Vega EL 11 - Oscillator; Humidity Change

Capacitive electrodes EL 4 … 20 mA - compact 9
Product description
+
–
0 %
5 %
10 %
15 % vol.
fully insulated
electrode
partly
insulated
electrode
Solid
humidity (%)
Level
measured
value
Fig. 1.3 Humidity change
Oscillator
The oscillator CAP E32 (H) Ex with the patented
processing (phase selective admittance
processing) extends the application range of
capacitive level measurement technology. This
function can be switched on, see 4 Set-up.
In conjunction with a fully insulated rod
electrode, the oscillator compensates even
strong conductive build-up.
Mounted in an individual rod or cable electrode
type EL, this oscillator ensures also the exact
measurement in solids with varying humidity
contents.
The oscillator processes the measuring
currents according to the phase position.
Measuring currents with a defined phase
shifting as they occur with build-up or humidity
changes are filtered out.
Humidity change
A humidty change in solids causes a change of
the dielectric constant figure (ε
r
). In parallel the
ohmic value of the medium changes. Due to the
change also a phase shifting of the measuring
currents is caused.
With a capacitive measurement already lowest
humidity changes cause measuring errors.
Typical products are, e.g. sand, aggregate in
the cement industry, hop or plastic granules
(after drying).
When using the oscillator CAP E32 (H) Ex
humidity changes of 15␣ % vol. do not influence
the accuracy of the measurement. Even
layering of product with different humidity do
not play a role for the measuring accuracy.
When the humidity contents exceeds 15␣ % vol.
1) Actual value level
1)
fully and partly insulated electrodes react
differently (see also “Fig. 1.3 Humidity
change“). Whereby the measured value on fully
insulated electrodes raises with steady level,
the measured value on partly insulated
electrodes drops.