What is “electromagnetic compatibility“? Is serving today to anything, or do we need the stupid word at all? Why do most consumer electronics fail to withstand the lightning strike
in the nearby power grid and why do people in the housing estates get an ever stronger WIFI? Does electromagnetic radiation around us (electro-smog) affect living organisms? EMC will not allow your neighbor to disturb your television when you’re just going to blow-dry of her hair. The internationally recognized abbreviation EMC comes from English “Electromagnetic Compatibility“. Every electrotechnical device radiates electromagnetic interference to its surroundings and is influenced by this environment simultaneously. EMC standards define the limits of electromagnetic interference that our appliances can radiate to the environment and the limits on which these appliances must be durable.
Electromagnetic compatibility as a separate scientific and technical discipline arose in the 1960s in the USA, and for a very long time it was in the interest of only a narrow circle of experts working in the military and aerospace industries. With the rapid development of electronics, especially microprocessor and communications technology in recent decades, and its penetration into every area of everyday life, EMC is increasingly affecting us all. HM Schlike, one of the founders of EMC, said in 1968: “The system itself can be completely reliable – it will be virtually worthless in operation if it is not electromagnetically compatible at the same time. Reliability and electromagnetic compatibility are inseparable system requirements that has to work at all times and in all circumstances. ”
Catastrophic consequences of EMC non-compliance in practice
- The destruction of the Tornado NATO fighter aircraft in 1984. The cause of the disaster was the interference of the electronic control system of the aircraft by electromagnetic waves. The aircraft flew 230 m at a speed of 800 km / h. over a high-power transmitter in Holkirchen near Munich, Germany. As a result of the failure of the automatic steering system, the plane crashed. Material damage was estimated at 100 million markers.
- Sinking British Sheffield Cruiser in 1982 during the Falkland War by an Argentine aircraft. The reason was the failure to comply with electromagnetic compatibility between the ship’s on-board communication device and its anti-aircraft system designed to interfere with target enemy missile navigation. This system caused such a major disruption in the cruiser’s own radio communication that it had to be switched off during a radio connection with a UK headquarters. And at that very moment, the Argentine plane exploded the Exocet missile, which had sunk the cruiser. Twenty people lost their lives.
- Pershing II-type racket in Germany due to electrostatic discharge. When the missile was transported, its drive was unintentionally fired with electrostatic electricity from the surrounding thunderstorm.
- Accidents in iron and steel works in the East Coast of the USA in 1983. The cause of the crash was the interference of the microprocessor control system of a crane carrying a liquefied pan with a liquid steal hand over. radio. The pouring pan has prematurely overthrown, and the hot metal killed one worker and four others seriously injured.
- Accident of the mass remote control system of the mining mechanisms in Náchodsko. The crash occurred when a 3,4 MW machine was connected to the 35 kV grid. The thrust device was a thyristor-controlled drive, with its drive connected directly to the grid without proper filtering and compensation. The disturbing feedback effect of the drive caused the collapse of the mass remote control system (and thus itself) not only in the vicinity of the mine, but virtually throughout the area of Náchod.
- For similar reasons, the emergency situation occurred in the Mělník sugar refinery after installing centrifuges with thyristor converters of 200 kW instead of classic rotary converters. After connecting them to a 22 kV power supply network, there has been such fluctuation and deformation of the supply voltage that there has been a group failure of the inverters due to voltage protections. At the same time, this degradation in the quality of the supply network was caused by the actual inverters, which were (according to the former habits) connected to the network directly without the necessary filtration and compensation. This has again created a paradoxical situation where the source of interference has become the victim of interference.
- Loss of radio communication between transmitters and receivers on the ships of Labské plavby and in the mines in the Ostrava region. In all these cases, there was intense interference that totally disabled radio communication on 1 to 2 MHz frequencies. In addition, in the mines, this interference also undermined the function of automatic emergency shutdown of the mining combine. The source of interference in the mines was a thyristor transducer, which was part of the combine harvester, the source of interference was a microprocessor control system containing power transistor feeders on ships..
