VEGA VEGACAL 67 4 … 20 mA_HART - two-wire - Manual (Page 10)

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3 Product description
VEGACAL 67 • 4 … 20 mA/HART - two-wire
31758-EN-130917
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Fig. 3: 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 measured
product is the dielectric. Due to the higher dielectric constant of the
product compared to air, the capacitance increases as the probe is
gradually covered.
The capacitance as well as the resistance change are converted by
the electronics module into a level-proportional signal.
4 … 20 mA/HART two-wire electronics for voltage supply and meas-
ured value transmission on the same cable.
The supply voltage range can differ depending on the instrument
version.
The data for power supply are specified in chapter "Technical data".
The optional background lighting of the display and adjustment
module is powered by the sensor. A certain level of operating voltage
is required for this. You can find the exact voltage specifications in
chapter "Technical data".
The optional heating requires its own operating voltage. You can find
details in the supplementary instructions manual "Heating for display
and adjustment module".
This function is generally not available for approved instruments.
3.3 Operation
The instrument can be adjusted with the following adjustment media:
•
With the display and adjustment module
•
with the suitable VEGA DTM in conjunction with an adjustment
software according to the FDT/DTM standard, e.g. PACTware and
PC
•
with manufacturer-specific adjustment programs AMS™ or PDM
•
With a HART handheld
Voltage supply