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Considerations
for the Selection of a Multipoint Assembly
Since each Multipoint
Thermocouple Assembly must be tailored
for the application, these designs lend
themselves to changes to fit the application.
To help the user select
the design that is best for the application,
the following factors should be considered:
1. Ease of Replacement
of Damaged Thermocouple Sensor
After installation and
usage for a period of time, it is possible
that one of the sensors may become defective
due to open circuit, short to ground,
or mechanical damage. It would be very
desirable to be able to replace the defective
thermocouple without the necessity of
removing the entire Multipoint Assembly
from the vessel. The Multipoint Types
are listed in the order of ease to replace
a defective sensor.
2. Ease of Installing
into Vessel
The cost to install
a Multipoint Assembly into a vessel can
become very expensive due to its weight,
and usually a Multipoint has to be installed
at the top of a vessel. This requires
the use of extended boom cranes to lift
the assembly and have it guided into the
appropriate nozzle or port. Listed by
types in the order of which is easiest
to install, with the easiest first:
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Types
4 and 5 can be coiled and are usually
lightweight so that one person can
carry the Multipoint Assembly to the
nozzle location and feed the assembly
into place.
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Types
1, 2 and 3 cannot be coiled and will
require mechanical assistance to hoist
into place with someone to guide the
assembly into position.
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Important Specifics
in Detailing the Selection
The selection should
state:
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The
Thermocouple Calibration: |
ANSI
MC 96.1 Type E, J, K, or T |
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Hot
Junction: |
Grounded
or Ungrounded |
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Number
of Temperature Sensing Points |
Indicate
number |
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Protection
Well: |
Material,
Size and Overall Length |
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Process
Connection: |
Flange
Size, Type, Rating and Material Compression
Fitting Size and Material |
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Secondary
Pressure Barrier Requirements: |
Describe |
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Junction
Box: |
NEMA
4, NEMA 4X, or NEMA 7 |
Note
: Should
RTD elements be used, Temperature and
Type should be specified.
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