electromagnetic compatibility

Military EMC design can be particularly vexing. Multiple environments combined with multiple threats lead to multiple requirements. The threat levels, and the resulting requirements, are usually more stringent than found in the commercial world.

A discussion topic between designers, namely those who only do circuit design and have no interest in the field of EMC, and compliance engineers attempting to meet regulatory compliance requirements, is the use of FR-4 as the core material for printed circuit board construction. Fiberglass Resin (FR) is low cost and has been used in almost every electrical product for decades, with exceptions such as military and satellite applications, harsh environmental conditions, and other unique uses. The disagreement lies with the extent that we can use FR-4 in high frequency applications and should we be concerned more with electrical performance or manufacturing and assembly.

The science of electromagnetic compatibility has been in exis­tence for several decades. As an art, it goes back much further, perhaps to the time of Edison when he was just beginning to experiment with practical electrical devices. I am sure that with some of his more sophisticated devices undesired interac­tions took place because of inadequate shielding or filtering. Certainly, with the advent of radio, incompatibility problems occurred as a result of the poor quality of transmitters and receivers. Perhaps the first formal recognition of electromag­netic compatibility problems occurred when the telephone and power companies found they had mutual coupling problems when their lines were carried on the same utility poles. Later on, the increasing use of the radio spectrum called for formal controls administered by departments in the post, telephone, and telegraph offices in many countries, or through the Feder­al Communications Commission in the United States.

The railway environment is generally regarded as a “severe” electromagnetic environment. For an electrified railway, Megawatts of power are required to be converted into the propulsion of trains in order to transport passengers or freight from one destination to another. The railway presents a complex electromagnetic environment made up of many systems including signalling, traction, telecommunications and radiocommunications.

Two of the more important publications in the area of Electromagnetic Compatibility (EMC) and Measurement Uncertainty (MU) are LAB 34 and CISPR 16-4-2. EMC and Measurement Uncertainty are receiving more attention as other CISPR Product Family Standards begin to adopt MU. LAB 34 is “The Expression of Uncertainty in EMC Testing” and is published by the United Kingdom Accreditation Service (UKAS). CISPR 16-4-2 is published by the International Electrotechnical Commission (IEC) and is titled “Specification for Radio Disturbance and Immunity Measuring Apparatus and Methods – Part 4-2: Uncertainties, Statistics, and Limit Modeling – Uncertainty in EMC Measurements.” This article compares and contrasts the two MU documents.