How to correctly use industrial thermocouple to control error release date: 2019 - 06 - 05 viewed: zero

Industrial thermocouple principle is based on the seebeck effect, namely: if is composed of two different composition homogeneous conductor closed loop, when when there is a temperature gradient at both ends in loop electric current passes through, then existed between both ends of the seebeck potential - Thermoelectric potential. Its value and the composition of industrial thermocouple metal material properties, related to the size of the hot end and cold end temperature difference, and the length of the hot electrode, the diameter size. Industrial thermocouple used correctly not only can be accurate temperature value to ensure that the product qualified, but also can save thermocouple materials consumption, save money and can guarantee the quality of the product. Industrial thermocouple in moderate temperature measuring error is often overlooked, is mainly due to incorrect installation, thermal conductivity, such as time lag error, they are industrial thermocouple in the use of the main error. The following talk how to correctly use industrial thermocouple, for your reference. One, improperly installed into the error of the 1, industrial thermocouple cannot be installed in a few measured medium flowing area, when measured with industrial thermocouple tube gas temperature, must make industrial thermocouple installation against the flow direction, and fully contact with the gas. 2, such as industrial thermocouple installation position and insertion depth cannot reflect the reality of the furnace temperature. Therefore thermocouples should not be in too close to the door and heating, the depth of the insert should be at least 8 ~ 10 times the diameter of the protection tube; 3, industrial thermocouple cold end is too close to the furnace temperature over 100 ℃; 4, industrial protective casing and the wall of the gap between unfilled adiabatic material overflow or cold air invading the furnace heating, industrial thermocouple protection tube and furnace wall hole when installation the space between the application of refractory mortar or insulating material such as asbestos rope jam to avoid cold and hot air convection and affect the accuracy of temperature measurement; 5, the installation of industrial thermocouple should as far as possible to avoid strong magnetic field and electric field, so should not be thermocouple and the power cable line in order to avoid interference caused by errors within the same catheter; Second, the introduction of thermal inertia error due to the thermal inertia in the industrial thermocouple instrument behind the change of the measured temperature, indicating value this influence is particularly acute in rapid measurement. For as much as possible USES the hot electrode a finer smaller industrial thermocouple protection tube diameter. Temperature measuring environmental permits, even protecting tube can be taken. Industrial thermocouple lag is characterized with its time constant. Due to measurement lags behind, with industrial thermocouple detect temperature fluctuations of the amplitude of the furnace temperature fluctuation amplitude is small. Measurement lags behind, the greater the industrial thermocouple, the smaller the fluctuation amplitude is and the actual temperature difference. When using time constant big industrial thermocouple temperature or temperature control, instrument display temperature fluctuation is small, but the actual furnace temperature fluctuations can be quite large. In order to accurately measure temperature, should choose small industrial thermocouple time constant. Time constant is inversely proportional to the heat transfer coefficient, and industrial thermocouple hot side is directly proportional to the diameter, material density and specific heat, such as to reduce the time constant, in addition to the increased heat transfer coefficient, the most effective way is to try to decrease the size of the hot end. In use in order to protect the industrial thermocouple, usually with a protective casing, this has greatly increased the industrial thermocouple time constant, the dynamic measurement precision becomes worse, namely industrial thermocouple temperature and the temperature difference is bigger. But reflected, in contrast, this makes operators easily mistaken for furnace temperature fluctuation is small. So in the heat treatment furnace temperature measurement, should decrease as far as possible to protect casing time constant, usually USES the material with good thermal conductivity, thin, small diameter of the tube wall protection casing, in the precision of temperature measurement, using unprotected casing bare wire thermocouple, but thermocouple is easy to damage, should be more positive and timely replacement. Three, thermal resistance error when industrial thermocouple protection tube in high temperature, such as protecting tube with a layer of ash, dust attached to the above, the thermal resistance increase, hinder the heat conduction, when the temperature is lower than the true value of measured temperature value. So keep industrial thermocouple protection tube in the process of using external cleaning is one of the measures to reduce the error. Four, insulation degree of variation and the introduction of error industrial thermocouple protection tube and wire plate too much dirt or salt slag between the thermocouple and the insulation of the furnace wall asked, at high temperatures is more serious, which not only causes the thermoelectric potential loss but also can introduce interference, the resulting error sometimes can reach on baidu.