VEGA VEGAFLEX 81 HART - integrated accumulator - Manual (Page 12)

12
3 Product description
VEGAFLEX 81 • HART - integrated accumulator
44640-EN-130430
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 fluidized 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 reflected. The other part passes through the upper product
and is reflected by the interface. The running times to the two product
layers are processed by the instrument.
TS
d1
h1
h2
d2
1
L2
L1
L3
Fig. 6: Interface measurement
1 Sensor reference plane (seal surface of the process fitting)
d1 Distance to the interface (HART value 1)
d2 Distance to the level (HART value 3)
TS Thickness of the upper medium (d1 - d2)
h1 Height - Interface
h2 Height - Level
L1 Lower medium
L2 Upper medium
L3 Gas phase
Upper medium (L2)
•
The upper medium must not be conductive
•
The dielectric constant of the upper medium must be known (input
required). Min. dielectric constant: rod version 1.6. You can find a
list of dielectric constants on our home page: www.vega.com
Functional principle - in-
terface measurement
Prerequisites for inter-
face measurement