Why are thermocouples expensive and what are the alternatives?

The main reasons for the high price of thermocouples are as follows:
High material cost
Use of rare metals: Rhodium and platinum in platinum-rhodium thermocouples are rare precious metals with scarce reserves on the earth. For example, S-type thermocouples contain 10% rhodium platinum-rhodium alloy wire and pure platinum wire, R-type thermocouples contain 13% rhodium platinum-rhodium alloy wire and pure platinum wire, and B-type thermocouples have a positive electrode of 30% rhodium platinum-rhodium alloy and a negative electrode of 6% rhodium platinum-rhodium alloy.
Complex extraction and processing: Extracting these rare metals from ores requires multiple complex processes such as ore dressing, smelting, and refining, which consumes a lot of manpower, material resources, and financial resources.
High manufacturing process requirements
High-precision manufacturing: In order to ensure the measurement accuracy and stability of thermocouples, high-precision processes and equipment are required for wire processing, welding, and assembly in the production process. For example, in the production of glass melt thermocouples, the sleeve is made of pure platinum and must be able to work for a long time in glass melts as high as 1650 degrees, which requires extremely high process requirements.
Strict quality inspection: It needs to undergo strict quality inspection and calibration to ensure that each thermocouple meets the relevant standards and usage requirements, and the inspection cost will also be allocated to the product price.
High R&D cost
Investment in technological innovation: In order to improve the performance of thermocouples, such as expanding the temperature measurement range, improving accuracy, and enhancing corrosion resistance, companies need to invest a lot of money in research and development. For example, iridium-rhodium thermocouples can meet the high-temperature temperature measurement of 1500-2000 degrees for aircraft and rocket engines, and tungsten-rhenium ultra-high temperature thermocouples can reach a range of 2800 degrees, which requires a lot of R&D investment.
Meet special needs: For some special environments and application scenarios, such as high pressure, strong corrosion, vacuum, etc., the development of special thermocouples requires higher R&D costs. For example, high-pressure thermocouples must not only withstand high pressures of more than 2,500 pounds, but also withstand the erosion of various corrosive gases and liquids in the measuring medium.
Special application scenarios
High-end field requirements: In high-end fields such as aerospace, metallurgy, and glass fiber manufacturing, the accuracy, stability, and reliability of thermocouples are extremely high, and these fields are willing to pay a higher price for high-quality thermocouples.
Irreplaceability: In some specific harsh environments such as high temperature and strong corrosion, thermocouples are currently the most effective temperature measurement tools. There are no other more suitable low-cost alternatives, making their prices relatively high.
There are several alternatives to thermocouples:
Other temperature sensors
Thermal resistors: Use the characteristics of the resistance of metal or semiconductor materials that change with temperature to measure temperature. It has high accuracy and good stability and is suitable for medium and low temperature measurements, such as -200℃ to 500℃. Common ones are platinum thermal resistors and copper thermal resistors, which can replace some thermocouple applications in industrial automation, HVAC and other fields.
Thermistor: It has a high temperature coefficient of resistance, high sensitivity, and fast response speed, but the temperature measurement range is relatively narrow, generally between -50℃ and 300℃, and is often used for temperature measurement and control of electronic equipment, automobiles, medical equipment, etc.
Non-contact temperature measuring instrument
Optical pyrometer: It uses the thermal radiation emitted by the object to measure the temperature. It is suitable for high temperature environments and can avoid the error caused by the contact thermal resistance of the thermocouple.
Infrared thermal imager: It generates thermal images by detecting the infrared radiation emitted by the object, which can intuitively display the temperature distribution on the surface of the object. It can measure the temperature quickly and over a large area. It is suitable for electrical equipment detection, building energy-saving detection, industrial equipment fault diagnosis and other fields.
Thermal radiation meter: It calculates the temperature by detecting the thermal radiation energy emitted by the object. It has a fast measurement speed and a short response time.
New temperature measurement technology
Fiber optic temperature measurement system: It uses optical fiber to transmit optical signals and measures the temperature by detecting the changes in optical signals. It has strong anti-electromagnetic interference ability and high measurement accuracy. It can be used for temperature measurement in harsh environments such as high voltage and strong electromagnetic interference.
Ion thermoelectric conversion technology: Relying on the Soret effect of ion diffusion to produce thermoelectric conversion, it can generate greater thermal power and can be used to collect low-grade thermal energy. It is expected to replace traditional thermocouples in some specific thermal energy collection fields.