. Looking at the primary platform operating
environment (i.e., sea, land, air) in relationship to the types of expected EM
threats will reveal important similarities and correlations between each of
these main types of environment. The
result is the table below, from UK Defence Standard 59-411,
Part 2.
Considering the EM threats detailed in the table
below will go a long way toward a more detailed definition of the overall EME
for a COTS application and give the assessor more information by which to
tailor both the EME and the desired EMI performance requirements. These two items together, the defined EME
and the tailored EMI requirements, will provide the basis against which to
conduct the risk assessment by comparing the actual COTS EMI performance.
One can then
further subdivide the EME descriptions into the different EM threats in each
scenario. Table 1 below shows
a categorization by platform type for which the EM environments can be
significantly different. Although there
are different environments for different situations, it may be necessary to
look at only the worst case threats when testing a system (for example, one
would not produce an aircraft that was compatible with the in flight EME but
not compatible with the airbase or shipboard EME). From this chart one can determine some of the
EM threats that need to be addressed for each platform and the relationship to
the other platform environments. As an
example, if the COTS equipment is to be used on a surface ship AND is to be
used on a submarine, the EMEs are different and the E3 test requirements are
different. Initially both required EMEs
need to be included for analysis.
Table 1 - EM Threats vs. Platforms
The
following diagram is provided to pose questions regarding major EM requirements
areas that may be asked and answered when considering a piece of COTS equipment
for use in a military EME. This can help
expand on the details noted from the initial EME assessment based on Table 1. A brief discussion of each question is
provided to give more clarity to the question.
If these questions are accurately answered, a good description of the
required EME has been assembled and a gap analysis can be conducted on the COTS
equipment documented EM performance. It
should be noted, that this list is only guidance. Additional environments may need to be added,
based on the nature of the product and where it is to be used. For example, the EMP section could be
expanded to include other hostile electromagnetic environments (EME), tailored to the expected
mission profile of the platform, which may include non-nuclear EMP (e.g.
E-bomb), high-powered microwave (HPM),
jammers, or other hostile electronic
warfare (EW) sources. While beyond the
scope of the examples provided in this document, it would be useful to
sub-divide the EME into friendly and hostile military environments, which would
be of use in determining COTS risks on non-combat platforms (engineering support vehicles,
costal patrol ships, transport aircraft) whose mission profile would see
them exposed to friendly EME, but would
not likely be exposed to hostile EME
such as EMP, high-powered microwave (HPM), jammers, or other hostile electronic warfare sources.
Define EME EME
Defined Go
To COTS
EMC Performance Environment & Mission And other considerations Unique application and/or
location requirements? Entire system located in same
location? Storage Requirements? Transportation Requirements? Repair Requirements? Intentional or Unintentional
Radiator? TEMPEST Requirements? Hull Generated
Intermodulation Interference? ESD Requirements? EMP Requirements? HERF Requirements? HERP
Requirements? HERO
Requirements? Operation Near Ordnance? Susceptibility
(EMV) Requirements? Lightning
Requirements?
Unique
application and/or location requirements?
Application and location requirements must be determined to ensure the COTS equipment is effectively
evaluated for use in the military application.
The application and/or location of the COTS equipment may not be according
to the classifications normally expected by the military standards. An example is stated in MIL-STD-464 which asks:
Both are different environments, but the above questions need
to be answered. Basically, these
questions are aimed at the COTS equipment being used on surface ships and
submarines. Answering both questions is
important to ensure one or both environment requirements are considered within
MIL-STD-464 when applicability is determined.
Comments about equipment used on shore stations, aircraft and other
platforms will be addressed later.
Entire system
located in same location?
A system may consist of several subsystems located within
different environments. A good example
is a radar. It tyically consists of an
antenna, control assembly, and a monitor, and all three are normally not
located in the same area and are potentially in different EMEs. Each subsystem EME needs to be defined and
evaluated, based on where each will be located.
Normally the entire system is looked at as a whole and the most
stringent E3 requirement is used for the analysis. A more effective approach in
the use of COTS might be to apply different EMEs (from MIL-STD-464, for
example) or different MIL-STD-461 requirements to the different pieces of the
system to better assess its overall performance. One could even take actual EME measurements in
each area with the antenna, control assembly, and monitor in place of using the
requirements of MIL-STD-464. In any
event, care should be exercised when determining the E3 requirements for a
system that consists of several subsystems not colocated in one EME.
Intentional or Unintentional
Radiator?
Intentional
radiators are devices that generate and emit RF energy by radiation or
induction on purpose as part of their operation. Typical Examples:
−
Radar Systems
− Portable Communication
Devices (PCDs) including cordless telephones, portable radios (“walkie-
talkies”), cell phones, and radio-frequency identification (RFID) systems
−
Remote Switches, door controls, alarms
−
Wireless Local Area Network (WLAN) and wireless laptop computers
Subsystems
and equipment that use, transform, or generate undesired EM energy as a
by-product of performing its mission are considered to be unintentional
emitters. Typical Examples:
−
Intentional radiators emitting other than the intended emission
−
Computers and associated peripherals
−
Televisions, cameras, and video equipment
−
Microwave ovens
−
Radio and radar receivers
−
Power supplies and frequency converters
−
Motors and generators
−
Electrical hand tools
Stating
that the proposed COTS equipment is an intentional or unintentional radiator is
a statement used in the national and international commercial community to
categorize and determine resultant testing scenarios.
EMSEC/TEMPEST
Requirements?
If EMSEC/TEMPEST is a requirement refer to “NSTISSAM TEMPEST/1-92 and CNSS
Advisory Memorandum TEMPEST 01-02” which provides testing methodology for
verifying compliance with TEMPEST requirements, which would be over and above
EMI testing.
Storage ,
Transportation and Other Non-Operational EME Requirements?
