ETS-Lindgren HI-3624(A) Survey Meter - Manual (Page 18)

18 | Operation
In other cases, the root-sum-squared resultant value of flux density may be
obtained by taking three orthogonal measurements of the field; in this case, the
sensor is successively oriented in three mutually perpendicular directions around
a fixed point and the individual readings recorded. The mutually perpendicular
directions will be denoted as X, Y, and Z. The resultant flux density is then found
by forming the root-sum-squared value from the individual readings as follows:
B = (Bx 2 + By 2 + Bz 2 ) 1/2
B = resultant flux density; B
x
= Reading in the X direction;
B
y
= Reading in the y direction; B
z
= Reading in the Z direction.
It does not matter which orientation of the field sensor is used for the X
orientation but the Y and Z orientations must be perpendicular to one another
and the X orientation.
The user may select the lower frequency of the band pass for the instrument as
either 30 Hz or 5 Hz. It should be noted that when the instrument is switched to
the 5 Hz lower frequency cutoff, the unit will be very sensitive to motion of the
sensor since movement within the earth's constant field will appear as a signal to
the instrument. When the sensor is accelerated or rotated within a constant field,
there will be an output from the sensor at a frequency corresponding to the
movement and this will usually include frequency components greater than 5 Hz.
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. For area surveys of ELF fields, the 30 Hz
cutoff will be more useful.