Magnet-physik EF 14 - AC Measuring Operation

Electronic Fluxmeter EF 14
BA
–
no.: 100514EBA02
December 9
th
, 2020
Page
36
or for the rise time of the magnetizing pulse at given area turns
max
max
r
u
NAB
t 
.
The following table shows flux densities and area turns that are typical in magnetizing
technology and the resulting limits for rise times:
B
m
ax
NA
t
r
3 T
100 cm²
> 0,75 ms
5 T
100 cm²
> 1,25 ms
7 T
100 cm²
> 1,75 ms
3 T
10 cm²
> 75 µs
5 T
10 cm²
> 125 µs
7 T
10 cm²
> 175 µs
To demagnetize or stabilize permanent magnets often an alternating capacitor discharge is used,
which generates sinusoidal field strength with exponentially decreasing amplitude. In this case
the Peak function shows in large numbers the maximum of the first amplitude. The maximum
of the second amplitude, which has an opposite sign, is shown below.
5.3 AC Measuring Operation
For a sinusoidal flux it is
)sin(
ˆ
)( tt  
with .2 f



Here is f the frequency and

ˆ
the amplitude of the flux.
The voltage induced by this flux in a measuring coil with N turns is
)cos(
ˆ
d
d
)( tN
t
Ntu 


.
The amplitude of this voltage depends on the frequency of the flux.
The fluxmeter integrates the voltage that is induced in the coil. The voltage at the output of the
integrator is
)sin(
ˆ
d)(
1
)(
a
t
RC
N
ttu
RC
tu  

.
Its amplitude is particularly independent of the frequency. As every flux can be represented by
a sum of sinusoidal fluxes, this is also true for a non-sinusoidal flux, as long as the frequency