1 Description of the measuring principle
Measuring principle
The VEGACAP series consists
of capacitive sensors for level
detection.
The instruments are designed for industrial use in all areas of
process technology and are universally applicable.
Probe, measured product and vessel wall form an electrical ca-
pacitor. The capacitance is influenced by three main factors.
Fig. 1: Functional principle - Plate capacitor
1 Distance between the electrode surfaces
2 Size of the electrode surfaces
3 Type of dielectric between the electrodes
The probe and the vessel wall are the capacitor plates. The meas-
ured product is the dielectric. Due to the higher dielectric constant
(DK value) of the product compared to air, the capacitance in-
creases as the probe is gradually covered.
A level change causes a change in capacitance which is pro-
cessed by the electronics and converted into an appropriate
switching command.
The more constant the conductivity, concentration and temper-
ature of a product, the better the conditions for capacitive meas-
urement. Changes in the measuring conditions are generally less
critical when detecting materials with high DK values.
The sensors are maintenance free and rugged and can be imple-
mented in all areas of industrial measurement engineering.
Whereas partly insulated versions are predominantly used for
solids, fully insulated versions are preferred for liquids.
Implementation in very adhesive or corrosive products is also no
problem. Since the capacitive measuring principle places no spe-
cial requirements on mounting, a host of different applicationscan
be equipped with VEGACAP series 60 level switches.
1.1 Application examples
Non-conductive liquids
Fig. 2: Level detection in non-conductive liquids
1 VEGACAP 62 level switch for full signalling/overfill protection
2 VEGACAP 66 level switch for empty signalling/dry run protection
3 VEGACAP 62 level switch for level detection - laterally mounted
Capacitive level switches have proven themselves for application
in non-conductive liquids (dielectric value < 5). They are used as
overfill protection systems (WHG) as well as dry run protection
systems. The mounting position is arbitrary (from above, laterally
or from below). Typical products are hydrocarbons or solvents.
Laterally mounted or applied with an angled probe from above,
the instrument switches reliably and very precisely, even in
changing products. When mounted from above, the switching
point can be changed afterwards and adapted to the application.
By compensating its own inherent capacitance, the instrument is
able to detect products with dielectric values >1.5 reliably.
Advantages:
l Insensitive
to buildup
l Overfill protection/Dry
run
protection
l Maintenance-free
l Very precise when mounted laterally or used with angled
probe
Description of the measuring principle
Capacitive – Level detection in liquids 3
29983-EN-071129
