Home » Types of Thermocouple Measuring Junction
Temperature Measurement

Types of Thermocouple Measuring Junction

Types of Thermocouple Measuring Junction

There are four types of thermocouple measuring junction constructions :

  1. Grounded Thermocouple Junction
  2. Ungrounded Thermocouple Junction
  3. Exposed Thermocouple Junction
  4. Isolated Thermocouple Junction

Grounded Thermocouple Junction

The grounded thermocouple junction is an integral part of the thermocouple sheath tip.

grounded thermocouple junction

Advantages:

  • 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.

Disadvantages:

  • 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.

ungrounded thermocouple junction

Advantages:

  • 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.

Disadvantages:

  • 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 sheath.

exposed thermocouple junction

Advantages:

  • recommended for measurement of noncorrosive static gas, or air.
  • very fast response time, faster than grounded junction.

Disadvantages:

  • 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 other.

Isolated thermocouple junction

Advantages:

  •  the elements are insulated from ground.
  • performs better than ungrounded or grounded junctions in a thermal cycling environment.

Disadvantages:

  • slower response time than a grounded dual thermocouple.

Reference : gilsoneng.com

Similar Articles:

Related Articles

Temperature Switch Working Principle

S Bharadwaj Reddy

Seebeck Effect Theory

S Bharadwaj Reddy

Calibration of Pyrometers using Black Body

S Bharadwaj Reddy

Why have been limits imposed on the frequency ratio for thermowells?

S Bharadwaj Reddy

Temperature Coefficient of Resistance (α)

S Bharadwaj Reddy

Interview Questions on Temperature Measurement

S Bharadwaj Reddy

Leave a Comment

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More

WordPress Image Lightbox