fafnir TORRIX XTS Series, Technical Documentation Manual

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Design and Function Page 4/ 47
3 Design and Function
The level sensors consist of a probe head (1) and a probe tube (4) made of stainless steel.
The probe tube is height-adjustable with a screw-in body (3) or mounted with a flange in
the tank or outside the tank as a bypass. A float (5) for measuring the product filling level
and another float (6) for continuous interface measurement move on the probe tube.
Figure 1: How the magnetostrictive measuring principle works
The sensor operates according to the magnetostrictive measuring principle. The probe tube
contains a wire (7) made of magnetostrictive material. The sensor electronics (2) transmit
pulses through the wire, which generate a circular magnetic field (8). Permanent magnets
(9) are used as filling level sensors which are installed in both the product float (5) and the
interface float (6). The magnetic field of the float magnets (9) axially magnetises the wire in
this area. The superposition of the two magnetic fields produces a torsional wave (10) at the
float position, which then propagates along the wire in both directions. One torsion pulse
runs directly to the probe head and the other one is reflected at the bottom end of the
probe tube. The time between the current pulse being transmitted and the two torsion
pulses arriving at the probe head is measured and the float position calculated. The position
of the interface float float is calculated by measuring a second pulse.
1 – Probe head
2 – Sensor electronics
3 – Screw-in unit
4 – Probe tube
5 – Product float
6 – Interface float
7 – Magnetostrictive wire
8 – Circular magnetic field
9 – Permanent magnet
10 – Torsion pulse
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