An EMC System Design Approach That Ensures MIL-E-6051 Safety Margins Are Incorporated

Abstract

This paper presents a comprehensive approach to Electromagnetic Compatibility (EMC) at the system level when it is required to demonstrate MIL-E-60S1 safety margins, briefly and are then used to derive the requirements for all subsystems down to each unit. The discussion is broken into two parts: intersystem and intrasystem compatibility. In both cases an apportionment method that ensures adequate system level margin is developed. A design example is worked out at the end to give a feel for the approach that is presented. System EMC requirements are discussed Introduction Electromagnetic Compatibility (EMC) of a complex system is extremely important and is a key ingredient to the success of a large Military or Aerospace program which is required to procure equipment that meet MIL-E-6051 specification. This specification states that all units in a system are required to demonstrate a 6 dB margin and all ordance a 20 dB margin. These are the margins that have to be designed and tested into a system in order to assure electromagnetic compatibility at the system level. The standard approach in most cases is to procure equipment that are certified to MIL-STD-461/462 and perform a limited EMC test while integrating them together. This unfotunately does not guarantee a 6 dB safety margin nor does it guarantee overall compatibility between the different subsystems, for the simple reason that the total number of boxes and their layout is not taken into account. It is also difficult to perform a system EMC test due to all the complex interactions between different subsystems and their interconnecting cables. The approach discussed below is a general one and applies to all programs, large or small, military or not. Before beginning the discussion, few definitions are given. unit: a stand alone component assembly: a collection of units that opperate together subsystem? several assemblies and units mounted system: a complete, self powered (in this case) entity: unit, assembly, subsystem or system together functionally independent equipment CH3169-0/92/0000-0012 $3.00 01992 IEEE 66 starting point of the EMC System Design is the system definition phase, during which the Electromagnetic Environment (EME) in which the system is intended to operate is characterized. The EME is defined based on the proximity of local transmitters, the presence of sensitive receivers, national or international frequency band constraints. This defines then the Intersystem Requirements which are to be met contractualy. Following the system definition phase, the system partitioning phase starts. It is during this phase that the system is divided into several subsystems that will perform the different functions. Intrasystem Compatibility, then, must be achieved in order that all subsystems will function harmoniously together. Figure 1 below shows a block diagram of the System Design Concept. Definition MIL-E-6051