Vega Capacitive electrodes EK … with signal conditionin Bedienungsanleitung PDF herunterladen (Seite 4)

4 Capacitive electrodes EK with signal conditioning instrument

Product description

1 Product description

1.1 Function and configuration

Capacitive electrodes series EK detect levels

of virtually any medium, unaffected whether

liquids, powders, granules or pastes. This is

also valid for adhesive mediums.

The electrode measures also the level ca-

pacitance and the ohmic resistance (admit-

tance processing). Hence also problematic

mediums and solids with fluctuating humidity

contents can be detected.

By the use of screening tubes and screen

segments, inactive areas can be provided on

the probe where pollution, condensation or

permanent build-up do not influence the

measuring result.

Measuring principle

Electrode, medium and vessel wall form an

electrical capacitor.

The capacitance of the capacitor is mainly

influenced by three factors:

- distance of the electrode plates (a)

- size of the electrode plates (b)

- kind of dielectricum between the electro-

des (c)

b

c

Fig. 1.1 Plate capacitor (schematic demon-

stration)

Electrode and vessel wall are the capacitor

plates. The medium is the dielectricum. Due

to the higher dielectric constant figure (DK-

value) of the medium against air, the capaci-

tance of the capacitor increases with raising

covering of the electrode.

Fig. 1.2 Capacitance change with covered

electrode

The capacitance change is converted by the

oscillator into a level proportional, floating

current in the range of 4 … 20 mA or into a

switching command.

Continuous level measurement

With the continuous level measurement, the

appropriate level is continuously detected

and converted into a level proportional signal

which is either directly indicated or further

processed.

You require a capacitive electrode series EK

with oscillator and a signal conditioning in-

strument VEGAMET, converting the propor-

tional current of the oscillator into

standardised current and voltage signals.

The continuous measurement requires a

constant dielectric constant figure e

r

, i.e. if

possible the medium should have steady

features.

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