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| Related Application Principles of Thermocouple |
| 2011-10-6 10:53:49 |
是工业上最常用的温度检测元件之一。 Thermocouples are one of the most commonly used temperature sensing elements in the industry. 优点是： ① 测量精度高。 Its advantages are: ① High measurement accuracy. 热电偶直接与被测对象接触， 所以 不受中间介质的影响。 Since the thermocouple is in direct contact with the measured object, it is not affected by the intermediate medium. ② Wide measurement range. 都 可 以 边续测量，某些特殊热电偶最低可 以 测到-269 ℃ ( 比 如金铁镍铬) ，最高可 以 达+2800 ℃ ( 比 如钨- 铼 ) 。 Common thermocouples can be continuously measured from -50 to +1600 ℃ . Some special thermocouples can measure as low as -269 ℃ ( such as gold-iron-nickel-chromium ) and as high as +2800 ℃ ( such as tungsten- 铼 ) . ③ Simple structure and easy to use. 并且 不受大小和开头的限制，外 面 有保护套管，用起来非常方便。 Thermocouples are usually composed of two different metal wires, and are not restricted by size and opening. There are protective sleeves on the outside , which is very convenient to use.
1 . The basic principle of thermocouple temperature measurement
者 半导体焊接起来，构成一个闭合回路 。 Solder two conductors or semiconductors of different materials to form a closed loop . 点 之间存在温差 的 时 侯 ，两者之间便产生电动势, 因 此 在回路中形成一个大小的电流, 这种现象称为热电效应。 When there is a temperature difference between the two attachment points of conductors A and B , an electromotive force is generated between the two , so a large current is formed in the circuit . This phenomenon is called the thermoelectric effect. Thermocouples use this effect to work.
2 . 以 及结构形成 Thermocouple types and structure formation
(1) The type of thermocouple
常用热电偶可分为标准热电偶和非标准热电偶两大类。 Generally used thermocouples can be divided into two categories: standard thermocouples and non-standard thermocouples. 标准热电偶是指国家标准规定了其热电势与温度的关系、允许误差、并有统一的标准分度表的热电偶，它有与 之相 配套的显示仪表可 以 供 应 选用。 The so-called standard thermocouple refers to a thermocouple whose national standard specifies the relationship between thermoelectric potential and temperature, the allowable error, and has a unified standard index table. It has a matching display instrument that can be used for selection. 非标准化热电偶在使用范围或数量级上 都 不及标准化热电偶，一般也没有统一的分度表，主要用于某些特殊场合的测量。 The so-called non-standardized thermocouples are not as good as standardized thermocouples in the scope or magnitude of use . Generally, there is no unified index table, which is mainly used for measurement in some special occasions.
Standardized thermocouples Since January 1 , 1988 , all thermocouples and thermal resistors have been produced in accordance with IEC international standards, and S , B , E , K , R , J , T seven standardized thermocouples have been designated as China's unified design types. Thermocouple.
(2) Structural form of thermocouple 因此 对它 有如下 结构要求： In order to ensure that the thermocouple works reliably and stably, it has the following structural requirements:
① The welding of the two thermal electrodes that make up the thermocouple must be firm;
该 很好地绝缘，以防 止 短路； ② The two hot electrodes should be well insulated from each other to prevent short circuit;
③ The connection between the compensation wire and the free end of the thermocouple should be convenient and reliable;
该 能保证热电极与有害介质充分隔离。 ④ The protective sleeve should be able to ensure that the hot electrode is fully isolated from the harmful medium.
3 ． Temperature compensation for the cold junction of a thermocouple
的 时 侯 ) ，而测温点到仪表的距离都很远，为了节省热 电偶材料，降低成本， 一般 通常采用补偿导线把热电偶的冷端延伸到温度比较稳定的控制室内，连接到仪表端子上。 Because the materials of thermocouples are generally more expensive ( especially when precious metals are used ) , and the distance between the temperature measurement point and the instrument is very long, in order to save thermocouple materials and reduce costs, compensation wires are usually used to cool the thermocouple. The terminal extends into the control room where the temperature is relatively stable and is connected to the instrument terminal. 的是 ，热电偶补偿导线的作用只起 到 延伸热电极，使 得 热电偶的冷端移动到控制室的仪表端子上，它本身并不能消除冷端温度变化对测温的影响，不起补偿作用。 It must be pointed out that the role of the thermocouple compensation wire only extends the hot electrode, so that the cold end of the thermocouple is moved to the instrument terminal in the control room. Play a compensation role. Therefore, other correction methods are needed to compensate for the effect on the temperature measurement when the cold junction temperature t0 ≠ 0 ℃ .
的 时 侯 必须注意型号相配，极性不能接错，补偿导线与热电偶连接端的温度不能超过100 ℃ 。 When using the thermocouple compensation wire , you must pay attention to the matching of the model, the polarity must not be wrong, and the temperature of the connection end of the compensation wire and the thermocouple cannot exceed 100 ℃ .