EMEs are different for different phases of an equipment’s
lifecycle, particularly for non-operational phases, such as for storage or
different modes of transportation. Storage and transportation EMEs can be of
major importance, especially if the requirements do not match the requirements
of MIL-HDBK-235 and
MIL-STD-464. While non-operational EMEs
might tend to be more benign than operational EMEs, there may be times when
items are stored or being transported near high powered transmitters. MIL-STD-464 can provide additional guidance
on these types of requirements.
Hull Generated
Intermodulation Interference? (IMI)?
The Navy
has a concern with controlling higher order modulation (IMI) products, most specifically
aimed at S-D equipment operating in the High Frequency (HF) band, to permit
effective use of the spectrum. This is a
consideration for shipboard COTS installations and will contribute to the
definition of the EME. If this is a
requirement for the COTS equipment, refer to MIL-STD-464 and the particular
requirements that are supplied.
ESD
Requirements?
ESD
occurs when the static electric field between two objects exceeds the
dielectric strength of the air between them.
ESD primarily affects systems at the component level. Examples of sensitive components that can be
damaged are:
·
Microcircuits
·
discrete
semiconductors
·
thick
film resistors
·
hybrid
devices
·
piezo-electric
crystals
ESD can
cause intermittent or upset (transient) failures as well as hard failures. Intermittent failures occur when the
equipment is in operation and is usually characterized by a loss of information
or temporary distortion of its functions.
Depending on the operational scenarios for the COTS equipment, the ESD
environment can be significantly strenuous such as in the case of equipment
exposed to vertical lift and in-flight refueling environments. Requirements and guidance are contained in
MIL-STD-464 and 1686 and MIL-HDBK-263.
EMP Requirements?
High-altitude
EMP (HEMP) is generated by a nuclear burst above the atmosphere which produces
coverage over large areas and is relevant to many military systems. This EME is classified and is currently
defined in MIL-STD-2169. EMP
requirements are normally imposed on equipment and subsystem enclosures when
they are located external to a hardened (shielded) platform or facility.
MIL-STD-461,
RS105, Radiated Susceptibility, Transient Electromagnetic Field is used to
verify the ability of the equipment under test (EUT) enclosure to withstand a
transient EM field such as that created by an EMP. The equipment or subsystem enclosure shall
not exhibit any malfunction, degradation of performance, or deviation from
specified indications. This requirement is applicable only if invoked by the
procuring activity. Potential equipment responses due to cable coupling are
controlled under CS116.
And
as previously mentioned, EMP requirements could be expanded to include other
hostile EME sources such as non-nuclear EMP, HPM and other hostile EW sources,
particularly for COTS use on combat platforms (as opposed to support
platforms).
COTS
equipment is not normally designed and tested to EMP requirements, only when
required by the military for specific applications. Therefore, EMP conformance can be a major
stumbling block in qualifying COTS equipment, imposing substantial design
changes and testing requirements.
HERF Requirements?
Hazards
of EM radiation to Fuels (and volatile materials) (HERF) is the potential
hazard that is created when volatile combustibles, such as fuel, are exposed to
EM fields of sufficient energy to cause ignition. HERF considerations will exist if the COTS
equipment is a RF transmitter of significant power and is to be located/operated
near volatile combustibles.
Requirements
to control EMR hazards to fuels are in MIL-STD-464. NAVSEA OP 3565/NAVAIR 16-1-529, VOLUME 2
provides procedures for establishing safe operating distances.
HERP Requirements?
Hazards
of EM radiation to Personnel (HERP) is the potential hazard that exists when
personnel are exposed to an EM field of sufficient intensity to heat the human
body. Radar and EW systems present the
greatest potential for personnel hazard and will most likely have HERP
requirements.
MIL-STD-464
requires compliance with current policy spelled out in DODI 6055.11, Protecting
Personnel from Electromagnetic Fields.
It identifies the controls for personnel exposure to Electromagnetic
Fields (EMF), EM radiation (EMR) and lists the present maximum permissible
exposure (MPE) levels. If the COTS equipment is an intentional EMF radiator
system refer to DODI 6055.11 for more information.
Host
nation requirements for HERP (RADHAZ) might be required if the system is to be
installed overseas. Refer to STANAG 2345
and Ministry of Defence Standard DEFSTAN 59-411 Part 5 for more international
requirement information.
HERO Requirements?
Hazards of Electromagnetic Radiation to Ordnance (HERO) is
the potential hazard that exists when ordnance, or explosive devices are
exposed to RF fields. HERO is the danger
of accidental ignition or dudding of electrically initiated devices (EIDs) in
ordnance due to RF fields. If COTS
equipment is to be operated near ordnance, ordnance safety requirements are
mandatory. It is possible that EMF levels can
cause premature actuation of ordnance EIDs.
RF energy of sufficient magnitude to fire or dud EIDs can be coupled
from the external EME, either by explosive subsystem wiring or by capacitive
coupling from nearby radiated objects. Possible consequences include both
hazards to safety and performance degradation.
If the COTS equipment is operated near ordnance, HERO safety analyses
must be undertaken to ensure that emissions from the COTS do not exceed the
maximum allowable EMR levels for the ordnance items.
Transportation,
shipping and other non-operational EMEs were mentioned previously, but HERO
represents a special case for which you need to understand the operational EME
for all of the Stockpile-to-safe separation sequences (S4). Thus, for HERO, the characterization of the
operational EME where ordnance is transported/stored, assembled/disassembled,
staged, handled/loaded, platform loaded, as well as the immediate post-launch
environment (vicinity of ship) would be required. And requirements will differ depending on the
procuring service.
A good
example of the problem is that, during shipment, storage, checkout and launch,
a missile will be exposed to different EME levels. While a missile would not likely be a COTS
item, it may incorporate COTS components in its design. Overall, the missile’s performance must not
be degraded by any specified EME. EMI
Performance requirements should ensure the COTS performance is not adversely
affected by any of the EME levels that will be encountered.
