The WRR series platinum rhodium thermocouples play an irreplaceable role in industrial high-temperature measurement due to their precise temperature measurement principle based on the Seebeck effect and carefully designed sturdy structure from the inside out. It is like a loyal sentinel wearing heavy armor, always sticking to the forefront of industrial furnaces, transforming the elusive high temperature of thousands of degrees into precise and reliable electrical signals, providing the most basic and critical data support for the intelligent and refined control of modern industry. It is truly a core equipment for industrial temperature measurement.
1、 Core principle: Practice of Seebeck Effect
The temperature measurement principle of WRR series platinum rhodium thermocouple is based on the classic "Seebeck effect". This effect indicates that in a closed circuit composed of two different materials of conductors or semiconductors, when there is a temperature difference between the two contacts, an electromotive force will be generated in the circuit, thereby forming a thermal current. This electromotive force is called thermoelectric potential, and its magnitude has a definite functional relationship with the temperature difference between the two contacts.
The WRR thermocouple is the carrier of this principle. It is not composed of a single platinum and rhodium, but has two main types:
WRR (also known as S-type): The positive electrode is made of platinum rhodium 10 alloy (containing 90% platinum and 10% rhodium), and the negative electrode is made of pure platinum.
WRR (also known as Type B): The positive electrode is made of platinum rhodium 30 alloy (containing 70% platinum and 30% rhodium), and the negative electrode is made of platinum rhodium 6 alloy (containing 94% platinum and 6% rhodium).
We refer to the temperature measuring end as the "measuring end" (or hot end) and insert it into the high-temperature test medium; The other end is called the "reference end" (or cold end), usually maintained at a known constant temperature (such as 0 ℃). When the measuring end reaches thermal equilibrium with the measured medium, a temperature dependent contact potential is generated at the measuring end due to the difference in positive and negative electrode materials. This thermoelectric potential signal is transmitted to the backend display instrument or control system through compensation wires. The instrument can accurately determine the temperature value at the measuring end by measuring the magnitude of the thermoelectric potential and querying or calculating according to the international standard scale.
B-type thermocouples have higher mechanical strength and stability at high temperatures due to the presence of rhodium on both electrodes. They can be used up to 1600 ℃ in the long term and 1800 ℃ in the short term, making them a powerful tool for measuring ultra-high temperatures in industry.
2、 Precision structure: Armor designed to resist the environment
By understanding its sensitive temperature measurement principle, one can understand how important its sturdy structure is. WRR thermocouples work in harsh environments such as flames, corrosion, and impact for a long time, and their structural design directly determines their service life and measurement accuracy. It mainly consists of the following parts:
1. Thermocouple wire: This is the core of the core, namely the platinum rhodium 10 platinum or platinum rhodium 30 platinum rhodium 6 precious metal wire mentioned earlier. They must have high purity and uniformity to ensure stable and accurate thermoelectric potential output.
2. Insulation material: In order to prevent a short circuit between two thermocouple wires, high-quality insulation material needs to be filled between them. High purity aluminum oxide or magnesium oxide tubes are usually used as insulation tubes. These materials not only have good insulation performance, but also can withstand high temperatures, have stable chemical properties, and effectively protect the wires.
3. Protective sleeve: This is the "first line of defense" for thermocouples facing harsh environments. It is like a sturdy armor, encapsulating the internal insulation tube and thermocouple wire as a whole. The material selection of protective casing is crucial and should be determined according to the usage environment:
High temperature environment: Corundum ceramic tubes (high-purity alumina) are commonly used, which can withstand high temperatures up to 1800 ℃, but have slightly lower thermal shock resistance.
Reductive atmosphere or molten metal: Special materials such as metal ceramics or molybdenum tubes are often used to resist chemical corrosion and erosion from molten metal.
Mechanical impact environment: High strength alloy steel outer casing will be used, and ceramic insulation pipes will be nested inside.
4. Wiring device: located at the tail of the thermocouple, including a junction box and terminal blocks. Its function is to reliably connect the electrodes of the thermocouple with the compensation wire and protect the connection point from external dust and water vapor. Splash proof or explosion-proof junction boxes are suitable for more demanding industrial sites.