Please Do Not Disturb

Article By : Rohde & Schwarz

The interference-free coexistence of numerous electrical and radio products cannot be taken for granted. Only targeted measures for EMC can ensure that cardiac pacemakers are not disrupted and aircrafts carry passengers safely to their destinations.

The biggest known EMC incident could have caused a global disaster, but it passed without serious consequences because the electrical devices that could have been affected simply didn’t exist. The response of the telegraph systems at the time, however, was a warning of the power of electromagnetic phenomena when high field strengths are involved.

Telegraph poles spewed sparks, shocked telegraph operators jerked clear of their equipment, ticker tapes caught fire, and strange messages were issued that nobody had sent. Auroras, normally only visible at high latitudes, could be seen as far as the equatorial region. Experts are convinced that a solar magnetic storm today as strong as that in 1859 would have a catastrophic impact on our high-tech infrastructure.

Statistically such a storm can be expected only around every 500 years. As opposed to protecting against nature, the protection of electrical devices against interference from other equipment has been common practice for a long time. In light of our ubiquitous wireless networking, it will be even more important in the future.

An issue becomes audible

Before radio propagation was discovered around 1900 and quickly exploited for communications, there was no sensory system that could make the lower frequency range of the electromagnetic spectrum humanly perceptible. As a result, for a long time, people had no idea of the amount of electrosmog being generated by electrical devices, especially motors, and it didn’t bother anyone for several decades.

Only with the advent of radio broadcasting in the 1920s and the continuous “monitoring” of part of the radio frequency band (at first only a small part) did the issue become apparent. Strong noise disturbed the already modest listening pleasure and clearly showed that there was just one electromagnetic spectrum for everyone, and that it needed to be handled carefully.

Only with the advent of radio broadcasting in the 1920s and the continuous “monitoring” of part of the radio frequency band did the issue become apparent.

Electromagnetic waves do not respect national boundaries

It was therefore both obvious and foresighted to put the formulation of technical protection recommendations in the hands of an international body. The “Comité international spécial des perturbations radioélectriques” (International Special Committee on Radio Interference) established in 1934, commonly known as CISPR and operating under the aegis of the International Electrotechnical Commission (IEC), is still an authoritative institution for the publication of standards for electromagnetic compatibility.

There are specific EMC standards for all product groups, including monitors. The picture shows a test receiver being used to measure conducted disturbance, which means disturbance signals that a device emits over the power lines.

Other committees and commissions, such as CENELEC, ETSI, FCC and ANSI, complement the work of CISPR and ensure that products containing electrical components are not marketed without regulatory approval. All market players and national designated bodies delegate representatives to the committees of these non-profit public service organizations, whose recommendations are given legal force by statutory resolutions.

As a leading manufacturer of T&M equipment, Rohde & Schwarz also participates in standardization, since even the best rules are useless if compliance cannot be checked by measurement at reasonable cost.

EMC measurements are made in electromagnetically shielded chambers, which ensure that only emissions coming from the DUT are measured. They also prevent the escape of interference emissions that are imposed on the DUT in immunity tests. As with an anechoic chamber, the inside walls, ceiling and floor are lined with an absorbent material that converts stray electromagnetic energy into heat to provide a “peaceful” electromagnetic environment.

In the EU, the CE mark on a product indicates that it conforms to the requirements of all relevant standards, including those for EMC. The FCC compliance label serves the same purpose in the USA. However, formal approval of every product is not practical because of the vast numbers of products and the associated costs, so this responsibility is borne by the manufacturers. They must ensure that their products comply with the standards.

Home appliances must also be tested. Here the washing machine is standing on a turntable to enable angle-dependent measurements.

Violators who are caught are subject to severe penalties, or at least a prohibition on the sale of their product. Even high-priced products sometime run afoul of the testers. For example, a test of e-bikes by Stiftung Warentest (a well-known German consumer organization) a few years ago generated a lot of medial attention because some bikes turned out to be interference sources. Even now, the EMC characteristics of many products leave something to be desired. A study by Germany’s Federal Network Agency in 2019 found that 21.5 % of the investigated products did not comply with the regulations.

Vehicles, aircraft and helicopters are exposed to strong fields to test their immunity to such fields. For this they must be placed entirely in suitably large test chambers.

The earlier EMC aspects are taken into account in product development, the less it costs to implement them. Undesirable emissions from a circuit can be detected and localized using field probes.

