Iwatsu SY-956, Инструкция по эксплуатации

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9
Since the excitation current sent through the excitation coil of the measuring yoke is the same for the 1st and
2nd measurements; B
ya
derived in the 2nd measurement is, in fact, the magnetic flux density of the magnetic
field strength H
ya
in the measuring yoke from the 1st measurement.
Finally, the 3rd measurement is explained next.
Reconnect Relay 1 and 3 to b-side. From the signal generator, generate an excitation sine wave signal of the
same frequency f (cycle T) used in the 1st and 2nd measurements, and send the excitation current i
1b
to the
excitation coil on the double-yoke this time. This excitation current i
1b
is converted into a voltage V
1b
with the
shunt resistor. At this point, an induced voltage V
3b
is generated at both ends of the B coil on the double-yoke.
This excitation current i
1b
, which is sent through the excitation coil on the double-yoke, needs to be adjusted so
that the magnetic flux density B
yb
in the double yoke is the same as the magnetic flux density B
ya
in the
measuring yoke obtained in the 2nd measurement. In reality, i
1b
is adjusted so that B
yb
and B
ya
match within the
Tolerance set in the measurement conditions.
Magnetic flux density B
yb
in the double-yoke is
(9).
When the magnetic path length of the double-yoke is L
yb
, the magnetic field strength H
yb
in the double-yoke can
be calculated from
Ampere’s Law:
(10).
H
yb
is the magnetic field strength when the magnetic flux density in the double-yoke is B
yb
. This B
yb
is also the
same as the magnetic flux density B
ya
in the measuring yoke from the 1st measurement, and thus, H
yb
turns out
to be the same as the magnetic field strength H
ya
of the measuring yoke from the 1st measurement. This is
because the B-H curve, which shows the relationship between magnetic field strength and magnetic flux
density, is the same for both the measuring yoke and double yokes of the same shape and material
composition.
Therefore, formula (10) can be written as
(11).
By modifying formula (2), the magnetic field strength H
p
of the single sheet can be calculated as
(12).
Therefore, by applying H
v
derived from the 1st measurement and H
ya
(=H
yb
) derived from the 2nd and 3rd
measurements into formula (12), the magnetic field strength H
p
of a single sheet at the time of the 1st
measurement can be obtained. The graph showing the relationship between this magnetic field strength H
p
of
the single sheet and the magnetic flux density B
p
of the single sheet derived from formula (5) is the B-H curve of
the sample single sheet.
B
yb
=
1
n
3
A
y
∫ V
3b
dt = B
ya
H
yb
=
n
1
i
1b
L
yb
=
n
1
V
1b
L
yb
R
s
H
yb
= H
ya
=
n
1
i
1b
L
yb
R
s
H
p
= H
v
− (
L
ya
L
p
) H
ya