WIKA Operating Instructions Level Transmitter
– BLM-SF-FM
5
1.1 Principle of operation
Inside the sensor’s pipe, a wire of magnetostrictive material is placed.
Periodically, a current impulse is sent through the wire, which in turn cre-
ates a circular magnetic field around the wire. This pulse starts a time
measurement. For the level transmission, a magnet mounted inside the
float is used. The magnetic field magnetizes the wire in this area.
By superposition of the two magnetic fields in the region of the float, a
mechanical torsion wave through the wire is created, which travels with the
material specific speed of sound in both directions (Wiedemann effect).
The torsion sound wave, running in d
irection of the sensor’s end is
reflected there. The sound wave running in direction of the detector is
transformed into an electric signal and the elapsed time is measured.
Liquid and interface level are calculated and transmitted through the sen-
sor’s interface.
Magnetostrictive wire
Magnetic field
Torsion impulse
Circular magnetic field
Torsion impulse
Magnet