Refer to
MIL-STD-464 and MIL-HDBK-240 for HERO requirements and evaluation guidance.
Additional guidance:
NAVSEA OP 3565/NAVAIR 16-1-529,
VOLUME 2 Electromagnetic Radiation
Hazards (Hazards to Ordnance)
AECTP-508/3 NATO HERO Guidance
OD 30393 Design Principles and Practices for Controlling
the Hazards of Electromagnetic Radiation to Ordnance (HERO Design Guide)
MIL-STD-1576 Electro-explosive Subsystem Safety
Requirements & Test Methods for Space Systems
EM Vulnerability (EMV)
(Susceptibility) Requirements?
EMV is
the characteristic of an item that causes it to suffer degraded performance, or
the inability to perform its specified task, as a result of the operational
EME. An item is said to be vulnerable if
its performance is degraded below a satisfactory level because of exposure to
the stress of an operational EME or transient. There are many different EME
levels that a COTS item will be exposed to during its life cycle. Many threats
will be seen only infrequently. However, if the COTS encounters an operational
EME corresponding to its susceptibility characteristics as observed in a
laboratory test, it may suffer degradation in performance, or not be able to
perform its specified task at all in that operational environment.
Lightning
Requirements?
Lightning
can affect a system in two distinct ways, directly or indirectly.
Direct
effects are any physical damage to the system structure or equipment due to the
direct attachment of the lightning channel. These effects include tearing,
bending, burning, vaporization, or blasting of hardware, as well as the
high-pressure shock waves and magnetic forces produced by the associated high
currents.
Indirect
effects are those resulting from electrical transients induced in electrical
circuits due to coupling of the EM fields associated with lightning and the
interaction of these fields with equipment in the system.
The fact that MIL-STD-461 is really a set of EMI
requirements intended to serve a wide range of platforms, from ships to
aircraft to submarines to fixed installations, special applications such as
“above and below deck” reflects that there are some tests that need to be
covered by another means. Lightning is one of them.
Operational
performance requirements related to EMC in MIL-STD-464do not directly correlate
to a set of tests specified in MIL-STD-461.
Conducting CS115 & CS116 as a prerequisite to EMP testing will
satisfy some of the requirements of MIL-STD-464 for lightning, however,
reference to more applicable military or commercial standards for requirements and guidance in the design of lightning
protection systems applicable to a specific platform.
Initially, refer to MIL-STD-464 for your electromagnetic
environmental effects (E3) interface requirements and verification criteria for
your airborne, sea, space, or ground system and then refer to the military and/or commercial
standard(s) that are requested. For instance, DO-160E provides lightning
transient test procedures.
Below is a list of lightning standards for your
reference. As can be seen from the
descriptions, lightning standards have been created based on specific
platforms, such as aircraft. It stands
to reason that an aircraft standard would not necessarily be the correct
standard applicable to testing munitions.
EUROCAE ED-84F Aircraft Lightning Environment and
related test waveforms
NFPA 78-89 Lightning
protection code
SAE ARP-5416 Aircraft
Lightning Test Methods
SAE AIR 1406-76 Lightning
protection & ESD
DEFSTAN 02-516 Guide to Lightning
Protection in HM Surface Ships
RTCA/DO-160E Environmental
Conditions and Test Procedures for Airborne Equipment, Section 22: Lightning
Induced Transient
DEFSTAN 59-411 Electromagnetic
Compatibility, Part 2, Electric, Magnetic & Electromagnetic Environment
STANAG 4327 Lightning
Munitions Assessment and Test Procedures
AOP 25 Lightning
discharges assessment and tests rationale and guidance
AECTP 505 Verification
methodology for the electromagnetic hardness of aircraft
NCS 10 Conducted
Susceptibility, Imported Lightning Transients (Aircraft / Weapons)
AECTP 508/4 Lightning, Munitions Assessment and
Test Procedures
Developing
a methodology to categorize COTS into specific groups can help to define the
overall EMI requirements, based on the category function and location
(primarily). One method is to categorize
equipment by Equipment Type according to Function (in relation to the use of
the equipment), which helps determine some primary EMI control
requirements. Category tables can be
created for major generic platform types, such as those listed in the
MIL-STD-461 Applicability Table. The
platform type helps determine the overall EME.
The combined EME and EMI requirements for each category and platform
must be carefully evaluated to ensure both minimal risk of EMI and reduced cost
to achieve EMC in the platform environment. This evaluation must include the
expected location, exposure, and use of the platform.
At the time of the drafting of
this guidance document, there exist few good categorization methodologies for
our purposes. The primary reason is that
generic categories will require extensive modification for each particular COTS
E3 risk assessment application, as often as not. Some thoughts and examples are presented so
that the reader may develop their own categorization schema as appropriate.
The best example thus far is shown
in Table 2 below, provided for shipboard equipment. It is based originally on a
categorization of shipboard equipment given in IEC International Standard
60533, Electrical and electronic
installations in ships – Electromagnetic compatibility and modified for Navy use in the
EM-TARTT EMI requirements tailoring tool (see Appendix H). Each category has associated with it
different EME and EMC requirements and equally important, different levels of
EM risk acceptability. The idea is that
using COTS in certain equipment groups that are less mission-critical or are
inherently more protected from the EME (based on location or installation) is
less risky that other uses.
