fafnir HART TORRIX, Technical Documentation Manual

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Design and function Page 4/37
The measuring principle illustrated in the following figure exploits the physical effect of
magnetostriction and is largely unaffected by temperature. The probe tube contains a ten-
sioned 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)
inside the float acts as the filling 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 probe 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 probe head is measured. From these propagation times, it is possible
to determine the current position of the float.
Figure 2: Operating principle of the TORRIX level sensor
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