- Accidents in health care facilities. The diagnostic unit at the intensive care unit of the hospital in Prague monitored the breath, pulse and temperature of the patients connected. However, the switching of the surrounding power appliances induced additional pulses in the cardioscope, which were evaluated as non-synchronous heartbeats. In addition, a faulty starter of the fluorescent lamp near a unit that switched every second caused continuous reports of crossing the heartbeat and blocked the measurement. The whole set, due to its utter immunity to interference, had to be replaced by another system from another manufacturer meeting EMC requirements.
- During each storm, a number of PBXs and terminal devices such as faxes, answering machines, and telephones are damaged by overvoltage. The reason is the insufficient resistance of these devices against overvoltage and inappropriate or missing overvoltage protection on the line.
It is clear, therefore, that low durability and overall non-compliance with EMC can only have tragic consequences.
European legislation defines the EMC issue with the basic standard IEC 1000-1-1 and related standards. In short, it is about making sure that any electrical equipment we buy is usable in the particular environment. For home environments, they are appliances from an electric toothbrush, computer, TV, microwave to an induction cooker.
Let’s take a look at the EMC’s criteria for our domestic appliances. Because of price hunting, most manufacturers of consumer electronics are pushing design criteria to the limit of mandatory standards. The customer then only has to accept the assumption that this or that will throw it into the container for a split impact in a moment.
The device must be sufficiently resistant to interference from the air and the mains and resistant to overvoltage in the network.
- Harmonic and interharmonic network voltage of the power grid (EN 61000-4-7)
- Short-term drops, short interruptions in mains voltage (EN 61000-4-11)
- Voltage and current pulse (IEC 1000-4)
- High-voltage shock and voltage impulses (EN 61000-4-5)
- Groups of rapid transient phenomena (burst) (EN 61000-4-4)
- Attenuated oscillation waves (EN 61000-4-12)
- Electrostatic discharges (EN 61000-4-2)
- Magnetic fields (EN 61000-4-8, EN 61000-4-9, EN 61000-4-10)
- High Frequency Electromagnetic Fields (EN 61000-4-3)
The interference produced by the equipment must not be greater than the following standards
- Compatible levels for low-frequency interference transmitted by line (EN 61000-2-2)
- A description of the environment of radiated phenomena and phenomena disseminated by lines not related to the network frequency (IEC 1000-2-3)
- Limits for harmonic current emissions (EN 61000-3-2)
- Limiting voltage changes, voltage fluctuations and flicker (EN 61000-3-3)
- EMC requirements for household appliances, power tools (EN 55014-1)
- and more…The issue of EMC is therefore a very complex field, which is of direct concern to us all.
EMC of biological systems
deals with the overall “electromagnetic background” of our environment and the permissible levels of interfering and useful electromagnetic signals (both natural and artificial) with regard to their effects on living organisms. Biophysical research to date is not clear about the impact of electromagnetic interference on people and other living organisms. The biological effects of the electromagnetic field depend on its nature, time of action, and the properties of the organism. Because the electromagnetic field biological receptors are not known, these effects are only assessed by non-specific reactions of the organism.
Every person reacts differently to the effect of the electromagnetic field, because his adaptive, compensatory and regenerative possibilities and abilities are individual. Therefore, it is very difficult to analyze changes in the organism, and on the basis of statistical results, generic conclusions can be drawn. This is one of the reasons why there are few specific clinical trials in the world yet, and those that exist are focused on higher exposure to the electromagnetic field in the work process. Unwanted influences on humans today can be considered not only the direct effect of the electromagnetic field at its workplace (the operation of transmitters, radars, etc.), but also the long-term influence of the modern environment, where we are instantly besides our own household appliances, WIFI from neighbors, a signal from several mobile operators and the like.
EMC biological systems are dealt with by some medical research institutes to assess the resistance of the human body to electromagnetic influences, their mechanisms of action, etc. In the high frequency and microwave fields the thermal effects that appear as a result of heating the tissues are relatively clear. The effects of electromagnetic field on the central nervous system, cardiovascular, hematopoietic and immune systems are attributed to so-called non-thermal effects, longer lasting exposure to relatively low power levels. However, neither these nor the genetic or carcinogenic effects have been unambiguously proven. These ambiguities have led to the existence of up to (orderly) large differences in acceptable doses of electromagnetic radiation in the hygiene standards in the world.