Subsequently, different EMI requirements are imposed. In the case of the IEC 60533 categories,
specific IEC EMI standards apply. In the
case of EM-TARTT, different tailored sets of MIL-STD-461 requirements are
generated. In any case, the acquisition
requirements should reflect that the equipment will operate at full performance
and will not present interference to other mission critical equipment.
|
Shipboard Equipment Categories |
|||
|
Category |
Equipment and Installation Groups |
Examples of Applicable Devices |
|
|
A |
RADIO COMMUNICATIONS
AND NAVIGATION EQUIPMENT |
Receivers,
Transmitters, Meteorology, GPS, INS, Gyro System, SATCOM, HF, VHF, UHF,
Magnetic Flux Compass, Misc. |
|
|
B |
POWER GENERATION,
PROPULSION, CONVERSION |
Motor
Generators, Motors w/sensors, Variable Speed Drive, Voltage regulators,
Breakers, Solid State Frequency Changer, Electric Drive System, Misc. |
|
|
C |
PULSE POWER INTENTIONAL
RADARS |
Navigation
Radar, Combat Radar, Sonar, I/O Systems, EW Emitter, IFF, TACAN, Beacons, HF,
Misc. |
|
|
D |
MACHINERY CONTROL,
SWITCHGEAR |
Ship
Control System, Local & Remote Controls, Damage Control, Switch Boards,
Electronic Control, Machinery Control, Steering Control, Data Acquisition
Units (DAU), PLC, Misc. |
|
|
E |
IT, C4I, INTERIOR
COMMS, DIGITAL |
Computers,
Servers, Routers, Wireless Voice/Data, Digital Equipment, UPS, Interior
Communications, Electronic Equipment Cabinets |
|
|
F |
PASSIVE SYSTEMS (NON
ELECTRONIC) |
Passive
Heaters, Transformers, Induction Motors, Rigging, Misc. |
|
|
G |
HULL, MECHANICAL &
ELECTRICAL |
Medical
Equipment, Fork Lifts, Conveyor Lifts, GP Test Equipment, Window Heaters,
Cranes, Winches/Electrical, Misc. |
|
|
H |
WEAPONS, GUNS, MISSILES |
Missiles,
Guns, Weapons, Misc. |
|
Table 2 - Shipboard Equipment Category Examples
Another example of categorization
is presented in MIL-STD-461C which contained categorization tables for the
three services with attendant EMI requirements for each category. MIL-STD-461C provided a series of equipment
and subsystem classes (Table 1-II in that document) that directed the user to
specific EMI requirements in different “Parts” of the document. The classes described use on specific
platforms (Class A), items support Class A items but not in critical areas
(Class B) and Miscellaneous/General Purpose items not associated with a
specific platform (Class C). Class C
includes a section for commercial electrical and electromechanical equipment
(Class C3). The user is directed to Part
10 of MIL-STD-461C which delineates EMI requirements for this class of
equipment. Some of these requirements
might represent appropriate EMI requirements to apply to COTS applications but
an analysis of -461C requirements versus currently acceptable EMI requirements
would be required. That is beyond the
scope of this document.
The
categorization concept would lead to the development of an EMI Requirements
Matrix, such as the one shown below in Table 3, which would show the acceptable
or desired EMI requirements for each category of equipment. Table
3 lists tailored EMI requirements from IEC 60533, which lists EU type
requirements for various equipment categories.
Bear in mind that the table below is designed to be applied to a wide
variety of equipment groups; in the case of a specific COTS E3 Risk Assessment,
the interest would be in a small number of specific group requirements (i.e.
specific lines listed in the table).
X: test required -: test not required)
It must
be noted that while “categorization” may be an acceptable way to assist in the
determination of expected EME and general EMI requirements for a COTS item,
there are currently no such tables developed for application by specific
services or on particular platforms.
That task may be undertaken in the future by the COTS E3 Working Group
and would require consideration of some of the following ideas:
Category
definitions may also factor in equipment criticality. The less critical the equipment (based on its
intended function relative to the platform/system mission), the more E3-related
risk is acceptable. Adding criticality
obviously tends to complicate categorization but it’s a distinction that will
be useful later in the risk analysis.
During the risk analysis portion of the assessment, the criticality of
the system helps determine level of risk “acceptability” (i.e., low, medium, or
high risk).
So how is
mission criticality to be defined?
Sample definitions, used in the EMP world, include:
·
Mission-critical
equipment (MCE).
Deemed by the procuring and/or operational authority to be essential to
successful performance of the ship’s mission.
·
Mission-critical
failure. Either
functional upset or damage which results in unacceptable performance
degradation as determined by the operational or procuring authority.
·
Mission-critical
subsystems. MCS
consists of all MCE and support equipment required to perform critical trans-
and post-HEMP attack missions. MCS refers to equipment that must be hardened to
perform missions specified to be accomplished during or after exposure to a
HEMP environment.
Similar definitions could be developed for a COTS
application for E3 risk assessment purposes.
A promising methodology of defining criticality is by
creating a “zoning matrix” of EME categories based on the platform EME (as
shown in Table 4 below) to create EMC requirements by group with which to
conduct the final risk assessment. This is an actual example provided courtesy
of the UK Aircraft Carrier Alliance. It
defines equipment criticality levels (1* through 5) and EME Zones, resulting in
categories A through E that define a minimum level of acceptable EMC
performance.
Table 4 – Shipboard Example of Criticality vs. EME Zones
Zones would equate to (based on the CVF
EMC Policy CVF-00005386 specifying four EME controlled zones):
–
Above Decks, Above Bridge Roof Zone > 2000 V/m
–
Above Decks, Below Bridge Roof Zone < 200 V/m
–
Below Decks, High EME Controlled Zone < 10 V/m
–
Below Decks, Low EME Controlled Zone < 3V/m
EMC Requirements (Groups A to E)
Note: these groups have been adapted for US DOD
based on the original material from UK Defstan 59-411.
Group A-: The Electromagnetic Environment (EME), which
these systems/equipments are likely to be located within, will be defined in MIL-STD-464C, MIL-STD-461F Above Deck Limits, MIL-HDBK-235, and for NATO EMEs,
AECTP-258/, requirements
will be applicable to the Group A systems/equipments also.
Group B-: MIL-STD-461F Above Deck Limits, requirements
will be applicable to the Group B systems/equipments.
