Pete Dorey The electromagnetic compatibility EMC risk assessment process described in Defence Standard contains four key steps to assess whether any protection, such as shielding racks and filters, is needed to reduce equipment susceptibility to harsh defence electromagnetic environments and to enhance compatibility with sensitive systems such as military radio. The target electromagnetic environment is usually specified in a User Requirement Document URD or System Requirement Document SRD , and is likely to be one of the default electromagnetic environments described in Def Stan , such as a ship below-decks environment. However, it may also be specified for a unique purpose, to ensure compatibility with specified systems, or tailored to a specific environment. However, obtaining the evidence of EMC compliance is often a major challenge.
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Military EMC Staff, Intertek February 1, The reliable operation of complex electronic communications, control and armament systems in extreme environments demands stringent design criteria and careful validation. Severe shock, vibration, heat, humidity and airborne contaminants are common in land, sea and air platforms.
Coupled with dense packaging, high-power radio and radar illumination, Hazards of Electromagnetic Radiation to Ordnance HERO , and a possible electromagnetic pulse EMP , the military equipment environmental requirements can be extreme indeed. In order to expedite equipment availability and reduce cost, the acquisition of commercial-off-the-shelf COTS equipment for US military applications is an attractive consideration. But many types of commercial equipment are unlikely to meet all military environmental requirements as manufactured, so some modification or re-design is usually needed.
The full cycle of US military product development from environmental assessment, to definition of requirements, to test reports, is carefully spelled out in the relevant military standards or ancillary documents for the applicable physical and electromagnetic environments.
These provide the design guidance, along with competent engineering practices, for a cost-effective and robust military product design. The starting point for EMC is self-compatibility, where the final product or system does not interfere with its own operation. As we shall see, this is the modest starting point for military EMC, which extends to both lower and higher frequencies than most commercial EMC standards and to both lower emission limits and much higher susceptibility requirements.
Test methods generally differ from their commercial counterparts in both setup and detail. History of Military EMC EMC problems in commercial applications were first noted worldwide in the s when early broadcast radios were being installed in automobiles.
Reception was degraded by ignition noise and electrostatic buildup caused by non-conductive rubber tires. It required shielding of the vehicle ignition system, regulator and generator. With the increased use of mobile military radio communications, SCL became inadequate. These specifications limited the levels of conducted and radiated emissions, and they set susceptibility levels which systems and equipment must reject.
These specifications also detailed the test configurations and methods for demonstrating compliance. Unfortunately, over this period of time, the various military EMC standards diverged from each other in test frequency ranges, limits and required test equipment. The differences made it quite expensive for a test lab or manufacturer to be fully equipped to test to all EMC specifications.
In the US Department of Defense enacted a comprehensive electromagnetic compatibility program that charged the military services to build EMC into all of their communications and electronics equipment. That program resulted in in military standards requirements , methods and definitions and acronyms. Subsequent revisions were designated B, C, and D. Prior revision levels A-E may still be specified for testing.
USA: Supporting Documentation The designer of military electronic equipment has an abundance of guidance available for successfully meeting the EMC demands of the intended operating environments.
MIL-STD-461 & DEF STAN 59-411 EMC Testing
To cater for particular interests of each of the three Service Arms of the MOD, their special requirements are noted as they arise, under the headings above. Although Part 1 is concerned primarily with EMC, the management and control procedures described can be applied across the E3 disciplines e. The MOD should ensure that their Prime Contractor recognises and exploits the economies arising from the degree of commonality which exists between EMC and these kindred subjects, with respect to equipment design, management and control procedures, and even test requirements where possible. This EMC Control Plan is in advance of formal specifications; however, priority will be given to managing EMC risks and performance in the following order: a safety e. The control plan defines the management and engineering procedures and techniques that are used to control EMC and EMC related design and validation activities. It details specific requirements and tailored limits to meet the various EMC operational environments and all safety requirements with specific consideration given to platform integration. Should additional advice be required, this can be obtained either from the Equipment Sponsor or from E3A See single point of contact.