F.W. Bell 8000 series, Инструкция по эксплуатации

Страница: 55 / 132

F.W. BELL 8000 Series Gauss/Tesla Meter Instruction Manual
Section 6 – Flux Density Measurement 6-8
Zeroing
Overview
“Zeroing” the probe and meter is one of the most important steps to obtaining
accurate flux density measurements. An ideal Hall effect sensor produces
zero output in the absence of a magnetic field, but the actual devices are
subject to variations in materials, construction and temperature. Therefore,
most Hall effect sensors produce some output even in a zero field and this will
be interpreted as a magnetic field signal by the meter.
In addition, the circuits within the meter can produce a small signal even when
there is no signal present at the input. This also will also be interpreted as a
magnetic field by the instrument.
Lastly, magnetic sources close to the actual field being measured, such as
those from electric motors, permanent magnets and the earth’s magnetic field
(roughly 0.5 gauss or 50
µ
T), can introduce errors in the final reading.
For most situations it is preferable to shield the probe from all external
magnetic fields prior to zeroing. For this reason the 8000 Series Meters are
provided with a “zero flux chamber” which is capable of shielding against fields
as high as 30mT (300G). The probe is simply inserted into the chamber before
the zeroing process is initiated.
Handle the Hall probe with care. Do not bend the stem or apply pressure
to the probe tip as damage may result.
In other situations the user may want the probe to be exposed to a specific
magnetic field during the zeroing process. As an example, consider zeroing
the probe when it is exposed to the earth’s magnetic field. This will cancel the
effect of the earth’s magnetic field for all future readings while the probe is in
that location.
Note: If a range is exceeded by the level of field while zeroing, that range
cannot be entered by the meter.
Note: A high reading when the probe is not in a magnetic field may be an
indication of a defective probe or other problem.