ETS-Lindgren HI-3627 ELF Magnetic Field Meter - Manual (Page 19)

HI-3627 Manual Page --11
4.0 Making Measurements
To begin making field measurements, plug the probe into the
meter. Turn the range switch to the right, increasing the
instrument's sensitivity until an upscale reading on the meter is
observed. The readings will be most accurate when maximum
deflection is observed. When an over range indication does
occur, the next larger range should be selected. It should be
noted that the meter movement is protected against deflection
past the top of scale. Therefore, the "Over Range" LED must be
relied on to indicate an over range condition.
It is not necessary to rotate the sensor to obtain a maximum
indication on the meter. The value of flux density is obtained by
taking three orthogonal measurements of the field. In this case,
the sensor has three separate coils oriented in three mutually
perpendicular directions around a fixed point. The resultant flux
density is then found by calculating the root-sum-squared value
from the individual RMS readings for each axis.
For area surveys of ELF fields, the 30 Hz cutoff will be more
useful. When the 5 Hz frequency cutoff is selected, the unit will
be sensitive to movement of the sensor. This is due to the
earth's constant magnetic field (approximately 500 mG). When
the sensor is accelerated or rotated within this constant field,
there will be an output from the sensor at a frequency
corresponding to the movement. Consequently, during such
movement, the meter will typically show significant upscale
indications. The 5 Hz frequency cutoff setting is primarily useful
for measurements at fixed coil positions such as near VDTs.