Vega VEGAFLEX 81 - 3.2 Principle of operation

9
3 Product description
VEGAFLEX 81 • Modbus and Levelmaster protocol
42283-EN-140430
3.2 Principle of operation
The VEGAFLEX 81 is a level sensor with coax probe for continuous
level or interface measurement, suitable for applications in liquids.
High frequency microwave pulses are guided along a steel cable or
a rod. Upon reaching the product surface, the microwave pulses are
reected.Therunningtimeisevaluatedbytheinstrumentandoutput-
ted as level.
d
h
1
Fig. 3: Level measurement
1 Sensorreferenceplane(sealsurfaceoftheprocesstting)
d Distancetotheinterface(HARTvalue1)
h Height - Level
Probe end tracking
To increase sensitivity, the probe is equipped with probe end tracking.
In products with a low dielectric constant, this function is very helpful.
This is the case, for example, in plastic granules, packing chips or in
vesselswithuidizedproducts.
Between a dielectric constant of 1.5 and 3, the function switches on, if
required. As soon as the level echo can no longer be detected, probe
end tracking is automatically activated. The measurement is contin-
ued with the last calculated dielectric constant.
The accuracy thus depends on the stability of the dielectric constant.
If you measure a medium with a dielectric constant below 1.5, probe
end tracking is always active. In this case, you have to enter the
dielectric constant of the medium. A stable dielectric constant is very
important here.
High frequency microwave impulses are guided along a steel cable or
rod. Upon reaching the product surface, a part of the microwave im-
pulsesisreected.Theotherpartpassesthroughtheupperproduct
andisreectedbytheinterface.Therunningtimestothetwoproduct
layers are processed by the instrument.
Application area
Functional principle -
level measurement
Functional principle - in-
terface measurement