Group C-: MIL-STD-461F Below Deck Limits, requirements
will be applicable to the Group C systems/equipments.
Group D-: EU Directive 89/336/EEC requirements, with
the levels explained in BS EN 61000-6-2 and BS EN 61000-6-4 are applicable as a
minimum to the Group D equipments. Group D equipments will be required to have
been CE Marked or Wheel Marked certified.
Group D equipments, which are located in the Above
Decks EME, will require evidence of acceptable performance levels achieved
while exposed to the more severe EME. Those Group D equipments that are located
in the Below Decks High EME Zone may require additional EM protective design
measures to mitigate the risk of not achieving an acceptable level of EMC.
Group E-: EU Directive 89/336/EEC
requirements, with the levels explained in BS EN 61000-6-1 and BS EN 61000-6-3
are applicable as a minimum to the Group E equipments. Group E equipments will
be required to have been CE Marked or Wheel Marked certified.
Group E equipments that are located in the Below Decks
High EME Zone may require additional EM protective design measures to mitigate
the risk of not achieving an acceptable level of EMC.
While this is an example of shipboard EME
criticality zones, a similar table can be produced for any platform/operational
EME such as a forward deployed ground vehicle or
When
determining the applicable EM environments and requirements, it is necessary to
recognize possible operational restrictions that may be acceptable and to
potential failure modes. A minimum separation between a COTS system and a
potential interference source may be acceptable if the separation does not
significantly restrict operations during deployment; or possibly certain
failure modes are not mission or safety critical and a lesser degree of
hardening of a COTS installation is acceptable.
Additional cost of testing non-critical systems is a small price to pay
to ensure systems operate safely during critical or battle conditions without
jeopardizing the ship’s mission.
Any
operational restrictions, minimum separations, etc. should be formally
documented by the Equipment Program Office based on recommendations from the
program E3 engineering technical authority, as well as agreeing on the details
of the scenarios to be used in the risk assessment analyses. Similarly, the frequency of occurrence of a
particular environment may be sufficiently rare to allow it to be ignored or be
considered only relevant to safety critical failure modes (e.g. for a direct
lightning strike, some systems may only be required to remain safe but not
necessarily suitable for service). Again the detail of the requirement needs to
be agreed to by the Program office and the E3 technical authorities.
The
previous paragraphs describe a variety of environments and EME and EMC
requirements that should be considered in the use of COTS, because COTS are not
typically designed for the rigorous military EME. All equipment, COTS included, will be
expected to perform effectively and not cause E3 degradation or damage to any
equipment it operates near. Although
there are different environments for different situations, it may be necessary
to look at only the worst case environments when considering the use of COTS in
a military EME. For example, one would
not manufacture an aircraft that was compatible with the EME in flight but not
compatible with the airport EME. The
remainder of this document focuses on a process by which to compare
subsystem/equipment EMC type requirements that COTS are typically designed to
against MIL-STD-461, which represents the requirements that the DOD would
typically impose.
DODI 4650.01 establishes DOD policy for
management and use of the EM spectrum and defines procedures for obtaining
required equipment spectrum certification (ESC). As of January 2009, it also requires DOD
Components acquiring spectrum-dependent systems to perform spectrum supportability
risk assessments (SSRAs). An SSRA is an
evaluation performed by the DOD Component on all spectrum-dependent systems,
INCLUDING COTS, to identify and assess EM spectrum and E3
issues that can affect the required operational performance of the system. These risks are reviewed at acquisition
milestones and managed throughout the system’s lifecycle. Specific task and data requirements for the
conduct of SSRAs are still emerging but your service Frequency Management
Office can provide guidance on the basic requirements.
Spectrum Supportability, a relatively
new term in the spectrum management and use area, is an assessment as to
whether the electromagnetic spectrum necessary to support the operation of a
spectrum-dependent equipment or system during its expected life cycle is, or
will be, available. A Spectrum Supportability Risk Assessment requires:
–
Equipment Spectrum
Certification,
–
Host Nation Spectrum
Supportability Assessment (including US&P)
–
EMC Analyses to
determine possible EM interactions requiring further analysis
Equipment Spectrum Certification (ESC)
Compliance is a statutory requirement for S-D systems, based on US Codes,
Public Law and OMB guidance that basically states:
1.
You cannot use the EM
spectrum without obtaining certification and a frequency assignment to operate,
and
2.
You cannot spend DOD/public
money to buy or build a system unless you know that it can obtain spectrum
supportability.
3.
It applies to any S-D
equipment used by the DOD and does not differentiate between COTS and DOD
developed systems.
The request for ESC, called the DD form
1494, Application for Equipment Spectrum Certification, is the vehicle by which
certification is achieved and is also used for implementing Host Nation
Coordination (HNC) and ascertaining frequency supportability within the
territories of foreign nations. NTIA now
requires the use of the EL CID form/format for submission of United States Government
(USG) ESC requests. In OCONUS operations,
the use of the spectrum for U.S. operations is by permission of the Host
Government and is formalized in an agreement between the U.S. and the Host
Government. To ensure EMC, the Host Government, in most cases requires the U.S.
to supply data concerning the S-D equipments, E3, to include inland spectral
plots, and equipment characteristics from a spectrum usage standpoint. There
are no exceptions for commercial off-the-shelf (COTS), non-developmental item
(NDI), receive-only, or Electronic Warfare (EW) systems when the equipment,
system or subsystem is to be operated outside the United States by the US DOD.
Spectrum Supportability and the Spectrum
Supportability Risk Assessment provide a documented plan/report to achieve
positive SS Determination and also document details of the following for each
piece of RF Spectrum Dependent equipment, system or subsystem:
–
J/F 12’s for each RF
piece of equipment
–
Status of Host Nation
Coordination
–
Known Spectrum
Supportability issues
–
Potential Operational
impact of known spectrum supportability deficiencies, particularly in foreign
countries
–
Program Risk (R/Y/G)
for each RF system, a spectrum supportability Risk summary, and Risk Mitigation
plans for spectrum supportability issues.
