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The measuring principle illustrated in Figure 2 exploits the physical effect of magnetostric-
tion and is largely unaffected by temperature. The probe tube contains a tensioned wire
(1) made of magnetostrictive material. The sensor electronics transmit current pulses (2)
through the wire, which generate a circular magnetic field (3). A magnet (4) contained in
the float acts as the level sensor. Its magnetic field applies an axial magnetic field to the
wire. The superposition of the two magnetic fields produces a torsional wave (5) at the
float position, which then propagates along the wire in both directions. One wave
propagates directly to the sensor head, the other propagates down to the bottom of the
probe tube and is reflected. The time between the current pulse being transmitted and
the wave arriving at the sensor head is measured. From these propagation times, it is
possible to determine the current position of the float.
Figure 2: operating principle of the XT-1000 level sensor
XT-1000
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