VEGA VEGABAR 82 4 … 20 mA - Operating Instructions - Manual (Page 9)

9
3 Product description
VEGABAR 82 • 4 … 20 mA
45027-EN-131010
Sensor element is the CERTEC ® measuring cell with robust ceramic
diaphragm. The process pressure deflects the ceramic diaphragm
and causes a capacitance change in the measuring cell. This capaci-
tance change is converted into an electrical signal and outputted as
measured value via the output signal.
The CERTEC
® measuring cell is available in two sizes:
•
ø 17.5 mm with small process fittings
•
ø 28 mm with large process fittings as well as all flange connec-
tions
The measuring cell design depends on the selected pressure type.
Relative pressure: the measuring cell is open to atmosphere. The
ambient pressure is detected in the measuring cell and compensated.
It thus has no influence on the measured value.
Absolute pressure: the measuring cell is evacuated and encapsu-
lated. The ambient pressure is not compensated and does hence
influence the measured value.
Relative pressure, climate-compensated: the measuring cell is
evacuated and encapsulated. The ambient pressure is detected
through a reference sensor in the electronics and compensated. It
thus has no influence on the measured value.
The following presentations show the installation of the CERTEC ®
measuring cell into the process fitting and the different seal concepts.
1
2
4
5
3
Fig. 3: Recessed installation of the CERTEC ® measuring cell
1 Measuring cell
2 Seal for the measuring cell
3 Diaphragm
4 Process fitting
5 Seal for the process fitting
Measuring system
Pressure types
Seal concepts
Recessed installation