–
An assessment of
spectrum supportability for acquisition Milestones
Spectrum Certification is but one
element of the risk assessment process but not the main focus of this guidance
document. Additional details on the ESC
process and requirements to achieve spectrum certification are provided at
Appendix B.
Military
and commercial EMC standards are similar in that both are concerned with
controlling emissions to and from surrounding equipment as well as identifying EM
susceptibilities of the equipment. That is where the similarities end. Unlike the commercial environment, the
military environment contains heavy concentrations of equipment in a confined
area, high powered transmitters, and very sensitive receivers. This means that “mutual compatibility”
between equipment is likely to pose greater problems in military
environments, and the requirements for EMC will be harder to meet.
“Equipment used in the military environment can often be classified as
“mission critical”, “mission essential” or even “safety critical”. For military applications, lives can depend
on electromagnetic compatibility between numerous electromagnetic devices in a
small area. This characteristic is not typically present
in commercial equipment and uses.
In the
United States, EMI requirements on general types of electronics were first
introduced by the FCC in 1979 for “computing devices” in the Code of Federal
Regulations (CFR) 47, Docket 20780. The requirements used today are essentially
the same and are limited to conducted emissions on alternating current (AC)
power interfaces and radiated emissions.
There are two sets of limits, one for residential areas and a second for
industrial areas. Separate FCC requirements in CFR 47, Part 18, are applicable
to industrial, scientific, and medical (ISM) equipment which intentionally use
RF energy in their basic operation. Requirements for both Part 15 (also
called low-power and non-licensed devices) and Part 18 devices are limited to radiated and
conducted emission controls that are dependent on the characteristics of the RF
source. The FCC does not yet mandate immunity (susceptibility) requirements for
general electronics thereby increasing the risk to the DOD of using FCC
approved part 15 or part 18 devices. Refer to Appendix A – EMC Compliance Requirements for a more detailed discussion
of FCC and European processes. The European Union, on the other hand, requires
equipment sold in Europe to meet both emission and immunity requirements. US
manufacturers who wish to sell their products in Europe must meet a variety of
these requirements. Member states of the
European Union have accepted and are regulated by the Electromagnetic
Compatibility (EMC) Directive 2004/108/EC and the Radio &
Telecommunications Terminal Equipment Directive (R&TTE). These directives are intended to guarantee
the free movement of apparatus and create an acceptable electromagnetic
environment in the Community territory. In
meeting the requirements of either directive, a Declaration of Conformity has
to be created by the manufacturer, a CE mark affixed (most electronic
equipment), and a technical file assembled that should include any test
reports, data, etc. related to compliance with EMI requirements.
The CE
mark on a piece of electronic equipment means that the manufacturer declares
that the product meets the EU requirements for that product category. However, it may or may not meet the EU EMC
Directive depending on what is noted in the Declaration of Conformity. If the device is declared in compliance with
the EMC directive then a Technical File must
be prepared that includes information on what EMC standards were applied, to
what standard it was tested
, and the test results. But buyers beware; manufacturers are allowed
to “self declare” compliance with the EMC Directive although there may not be
any actual data to review.
Figure 2 - Gap Analysis Process
The gap
analysis process identifies the shortfalls between the commercial tests
required/performed on the equipment and the tailored military EMC/EMI
requirements on the equipment in its intended operational environment. In order to achieve this, the commercial EMC
standards, test methods and limits applied to the COTS equipment must be
identified and compared to the military standard, test methods and limits that
represent the environment in which the military equipment is to be operated.
The first stage is therefore to identify the commercial EMC/EMI requirements, standards,
test methods and limits applied to the COTS equipment (frequency ranges,
limits, CE/RE/CS/RS test types, etc.), either for design and/or test purposes
and the actual tests performed
Step one
is to identify the Commercial EMC standards to which equipment claims
compliance and to obtain and analyze any available test data. Create a list of commercial standards that
the COTS equipment has been tested to and verified as per the Declaration of
Conformity and/or test reports supplied by the manufacturer. During this exercise, one must ensure the
test reports reflect the testing of the whole system and not just a portion of
the system. An example would be a
commercial test report for a radar system which might reflect the test results
performed on the control unit only and not the antenna and/or visual display component
which make up the system. Therefore, the test report is only good for a
part of the system. This assumes that
the antenna is on the mast, the control unit below deck, and the visual display
component is on the bridge. In this
scenario, it is suggested that an analysis needs to be performed on each piece
of the system. The amount of testing of a
COTS subsystem that may
be reduced can be based on the actual location of the pieces of the system.
To evaluate the manufacturer’s equipment testing,
you should assemble all
official EMC test data and reports (from the manufacturer) that were
needed to:
Note:
Reports may reflect actual testing on another product. If applicable, request a copy of the engineering
justification for grandfathering the system under another product’s test
results.
See Appendix A for more information on CE Mark and FCC
compliance requirements and how to obtain test data. Included in Appendix A is a generic
questionaire that might be used to gather pertinent EMC data on a COTS item.
Compile
a list of tailored tests from MIL-STD-461F that reflect the minimum
desired test requirements that the COTS equipment must meet based on the
equipment categorization and EME definition developed previously (Section III). The Navy’s EM-ARTT (www.em-tartt.us) is a database tool that
can help define EMI
requirements based on system technical parameters, location, and use. EM-TARTT
is strictly for shipboard applications. Within
this document, EM-TARTT results pertain only to the examples presented herein.
To learn more about EM-TARTT refer to Appendix H.
