Platinum-rhodium thermocouples — Types R, S, and B — are the primary standard sensors for high-temperature measurement above 600°C. Thermometrics manufactures noble metal thermocouple assemblies with alumina and MgO insulation, calibrated to IEC 60584 and ASTM E230 with NIST-traceable certificates.
| Type | Conductors | Range | EMF @ 1000°C | Tolerance Class 1 | Primary Use |
|---|---|---|---|---|---|
| Type R | Pt-13%Rh (+) / Pt (−) | 0 to 1480°C | 10.506 mV | ±1.0°C or 0.25% | Lab calibration, furnace monitoring, ITS-90 reference |
| Type S | Pt-10%Rh (+) / Pt (−) | 0 to 1480°C | 9.587 mV | ±1.0°C or 0.25% | Silver/gold freezing point calibration, primary standard |
| Type B | Pt-30%Rh (+) / Pt-6%Rh (−) | 600 to 1820°C | 4.834 mV | ±0.5% above 800°C | Glass furnace, ultra-high temperature; negligible output below 50°C |
| Configuration | Insulation | Protection | Application |
|---|---|---|---|
| Bare wire, twin-bore alumina | 99.7% Al₂O₃ twin-bore rod | MgO outer tube or none | Laboratory, calibration furnace |
| MIMS (Pt sheath) | MgO | Pt or Pt-Rh sheath | High-purity, low-contamination |
| Industrial assembly w/ head | Twin-bore alumina + MgO outer | Inconel or ceramic protection tube | Plant furnace, AMS 2750 control TC |
| Survey assembly (bayonet) | Ceramic beads or twin-bore rod | None or alumina slip tube | AMS 2750 / CQI-9 TUS |
Noble metal thermocouple wire is extremely sensitive to contamination from metallic vapors, carbon, sulfur, hydrogen, and silicon. Thermometrics uses dedicated handling procedures, dedicated tooling, and protective packaging to prevent contamination during manufacturing. Alumina insulation (not silica) is specified for all noble metal assemblies to prevent SiO₂ reduction at the junction.
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