What is the lifespan of Type S and Type T thermocouples

Type S and Type T thermocouples have very different lifespans. The primary factors that determine this include the type of material, the temperature at which they work, the atmosphere around them, and the preventive measures used. Type S thermocouples usually last longer in clean, high-temperature, oxidizing situations. Type T thermocouples, on the other hand, work well in low-temperature, dry, or humid circumstances and last for several years.




I. Type S Thermocouples: Good for long-term high-temperature measurement since they are very stable with precious metals



Type S thermocouples (platinum-rhodium 10-platinum) are thermocouples made of precious metals that resist oxidation at high temperatures and stay stable for a long time. In perfect conditions, they could run for more than 2000 hours.



1300 degrees Celsius is the long-term working temperature.



1600°C is the short-term tolerance temperature.



Actual lifespan performance: It can work stably for 1–3 years at 1100–1300°C for long periods of time, and it can last more than 3 years in some cases. However, if it is exposed to reducing atmospheres (like H₂ or CO) for a long time, the thermoelectric wire is likely to "platinum embrittlement" and break, which shortens its lifespan by a lot; It is very easy to get dirty; dust, metal vapor, or carbon deposits will speed up the process of deterioration and cause thermoelectric potential drift.



Pros: It is quite accurate at measuring high temperatures, stays stable, and is useful for long-term high-temperature monitoring. It was also utilized as an interpolation tool for the international temperature scale ITS-90.



Limitations: High cost, not good for situations with sulfur or that reduce sulfur, and not very sensitive.







Type T thermocouples: Very accurate at low temperatures, however they can oxidize and break down at medium and high temperatures.



Type T thermocouples (copper-constantan) are made of base metals, are cheap, and are often employed in systems that work at low temperatures. They are said to be able to run for 10,000 hours straight.



Standard temperature for operation: -200 to 350 degrees Celsius



Short-term temperature resistance: 400 degrees Celsius



Actual lifespan performance: In low-temperature systems like refrigerators, air conditioners, and refrigeration equipment, the service life is usually 3 to 5 years. Above 350°C, the copper positive electrode oxidizes easily, which can cause thermoelectric potential drift or even wire breakage. In humid or sulfur-containing environments, the constantan negative electrode corrodes easily, which can affect signal stability.



Benefits: inexpensive, very accurate, and very linear. They are especially effective for measuring temperature very precisely between -200 and 0 degrees Celsius, with a yearly stability of less than ±3μV.



Limitations: It doesn't resist oxidation well at high temperatures, hence it can't be used to monitor high temperatures in oxidizing environments.







III. A look at the main things that affect lifespan



Table: Type S thermocouple Type T thermocouple



Operating Temperature: Higher temperatures cause faster degradation, however the upper limit is substantially higher than that of the T-type. Oxidation speeds up over 350°C, thus it can't be used for long periods of time.



Atmosphere: Only good for oxidizing and inert settings; stay away from gasses that lower the temperature. Can be utilized in places with low oxygen levels, but stay away from sulfides and heavy humidity.



Protective Measures: To make them last longer, it is best to use corundum or silicon carbide protective tubes. To stop rust and oxidation, it is best to put in a sealing sleeve.



Calibration Suggestions: Every 12 to 18 months, calibrate; if the error goes over the limits, replace. To make sure they are accurate, replace them every three to five years or calibrate them regularly.







IV. How to Make Thermocouples Last Longer



Don't let things get too hot: Only use them within the temperature range they are rated for.



Choose the right protective tubing:



For S-type, we suggest tubing made of 99% pure alumina (corundum).



T-type: You can choose between stainless steel or fully sealed ceramic tubing.



Regular calibration and maintenance: Make sure that the thermoelectric potential decay is within the acceptable error range (±3℃, for example).



To reduce mechanical vibration and thermal shock, be careful when installing and don't let it go through hot and cold cycles too often.