Table 5 - Applicability of MIL-STD-461F Test Methods
(Per MIL-STD-461F Table 5)
Table 5summarizes
the applicability of MIL-STD-461F EMI requirements for equipment and subsystems
intended to be installed in, on, or launched from various military platforms or
installations. Refer to MIL-STD-461F for
specifics on the use of the table and the legend definitions.
Unfortunately, it’s not as simple as
applying the MIL-STD-461F tests from the applicability matrix but that’s a good
starting point. When defining an
acceptable set of EMI control requirements for a COTS item, the
previously defined EME, the equipment
categorization exercises discussed in Section III and the determination of equipment
and platform criticality must be taken into account. All these factors contribute to the
definition and tailoring of
specific MIL-STD-461F (and other EMI control) requirements and tests that would
ideally apply in the risk assessment process.
An in-depth discussion of tailoring MIL-STD-461F requirements is beyond
the scope of this document but understanding how the requirements were tailored
is an important part of the risk assessment process. Information on tailoring EMI requirements is
available from DOD service EMC organizations and experts. Below is an example from a Terma Scanter
Radar COTS installation which compares the desired and actual EMI requirements.
|
Desired MIL-STD-461 |
Associated EU Commercial Std |
From Test
Reports |
Tailored MIL-STD-461 Via EM-TARTT*** |
||
|
Conducted Emissions |
CE101 CE102 CE106 |
CISPR 11 EN 55022 EN 61000-3-2 EN 61000-3-8 EN 61000-6-3 EN 61000-6-4 |
EN 61000-3-2 EN
61000-3-3 * EN
50081-1 EN 55022 |
CE102 |
|
|
Radiated Emissions |
RE101 RE102 RE103 |
CISPR 11 EN 55022 EN 61000-6-3 EN 61000-6-4 |
* EN 50081-1
EN 55022 |
RE101 RE102 RE103 |
|
|
Conducted Susceptibility |
CS101 CS116 |
EN 61000-4-4 EN 61000-4-5 EN 61000-4-6 EN 61000-4-12 EN 61000-4-13 EN 61000-4-16 EN 61000-4-25 EN 61000-6-2 |
EN 61000-4-4 EN 61000-4-5 EN 61000-4-6 EN 61000-4-11 EN 61000-6-2 EN 50082-2 |
CS116 |
|
|
Radiated Susceptibility |
RS101 RS103 |
EN 61000-4-3 EN 61000-4-5 EN 61000-4-6 EN 61000-4-8 EN 61000-4-9 EN 61000-4-10 EN 61000-4-20 EN 61000-4-25 EN 61000-6-2 |
EN 61000-4-2 EN
61000-4-3 EN
61000-6-2 ** EN
50082-2 |
RS101 RS103 |
|
|
* Replaced by BS EN 61000-6-3 **
Superseded BS EN 61000-6-2 *** EM TARTT used for
shipboard examples only; specific tailoring shown in Table 6 |
|||||
Table 6 - Terma Scanter 2001 - Example EMI Requirements
Comparison
Tailored Shipboard EMI Requirements from EM TARTT - Example
|
|
CE101 |
CE102 |
CE106 |
CS101 |
CS103 |
CS106 |
CS109 |
CS114 |
CS115 |
CS116 |
RE101 |
RE102 |
RE103 |
RS101 |
RS103 |
RS104 |
|
All
subsystems |
|
X |
|
|
|
X |
|
|
|
|
X |
X |
X |
X |
X |
|
|
Antenna
only |
X |
X |
|
|
|
X |
|
X |
|
|
X |
X |
X |
|
X |
|
|
Control
Unit only |
X |
|
|
X |
|
X |
|
X |
|
|
X |
X |
|
|
X |
|
|
Display
only |
|
X |
|
X |
|
X |
|
|
|
|
X |
X |
|
X |
X |
|
|
Display
only- Below Deck |
|
X |
|
X |
|
X |
|
|
|
|
X |
X |
|
X |
X |
|
Table 7 - Terma Scanter 2001 Example EMI Requirements
Gap
Analysis is the most critical step in the evaluation process. Significant E3 engineering experience and
operational understanding is a necessity for conducting these comparisons and
applications. It would be ideal if
simple, direct comparisons of particular commercial standards with MIL-STD-461
counterparts were possible.
Unfortunately, comparisons are rarely straightforward and it is almost
impossible to call a particular commercial standard a one-for-one replacement
for a MIL-STD-461 test. The major
difficulty is that there are truly very few 1 to 1 direct mappings
between commercial standards and MIL-STD-461F test methods for a
variety of reasons, such as the environment for which the standard was intended
and by whom the standards were written.
ENGINEERING
PRACTICE STUDY (EPS) 0178, March 2, 2001, Results Of Detailed Comparisons of
Individual EMC Requirements and Test Procedures Delineated in Major National
and International Commercial Standards With Military Standard MIL-STD-461E, is
an excellent reference in comparing commercial to military standards. Even though it was published in 2001, the
standard comparisons are still valid in identifying the gaps in testing between
standards. The document is available in
the DAU ACC EM and Spectrum Compliance SIA Library:
https://acc.dau.mil/CommunityBrowser.aspx?id=128255&lang=en-US
From EPS
0178, on the challenges of conducting the comparisons:
“4.3.3 Differences Between
Commercial and Military Standards. For orientation purposes we itemize below
the most significant differences between commercial and military standards.
a) Requirements in the VLF range
for submarines are unique because of critical dependence on the reception of
sonar and VLF electromagnetic signals.
b) There is a high concentration
of electronic equipment aboard ships and other military platforms including
emitters and sensitive receivers. For this reason, military radiated emission
limits are more severe than corresponding commercial limits. The military also
places high immunity requirements on devices exposed to nearby intentional
emitters.
c) The general availability of
grounded conducting surfaces (ground planes) for mounting equipment on military
platforms. Most commercial equipment (when it is light in weight or portable)
is mounted on an ungrounded table top. However, this difference is not pervasive,
e.g. floor mounted commercial equipment is frequently bonded to a ground plane.
d) Some frequency ranges are more
extensive in military requirements than they are in commercial requirements,
hence if equipment is tested to meet commercial requirements, additional
testing may be needed for military use
These differences make it
impossible to find commercial qualified equipment that is completely equivalent
to one meeting military requirements. This means that a detailed analysis is
required to determine the adequacy of equipment tested to commercial
requirements to meet the requirements of a particular military environment.”
