F.W. Bell 7030, Инструкция по эксплуатации

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F.W. BELL Model 7030 Gauss/Tesla Meter Instruction Manual
6-8 Section 6 – Flux Density Measurement
ZEROING Overview
“Zeroing” the probe and instrument 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 actual devices are subject to variations
in materials, construction and temperature. Therefore, most Hall effect sensors
produce some output even in a zero field. This will be interpreted by the instrument
as a magnetic field signal.
Also, the circuits within the instrument can produce a signal even when there is no
signal present at the input. This 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.
The zero operation is performed for both ac and dc modes of operation. While in dc
mode, the zero point can be adjusted manually. When the zeroing process is
initiated, the instrument performs separate zeroing sequences for ac and dc mode
operation. Both sequences occur regardless of whether a channel is in ac or dc
mode, and each has its own considerations. Zeroing can be performed on all
channels simultaneously or independently.
NOTE: The process of zeroing also affects other functions such as corrected analog
output signals, the hold and relative, and the field classifiers. Uncorrected analog
outputs are not affected.
ac Zeroing
There are two modes of ac zeroing, basic and advanced. For most purposes, basic
ac mode zeroing is sufficient and is set as the default. Basic ac mode zeroing is
performed internal to the instrument and is not affected by the presence of magnetic
fields. The use of a “zero flux chamber” is not required for basic ac mode zeroing.
This is advantageous for situations when the probe is to be purposely exposed to a
magnetic field during zeroing. This situation is described under the next sub-
heading
dc Zeroing.
Advanced ac zeroing is only required when measuring ac fields on the lower ranges
of the instrument. Advanced ac mode zeroing is enabled from a “checkbox” in the
SYSTEM menu. This mode requires a substantially longer zeroing period, but is
required for rated ac accuracy on the lower ranges. The probe must be shielded in a
“zero flux chamber” prior to initiating the zeroing procedure when using advanced ac
zeroing.
Typically it is only necessary to use advanced ac zeroing once when a new probe is
installed. Advanced ac zeroing data for the probe is stored, including after the
instrument has been shut off. The advanced ac zeroing mode may then be disabled
and basic ac zeroing used thereafter. The only exception is when continued
measurement of low range ac fields are being made.