The maximum magnetic field associated with household
appliances of various types at various distances.
SAMPLE-SELECTION
Convenience. Appliances were selected that were immediately
available, such as those found in the homes of the investigator
and his associates.
SAMPLE-SIZE
95 different devices, of 27 types.
MEASURED-PARAMETER
Single-axis magnetic flux density
METHODOLOGY
The protocol attempted to locate the maximum field
measurement at fixed distances from the appliance. At the
beginning of a measurement sequence, the magnetic fields
near the surface of the appliance were surveyed in order to
locate the region of the maximum flux density. Maximum
field readings were then made along a path perpendicular to
the appliance from this point at fixed distances. The
maximum magnetic flux density at each distance was found by
rotating the probe slowly by hand in all directions until a
maximum was found.
Handheld and portable devices were surveyed on all sides
with the exception of bottoms of appliances that normally
sat on the floor. Large stationary appliances were surveyed
only on those surfaces that were normally exposed or
accessible. Distance measurements were always made relative
to the outer surfaces of the appliance.
An air-coil probe was used for measurements where the
distance to the appliance was less than 30 centimeters.
Foam plastic spheres were used with the air-coil probe to
maintain the distance to the appliance during measurements.
A ferrite-coil probe was used for larger distances. The
distance between the appliance and the ferrite-coil probe
distance was maintained by aligning a mid-probe reference
mark against a meter stick.
Calibrations of the probes were conducted with a 1-meter
radius Helmholtz coil-pair, where coil spacing equaled the
radius.
Care was taken to ensure the measurements represented fields
from the appliance and not other sources. All appliances
and equipment in the region of the appliance under test were
turned off. The test unit was turned on and off while
monitoring the field level. A reading that dropped from
mid-scale to or near zero confirmed the device as the field
source. Devices with low fields could often be
discriminated by rotating the device so that its field was
perpendicular to the ambient field and using the highly
directional probe to discriminate between them. A few large
appliances were measured during early morning hours when
ambient fields were lowest.
INSTRUMENT-NAME
SAMPLING-INTERVAL
Not applicable (not a time-series).
SAMPLING-DURATION
Not applicable (not a time-series).