From annoying to dangerous

The aim of EMC standards is to ensure that a product that should not emit disturbance signals—such as a motor or a microwave oven – complies with this requirement, or that a product approved for radio or broadcast operation—such as a WLAN device—conforms to the requirements of the applied standard and does not disrupt or disturb other wireless services. In addition, all products must be immune to external electromagnetic interference within the scope of prescribed limits. Failure to fulfill these conditions can lead to anything from simple annoyance to serious incidents.

For example, the crash of a German Tornado aircraft was clearly due to the response of the onboard avionics to the strong radio signal from a shortwave transmitter that the aircraft flew over at low altitude. As a result, the aircraft manufacturer was compelled to make design changes. From Japan the press reported on industrial robots that started moving in the presence of people, presumably under the influence of radiated emission from the factory, which were claimed to have led to several fatalities.

The many relatively minor incidents include reception of the sound of a crying baby in an aircraft cockpit as a result of unapproved babyphones, jammed garage doors due to military radio, or drivers locked out of their vehicles because their remote keyless entry system suddenly stopped working because the signal was swamped by electromagnetic interference on the same frequency.

Vehicles as touchstones

A blocked keyless entry system is annoying, but usually not dangerous. However, modern cars are full of electrical and electronic components with more and more safety-related functions. The electromagnetic compatibility of all onboard systems is essential because only safe vehicles can be approved. Several EMC standards specifically for the automotive sector, for example for immunity to disturbance coupled into the wiring, aim to ensure this. Additional regulations apply to radio devices, which are being installed in vehicles in increasing numbers.

Along with classical EMC, the peaceful coexistence of a wide variety of radiocommunications services is becoming more and more important, not only in vehicles. Mobile communications and short-range technologies such as Wi-Fi and Bluetooth®, along with GPS, radio and remote control functions and radars in the case of vehicles, are often integrated in the same product and must work together without causing mutual interference. With improper implementation of wireless technology, useful signals can easily become interference signals. Suppliers and vehicle manufacturers take this issue very seriously, if only for liability reasons, and operate sophisticated test facilities.

EMC test chambers are among the most impressive test facilities anywhere. The largest ones can accommodate an entire aircraft.

Life and limb at stake

EMC issues have especially serious consequences in the medical sector, where life and health depend on the reliable operation of equipment or implants. Numerous cases are known in which earlier generations of cardiac pacemakers, when the presence of radio signals did not have to be considered in such detail, were sensitive to external interference and sometimes skipped a beat.

Nintendo, for example, explicitly pointed out in the safety instructions for its DS game console that it should be kept at least 9 inches away from persons with a cardiac pacemaker when the wireless function was enabled. There were (and still are) similar recommendations for mobile phones. Although today’s implants are considered immune in this regard, especially now that manufacturers are aware of the hazards, considerable caution is necessary in product development.

There’s a good reason why the national Food and Drug Administration in the USA reserves the right to approve medical devices that also have wireless interfaces, for which the Federal Communications Commission (FCC) is normally responsible. Manufacturers of medical devices must demonstrate in detail how they counter potential hazards and which test methods have been used to prove electromagnetic compatibility. If there are not yet any standards for an innovative device, the manufacturer must proactively ensure that the device operates without interference in the intended application area, and if necessary hemust develop suitable test methods. For example, EMC specialists at Rohde & Schwarz are currently collaborating with a test house on a test procedure for the next generation patient monitors of a large medical equipment manufacturer.

Hospitals, and especially intensive care stations, must be able to rely on the interference immunity of the equipment used for patient care and monitoring. For safety reasons, it is still common practice to prohibit mobile communications devices across the board, at least in operating theaters.

In addition, more and more medical devices are also emitting radio signals because wired connections for data transmission are being replaced by wireless links, such as Bluetooth. Remote medicine is increasingly relying on low-latency 5G mobile networks for real-time applications. Integrated test solutions, such as those developed by Rohde & Schwarz, focus not only on the EMC and coexistence capability of DUTs, but at the same time their functional parameters (radio and data performance). This accelerates and reduces the cost of testing increasingly complex technology.

Protecting our digital lifestyle

The number of radio products has exploded since the turn of the century and vastly exceeds the number of people on the planet. Smart cloud-based and wireless services are penetrating all areas of life. Wireless home networking is mainstream, and vehicles networked with their environment will be reality within the foreseeable future. All of these accomplishments require the restrictive utilization of limited frequency resources. Standards define the boundaries within which the technology can operate, but demonstrating that everything is OK—or not—is only possible with special T&M equipment.


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