Thermocouple/probe knowledge four. Types and Structures of Thermocouples/Probes (1) Types of Thermocouples/Probes Common thermocouples/probes can be divided into: 1, standard thermocouple/probe 2, non-standard thermocouple / probe two major categories. The so-called standard thermocouple/probe is a thermocouple/probe whose national standard stipulates the relationship between thermoelectric potential and temperature, tolerance, and a unified standard indexing table. It has its own display instrument for selection. Non-standardized thermocouples/probes are less than standard thermocouples/probes on the range of use or on the order of magnitude, and there is generally no uniform indexing table, which is mainly used for measurement in certain special occasions. (2) Structure of Thermocouple/Probe In order to ensure reliable and stable operation of the thermocouple/probe, the structural requirements for it are as follows: (3). Cold-junction temperature compensation Because thermocouple/probe materials are generally more expensive (especially when precious metals are used), the distance from the temperature measurement point to the instrument is very long. In order to save the thermocouple material and reduce the cost, compensation wire is usually used to heat the power. The cold end (free end) of the couple/probe extends into a relatively stable temperature control room and is connected to the meter terminals. It must be pointed out that the role of the thermocouple/probe compensation wire is only to extend the thermode, so that the cold junction of the thermocouple/probe can be moved to the instrument terminal of the control room. It does not eliminate the influence of the temperature change of the cold junction on the temperature measurement. Compensation effect. Therefore, other correction methods need to be used to compensate for the effect of temperature at the cold junction temperature t0≠0°C. Disposable Urine Bag,Disposable Catheter Bags,Pediatric Urine Collection Bag,Disposable Incontinence Urine Bag Henan Diyi Medical Technology Development Co.,Ltd. , https://www.diyimedical.com
One, thermocouple/probe is one of the most commonly used temperature detection components in the industry. Its advantages are:
1 high measurement accuracy. Because the thermocouple/probe is in direct contact with the measured object, it is not affected by the intermediate medium.
2 wide measurement range. Commonly used thermocouple/probe can be measured from -50~+1600°C. Some special thermocouple/probe can measure -269°C thermocouple/probe thermocouple/probe (such as gold, iron, nickel, chromium). +2800°C (eg Tungsten-Rhodium).
3 simple structure, easy to use. The thermocouple/probe is usually composed of two different wires, and is not limited by the size and the beginning. It has a protective sleeve and it is very convenient to use.
Second, what is a thermocouple Thermocouple is a temperature sensing element, which is a contact temperature measurement in temperature measurement. It can convert the temperature signal into a thermoelectric signal. Through the cooperation of the electrical measuring instrument, the measured temperature can be measured.
Third, thermocouple/probe temperature measurement principle Two or different materials of conductors or semiconductors A and B are welded together to form a closed loop. When there is a temperature difference between two sticking points 1 and 2 of conductors A and B, two The electromotive force is generated between them, and thus a current of a size is formed in the loop. This phenomenon is called a thermoelectric effect. This is the so-called Seebeck effect. Thermocouples/probes work with this effect.
Conductors A and B are called hot electrodes. The higher temperature end (T) is called the working end (usually welded together); the lower temperature end (To) is called the free end (usually at a constant temperature).
According to the relationship between thermoelectric and temperature functions. Thermocouple index table can be made. The index table was obtained at a free end temperature of To = 00C. Different thermocouples have different index tables.
When the third metal material is inserted in the thermocouple circuit, 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 access circuit. Therefore, when the thermocouple measures temperature, it can be connected to the measuring instrument. After the thermoelectric potential is measured, the temperature of the measured medium can be known.
In theory, any two conductors can be made into thermocouples, but in fact not all materials can make thermocouples, so the following must be satisfied for hot electrode materials:
(1) Thermocouple materials can produce higher thermoelectric potentials when they are exposed to temperature. The relationship between thermoelectric potential and temperature is preferably linear or nearly linear.
(2) High temperature can be measured and applied in a wide range of domestic temperatures. After long-term use, the physical, chemical and thermoelectric properties remain stable;
(3) The temperature coefficient of resistance of the material is required to be small, the resistivity is high, the conductivity is good, and the heat capacity is small;
(4) Good reproducibility, ease of mass production and interchangeability, and ease of development of a unified indexing table;
(5) Good mechanical properties and uniform material;
(6) Rich in resources and cheap in price.
Standardized Thermocouples/Probes Since January 1, 1988, thermocouples/probes and thermal resistances have been produced in accordance with IEC international standards, and seven standardized thermocouples S, B, E, K, R, J, and T have been designated. The probe is a unified design thermocouple/probe in our country.
1 The welding of the two hot electrodes that make up the thermocouple/probe must be secure;
2 The two hot electrodes should be well insulated from each other to prevent short circuits;
3 The connection between the compensation wire and the free end of the thermocouple/probe must be convenient and reliable;
4 The protective sleeve should ensure that the hot electrode is fully isolated from harmful media.
When using thermocouple/probe compensation wire, it must pay attention to the model matching, the polarity can not be connected wrong, the temperature of compensation wire and thermocouple/probe connection end can't exceed 100°C.
Thermocouple/probe knowledge