GROUNDED THERMOCOUPLE JUNCTION
The grounded thermocouple junction is an integral part of the thermocouple sheath tip :
• fast response time in relation to ungrounded and isolated junctions.
• protects the wires from environmental chemicals and corrosives.
• prolongs the operational life of the thermocouple. Longer lifespan than the
exposed junction thermocouple.
• it is recommended for high pressure applications.
• it is the least expensive construction.
• thermal expansion of sheath material may differ from element to cause mechanical
stress and work hardening of metals.
• ground loops may cause interference with instruments.
• faults in insulation are more difficult to detect.
UNGROUNDED THERMOCOUPLE JUNCTION
The ungrounded thermocouple junction is electrically insulated and electrically
isolated from the outer sheath material. In a dual ungrounded thermocouple, one
common junction is electrically insulated from the outside sheath.
• the thermocouple junction is isolated from the ground.
• defects in the MgO insulation can be detected by measuring resistance from
loop to sheath.
• long term drift under cycling conditions is minimized.
• response time is usually slower than grounded thermocouples.
• more expensive than grounded thermocouples.
EXPOSED THERMOCOUPLE JUNCTION
The exposed thermocouple junction extends beyond the protective metallic
• recommended for measurement of noncorrosive static gas, or air.
• very fast response time, faster than grounded junction.
• cannot be used in an environment with a high percentage of solids, high pressure,
or flowing material since the junction is exposed to this environment.
ISOLATED THERMOCOUPLE JUNCTION
Isolated thermocouple junctions are used in a dual or triple thermocouple when
the junctions are isolated from the outer sheath material as well as from each
• the elements are insulated from ground.
• performs better than ungrounded or grounded junctions in a thermal cycling
• slower response time than a grounded dual thermocouple.
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