A precious metal thermocouple is a high-precision temperature sensor based on the Seebeck effect (thermoelectric effect). It is primarily made of precious metals such as platinum (Pt) and rhodium (Rh) and is widely used in industrial temperature measurement applications requiring high temperature and stability. Its core advantages lie in its high temperature measurement accuracy, good long-term stability, and strong oxidation resistance, making it suitable for extreme high-temperature environments in glass, ceramics, metallurgy, and aerospace industries.
I. Main Types and Technical Characteristics
Precious metal thermocouples mainly include three types: S-type, R-type, and B-type. All use platinum-rhodium alloys as electrode materials, but their composition and performance differ:
S-type Thermocouple (Platinum-Rhodium 10-Platinum)
Positive electrode: Platinum-rhodium alloy containing 10% rhodium; Negative electrode: Pure platinum
Long-term operating temperature: 1300℃, short-term operating temperature: [not specified] 1600℃
Features: Highest accuracy, good stability, commonly used for standard temperature measurement or laboratory calibration.
Disadvantages: Low thermoelectric potential, low sensitivity, expensive.
R-type thermocouple (Platinum-Rhodium 13-Platinum)
Positive electrode: Platinum-rhodium alloy containing 13% rhodium; Negative electrode: Pure platinum.
Operating temperature similar to S-type (long-term 1300℃, short-term 1600℃).
Compared to S-type, the thermoelectric potential is slightly higher by about 15%, and the reproducibility at high temperatures is better.
Mostly used in precision temperature measurement applications under the American standard system.
B-type thermocouple (Platinum-Rhodium 30-Platinum-Rhodium 6, also known as double platinum-rhodium)
Positive electrode: Platinum-rhodium alloy containing 30% rhodium; Negative electrode: Platinum-rhodium alloy containing 6% rhodium.
Long-term operating temperature can reach 1600℃, short-term measurement... 1800℃
Significant Advantages: Extremely low thermoelectric potential within the 0~50℃ range, typically requiring no compensation wires.
Suitable for higher temperature range applications such as industrial furnaces and vacuum furnaces.
II. Typical Application Scenarios
Due to their high temperature resistance and high stability, precious metal thermocouples are widely used in the following fields:
Glass Manufacturing: Monitoring the temperature of molten glass furnaces to ensure process stability.
Ceramic Sintering: Achieving precise temperature control in high-temperature sintering lines.
Iron and Steel Metallurgy: Temperature monitoring in critical stages such as steelmaking furnaces, blast furnaces, and hot blast stoves.
Aerospace: High-reliability scenarios such as engine testing and high-temperature combustion chamber testing.
Laboratories and Metrology Institutions: Used as a standard for temperature calibration, providing traceability.
III. Selection and Usage Recommendations
Temperature Range Matching:
If the temperature measurement is concentrated between 1000~1300℃, it is recommended to use type S or type R.
If long-term measurements above 1300℃ or close to 1600℃ are required, choose... Type B
Environmental Requirements: Suitable for oxidizing and inert atmospheres; not suitable for reducing atmospheres or environments containing sulfur or metal vapors.
Protective Tube Material: Commonly used high-temperature resistant materials such as corundum tube, high-alumina tube, and silicon carbide to prevent corrosion or mechanical damage to the thermocouple.
Calibration and Maintenance: High-precision applications require regular calibration. Traceable calibration should be performed in a laboratory using a fixed-point method or comparative method to ensure data accuracy.
IV. Market Product Reference
Tiankang Precious Metal Thermocouple
Measuring Range: 0~1800℃, Price: 80.00 RMB, Suitable for high-temperature industrial temperature measurement.
Dingyao Cable Company sells Precious Metal Thermocouples
Measuring Range: 0~1200℃, Graduation No. K, Price: 5795.00 RMB
