Siemens SITRANS P - Manual (Page 152)

SITRANS P measuring instruments for pressure
Remote seals for transmitters and pressure gages
Technical description
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Response time
The response time is dependent on the following factors:
• Internal diameter of the capillary: The bigger the internal diam-
eter, the shorter the response time
• Viscosity of the filling liquid The greater the viscosity, the
longer the response time
• Length of the capillary: The longer the capillary, the longer the
response time
• Pressure in the pressure measuring system: The higher the
pressure, the shorter the response time
Recommendations
The following should be observed to obtain an optimum combi-
nation of transmitter and remote seal:
• Choose the biggest possible diameter for the remote seal. The
effective diameter of the seal diaphragm is then bigger and
the temperature error smaller.
• Choose the shortest possible capillary. The response time is
then shorter and the temperature error smaller
• Choose the filling liquid with the least viscosity and the small-
est coefficient of expansion. Make sure, however, that the fill-
ing liquid meets the process requirements with regard to pres-
sure, vacuum and temperature. And ensure that the filling
liquid and the medium are compatible with one another.
• Note the following points for use in the vacuum range:
- The pressure transmitter must always be positioned below
the lowest spigot.
- The operating range of some filling liquids is very limited with
regard to the permissible temperature of the medium.
- A vacuum-proof seal is necessary for continuous operation
in the low-pressure range.
• Recommendations for the minimum span can be found in the
section "Technical data".
Note
The remote seals listed here are a selection of the most common
designs. On account of the large variety of process connections,
certain remote seals which are not listed here may be available
nevertheless.
Other versions can be:
• Other process connections, standards
• Aseptic or sterile connections
• Other dimensions
• Other nominal pressures
• Special diaphragm materials, including coatings
• Other sealing faces
• Other filling liquids
• Other capillary lengths
• Sheathing of capillaries with protective hose
• Calibration at higher/lower temperatures etc.
Please contact your Siemens Regional Office for more infor-
mation.
© Siemens AG 2008