Siemens SITRANS P - Manual (Page 150)

SITRANS P measuring instruments for pressure
Remote seals for transmitters and pressure gages
Technical description
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Overview
In many cases the pressure transmitter and the measured me-
dium have to be physically separated. It is then necessary to use
a remote seal.
The remote seals can be used with the following SITRANS P
pressure transmitter series:
• Pressure (P300, DS III, DS III PA, DS III FF)
• Absolute pressure (P300, DS III, DS III PA, DS III FF)
• Differential pressure and flow (DS III, DS III PA, DS III FF)
Note
When configuring your remote seal, be sure to read the informa-
tion about transmission response, temperature error and re-
sponse time to be found in the sections "Function" and "Technical
data". Only then will the remote seal work to optimum effect.
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Benefits
• No direct contact between the pressure transmitter and the
medium
• Individual configuration of the pressure transmitter for perfect
adaptation to the operating conditions
• Available in many versions
• Specially designed for difficult operating conditions
• Quick-release versions available for the food industry
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Application
Remote seal systems should be used if a separation between
the measured medium and the measuring instrument is essential
or appropriate.
Examples of such cases:
• The temperature of the medium is outside the limits specified
for the pressure transmitter.
• The medium is corrosive and requires diaphragm materials
which are not available for the pressure transmitter.
• The medium is highly viscous or contains solids which would
Siemens FI 01 · 2009block the measuring chambers of the
pressure transmitter.
• The medium may freeze in the measuring chambers or pulse
line.
• The medium is heterogeneous or fibrous.
• The medium tends towards polymerization or crystallization.
• The process requires quick-release remote seals, as neces-
sary e.g. in the food industry for fast cleaning.
• The process requires cleaning of the measuring point, e.g. in
a batch process.
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Design
A remote seal system consists of the following components.
• Pressure transmitter
• One or two remote seals
• Filling liquid
• Connection between pressure transmitter and remote seal (di-
rect mounting or by means of capillary)
The volume in contact with the measured medium is terminated
by a flat elastic diaphragm lying in a bed. Between the dia-
phragm and the pressure transmitter is the filling liquid.
In many cases, a capillary has to be connected between the re-
mote seal and the pressure transmitter in order e.g. to minimize
temperature effects on the latter when hot media are involved.
However, the capillary influences the response time and the tem-
perature response of the complete remote seal system. Two
capillaries of equal length must always be used to connect a re-
mote seal to a pressure transmitter for differential pressure.
The remote seal can be optionally equipped with a projecting di-
aphragm (tube).
Remote seals of sandwich design are fitted with a dummy
flange.
Designs
Diaphragm seal
With diaphragm seals, the pressure is measured by means of a
flat diaphragm which rests in a bed.
The following types of diaphragm seals exist:
Diaphragm seal of sandwich design without (left) and with a projecting
diaphragm (tube)
• Sandwich design
• Sandwich design with projecting diaphragm (tube) to DIN or
ASME which are secured using a dummy flange.
Diaphragm seal of flange design without (left) and with a projecting dia-
phragm (tube)
• Flange design
• Flange design with projecting diaphragm (tube) to DIN or
ASME, secured using holes in the flange.
Quick-release diaphragm seal
• Quick-release remote seals, e.g. to DIN 11851, SMS standard,
IDF standard, APV RJT standard, clamp connection, etc.
• Miniature diaphragm seal with male thread for screwing into
tapped holes
• Remote seals with customer-specific process connections
© Siemens AG 2008