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West Instruments
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New Design for Multipoint
Thermocouple
For Custom Thermocouples specific to
your process or application,
contact ThermX for application assistance.
Multipoint Temperature Profiling Sensors measure the temperature
at different points along its length. Its unique design is made with
an ungrounded (isolated) junction with multiple measuring points arranged
along the length of the probe. It accurately measures temperatures up
to 2100°F with lengths varying up to 200 feet. This design uses
a hard packed MgO insulation like a traditional thermocouple, except
it uses a larger single (+) positive conductor as the center conductor
with multiple (-) negative conductors around it. The benefit is a larger
conductor size in a smaller flexible package.
These sensors are frequently used in chemical and petrochemical industries
because they provide an excellent temperature profile for chemical reactors,
catalytic crackers, fractionation towers, and fluidized bed catalyst
tanks.
SPECIFICATIONS:
Compacted MgO Insulation 99.4% minimum purity
Insulation Resistance: 500 megohms at 500 VDC minimum
Thermocouple Calibration:
Type "K" & "N" Standard or Special Limits of
Error (Class I & II)
Type "J" & "E" Standard Limits of Error (Class
II) - (Special Order)
Standard Sheath Materials: 316 SS, 310 SS, Inconel 600 (nickel
alloy 600)

DESIGN RULES
- Number of Points: Up to 15 points (depends on OD of cable,
see table below)
- Minimum distance between measuring points (junctions): 1.0"
(25.4 mm)
- Point Location Tolerance: O.D. of cable, or .3% of length, whichever
is greater
- Inner Wire: Positive
- Outer Wires: Negative
- Minimum Bend Radius = 10 times the sheath diameter
- Shipment Standard: 24" or 33'' diameter coil (consult for
special requirement)
- Pressure rating dependent on design specification
Standard Outside Diameter,
Points, & Maximum Lengths
|
O.D (inches)
|
Tolerance
|
Max # of Points
|
Normal Length
|
Max Length
|
Notes*
|
.313"
|
± .003" (7.95mm)
|
Up to 19
|
250 feet
|
500 feet
|
Type K Max 2100°F
|
.250"
|
± .002" (6.35mm)
|
Up to 13
|
400 feet
|
800 feet
|
Type K Max 2100°F
|
.188"
|
± .002" (4.78mm)
|
Up to 10
|
700 feet
|
1400 feet
|
Type K Max 2100°F
|
.125"
|
± .002" (3.18mm)
|
Up to 7
|
1600 feet
|
3200 feet
|
Type K Max 1960°F
|
*Maximum temperatures per ASTM E-608, sheath material
will determine max usable temperature.
Dimensional Information: Wall
Thickness & Wire Diameters
|
Number of Thermocouple Measuring Points
|
Wall Thickness (Percent of Diameter)
|
Outer Wire Size (Percent of Diameters)
|
Inner Wire Size (Percent of Diameter)
|
Transition Size from MI Cable to Leadwire*
|
2 - 4
|
11.8%
|
11.0%
|
15.5%
|
.50" x 1.5"
|
5 - 7
|
11.8%
|
8.5%
|
11.7%
|
.75" x 3.0"
|
8 - 10
|
11.8%
|
8.0%
|
10.3%
|
.75" x 3.0"
|
11 - 13
|
11.8%
|
7.6%
|
11.4%
|
.75" x 3.0"
|
14 - 16
|
11.8%
|
7.2%
|
12.1 %
|
1.0" x 3.0"
|
* Epoxy potting temperature rating 300°F/150°C
with 600°F/320°C epoxy available upon request.
Sample Drawings
of Multipoint Thermocouples



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