Field Finder
Field Finder
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© Enviromentor AB 1998 reg. 98.011/Eng
4. Analyse the measurement readings and assess
the need for remedial action, such as rearranging
the furniture in the room and/or moving pieces
of electrical apparatus. The sources of the elec-
tric fields may be located in adjacent rooms.
Certain materials, not only metals, can also
function as antennas as they capture fields
and increase their spread. Plasterboard and
chipboard can have this effect.
4.2
Magnetic fields
Below is a suggestion as to how to measure a
magnetic field in a room within the frequency
range 30 Hz to 2,000 Hz.
1. Start by carrying out a preliminary measurement
with all the pieces of electrical equipment swit-
ched on and make a rough estimate of what field
sources are present in the room. Draw a sketch
of the room. Then measure a number of points
at 1–3 metre intervals and write down the values
measured on the sketch. Measure the magnetic
field at floor level as well as 0.8 and 2 metres
above the floor.
2. Then carry out a measurement with all the
electrical apparatus in the room switched off
to get an idea of the extent of the background
fields in the room. Remember that it is probably
not sufficient simply to switch off the pieces
of apparatus - you will usually need to unplug
them in order to completely eliminate the fields.
In some cases, the background magnetic fields
can be more powerful than the magnetic fields
from the apparatus in the room.
50 cm
50 cm
Overhead view.
Side view.
Cont.
Electric field.
Electric fields from our surroundings.
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How electric fields arise
An electric field arises between two objects with diffe-
rent electric potentials. If two plates made of electri-
cally conductive material are connected to a voltage
source, one of the plates will have a positive charge
while the other will have a negative charge. A vol-
tage arises between the plates and thereby an elec-
tric field. The strength of the field depends on how
high the voltage is and the distance between the objects.
In a similar way, we are continually exposed to
electric fields from pieces of apparatus and elec-
trical installations in our surroundings. The size
of the fields around us are difficult to predict as
they depend on the connection between the sources
of the fields, the people and earthing. There are
often a number of different sources of varying
strengths in a single room.
Objects that are not connected to electricity can
also be affected by electric fields. A metal object
can be capacitively charged by nearby cabling or
other objects connected to electricity. In simple
terms, the metal object functions as an antenna,
capturing the electric field and helping it to grow.
Examples of such objects include desk frames
and electrical devices with non-earthed metal
casings. Some types of building material (plaster-
board walls, chipboard) can also capture electric
fields and increase their spread. When measuring
fields in a room which has plasterboard walls, it
can sometimes be seen that the fields spread out
along an entire wall surface with the highest readings
being concentrated around sockets and switches.
Electric fields can be reduced through screening
and earthing. It is possible to use shielded cabling
or to place screening material around the object
that is to be screened off. In order for the screening
to be effective, it is important for the screening
material to be properly earthed. If this is not the
case, screening can have the opposite effect –
the fields increase in size.
