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The thermoelectromotive force of the armored thermocouple will increase as the temperature of the measuring end rises
2012-4-12 9:56:41

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.

的工作原理是由两种不同成份的导体两端经焊接,形成回路,直接测温端叫测量端,接线端叫参比端。 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. Several errors of armored thermocouples: Armored thermocouples have the advantages of bending, high voltage resistance, fast thermal response time, and ruggedness. Armored thermocouples are the same as fabricated thermocouples. As temperature sensors, they are usually armored. Thermocouples are used in conjunction with display instruments, recorders, and electronic regulators. 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.


1: Errors introduced by improper installation, such as the location of the thermocouple installation and the depth of insertion cannot reflect the true temperature of the furnace. In other words, the thermocouple should not be installed too close to the door and the place of heating, and the depth of insertion should be at least the protection tube 8 to 10 times the diameter; the space between the thermowell's protective sleeve and the wall is not filled with heat-insulating material, causing the furnace to overflow or cold air to enter, so the gap between the thermocouple's protective tube and the hole in the furnace wall should be refractory mud or asbestos rope Wait for the insulation to be blocked to prevent the convection of hot and cold air from affecting the accuracy of the temperature measurement. The cold end of the thermocouple is too close to the furnace to make the temperature exceed 100 ° C. The installation of the thermocouple should avoid strong magnetic fields and strong electric fields as much as possible, so you should not use The thermocouple and the power cable are installed in the same conduit to avoid interference and introduce errors; the thermocouple cannot be installed in the area where the measured medium rarely flows. When using the thermocouple to measure the gas temperature in the pipe, the thermocouple must be opposed to the flow direction Installed and fully exposed to gas. 2: Errors introduced by poor insulation, such as thermocouple insulation, excessive dirt or salt residue on the protection tube and wire drawing board, which results in poor insulation between the thermocouple and the furnace wall, which is more serious at high temperatures, which not only causes thermoelectricity The loss of potential also introduces interference, and the error caused by it can sometimes reach Baidu. 3: Misunderstanding due to thermal inertia Because the thermal inertia of the thermocouple makes the indicator value 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 lag, the smaller the amplitude of the thermocouple fluctuations 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 has small fluctuations, the actual furnace temperature fluctuations may be large. In order to accurately measure the temperature, a 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 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 size of the hot end. . In use, usually a material with good thermal conductivity, a thin tube wall and a small inner diameter protective sleeve. In a more precise temperature measurement, a bare wire thermocouple without a protective sleeve is used, but the thermocouple is easily damaged and should be corrected and replaced in time. 4: Thermal resistance error At high temperature, if there is a layer of coal ash on the protective tube and dust is attached to it, the thermal resistance increases and hinders heat conduction. At this time, the temperature indication is lower than the true value of the measured temperature. Therefore, the outside of the thermocouple protection tube should be kept clean to reduce the error.

公称压力:一般是指在工作温度下保护管所能承受的静态外压而破裂。 Nominal pressure of armored thermocouple : Generally refers to the static external pressure that the protection tube can withstand at operating temperature and rupture.
Minimum insertion depth of thermocouple: should be no less than 8-10 times the outer diameter of its protective sleeve (except for special products)
Insulation resistance: When the ambient air temperature is 15-35 ° C and the relative humidity is less than 80%, the insulation resistance is ≥5 Megohm (voltage 100V). Thermocouple with splash-proof junction box, when the relative temperature is 93 ± 3 ℃, the insulation resistance is ≥0.5 megohm (voltage 100V). The insulation resistance at high temperature: the thermocouple at high temperature, its thermal electrode (including double branch type) ) The insulation resistance (per meter) between the protective tube and the two hot electrodes should be greater than the value specified in the table below.