8.4.6 E
XPERIMENT
: D
ISTANCE
M
EASUREMENT
This example experiment bases on the fact, that a
ferromagnetic metal brought into the centre of a coil
changes the inductance of the coil.
The schematics in Fig. 51 shows that the reference
output of the lockin amplifier generates an alternating
current in the coil and thus an alternating magnetic field.
The series resistor R2 is used to measure this current.
The metal sphere is approached from the top. It is
centrally mounted to a screw with a 0.8 mm /turn threat,
so that 25 turn end up to be 20 mm distance.
The operation frequency for this experiment is chosen to
be 39.0625 kHz, just high enough that the inductive
current amplitude can be easily measured vs. distance:
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20
Page 58 (70)
Figure 50: Coil connected to the USBLockin
Figure 51: Circuit diagram of the distance measurement
qucs/Distance.sch
Figure 52: Curve diagram showing the Amplitude over the distance. Amplitude = 1V / 0.1 V,
t
= 20 ms, f = 39062.5
Hz
distance [mm]
0
5
10
15
20
0,325
0,33
0,335
0,34
0,345
0,35
Ampl. 1V
Ampl. 100 mV [*10]
