Measurement Of The Maxima Of Magnetizing Impulses - Magnet-physik EF 14 Operating Instructions Manual

Electronic Fluxmeter
only a few ohms and can therefore be neglected. In this case the coil resistance in the coil menu
can simply be set to 0. If the coil resistance exceeds about 100 Ω it should be measured and
entered.
Then the EF 14 calculates the magnetic flux using the formula

R 100 kΩ
  
100 kΩ
  is the flux after and  the flux before resistance correction. The user can apply this
where
formula to calculate the output voltage at the analog output.

5.2 Measurement of the Maxima of Magnetizing Impulses

Main application of the Peak function in DC mode is the measurement of the maxima of
magnetizing impulses.
A magnetizing pulse is generated using a capacitor discharge. It causes a high current pulse in a
connected magnetizing coil or fixture that generates the required magnetic field. The field
strength can be measured with a coil.
Caution!
If a coil is exposed to fast changing, high magnetic fields, high voltages can
be induced. These can destroy the coil itself or a connected measuring
instrument.
The induced voltage u is calculated as follows:

u
Here are NA the area turns of the coil, B the flux density and t the time.
Thus the acceptable change of the flux density, dB/dt, is limited by the maximum input voltage
of the fluxmeter, u
max
The change of flux density can be approximated by the quotient of maximum flux density and
rise time of the magnetizing impulse,
d B
d t
From this follows for the largest acceptable area turns
NA 
BA – no.: 100514EBA02


,
d B

NA .
d t
= 60 V, and from the area turns of the coil.
B

.
max
t
r
u t
max r
B
max
th
December 9 , 2020
EF 14
Page 35