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The smaller the amplitude of the armored thermocouple fluctuations, the larger the difference between the actual furnace temperature and the actual furnace temperature.
2012-4-11 9:43:30

具有能弯曲、耐高压、热响应时间快和坚固耐用等优点,铠装热电偶与装配式热电偶一样,作为测量温度的传感器,通常铠装热电偶和显示仪表、记录仪和电子调节器配套使用,同时,铠装热电偶亦可以作为装配式热电偶的感温元件。 Armored thermocouples have the advantages of bending, high voltage resistance, fast thermal response time, and ruggedness. Like armored thermocouples, armored thermocouples are used as temperature sensors. Armored thermocouples and display instruments, recorders, and Electronic regulators are used together. At the same time, armored thermocouples can also be used as temperature sensing elements for assembled thermocouples. Armored thermocouples can directly measure the temperature of liquid, steam and gaseous media and solid surfaces in the range of 0 ℃ ~ 1100 ℃ in various production processes. The working principle of the armored thermocouple is that two ends of two different composition conductors are welded to form a loop. The direct temperature measurement terminal is called the measurement terminal, and the terminal is called the reference terminal. When there is a temperature difference between the measuring end and the reference end, a thermal current will be generated in the loop. Connect the display instrument, and the instrument will indicate the corresponding temperature value of the thermoelectromotive force generated by the thermocouple. The thermoelectromotive force of the armored thermocouple will increase as the temperature of the measuring end rises. The size of the thermoelectromotive force is only related to the material of the armored thermocouple conductor and the temperature difference between the two ends, and has nothing to do with the length and diameter of the thermoelectrode. The structure of armored thermocouple is made of conductor, insulated magnesia and 1Cr18Ni9Ti stainless steel protective tube after repeated drawing. The armored thermocouple product is mainly composed of junction box, terminal and armored thermocouple. Various installation fixtures. There are two types of armored thermocouples: insulated and shell-type.

安装不当引起的误差:如铠装热电偶安装的位置及插入深度不能反映炉膛的真实温度等,换句话说,铠装热电偶不应装在太靠近门和加热的地方,插入的深度至少应为保护管直径的8~10倍;铠装热电偶的保护套管与壁间的间隔未填绝热物质致使炉内热溢出或冷空气侵入,因此铠装热电偶保护管和炉壁孔之间的空隙应用耐火泥或石棉绳等绝热物质堵塞以免冷热空气对流而影响测温的准确性;热电偶冷端太靠近炉体使温度超过100℃;热电偶的安装应尽可能避开强磁场和强电场,所以不应把铠装热电偶和动力电缆线装在同一根导管内以免引入干扰造成误差;铠装热电偶不能安装在被测介质很少流动的区域内,当用铠装热电偶测量管内气体温度时,必须使铠装热电偶逆着流速方向安装,而且充分与气体接触。 Errors caused by improperly installed armored thermocouples : such as the location and insertion depth of armored thermocouples cannot reflect the true temperature of the furnace, in other words, the armored thermocouples should not be installed too close to the door and heated place, and inserted The depth should be at least 8 to 10 times the diameter of the protective tube; the distance between the protective sleeve of the armored thermocouple and the wall is not filled with adiabatic substances, causing the furnace to overflow or cold air to enter, so the armored thermocouple protects the tube and the wall The gap between the holes should be blocked with heat-insulating materials such as refractory mud or asbestos rope to prevent the convection of hot and cold air and affect the accuracy of temperature measurement; the cold end of the thermocouple is too close to the furnace body to make the temperature exceed 100 ° C; the installation of the thermocouple should be avoided as much as possible Open a strong magnetic field and a strong electric field, so the armored thermocouple and the power cable should not be installed in the same conduit to avoid interference and introduce errors; the armored thermocouple cannot be installed in the area where the measured medium rarely flows. When installing a thermocouple to measure the temperature of the gas in the tube, the armored thermocouple must be installed against the flow direction and fully contact the gas. Errors caused by poor insulation of armored thermocouples: If the armored thermocouples are insulated, too much dirt or salt slag in the protection tube and the wire drawing board results in poor insulation between the armored thermocouples and the furnace wall, even at high temperatures. Seriously, this will not only cause the loss of thermoelectric potential, but also introduce interference, and the errors caused by it sometimes reach Baidu.

热惰性引起的误差:由于铠装热电偶的热惰性使仪表的指示值落后于被测温度的变化,在进行快速测量时这种影响尤为突出。 The error caused by the thermal inertia of the armored thermocouple: Because the thermal inertia of the armored thermocouple causes the indicator value to lag behind the change of the measured temperature, this effect is particularly prominent when performing fast measurements. Therefore, thermocouples with thinner thermal electrodes and smaller protective tube diameters should be used whenever possible. When the temperature measurement environment permits, you can even remove the protective tube. Due to the measurement lag, the amplitude of the temperature fluctuation detected by the thermocouple is smaller than the amplitude of the furnace temperature fluctuation. The larger the measurement hysteresis, the smaller the amplitude of the fluctuation of the armored thermocouple and the larger the difference from the actual furnace temperature. When using a thermocouple with a large time constant to measure or control the temperature, although the temperature displayed by the meter fluctuates very little, the actual furnace temperature may fluctuate greatly. In order to accurately measure the temperature, an armored thermocouple with a small time constant should be selected. The time constant is inversely proportional to the heat transfer coefficient, and is proportional to the diameter of the hot end of the armored thermocouple, the density of the material and the specific heat. To reduce the time constant, in addition to increasing the heat transfer coefficient, the most effective way is to minimize the heat End size.