What Is Thermocouple Drift?

Thermocouple drift refers to the gradual change in a thermocouple’s output signal over time, leading to inaccurate temperature readings. This occurs when the voltage-temperature relationship of the thermocouple shifts due to changes in the physical or chemical properties of the thermocouple wires.

Causes of Thermocouple Drift:

1. Oxidation & Contamination
    
   • Exposure to oxygen at high temperatures causes oxidation, altering the thermocouple material and changing its voltage output.
      
   • Contaminants such as moisture, chemicals, or metal vapors can diffuse into the thermocouple wires, affecting their composition.
      
2. Thermal Cycling & Aging
    
   • Repeated heating and cooling can cause microstructural changes in the metal, leading to gradual shifts in the thermoelectric properties.
      
   • Prolonged exposure to extreme temperatures can cause grain growth, reducing stability.
      
3. Diffusion Effects
    
   • At high temperatures, atoms from the thermocouple conductors can diffuse into each other or react with their surrounding insulation, leading to composition changes and altered output.
      
4. Mechanical Stress & Handling
    
   • Bending, twisting, or vibrations can strain the wires, introducing inconsistencies in the thermoelectric signal.
      
5. Electrical Interference
    
   • Ground loops or electromagnetic interference from nearby equipment can introduce noise into the signal, mimicking drift.

Effects of Thermocouple Drift:

• Gradual loss of accuracy
   
• Increased deviation from actual temperature
   
• Unreliable measurements, affecting process control and product quality

How to Minimize Thermocouple Drift:

• Use thermocouples rated for the specific temperature and environment
   
• Protect thermocouple conductors with appropriate sheathing and insulation
   
• Perform regular accuracy checks and calibrations

Replace thermocouples when significant drift is detected