EPS 0178
Table 5.1 provides a high-level comparison matrix of commercial and military
requirements and more detailed explanations of each comparison in Section
6. Annex A of EPS 0178 provides even
more detailed discussions for E3 experts who have the skills necessary to apply
the guide to specific procurements. It
is highly recommended that the reader obtain and review EPS 0178 for more
detail on the challenges of conducting these comparisons.
A
Practical Paper, Risk Analysis by the Use
of Commercial Equipment in a Military Environment by Henk A. Klok is
another excellent and applicable reference.
It provides a more global explanation of the difficulty of conducting
standard comparisons from a European perspective. Mr. Klok discusses the differences between
MIL-STD 461D/462D and civil EMI-requirements with respect to measurement
methods, frequency range and limits.
Rather than comparing individual tests, he groups tests into the four
primary categories: CE, CS, RE and
RS. He also discusses the
electromagnetic environment on board Navy ships and evaluating the risk of
using COTS equipment in that environment.
A few of the assumptions made in the theoretical approach of the
comparison are verified by using measurement data taken from commercial
equipment. This paper and others are
available in the DAU Acquisition Community Connection EM Spectrum Special
Interest area at acc.dau.mil (look for the Technical Articles
section).
Table 8
chart is from the United Kingdom Ministry of Defence Standard, DEF STAN 59-411,
Electromagnetic Compatibility Management & Planning. It can be used to identify many of the
factors that affect test severity that apply to the equipment being evaluated.
Table 8 - EMC Gap Analysis Factors
Affecting Test Severity
The
final step in the gap analysis is to identify “missing” tests. In other words, what military EMI
requirements are not reflected in the commercial tests that were conducted?
List these additional (full or verification) tests that need to be
considered and/or performed to verify COTS equipment’s ability to meet EMC requirements
in the defined
military environment.
An
example of a “missing test” might
be a verification test which would be added because the “frequency range”
scanned in a commercial standard is incomplete for a required military
environment. As can be seen above in
Table 8, “frequency range” occurs in all the different test types given. The reason is normally based on the high
concentration of other equipment operating in the same frequency range in a
military environment. The concern would
be interference with other equipment. Remember,
commercial standards are written for commercial applications and not military
applications: that is why there is a gap between commercial and military
standards.
Another
example would be “limit levels.” Table 8
reflects that all Test Types have “limit levels” associated factors affecting
test severity. Depending upon the test,
the commercial standard’s limit level is normally less stringent because they
do not take into consideration the close proximity and concentration of
radiators and receivers in most military environments. Limit levels also
reflect differences in test receiver bandwidths used in various radiated and
conducted emissions tests. Different susceptibility (immunity) tests use
different modulated signals as well. There are exceptions to the
phenomena. Therefore, every gap should
be examined and an engineering analysis conducted to determine it’s specific application
to the required equipment environment.
Once the gaps between individual tests have been
identified, they can each be assigned a risk rating of Low, Medium, or High
depending on the extent of the assessed differences. The assignment of a risk
rating is subjective but an attempt is made herein to provide a method to standardize
the process as much as possible. As previously mentioned, the risk rating
assignment is the responsibility of the Program Office, but E3 engineers should
provide recommendations based on their professional experience conducting risk
assessments.
The risk
rating assigned to the gaps identified from the evaluation of the COTS EMC
compliance evidence must be compared to the criticality of the COTS equipment
and the criticality of the environment or platform in which the COTS equipment
will be operated. This comparative analysis forms
the basis for the final risk assessment. Generally, the greater the criticality of the
COTS equipment, the lesser the degree of susceptibility risk will be permitted
to the COTS item. The greater the criticality of the environment or platform,
the lesser the degree of emissions risk will be permitted to the environment or
platform. This concept is summarized in
Table 9, UK MoD and Defence Standard 59-411.
Table 9 - Guide to Minimum Acceptable
Risk Resulting from EMC Gap Analysis
Table 9 talks
to the ACCEPTABILITY of the risks. Where
Emission and Susceptibility is listed as “Low”, that means that the
acceptability of undesirable EM emissions is Low (or high risk, in other
words).
The
risks identified in the gap analysis process must now be compared to the
criticality of the COTS equipment and the criticality of the environment or
platform in which the COTS equipment will be operated. Nil to Low risk will generally be acceptable.
In some non-critical situations Low to Medium risk may be acceptable. In all
cases a High risk is most likely unacceptable unless some mitigating action or
additional testing is applied.
In the assignment of risk severity, it is useful to examine
how the services define and categorize EMI problems encountered during
testing. Consider the following:
The
point of this discussion is that it is useful to develop and document a set of
risk severity categories for the issues identified during the gap analysis
process. The individual gaps identified
can be treated as though they are EMI problem failures discovered during
testing. Then they can be categorized in
a manner similar to the EMI test failure categories above.
If there
are missing tests, as discussed in the previous section, the lack of data by
which to assess particular EMI requirements must be included in the risk
assessment. One mitigation technique to
rectify a lack of data in a specific area is obviously to conduct additional
testing.
Table 10
provides a gross assessment of the acceptability of equipment that conforms to
the most prevalent commercial standards for use on typical military
platforms. It may represent a good
starting point for a specific gap analysis effort but, in general, should be
used only as a guide to the noted military platforms.
.
Table 10 - Assessment of Commercial Standards vs. MIL-STD-461