Vega VEGABAR 87 Operating Instructions Manual page 10

3 Product description
Measuring system tem-
perature
Pressure types
Seal concept
10
pressure causes a resistance change which is converted into a cor-
responding output signal and output as measured value.
The METEC measuring cell is the measuring unit. It consists of
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the ceramic-capacitive CERTEC
temperature-compensated isolating system.
Fig. 4: Configuration of the METEC
1 Process diaphragm
2 Isolating liquid
3 FeNi adapter
4 CERTEC measuring cell
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Temperature sensors in the ceramic diaphragm and the ceramic base
of the CERTEC measuring cell detect the actual process tempera-
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ture. The temperature value is output via:
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The display and adjustment module
•
The current output or the additional current output
•
The digital signal output
The measuring cell design depends on the selected pressure type.
Relative pressure: the measuring cell is open to the atmosphere.
The ambient pressure is detected in the measuring cell and compen-
sated. It thus has no influence on the measured value.
Absolute pressure: the measuring cell contains vacuum and is
encapsulated. 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 measuring system is completely welded and hence sealed
against the process. The sealing of the process fitting against the
process is carried out by a seal provided on site.
measuring cell and a special,
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4
3
2
1
measuring cell with VEGABAR 87
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VEGABAR 87 • 4 ... 20 mA/HART