The NiCrSi-NiSiMg thermocouple, also known as the Type N thermocouple, represents a significant advancement in base metal thermocouples, designed to address the limitations of the widely-used Type K thermocouple. By enhancing thermal stability and lifespan, Type N thermocouples have become a superior choice for industries requiring precise temperature control and extended service life.
Composition and Key Characteristics
Positive Leg (NiCrSi or NP)
Chemical Composition (wt%):
Ni: 84.4%, Cr: 14.2%, Si: 1.4%.
Density at 20℃: 8.5 g/cm³
Melting Point: 1410℃
Tensile Strength (Annealed): ≥620 MPa
Elongation: ≥25%
Resistivity at 20℃: 0.97 µΩ·m
Negative Leg (NiSiMg or NN)
Chemical Composition (wt%):
Ni: 95.5%, Si: 4.4%, Mg: 0.1%.
Density at 20℃: 8.6 g/cm³
Melting Point: 1340℃
Tensile Strength (Annealed): ≥550 MPa
Elongation: ≥30%
Resistivity at 20℃: 0.33 µΩ·m
Advantages Over Type K Thermocouples
Reduced EMF Drift:
Type N thermocouples exhibit significantly improved resistance to thermal electromotive force (EMF) drift, which is a common issue with Type K thermocouples. This ensures consistent and accurate temperature readings over extended periods.
Enhanced Stability:
Unlike Type K thermocouples, which are prone to short-term EMF instability due to environmental factors, Type N offers reliable performance even in harsh operating conditions.
Longer Lifespan:
Thanks to its robust composition, Type N thermocouples endure higher operating temperatures and prolonged exposure to oxidative and reductive atmospheres, outlasting Type K thermocouples in similar environments.
Broader Temperature Range:
Type N operates efficiently across a wide range, from -200℃ to 1300℃, making it suitable for demanding industrial applications.
Performance Standards
Type N thermocouples conform to IEC 60584-1 standards. The table below highlights their thermal EMF characteristics compared to Pt67 at various temperatures:
Temperature (℃) | EMF (mV) – NP | EMF (mV) – NN | EMF Difference (NP-NN) |
100 | 1.755–1.813 | 0.975–1.005 | 2.730–2.818 |
200 | 3.910–3.976 | 1.954–1.988 | 5.864–5.962 |
400 | 8.880–8.959 | 4.035–4.075 | 12.915–13.033 |
600 | 14.307–14.433 | 6.212–6.274 | 20.519–20.707 |
800 | 20.012–20.180 | 8.318–8.402 | 28.330–28.582 |
1000 | 32.313–32.525 | 8.807–8.907 | 41.12–41.432 |
Applications
Industries that demand precise and stable temperature measurement, such as aerospace, metallurgy, energy, and chemical processing, can benefit greatly from Type N thermocouples. Their enhanced lifespan and resistance to environmental degradation make them ideal for critical applications.
Conclusion
The Type N thermocouple, with its NiCrSi (NP) and NiSiMg (NN) components, offers a robust, reliable, and accurate solution for industrial temperature measurement. Its superior performance and longevity make it a valuable upgrade from Type K thermocouples, ensuring consistent performance in the most demanding environments.