Should we be worried?

Any equipment containing electrical or electronic components may suffer malfunctions or damage due to electromagnetic disturbances. The equipment itself may also be a source of electromagnetic disturbance. If equipment exhibits temporary or quasi-permanent malfunctions due to an electromagnetic disturbance, the reason will not be found in broken parts; to find the reason for the malfunction special faultfinding techniques are needed.

 

Most electronics today are more or less governed by software controlling microcomputers or processors. If the hardware, which the processor controls, is not working correctly due to an electromagnetic disturbance, then the equipment will fail in operation. It does not help whatever software the equipment is programmed with.

 

There is today a lot of talk about robots taking over many routine activities from us human beings, like housekeeping, accompanying oldies, guiding in museums, and self driving cars. All those robots will contain electronic circuits with digital controllers and microcomputers.

 

The 5th generation of mobile communication will soon be on the market. This will make it possible to perform remote control of equipment, for instance remotely controlled car and train traffic management, and surgery. IoT (Internet of things) will presumably explode.

 

Any part of the electronics incorporated in all those devices may be disturbed if not properly designed and tested for their intended electromagnetic environment. Is every person (not just designers!) involved in those robotic projects aware of this?

 

For example: we remember the times then the car industry implemented electronically controlled ignition systems: the cars stopped nearby strong radio transmitters. Will we experience similarities with robots and all the new smart and sophisticated equipment ? Hopefully not, if management got the message we are trying to convey here.

Redundancy

A few words about redundancy related to EMC: if you have two identical systems intended to make up for each other and both are installed in the same electromagnetic environment, it is very likely that if one fails because of the electromagnetic ambient, both systems will fail simultaneously! Two systems or components intended to be redundant for each other need to be designed differently by different designers!

EMC and Quality

The quality of equipment is good enough if the equipment fulfills its functions with the specified characteristics in its intended environment as the user is expecting. If the equipment fails due to an electromagnetic disturbance in its intended electromagnetic environment, it is regarded as not fulfilling the expected quality. Reciprocally, the equipment should not produce disturbances which may cause malfunctions in other equipment. There is a duality between the environment and the apparatus.

 

We may conclude that the electromagnetic compatibility characteristics of the equipment is one major part of the quality of that equipment.

 

An electronic system, that is able to function compatibly with other electronic systems and which does not produce or is not susceptible to electromagnetic disturbances, is said to be electromagnetically compatible with its environment. Thus, again, EMC (= electromagnetic compatibility) is a part of the quality of a product, and as such it is the responsibility of the quality manager in the organisation, company or project.

 

Implementing and maintaining enough EMC in a piece of equipment rely on the different categories of designers: i.e. electronic and mechanical designers, installation planners, manufacturing line process control and QC, maintenance and field engineers, etc. Marketing and sales persons should inform customers about EMC and they should of course analyze the environment in which the equipment shall work and pass that information on to the designers.

 

In that sense, good EMC performance of equipment, even if it adds short-term costs in the development and test phases of a product, becomes a long-term advantage that may be put forward in the product quality advertised to customers. Since apparatus with electronic components is built up by hardware (plastics, metal, etc) and put together and installed by mechanical designers, it will be that personal category that sets the final EMC characteristics of the apparatus.

 

So, education is vital if EMC is to be achieved!

Some Definitions

• Electromagnetic environment (EE): The amount of all electromagnetic phenomena existing in a given volume.
• Electromagnetic disturbance (EMD): An electromagnetic phenomenon, which may cause unacceptable degradation of functionality or performance of a component, apparatus or system.
• Electromagnetic interference (EMI): Degradation of functionality or performance of a component, apparatus or system due to an electromagnetic disturbance.
• Electromagnetic compatibility (EMC): The ability of a piece of equipment or apparatus to function satisfactorily in its electromagnetic environment without adding unwanted electromagnetic disturbance to this environment.

 

EMI it thus the opposite of EMC! We don´t want EMI, we want EMC!

 

Note that an apparatus is both affected by and affects the electromagnetic environment!

Electromagnetic Phenomena

There is always an electronic environment everywhere and it is manifested by several different types of electromagnetic phenomena at different levels. Examples: variations in the geomagnetic field, lightning currents and fields, static electricity and its violent discharges, radio and radar fields, voltage and current transients on power cables, unwanted radio frequency fields emitting from apparatus and its cables, and more.

 

The levels of those electromagnetic phenomena are different in different locations and you may take different precautions in different locations, or in EMC-terms, in different electronic environments. If you are in a city, you don’t worry too much about lightning. If you are out in the mountains and a thunder storm is approaching, you should take certain precautions.

 

In an urban environment you usually have a good connection to the internet with your mobile phone, but out on the sea you need a VHF or shortwave radio device to have a connection with the rest of the wold. It may, however, be that the reception of your mobile device is disturbed (= no connection) by radio field emission from nearby electronic devices like computers or switch mode power supplies.

