FEATURE EMC & THERMAL MANAGEMENT EMC complexities explained...
Paul Bandy, head of product development at Aerco offers some useful guidance on the available options for solving key EMC issues
G
iven the integration complexities of modern electronic devices,
ectromagnetic compatibility (EMC) - (ensuring different devices can share a common electromagnetic environment without adverse effects on each other) is of more importance now than ever. Along with this, the possibilities of RFI/EMI has also increased. Electromagnetic interference (EMI) and
radio frequency interference (RFI) as it is also called when in the radio frequency spectrum, causes the unintended generation, propagation and reception of electromagnetic energy, which interferes with correct functioning of devices and systems, and can even cause physical damage in some cases. Fortunately, long gone are the days when interference from drills, lawnmowers and even passing traffic made radios buzz and TV pictures distort, but nonetheless, engineers have to take steps to ensure a “clean” electronic environment. EMI is caused by electrical noise on a
signal or power line. RFI is due to electromagnetic interference at radio frequencies (3kHz to 300GHz). Both man-made and natural sources generate changing electrical currents and voltages that can cause EMI/RFI: common sources are power supplies, aerials and antennas, radar sources, mobile phones, automotive ignition systems and thunderstorms. The effects can be highly damaging, and include unplanned switching of control equipment, poor sound or image quality and even complete system failure. Consequences could be very severe in
critical systems employed in, for example, rail track signal controls and air traffic control systems, but electronics designers are well aware of these issues and electronics manufacturers incorporate many solutions into their products.
OVERCOMING THE PROBLEMS Conducted emissions occur in an active circuit operation and are created by the variation of current drawn by a circuit from its power leads. The most common way of dealing with this is with the use of capacitive or inductive filtering: the primary function of such a filter is to
30 OCTOBER 2017 | ELECTRONICS
connectors can remove the need for a bulkhead and provide a weight and space-saving solution in multiple applications.
RADIATED EMISSIONS Radiated emissions refer to electromagnetic energy generated from an electronic device which escapes from it and its enclosure. Partial or full enclosure shielding, or screening and individual cable screening, can contain this radiation. Enclosures, gaskets, foils, shielding and screening products from a reputable specialist company such as P & P Technology provide EMI compliance, together with the assurance of robust, quality products made to international manufacturing standards. Modern, high-density connectors
reduce the intensity of the high frequency or RF current and voltages that would cause interference. A capacitor acts as a “path to ground/earth” for signals but only at high frequency – where the “noise” is located. Inductors reject the “noise” and send it
Figure 1b: Figure 2b:
back down the line, but permit DC signals to pass through. Low pass filters are designed to pass all frequencies below a specific cut-off level. Combinations of capacitive and inductive configuration filters can be specified to deliver various performance characteristics. Increasingly, protection against EMI is a legislative and contractual requirement, particularly in telecommunications, avionics, industrial and defence equipment and must meet worldwide electromagnetic standards and legislation to provide protection and reliability. Off-the-shelf products that meet the
demands of signal and power supply filtering are available. Some examples include the Oxley range of discrete and multiline filter solutions. Oxley filtered
Figure 1:
Oxley EMC products from Aerco
handling both power and signal contacts with tightly packed cable bundles are a potential risk area for electromagnetic interference. Reputable manufacturers have developed backshells and termination methods that protect cable bundles and individual wires. EMI filtered connectors from EMI Solutions, for example, offer the convenience and flexibility of standard configurations but with shielding at the interface and through the connector area. They suit a very extensive range of applications including military communications, aerospace, C4 systems and power distribution. At lower cost than EMI filtered
connectors, but still a highly-effective method of connector filtering, chip capacitor EMI flex filter inserts with various capacitances press into male connectors and reduce the higher frequency signals passing through.
… AND FINALLY Interference is due to basic physics and so cannot be totally eliminated, but there are many proven, reliable products and methodologies available. Effective control is largely a question of understanding the problem and selecting the correct product for the specific application. This is where the advice of an experienced and knowledgeable design and distribution partner can be invaluable, saving design time by avoiding incorrect choices and ultimately providing the correct solution within customer timescales.
Aerco
www.aerco.com 01403 260206
/ ELECTRONICS
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