A thermocouple is a temperature sensor based on the thermoelectric effect. It consists of two wires made of different metal materials. When the two metals at the connection point (hot junction) are exposed to a temperature change, a thermoelectric potential (voltage) related to the temperature is generated.

The core technology in the application of thermocouples is cold junction compensation. Common methods of cold junction compensation include:

• Ice point method: Place the cold junction in an ice-water mixture (0°C). This is the most accurate method in the laboratory.
• Constant temperature bath method: Place the cold junction in a constant temperature device to maintain it at a fixed known temperature (such as 50°C).
• Compensation wire method: Use cheap metal wires with the same thermoelectric characteristics as the thermocouple electrode materials to extend the cold junction from the site with large temperature fluctuations to the control room with stable temperature.
• Note: The compensation wires must match the thermocouple's scale number, and the positive and negative poles must not be reversed.
• Electronic automatic compensation method: This is the most commonly used method in modern temperature transmitters and instruments. A precise temperature sensor (such as a thermistor or integrated circuit temperature sensor) is placed at the instrument's terminal to measure the cold junction temperature To in real time, and then the instrument's microprocessor automatically performs mathematical compensation calculations based on this temperature value.

• High Temperature Measurement: It is the preferred sensor for measuring high temperatures (up to 1800°C).
• Fast Response: The measuring end is a welded point, allowing for a very small size.
• Durable: Good mechanical strength, capable of withstanding vibration and shock.
• Low Cost: (Standard thermocouple types) relatively low cost.
• No External Power Supply Required: Generates its own potential signal.

Thermocouples are usually identified by letter designation codes, and different codes have different characteristics and application ranges.

• Industrial automation: Real-time temperature control of blast furnaces in steel mills (1500°C), petrochemical distillation towers, and power boilers.
• New energy industry:
  • Temperature control of photovoltaic monocrystalline silicon growth furnaces (with ±0.2% accuracy required) and temperature monitoring of hydrogen electrolyzers.
  • The annual usage of K-type thermocouples in lithium battery thermal management systems has increased by 35%.
• Aerospace: Temperature monitoring of rocket engine combustion chambers (3000°C) and the surface temperature of spacecraft during re-entry into the atmosphere.
• Medical and scientific research: Temperature calibration of MRI equipment and high-temperature phase change research of materials.