Preface to the lecture, 1

18

 

Electro Smog

 

Typical measurement set up to measure the emission of 

interferences bound to a conductor

 

A: shielded 

link 

conductor

 

B: 

bundle of conductors folded like a meander

 

C: 

connection to the reference mass

 

ME:  receiver of interference signal

 

NNB: Simulation of network

 

PO: test 

object

 

 

Fig. 2.5:    Measurement set up to measure the emission of 

interferences bound to a conductor,

 

:     Ernst Habiger: EMV, Huthig Buch Verlag Heidelberg (1992), 

ISBN 3-7785-2092-X

 

---

Tasks

 

19

 

2.5 Electro-Smog

 

There is almost no end to the possibilities of variation and one needs already a lot of 

overview and experience to determine the field strength maximum. Nevertheless we have 

to ask ourselves if in this way really all emissions of interference are understandable, that 

popularly are described as ,,electro smog".

 

Smog is the combination of the terms Smoke and Fog. It therefore describes a pressure on 

the environment with fog like smoke. When for instance in the case of smog alarm all 

interference sources are switched off, which means all kilns are brought to a stop and all 

automobiles are stopped, than the fog like smoke therefore still is not vanished from the 

air. It just distributes itself and dissolves only very slowly.

 

The transfer of the smog idea on the electromagnetic interference radiation is bound to fail 

because, when the test object is switched off no emission of interference at all is detectable 

with the usual measurement means. Nevertheless the rainbow-press is trying to enumerate 

almost all electromagnetic field phenomena under the term ,,electro smog" without 

consideration of the fact that this term is not at all a collection term. 

From the sight of an expert one can only speak of smog when something like smog 

remains and stays active further after the switching off of an electro technical apparatus. It 

should be a phenomenon that is not understandable by the standardized measurements of 

interference radiation. Such a phenomenon would be e.g. the vortex of the electric field. 

However vortices are virtually not measurable in a direct way because they have the 

unpleasant property to whirl about around the measurement probe. But they will be 

detectable by their eddy losses and in the case of the electric field vortex appear as noise. 

Until now the standardizer however haven't planned to investigate the influence of an 

apparatus on the noise in the environment. Here we still grope in the dark.

 

At least the vortex shows a storing property that would justify the use of the idea "smog". 

We'll have to investigate the phenomenon.

 

---

20

 

EMC-techniques to measure the stability against interference

 

 

Fig. 2.6:  Picking up of interference voltages in network lines.

 

:     Ernst Habiger:  EMV, Huthig Buch Verlag Heidelberg (1992), 

ISBN  3-7785-2092-X

 

---

Tasks 

21

 

2.6 EMC-techniques to measure the stability against interference

 

The question is: what kind and what intensity of an electromagnetic interference can an 

apparatus cope with without limiting it regarding its technical function. 

For that test generators are used and with their help interference signals are produced in 

the test object. Fig. 2.6 shows the possibilities of a symmetrical, of an unsymmetrical and 

of an asymmetrical production of interference voltage signals in the power supply lines of 

an examinee. Over and above that the testing possibilities and testing methods are 

numerous. In principle the following processes are used:

 

1.

 

The simulation and production of interference factors typical for the network like 

harmonic waves on network voltages, overlapping signal voltages, changes of network 

voltage, decrease of network voltage, network interruptions, network unsymmetries and 

network frequency changes. 

2.

 

The production of both energy-poorer and energy-richer interference impulses like they 

can form in energy-networks by switching acts or by the effect of lightning (burst). 

3.

 

The simulation of the course of events when static electricity discharges. 

4.

 

Low-frequency magnetic fields like those that can form by network frequency operating 

and loading currents or by short-circuit and lightning currents in the form of a pulse. 

5.

 

The stability against interference against the influence of an electromagnetic field also 

called radio interference firmness. For this purpose high-frequency generators and 

broadband antennas are used to expose the examinee to electromagnetic fields in a 

frequency range between 10 kHz and 18 GHz. At the moment tests are only performed 

between 27 and 500 MHz. The modulation of the carrier wave should be possible to be 

able to imitate the interferences by radio technology as realistic as possible. Thereby 

the field strength values can by all means reach up to several 100 V/m. 

In accordance with expectation the result of this irradiation with an outside field is that 

every conduction path and every wire can act as an antenna and therefore can produce 

high-frequency currents and measurable potentials. Building parts of the analog techno- 

logy as a consequence battle with problems of drift whereas with digital logic parts and 

computer parts the danger exists that switching states change unintentionally. Let us 

remember again the overlap effect of fig. 1.4. The electromagnetic wave itself marches 

w i t h  the speed of light through the examinee. When a small part of the wave finds an 

object that it can use as an antenna than the localized overlap comes into play. This than as 

a cause is responsible for the effective and measurable antenna currents. Until here the text 

books help us to explain the problems that happen and to remove them logically.

 

However time and again cases are reported where textbook physics can't help us any 

further. Spectacular cases even came to court like e.g. the ABS (Antilock Braking System) 

of a truck that had failed due to EMC-interference radiation. As a consequence the brakes 

had failed. When after that the local radiation pollution is measured no anomaly at all can 

be

 

discovered. The measurable field strength is not higher as is usual in the whole area. 

Maybe you also have made the experience that often the causes can't be found when your 

computer suddenly "crashes" out of the blue.

 

Here the mentioned vortex of the electric field is capable to deliver plausible explanations 

because it is not bound to the geometry of an antenna and in addition is highly active 

without being detectable with the usual EMC measurement methods of the interference 

radiation measurement!

 

---