VEGA VEGADIF 34 … 51 - Manual (Page 52)

52 VEGADIF 34 … 51
20094-EN-030731
1 Transmitter
2 Block valve
3 Adjustment pot
4 Dosing valve
5 Vent or drain valve
VEGADIF 51
Installation on closed vessels with overlaid
pressure
In a closed, pressurised vessel, the level of a
product is determined by measuring the hy-
drostatic pressure. The sum of the hydro-
static pressure and the overlaid pressure acts
as total pressure on the bottom. The hydro-
static pressure is therefore the difference
between total pressure and overlaid pressure.
The transmitter receives the total pressure on
the plus side via the isolating diaphragm and
the overlaid pressure on the minus side.
The isolating diaphragm must be mounted on
the vessel in such a way that the isolating
diaphragm is completely covered by the
product even at min. level.
Example VEGADIF 45:
Transmitter directly flanged
∆ p
h = ––––––
ρ • g
Installation connections
The differential pressure is determined by the
transmitter as follows:
∆
P
= p
F
+ p
D
– (p
k
+ p
D
)
∆
P
= p
F
– p
k
∆
P
: Differential pressure
p
F
: Hydrostatic pressure of the liquid column
p
D
: Static pressure of the steam
p
k
: Hydrostatic pressure of the condensate column
(constant)
Zero is determined to a negative differential
pressure p
F
– p
k
.
Installation on closed vessels with overlaid
steam pressure and heated comparative
column
This installation is a variant of the one de-
scribed previously. In this case, the conden-
sate column is covered by a tube (of larger
nominal diameter) which is filled with the meas-
ured product and acts a communicating pipe.
Through the resulting temperature equalisa-
tion, the density is the same in both columns.
The outer pipe must therefore be insulated -
not the adjustment vessel however (the con-
densate heat must be dissipated).
This arrangement is preferred for measuring
substances with higher density because it
delivers more accurate measurement results.
The previously described technical conditions
also apply to this measurement set-up.
1) Der Messumformer kann entsprechend den
vorhergehenden Darstellungen auch über eine
Wartungseinheit angeflanscht werden.