 

In a regular home or office you usually don’t think about electrical safety, but in an electric switch station you had better keep your hands in your pockets. In the streets or out in the countryside you don’t have to worry about strong electromagnetic fields, but on a military ship it’s different; powerful radio transmitters and radars expose electronics to very high field intensities.

 

We have today what is called Intentional EMI, which is rather scary. By the use of apparatus generating strong radio signals disturbing radio reception or strong electromagnetic pulses (fields or currents), it is possible to interfere with or destroy electronic devices and systems. If you are responsible for security in your organisation, you should be worried.

 

So, you are to some extent aware that there are different electronic environments. The conclusion is thus to design for those electronic environments. The borders between different ”everyday” electronic environments are not so well defined and it may be that you have to choose between the worst case or a ”normal” electronic environment. Don’t forget to put your choice in the technical specification of you apparatus!

 

To design for the EMC it has been shown that by designing different ”environmental shells”, or zones, with controlled electromagnetic environments, it is possible and not necessarily difficult to manage EE’s.

EMD types

Having mentioned a few types of different EMD’s here is an attempt to list the most common types of electromagnetic phenomena threatening equipment:

• Static electricity. As long it’s static it rarely affects electronic circuitry, but if there is a discharge (ESD), it becomes a threat causing destruction or heavy upsets in electronics.
• Lightning: heavy currents, large electric and magnetic fields.
• Variations in the geomagnetic field causing induced voltages in large systems like power transmission and railways.
• Power quality, or lack of.
• Over- and under-voltages, lasting for long or short times.
• Harmonic currents from switching devices.
• Low frequency electric or magnetic fields.
• Low and high intensity fields from radio and radar transmitters.
• Low level radio frequency unintentional emissions (conducted and radiated) from electronics (may cause interference in for example radio receivers (RFI)).
• Intentional radio signals causing interference in radio receivers (antenna to antenna interference).
• Electromagnetic pules (EMP) from nuclear bombs.
• IEMI, intentional EMI: this is a threat caused by people (i.e. criminals or terrorists) who want to upset or destroy systems with electronic ”weapons”, i.e. simple radio transmitters causing upset in radio receivers. May be called electromagnetic sabotage.
• Electromagnetic military weapons (maybe regarded as part of IEMI).
• Jamming of radio communication, both unintentional and intentional (may also be regarded as part of IEMI).

EMC Characteristics

The EMC characteristics of an apparatus is usually divided in some main categories due to the type of coupling mechanism involved and the coupling ”direction” (in to or out of the apparatus) of the electromagnetic phenomenon:

 

Conducted immunity (sometimes ”susceptibility” is used) or emission: the disturbance is coupled to the apparatus, or it emanates from it by conduction, usually via cables (signal or power).

 

Radiated immunity (sometimes ”susceptibility” is used) or emission: the disturbance is coupled to the apparatus or it emanates from it by electromagnetic fields. Here, both fields from and to the apparatus itself and the cables connected to it, are involved.

 

The EMC characteristics are mostly measured by standardized test methods. Europe and most worldwide countries have issued legislation requiring a minimum of EMC characteristics for an apparatus. In Europe also installations have EMC requirements.

 

EMC Strategy and Techniques

There is one general strategy when trying to control the different electromagnetic environments: the zoning strategy. We simply create zones, or volumes, with different and defined electromagnetic environments.

 

To create the zones we use grounding and shielding techniques together with filtering. EMC design is a major part of the hardware design fulfilled by hardware designers.

 

But, of course, before we implement EMC techniques, we try to design our circuitry for the best signal integrity and behavior as possible. We also try to design for the best immunity and less emission by the build up of the circuits and installations without the use of ”extra” devices or material.

 

For an organisation, company or project it is vital that EMC issues are addressed at the very beginning of a project, that there is an EMC culture in the company and that there are EMC knowledgeable personnel at hand.

Experience

It is our experience so far that the computer and mobile phone manufacturers together with car manufacturers mainly reach the goal of achieving good enough EMC in their products. For other product types there is a gliding scale from good to bad, or lack of, EMC behavior. The worst category is the installation business. In this branch there is a lot to do to make the installation a good foundation for installed apparatus to work properly.

Summary

We may conclude this short EMC text with some statements based on our experience:

• Without good enough EMC characteristics there will be upsets or destruction in the equipment sooner or later: the software cannot handle the situation.
• The quality manager is to be blamed if there are failures due to lack of EMC characteristics.
• Management, marketing and sales personal, installation and service personnel (and sometimes the user) need to know the basics of EMC.
• Do not rely on software in EMC design.
• Minimum EMC requirements are mandatory by law.
• EMC characteristics have to be designed into the equipment.
• Hardware designers need to know a lot about EMC techniques.
• EMC is rarely a subject in technical high schools; thus, you need both to take short classes in EMC and to teach yourself.
• EMC is how to use electromagnetic theory besides the ”normal” design procedures. (Normal engineering education teaches how circuits do work. EMC education and experience teaches why they will not work !)

Hopefully we have given the answers to the initial questions and some thoughts on how to succeed in taking control over the electromagnetic environment.

 

Michel Mardiguian & Ulf Nilsson