VEGA VEGADIF 65 Foundation Fieldbus - Manual (Page 11)

11
3 Product description
VEGADIF 65 • Foundation Fieldbus
36130-EN-130417
A metallic measuring cell is used as sensor element. The process
pressures are transmitted via the separating diaphragms and filling
oils to a resistance measuring bridge (semi-conductor technology).
The difference between the acting pressures generates a change in
the bridge voltage. This change is measured, further processed and
converted into a corresponding output signal.
The markings "+" and "-" on the process component in chapter
"Mounting and connection instructions" must therefore be noted when
connecting to the process. The pressure acting on "+" goes positive,
the pressure acting on "-" goes negative into the calculation of the
pressure difference.
The configuration of the measuring cells differs depending on the
measuring range:
1
2
3
4
5
1
p
2
p
Fig. 8: Metallic measuring cell 10 mbar and 30 mbar - p
1
and p
2
process pres-
sures
1 Measuring element
2 Silicone diaphragm
3 Separating diaphragm
4 Filling oil
5 Integrated overvoltage arrester
1
p
2
p
1
2
3
4
Fig. 9: Metallic measuring cell from 100 mbar - p
1
and p
2
process pressures
1 Measuring element
2 Overload diaphragm/Middle diaphragm
3 Filling oil
4 Separating diaphragm
Power is supplied via the H1 Fieldbus. A two-wire cable according to
Fieldbus specification serves as carrier of both power and digital data
for multiple sensors. This cable can be operated in two versions:
•
via an H1 interface card in the control system and additional power
supply
Functional principle
Power supply and bus
communication