The thermocouple measurment errors 's reasons (1) .Insertion Depth When the thermocouple is inserted into the measured object, the heat flow will be generated along the sensor body. When the ambient temperature is low, there will be heat loss, which will cause the temperature of the thermocouple and the measured object to be inconsistent, resulting in measurement errors. The error caused by heat conduction is related to the insertion depth and the insertion depth is related to the material of the protective tube. The insertion depth for metal protection tube should be deeper (about 15-20 times the diameter) because of its good thermal conductivity; the insertion depth for ceramic material is can be shallower(about 10-15 times the diameter). For engineering temperature measurement, the insertion depth is also related to whether the measurement object is static or flowing. For example, the measurement of the temperature of flowing liquid or high-speed air flow will not be subject to the above restrictions,the insertion depth can be shallower. (2) .Response Time The basic principle of contact temperature measurement is that the temperature measuring element should reach thermal equilibrium with the measured object. Therefore, it is necessary to maintain a certain period of time to make the two reach thermal equilibrium when measuring the temperature. The holding time is related to the thermal response time of the temperature measuring element, and the thermal response time mainly depends on the structure of the sensor and the measurement conditions. For gaseous, especially static gases, it should be maintained for at least 30 minutes to reach equilibrium; for liquids, the fastest time should be more than 5 minutes. For the measured temperature field with constantly changing temperature, especially the instantaneous change process, the response time of the sensor is required to be at the millisecond level. Otherwise the ordinary temperature sensor will not only lag because it cannot keep up with the speed change of the measured object, but also measurement errors occur due to failure to reach thermal equilibrium. Therefore, it is best to choose a sensor with a fast response speed. For thermocouple, in addition to the influence of the protective tube, the diameter of the thermocouple’s measuring end is also the main factor, the smaller the diameter of the measuring end and conductor wire, the shorter the thermal response time. (3) .Heat Radiation The thermocouple inserted into the furnace is heated by the heat radiation emitted by the high temperature object. If the gas in the furnace is transparent and the temperature difference between the thermocouple and the furnace wall is large, there will be a temperature measurement error due to the thermal radiation between the thermocouple and the furnace wall. Therefore, in order to reduce the thermal radiation error, the temperature of the furnace wall should be as close as possible to the thermo...

In order to ensure that the Mineral insulated thermocouple calibration can meet the relevant requirements of the specification, the main work is to reduce the uncertainty of the thermocouple calibration as much as possible. Precision thermocouple calibration furnace has a wide uniform temperature zone, wide corresponding jack temperature uniform temperature zone and good temperature stability. 1. Issues Issues with the previous calibration furnace is that the furnace body used a horizontal tubular heating furnace structure, while it used a single-section heating wire made of unequal distances for heating. This heating method can effectively ensure that the central area obtains a wide isothermal working area. However, there are serious problems in the actual application process. The worst issue is short distance of the isothermal zone. Therefore, when performing calibration work, not only the heat conduction of the tested thermocouple will affect the actual temperature field, but also the external heat transfer of the test furnace itself, which will lead to certain errors in the results of the thermocouple test. For the above effects, it can be specifically manifested as inconsistent heat exchange conditions between the calibration furnace and each tested thermocouple, and at the same time, there are certain differences in the heat balance points at different times. (1) .Influence of temperature field For the heat exchange status and heat balance point between the furnace and the tested thermocouple, the change of the temperature field in the calibration furnace working area will affect the results. Specifically, the most direct result of the change in the temperature field is the impact on the temperature of the measuring end of the standard thermocouple and the calibrated thermocouple, temperature will also vary with the change of position. The first thing to do when calibrating an assembled thermocouple is to disassemble the protective tube and then place the thermal electrode and insulating tube with the standard thermocouple in the calibration fire for comparison. Through a certain comparison, it can be known that the temperature of the measuring end between the standard thermocouple and the calibrated thermocouple is so small that it is almost negligible, which will not cause very large uncertainty. When the calibration diameter of the calibrated MI thermocouple is very large, the measuring end node of the thermocouple will need a very large distance because it is in the metal protective tube, and then the measuring end of the standard thermocouple will appear, which will cause temperature differences. In the actual calibration process, when MI thermocouple are tied together, the phenomenon of axial heat conduction will occur at this time, and the temperature field at this time will be much worse than the temperature field environment at no-load. At the same time, in the working area of the horizontal furnace itself, there will be radial con...

1. Different Principle Thermocouple is the most widely used in temperature measurement. The principle of thermocouple is based on the thermoelectric effect, two different conductors or semiconductors are connected into a closed loop. When the temperatures at two junctions are different, the temperature in the loop A thermoelectric potential will be generated. This phenomenon is called the thermoelectric effect, also known as the Seebeck effect. Through the measurement of this thermoelectric potential, the temperature value is finally obtained. The temperature measurement principle of thermal resistance is based on the characteristic that the resistance value of a conductor or semiconductor changes with temperature. 2. Different temperature range Thermocouple has a wide range of measurement continuously from -50°C to 1600°C. Some special thermocouple can measure as low as -269°C and as high as 2300°C; the temperature range of platinum thermal resistance is generally -200°C-800°C, copper thermal resistance is -40°C-140°C. Platinum thermal resistance belongs to medium and low temperature measuring device. 3. Different types & structures 3.1. Types Thermocouple is divided into two categories: normal thermocouple and unsusal thermocouple. normal thermocouple is divided into eight different divisions, namely B, R, S, K, N, E, J and T, where B, R, S thermocouple belonging to the platinum series, because platinum is a noble metal, they are also called noble metal thermocouple, and the remaining models are called base metal thermocouple. Unsusal thermocouple is not as good as normal thermocouple in terms of range or magnitude of use, and generally there is no unified graduation table, and are mainly used for measurement in some special occasions. The common types of thermal resistance are copper thermal resistance and platinum thermal resistance. 3.2. Structures The structure of the thermocouple: The welding of the two thermal electrodes that make up the thermocouple must be firm; The two thermal electrodes must have good insulation properties to prevent short circuits, and the connection between the thermocouple compensation wire and the free end of the thermocouple must be convenient and reliable; The protective sleeve should ensure that the hot electrode is fully isolated from harmful substances. The structure of the thermal resistance: Most of them are made of pure metal materials, and the change of the resistance of various wires such as the lead wire of the thermal resistance body will affect the temperature measurement. 4. Different fields of application Thermocouple is a component whose thermal electromotive force (voltage) changes with temperature, and a thermal resistor is a component whose resistance changes with temperature. Generally, thermocouple is used in a high temperature environment, and a thermal resistor is used in a low temperature environment. If the temperature difference exceeds 500°C, the resistance v...