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West Instruments

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