Thermocouple correct use
发表日期：2016-01-09
The correct use of the thermocouple can not only get the accurate temperature value, to ensure that qualified products,
But also can save consumption of thermocouple materials, we save money and can ensure the product quality. Not installed correctly, the thermal conductivity and the time lag error, which is the main error in the use of the thermocouple.
1, the introduction of improper installation error
Such as position and insertion depth of thermocouple installation can not reflect the real temperature of the furnace, in other words, the thermocouple should be installed in the not too close to the door and heating, the insertion depth should be at least 10 times the diameter of the protective tube to 8; the casing pipe and the thermocouple on the wall of the interval between the unfilled material causing overflow or heat insulation the intrusion of cold air, so between the thermocouple protection tube and furnace wall hole gap application of refractory mud or asbestos rope insulation material blocked so as not to cold and hot air convection and affect the accuracy of the temperature measurement; thermocouple cold end is too close to the furnace body temperature exceeds 100 DEG C; the thermocouple installation should avoid as far as possible, strong magnetic field and strong electric field, so should not the thermocouple and the power cable line in the same duct in order to avoid the interference caused by the introduction of error; thermocouple cannot install area rarely flows in the measured medium, when using heat Thermocouple measuring tube gas temperature, thermocouple must make against the direction of flow and full contact with the gas installation.
Error 2, insulation variation introduced
Such as thermocouples insulated, protective tube and tailpiece dirt or salt slag had much cause of thermoelectric dipole dipole and the furnace wall insulation bad, at high temperature is more serious, it will not only caused thermal potential of loss but also introduce interference, the resulting error sometimes up to Baidu.
3, the introduction of thermal inertia error
Due to the thermal inertia of thermocouple makes the instrument indication value behind the change of the measured temperature,
In the rapid measurement of this effect is particularly prominent. It should be as far as possible the use of thermode is fine, the smaller diameter of thermocouple protection tube. The temperature environment permits, even can be protected to pipe. Due to the presence of measurement lag, the amplitude of temperature fluctuations detected by the thermocouple temperature fluctuation amplitude is small. The greater the measurement delay, amplitude fluctuation of the thermocouple is smaller, and the actual temperature difference is bigger. When the time constant of thermocouple or temperature control, temperature display instrument although volatility is very small, but fluctuations in the actual temperature of the furnace can be very large. In order to measure the temperature accurately, should choose the time constant of thermocouple. In addition to increasing the heat transfer coefficient, the most effective way is to minimize the size of the hot end time constant and the heat transfer coefficient is inversely proportional, proportional to the density and specific heat and heat end of thermocouple diameter, material, such as to reduce the time constant. In use, the material with good thermal conductivity is usually used, and the protective sleeve with thin wall and small inner diameter is used. In the more precise temperature measurement, the bare wire thermocouple with no protection sleeve is used, but the thermocouple is easy to be damaged, and it should be corrected and replaced in a timely manner.
4, thermal resistance error
At high temperature, such as the protection of a layer of coal ash, dust attached to the above, the increase in thermal resistance, blocking the conduction of heat, then the temperature is lower than the true value of the measured temperature. Therefore, the outer part of the thermocouple protection tube should be kept clean so as to reduce the error.
But also can save consumption of thermocouple materials, we save money and can ensure the product quality. Not installed correctly, the thermal conductivity and the time lag error, which is the main error in the use of the thermocouple.
1, the introduction of improper installation error
Such as position and insertion depth of thermocouple installation can not reflect the real temperature of the furnace, in other words, the thermocouple should be installed in the not too close to the door and heating, the insertion depth should be at least 10 times the diameter of the protective tube to 8; the casing pipe and the thermocouple on the wall of the interval between the unfilled material causing overflow or heat insulation the intrusion of cold air, so between the thermocouple protection tube and furnace wall hole gap application of refractory mud or asbestos rope insulation material blocked so as not to cold and hot air convection and affect the accuracy of the temperature measurement; thermocouple cold end is too close to the furnace body temperature exceeds 100 DEG C; the thermocouple installation should avoid as far as possible, strong magnetic field and strong electric field, so should not the thermocouple and the power cable line in the same duct in order to avoid the interference caused by the introduction of error; thermocouple cannot install area rarely flows in the measured medium, when using heat Thermocouple measuring tube gas temperature, thermocouple must make against the direction of flow and full contact with the gas installation.
Error 2, insulation variation introducedSuch as thermocouples insulated, protective tube and tailpiece dirt or salt slag had much cause of thermoelectric dipole dipole and the furnace wall insulation bad, at high temperature is more serious, it will not only caused thermal potential of loss but also introduce interference, the resulting error sometimes up to Baidu.
3, the introduction of thermal inertia error
Due to the thermal inertia of thermocouple makes the instrument indication value behind the change of the measured temperature,
In the rapid measurement of this effect is particularly prominent. It should be as far as possible the use of thermode is fine, the smaller diameter of thermocouple protection tube. The temperature environment permits, even can be protected to pipe. Due to the presence of measurement lag, the amplitude of temperature fluctuations detected by the thermocouple temperature fluctuation amplitude is small. The greater the measurement delay, amplitude fluctuation of the thermocouple is smaller, and the actual temperature difference is bigger. When the time constant of thermocouple or temperature control, temperature display instrument although volatility is very small, but fluctuations in the actual temperature of the furnace can be very large. In order to measure the temperature accurately, should choose the time constant of thermocouple. In addition to increasing the heat transfer coefficient, the most effective way is to minimize the size of the hot end time constant and the heat transfer coefficient is inversely proportional, proportional to the density and specific heat and heat end of thermocouple diameter, material, such as to reduce the time constant. In use, the material with good thermal conductivity is usually used, and the protective sleeve with thin wall and small inner diameter is used. In the more precise temperature measurement, the bare wire thermocouple with no protection sleeve is used, but the thermocouple is easy to be damaged, and it should be corrected and replaced in a timely manner.
4, thermal resistance error
At high temperature, such as the protection of a layer of coal ash, dust attached to the above, the increase in thermal resistance, blocking the conduction of heat, then the temperature is lower than the true value of the measured temperature. Therefore, the outer part of the thermocouple protection tube should be kept clean so as to reduce the error.
