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technical article
Factors Influencing Thermocouple Shunt Error
2011-9-22 17:18:14

     铠装热电偶 高温下 产生分流误差的现象, 所以开始 引起 人们的重视, 因此 了解分流误差的影响因素, 并采取适当对策以减少或 消除分流误差的影响 是很有必要的 Because of the phenomenon of shunt error caused by armored thermocouples at high temperature, people began to pay attention to it . Therefore , it is necessary to understand the influencing factors of shunt error and take appropriate countermeasures to reduce or eliminate the effect of shunt error .
直径 ( 1 ) Diameter of armored thermocouple
     来说 , 只将热电偶中间部位加热。 For a K -type armored thermocouple with a length of 9 meters , only the middle part of the thermocouple is heated. 表明:分流误差的大小与 它的 直径的平方根成反比( 直径过细, 遵守此规律) , 也就是 直径越细, 分流误差越大。 The experimental results will show that the magnitude of the shunt error is inversely proportional to the square root of its diameter ( but the diameter is too small to follow this rule) , that is, the smaller the diameter , the greater the shunt error. 直径 3.2mm 铠装热电偶 将产生分流误差。 When the temperature of the middle part is higher than 800 , a shunt error will occur for a 3.2mm diameter thermocouple . 对于 直径 6.4mm 直径 8mm 铠装热电偶 , 当中间部位的温度为 900 , 未发现分流误差。 But for the thermocouples with a diameter of 6.4mm and a diameter of 8mm , when the temperature in the middle part is 900 , the shunt error is still not found. 直径 6.4mm 热电极丝 直径为1.4mm 8mm (热电极丝直径为 2.0mm )的铠装热电偶 , 当中间部位温度为 1100 , 直径为 8mm 的铠装热电偶产生的分流误差仅为 直径 6.4mm 的一半。 For a thermoelectric wire with a diameter of 6.4mm , the shunt error caused by a thermocouple with a diameter of 8mm when the temperature of the middle part is 1100 for a sheathed thermocouple with a diameter of 1.4mm and 8mm (the diameter of the thermoelectric wire is 2.0mm ) Only half of the diameter of 6.4mm . 也就是 50% )近视于两种铠装热电偶电极丝直径的平方比 This value ( that is, 50% ) is short-sighted compared to the square ratio of the diameters of the two armored thermocouple electrode wires . The ratio of the electrode wire diameter square is the resistance ratio of the electrode wire. 尽可能选用粗直径的铠装热电偶 Therefore , in order to reduce the shunt error , a thick-diameter armored thermocouple should be selected as much as possible.
( 2 ) Temperature in the middle
     温度的升高, 呈指数关系增大。 If the temperature in the middle part exceeds 800 , a shunt error may occur , and its size will increase exponentially with the increase of temperature . 尽可能避免超过800 Therefore , in addition to the measurement end , other parts should be avoided as much as 800 as much as possible .
   Length and position of heating belt in the middle
    中间部位加热带温度高于800 , 它的 加热带的长度越长, 距离测量端越远 , 分流误差越大。 If the temperature of the heating zone in the middle is higher than 800 , the longer the heating zone is, the farther it is from the measuring end , the greater the shunt error. 尽可能 缩短加热带长度, 并且不要在远离测量端处加热 , 以减少分流误差。 Therefore , the length of the heating band should be shortened as much as possible , and not heated away from the measurement end to reduce the shunt error.
( 3 ) Resistance of thermocouple wire
    铠装热电偶 的直径相同时, 分流误差将 随热电偶丝的电阻增大而增加。 If the diameter of the armored thermocouple is the same , the shunt error will increase as the resistance of the thermocouple wire increases. 好。 Therefore , it is best to use a thermocouple wire with low resistance . 如:直径相同的S 铠装热电偶 K 型热电偶相比 , 它的 分流误差 减少40% For example : compared with the K -type thermocouple , the S -type armored thermocouple with the same diameter will reduce the shunt error by 40% . 采用S 型热电偶测量炉内温场分布 , 费用高, 是比 较准确。 Therefore , S -type thermocouples can be used to measure the temperature field distribution in the furnace . Although the cost is high , it is relatively accurate.
( 4 ) Insulation resistance
    随温度的升高呈指数降低, 分流误差的大小主要取决于高温部分的绝缘性能 At high temperature, the resistivity of the oxide will decrease exponentially with increasing temperature. The magnitude of the shunt error mainly depends on the insulation performance of the high temperature part . The lower the insulation resistance , the easier it is to generate a shunt error. 绝缘电阻增加10 倍或 减少 1/10 , 它的 分流误差也随 减少至1/10 增大10 倍。 If the insulation resistance increases by 10 times or decreases to 1/10 , its shunt error also decreases to 1/10 or increases by 10 times. 尽可能采用直径粗的铠装热电偶, 增加绝缘层厚度。 In order to reduce the shunt error , a thicker armored thermocouple should be used as much as possible to increase the insulation thickness. 没有 果的 , 那么 只好采用装配式热电偶 If the above measures are not effective , then we must use assembled thermocouples .