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WIKA operating instructions level sensor model FFG

13445627.01 12/2010 GB/D/F

The level sensor shown in gure 2 serves for the continuous

measurement of uids. To transmit the liquid level value to the sensor, a

oat is sliding on the sensor tube. The operating principle of the sensor

is based on the magnetostriction eect. The oat contains a magnet

while a wire made of magnetostrictive material is installed under tension

inside the sensor tube. The magnetic eld of the oat is twisting the

wire. A second, temporary magnetic eld is generated along the wire by

a current pulse within the wire. The superposition of the two magnetic

elds will release a mechanical wave on the wire.

At the end of the wire within the sensor head, the mechanical wave is

converted by a piezo-ceramic transducer into an electrical signal. The

starting point of the mechanical wave and, hence, the oat position is

then determined by measuring the transit time.

The results of such measurements are feasibility-tested by a microcon-

troller located in the sensor head and are then converted into a current

value by a digital analog transformer. The sensor is provided with a

2-wire connection so that the current consumption indicates the position

of the oat at the same time. The current values are restricted to a range

of between 3.5 ... 23 mA.

2. Description of functions and design

Fig. 1: Level sensor system model FFG

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