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Alex Electronics Co.
Theory of Operation
The principle of operation is based on the change of capacitance
between the probe and the silo or vessel wall.
The probe and the vessel wall form a capacitor C
When the vessel is empty, the isolation medium between the two
electrodes of the capacitor (probe and vessel wall) is air which
has a dielectric constant ɛr =1
When the material inside the vessel covers the probe, the
insulation medium between the two electrodes (probe and vessel
wall) changes to give a higher value of dielectric constant ɛr >1
This change in the capacitance value is monitored by the electronic
card (inside the head house) which converts it to equivalent 4 - 20
mA output signal.
SM720 Capacitive Level Transmitter
Fig.2: Theory of operation
X
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