Thermocouple Circuit

Thermocouples, also known as thermocouples, are the earliest thermoelectric detection devices. Their working principle is the thermoelectric effect. For example, a junction composed of two different conductor materials can generate an electromotive force at the junction. The magnitude and direction of this electromotive force are related to the properties of the two different conductor materials at the junction and the temperature difference between the two junctions. If these two different conductor materials are connected into a loop, when the temperatures at the two joints are different, a current will be generated in the loop. This phenomenon is called the thermoelectric effect or the Seebeck effect. The materials that make up the thermocouple can be either metals or semiconductors. In terms of structure, it can be either a wire or strip entity, or a thin film made using vacuum deposition technology or photolithography technology. Solid thermocouples are mostly used for temperature measurement, and thin-film thermocouples (composed of many thermocouples connected in series) are mostly used to measure radiation, for example, to calibrate various light sources, measure various radiation quantities, and serve as radiation receiving elements for infrared spectrophotometers or infrared spectrometers.
In a circuit, a closed circuit with a temperature difference between two points is called a thermocouple circuit.

Thermocouple Application Examples
Thermocouple circuits can generally measure temperature and can also be used as sensors. When the external temperature changes, some control can be performed. For example, controlling water temperature, air temperature, etc.

Advantages of Thermocouple Thermometers
Thermocouples are one of the most commonly used temperature detection elements in industry. The working principle of thermocouples is based on the Seebeck effect, that is, the two ends of two conductors of different components are connected into a loop. If the temperatures of the two connection ends are different, a thermal current is generated in the loop. Its advantages are:
① High measurement accuracy. Because the thermocouple is in direct contact with the object being measured, it is not affected by the intermediate medium.
② Wide measurement range. Commonly used thermocouples can measure continuously from -50~+1600℃. Some special thermocouples can measure as low as -269℃ (such as gold, iron, nickel, and chromium) and as high as +2800℃ (such as tungsten-rhenium).
③ Simple structure and easy to use. Thermocouples are usually composed of two different metal wires, and are not limited by size and opening. They have a protective sleeve outside, which is very convenient to use.

1. Introduction to thermocouple:
Thermocouple is a contact temperature measuring instrument and is one of the most commonly used temperature detection instruments in industrial production.

2. Working principle of thermocouple:
Thermocouple is a temperature sensing element, which converts temperature signal into thermoelectric potential signal, and converts it into the temperature of the measured medium through electrical instruments. The basic principle of thermocouple temperature measurement is that two homogeneous conductors of different components form a closed loop. When there is a temperature gradient at both ends, current will pass through the loop. At this time, there is Seebeck electromotive force between the two ends - thermoelectric potential, which is the so-called Seebeck effect. The two homogeneous conductors of different components are thermocouples, the end with higher temperature is the working end, and the end with lower temperature is the free end, which is usually at a constant temperature. According to the functional relationship between thermoelectric potential and temperature, a thermocouple scale is made; the scale is obtained under the condition that the temperature of the free end is 0 ℃, and different thermocouples have different scales. When a third metal material is connected to the thermocouple loop, as long as the temperature of the two contacts of the material is the same, the thermoelectric potential generated by the thermocouple will remain unchanged, that is, it will not be affected by the third metal connected to the loop. Therefore, when measuring temperature with a thermocouple, a measuring instrument can be connected, and after measuring the thermoelectric potential, the temperature of the measured medium can be known.

3. Advantages of thermocouples:
Thermocouples are commonly used temperature measuring elements in industry, with the following characteristics:
① High measurement accuracy: Thermocouples are in direct contact with the object being measured and are not affected by the intermediate medium.
② Fast thermal response time: Thermocouples react sensitively to temperature changes.
③ Large measurement range: Thermocouples can continuously measure temperature from -40~+1600℃.
④ Reliable performance and good mechanical strength.
⑤ Long service life and easy installation.
IV. Types and structures of thermocouples:
(1) Types of thermocouples
Thermocouples include K-type (nickel-chromium-nickel-silicon) WRN series, N-type (nickel-chromium-silicon-nickel-silicon-magnesium) WRM series, E-type (nickel-chromium-copper-nickel) WRE series, J-type (iron-copper-nickel) WRF series, T-type (copper-copper-nickel) WRC series, S-type (platinum-rhodium 10-platinum) WRP series, R-type (platinum-rhodium 13-platinum) WRQ series, B-type (platinum-rhodium 30-platinum-rhodium 6) WRR series, etc.
(2) Thermocouple structure:
The basic structure of a thermocouple is a hot electrode, an insulating material and a protective tube; and it is used in conjunction with a display instrument, a recording instrument or a computer. In field use, thermocouples suitable for various environments are developed based on various factors such as the environment and the medium being measured. Thermocouples can be simply divided into assembled thermocouples, armored thermocouples and special forms of thermocouples; according to the use environment, there are high temperature resistant thermocouples, wear-resistant thermocouples, corrosion-resistant thermocouples, high pressure resistant thermocouples, explosion-proof thermocouples, thermocouples for aluminum liquid temperature measurement, thermocouples for circulating fluidized bed, thermocouples for cement rotary kiln, thermocouples for anode baking furnace, thermocouples for high temperature hot air furnace, thermocouples for gasification furnace, thermocouples for carburizing furnace, thermocouples for high temperature salt bath furnace, thermocouples for copper, iron and molten steel, oxidation-resistant tungsten rhenium thermocouples, thermocouples for vacuum furnace, platinum rhodium thermocouples, etc.