VEGA VEGAPULS 81 - Manual (Page 42)

42 VEGAPULS 64 and 81
Optimization of the penetrated substance
If it is not possible to gate out the interfering
reflection when penetrating a vessel or a win-
dow, the interfering reflection can be nearly
deleted by the optimized thickness of the
penetrated medium.
The interfering reflections are composed of
two single reflections. One reflection when
penetrating the substance and one reflection
when the waves leave the penetrated sub-
stance.
It is a special feature of the reflection on the
incoming surface, that it is reflected with a
phase jump of half wavelength. The signals
reflected on the outgoing surface are reflected
without phase jump.
Two false reflection on the wave incoming
surface (with phase jump) and on the wave
outgoing surface (without phase jump) which
are eliminating one another
D
Emitted wave
Reflection with
phase jump
Plastic vessel
ceiling
Reflection without
phase jump
Mounting and installation: Measurement through the vessel wall
Sensor too close to the outer vessel wall
Wrong
If you want to measure through the wall of a
plastic vessel, make sure that the sensor is not
too close to the outer wall of the vessel. The
emission cone of the sensor must detect the
product well and must not detect the vessel
ambient or the vessel wall.