F.W. Bell 5060, Instruction Manual

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OPERATING INSTRUCTIONS
3-13
ZERO FUNCTION
“Zeroing” the probe and meter is one of the most important steps
to obtaining accurate dc flux density measurements. The ideal
Hall generator produces zero output in the absence of a magnetic
field, but actual devices are subject to variations in materials,
construction and temperature. Therefore most Hall generators
produce some output even in a zero field. This will be interpreted
by the meter as a flux density signal.
Also, the circuits within the meter can produce a signal even when
there is no signal present at the input. This will be interpreted as a
flux density signal. Lastly magnetic sources close to the actual
field being measured, such as those from electric motors,
permanent magnets and the earth (roughly 0.5 gauss or 50
µ
T),
can induce errors in the final reading.
It is vital to remove these sources of error prior to making actual
measurements. The process of “zeroing” removes all of these
errors in one operation. The meter cancels the combined dc error
signal by introducing another signal of equal magnitude with
opposite polarity. After zeroing the only dc signal that remains is
that produced by the probe when exposed to magnetic flux.
NOTE: Zeroing the meter and probe affects only the static (dc)
component of the flux density signal.
There may be situations when the user prefers to shield the probe
from all external magnetic fields prior to zeroing. Provided with
the meter is a ZERO FLUX CHAMBER which is capable of
shielding against fields as high as 30 mT (300 G). The probe is
simply inserted into the chamber before the zeroing process
begins.