Noble Metal Thermocouples — Type R, S & B

Noble-Metal Probe Protection Strategy

Noble-metal builds are specified around the protected tip, ceramic insulation system, and contamination control needed for furnace and heat-treat service.

Noble Metal Assembly Types

Type R, Type S, and Type B Materials

Noble-metal thermocouples use platinum and platinum-rhodium conductor combinations. Type R uses a platinum-rhodium positive leg with a platinum negative leg. Type S also uses a platinum-rhodium positive leg with a platinum negative leg, with a different rhodium percentage than Type R. Type B uses platinum-rhodium on both legs and is selected for very high-temperature applications where its range and stability fit the process.

When Noble Metal Makes Sense

Because these assemblies use precious-metal conductors, they are usually reserved for labs, high-temperature furnaces, heat-treat programs, calibration-critical applications, and process points where base-metal thermocouples are not the right fit.

Contamination Sensitivity

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.

Calibration & Recalibration

• Initial calibration: NIST-traceable and aligned to ITS-90.
• AMS 2750 interval for Type R/S: annually or as used.
• Typical Type S uncertainty: ±0.3°C at 1000°C.
• Repair and recalibration: available under AS9100D-controlled processes.