Siemens SITRANS P - Manual (Page 182)

SITRANS P measuring instruments for pressure
Remote seals
Measuring setups
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Overview
This section shows examples of typical measuring setups for us-
ing SITRANS P pressure transmitters with and without remote
seals.
Equations for calculating start of scale and full scale are pro-
vided for each example.
Questionnaires are included to help you select the right combi-
nation of remote seal and pressure transmitter.
Installation
Remote seals of sandwich design are fitted between the con-
nection flange of the measuring point and a dummy flange. Re-
mote seals of flange design are fitted directly on the connection
flange of the measuring point. The respective pressure rating of
the dummy flange or the flanged remote seal must be observed.
The pressure transmitter should be installed below the connec-
tion flange (and below the lower connection flange in the case of
differential pressure transmitters). This arrangement must be
used in the low-pressure range.
When measuring at pressures above atmospheric, the pressure
transmitter can also be installed above the connection flange.
The capillaries between the remote seal and the pressure trans-
mitter should be as short as possible to obtain a good transmis-
sion response.
Offset of measuring range
If there is a difference in height between the two connection
flanges when measuring with two remote seals, an additional dif-
ferential pressure will result from the oil filling of the remote seal
capillaries. This results in a measuring range offset which has to
be taken into account when you set the pressure transmitter.
An offset in the measuring range also occurs when combining a
remote seal with a transmitter if the remote seal is not installed at
the same height as the transmitter.
Pressure transmitter output
If the level, separation layer or density increase in closed ves-
sels, the differential pressure and hence the output signal of the
pressure transmitter also increase.
For an inverted relationship between the differential pressure
and the output signal, the start-of-scale and full-scale values of
the SITRANS P must be interchanged.
With open vessels, a rising pressure is usually assigned to an in-
creasing level, separation layer or density.
Influence of ambient temperature
Temperature differences between the individual capillaries and
between the individual remote seals should be avoided.
Temperature variations in the area of the measuring setup cause
a change in volume of the filling liquid and hence measuring er-
rors.
Notes
• For the separation layer measurement, the separation layer
has to be positioned between the two spigots. Also you must
make sure that the level in the container is always above the
top spigot.
• When measuring density, make sure that the level of the me-
dium remains constant. The level should be above the top
spigot.
Possible combinations of pressure transmitters and remote
seals
Type of installation Pressure transmit-
ters Remote seals
A/B 7MF4033
7MF4034
7MF4035
7MF8023
7MF8024
7MF8025 7MF4900
7MF4910
7MF4920
C
1
and C
2
7MF4233
7MF4234
7MF4235 7MF4900
7MF4910
7MF4920
(vacuum-proof design
in each case)
7MF4333
7MF4334
7MF4335 7MF4901
7MF4921
D 7MF4433
7MF4434
7MF4435 7MF4903
7MF4923
E 7MF4433
7MF4434
7MF4435 7MF4913
G, H and J 7MF4433
7MF4434
7MF4435 7MF4903
7MF4923
© Siemens AG 2008