Decalibration

• Decalibration is when the physical makeup of the thermocouple is altered so that it does not conform to certain standards. This may be caused by contamination from its insulation, or by the diffusion of particles into the metals from the atmosphere when the temperature is high.
  
  

Soldering

• The metals that are used to make thermocouples are joined together by welding or soldering. If the connection is poor, the thermocouple will not operate properly.
  
  

Thermal Shunting

• Thermal shunting occurs when the thermocouples slightly alter the temperature they are to measure. They are made with thin wires to mitigate this effect, but this thinness makes them prone to stress, strain and contamination.
  
  

Noise

• They also have small output signals due to the thinness of the wires. This makes them susceptible to noise.
  
  

Age

• Their measuring capabilities change as they age. They become prone to stress, strain and corrosion.
  
  

Green Rot

• Thermocouples that are made with chromium are subject to green rot. This happens in high temperature environments where this is not enough oxygen so that the chromium becomes oxidized, and so turns green and corrodes.