ETS-Lindgren HI-3627 ELF Magnetic Field Meter - Manual (Page 24)

Page -- 16 HI-3627 Manual
return currents. Establishing what the ambient magnetic field
environment is in a home usually requires numerous
measurements throughout the home, with at least one
measurement within each room. Normal practice would include
at least one field measurement taken near the center of each
room. A more thorough approach would include five
measurements in each room, one at the center and one near
each corner of the room. A reasonable technique is to position
the sensor at a point approximately one meter from each room
corner for the flux density measurement. This avoids, to an
extent, placing the sensor immediately next to wiring which
may be hidden within the walls of the room and which may
yield unrealistically high values of flux density compared to what
most individuals within the room might be exposed. A possible
protocol for making the measurements is outlined in the
California Department of Health Services paper on suggested
protocol for measuring 60 Hz magnetic fields in residences (3).
Surveys of the areas near electrical appliances will usually reveal
higher values of flux density due to the currents flowing within
motors or heating elements. This may influence the location of
beds, and other locations of extended occupancy. In
characterizing the magnetic fields near obvious sources, such as
appliances, it is often helpful to measure and record the flux
density value at intervals of a few inches (or centimeters)
beginning near the surface of the device. These data will help
provide a perspective on the spatial extent of the elevated field
levels and the significance of the levels relative to other values
determined elsewhere within the home. Field measurements
should take into account the likelihood that individuals may have
access to areas where measurements are contemplated.
Because 60 Hz magnetic fields produced by the use of
electricity within the home are dependent on the magnitude of
current flowing within wires or the operation of appliances, flux
densities will be seen to vary with time, being greater when
more electrical power is being used. For example, when heating
or air conditioning systems turn on or the compressor within a
refrigerator cycles on, the flux density will increase.