Iwatsu SY-956, Инструкция по эксплуатации

Страница: 14 / 44

4
Chapter 2 Before Measurement
There are several points users need to know before taking measurements with this instrument.
■
2.1 For proper measurement
● In order to correctly measure and evaluate samples made of a variety of materials, there are things to be
aware of other than excitation conditions.
(1) Conduct a comparative measurement with samples of the same shape (size).
Distribution of magnetic flux density in an excited sample is known to change not only with changes in the
manufacturing process of the samples but also with changes in the sample shape (size). Warpage of a sample
also needs attention, as it affects the air gaps against the yoke.
The following is an example of the geometry dependence of samples, as researched in our company.
[Measurement Examples of Geometry Dependence]
Figure 2-1 shows a B-H carve of a 0.1
t
×5.0
w
×107
L
permalloy band (See Fig. 2-2).
The blue curve shows results when the band was an
oval. The yellow curve shows results when the band was
a circle.
This shows how the saturation magnetic flux density
changes drastically when the shape changes.
This measurement result also possesses reversibility.
Fig. 2-1 Geometry dependence of a B-H curve
Fig. 2-2 Permalloy band
(2) Conduct a comparative measurement, using the same B (magnetic flux density) coil.
Although 2 types of B coils are provided with this instrument, it is the best practice for users to wind a B coil by
themselves with consideration to the following (a) to (c):
(a) Always use the same wire for winding.
Eddy current loss generated in the windings by the
yoke’s leakage flux may change when the size of the wire
changes.
(b) Always wind the same number of turns at the same location on the sample.
B to be measured is equivalent to the average magnetic flux density at the location of turns. Therefore, when
the location of turns on a B coil is changed, B may change even with the same sample, as magnetic properties
differ depending on the location of the sample. Similarly, when the number of turns is changed, B may change
even with the same sample, as changing the number of turns is equivalent to changing the testing location.
(c) Always wind tightly around the sample without overlapping.
If air-gaps are formed between the sample and the winding, correct measurement may become impossible, as
leakage flux is interlinked with the gaps of turns. The influence of the gaps is more prominent when the
permeability of a sample is low.
These considerations apply to the 2 provided B coils with different numbers of turns and hole sizes. Use the
same B coil when conducting a comparative measurement.
The example below shows the influence of air gaps, using our B Coil.