B-H ANALYZER SY-8218
/ SY-8219
19
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4.3 Calculation of gain and current necessary for power amplifier
●
When using a power amplifier, its gain and current should be predicted in advance. The procedure is described below.
The explanation below is written assuming that a waveform to be observed is an ideal sine wave or an ideal symmetry square wave with
Duty of 50%. Under a measurement condition which is not in this ideal state because of characteristics of a sample, the obtained gain
below should be used as a standard.
■
Prediction of gain by using Max. magnetic flux density Bm
The following is the procedure to predict a gain necessary for a power amplifier using Max. magnetic flux density Bm generated in a sample.
Fig.4-4 Measurement system
①
Define the measurement frequency f and the Max. magnetic flux density Bm to be generated in the sample, and then obtain Max. induced
voltage V
2
m using expression (4.9) if the excitation signal is a sine waveform or using expression (4.10) if it is a symmetry square waveform
with Duty of 50%.
For excitation signal of sine wave:
(4.9)
For excitation signal of symmetry square
(4.10)
waveform with Duty of 50%
:
If V
2
m exceeds 200[V], this product cannot make measurement; i.e. Maximum measurement induced voltage of this product is
200[V].
Never enter any voltage exceeding 200[V] in this product. Otherwise, it may fail. Moreover, do not use the power amplifier
exceeding the rated power. Otherwise, it may fail.
②
Next, obtain the maximum exciting voltage V
1
m which is obtained by converting Max. induced voltage V
2
m into the primary turns side, using
expression (4.11). It can be applied independent of a type of the exciting signal.
(4.11)
If V
1
m exceeds the maximum output voltage of the power amplifier to be used, it is considered that any measurement cannot be
made under this condition.
Originally at this step, in consideration of the voltage descent of the shunt resistance, the current that flows to
the primary side of the sample is not predictable. Moreover, the voltage descent of this shunt resistance is not considered because it is small.
③
Using results above, obtain the gain G required for the power amplifier using the maximum signal output voltage
V
0
m=2.8[V
0-p
]
of this
product and expression (4.12).
(4.12)
④
Set the power amplifier to a value which exceeds the obtained gain G and is the lowest in the settable gains.
Le: Effective length of magnetic path
Ae: Effective net core area
N
1
: No. of primary turns
N
2
: No. of secondary turns
V
2
m: Max. induced voltage
V
1
m: Max. exciting voltage
V
0
m: Max. signal output voltage
i
1
m: Max. exciting current
Hm: Max. magnetic field
Bm: Max. magnetic flux density
G:
Power amplifier gain
Rs: Shunt
resistance
value
R
S
信号発生器
パワ－アンプ
N
2
N
1
1次巻線
2次巻線
i
1m
V
2m
V
1m
B
m
H
m
V
0m
G
e
m
m
A
B
N
f
V
2
2
2
e
m
m
A
B
N
f
V
2
2
4
m
m
V
N
N
V
2
2
1
1
m
m
V
V
G
0
1
Power amplifier
Secondary turns
Primary turns
Signal generator