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MERCAP – INSTRUCTION MANUAL
7ML19981CM01.1
Characteristics
The following characteristics apply to all general connection configurations:
•
The standard Mercap insulated electrode is designed for use in both
conducting and non-conducting liquid applications.
•
All electrodes consist of an active shield portion and a measurement portion,
which combine to form the complete electrode.
•
The sum of the active shield length and the measurement length is the total
insertion length.
•
The active shield design provides continuous immunity to the known changes
in conditions at the top of many vessels, where levels of vapours, dust, and
condensation are constantly changing.
•
All changes in capacitance due to temperature and pressure changes that
could cause small changes in the seal geometry are also isolated from the
measurement signal because they are not included in the starting
capacitance of the electrode by virtue of the action of the active shield.
•
Due to the well-controlled diameter of the electrodes and insulation, a linear
output is achieved over a wide range of capacitance values (3.3 to 3300 pF).
•
The end seal is formed as an integral part of the electrode lining, giving
smooth and uniform insulation characteristics (tested to 55 kV).
•
Standard single cone usage
•
Secondary cone usage
General Design Principles
The Mercap capacitance level instrument combines an optimum combination of mechanical
and electrical/electronic principles in its design. Combining a single transmitter with as few
electrode configurations as possible maximizes the number of potential applications while it
minimizes the complexity of the instrument.
In principal, the standard threaded process connection (S-Series) with PFA insulated
electrode, including the active shield, provides good results in all measurement situations that
are within the temperature, pressure, and corrosive capabilities of the materials and seals.
This is true over a wide range of dielectric constants in both non-conducting and conducting
materials.
Applications outside of the standard capabilities of the S-Series would require a different
design configuration. These non-standard applications include:
Non-Standard Application
Mercap Configuration
Non-metallic tanks with both conducting
and non-conducting liquids.
Use a stilling well to provide second
electrode reference.
Non-conducting liquids in spherical and
horizontal-cylindrical tanks.
Use a stilling well as linearizer.
Highly corrosive materials requiring no
metallic wetted parts.
Use flange mount with D, DD seal
version.
High pressure and temperature (greater
than 200 bar) with conductive liquid.
Use HP version.
Sanitary/food safe applications.
Use Mercap MCP 03.
