Industrial thermal resistance installation and use of matters needing attention

Industrial thermal resistance is a temperature sensing element that converts a temperature into a thermoelectric potential, and a secondary instrument is used to determine the temperature value by measuring the thermoelectric potential. With simple structure, stable performance, easy use, high measurement accuracy and wide temperature measurement range, it is widely used in heat treatment in production, scientific research and mechanical industry to measure and control temperature.

Industrial thermal resistance installation principle: 1) The measuring end of the thermocouple should be in a place that can truly represent the temperature of the measured medium. When installing a thermocouple on the pipe, the end of the protective pipe should be approximately 5 to 10 mm above the centerline of the pipe. 2) The thermocouple should have a sufficient depth of insertion. Generally at least 8 to 10 times the outside diameter of the thermocouple protection tube. 3) In order to prevent heat loss, the thermocouple protective tube should be exposed outside the equipment as short as possible, and add insulation layer. 4) If the measured medium has a negative pressure or is a harmful gas, the thermocouple must be tightly sealed to prevent external cold air from entering, affecting the accuracy of the measurement, or causing harmful gases to overflow and pollute the air. 5) The place where the thermocouple is installed should try to avoid other heat sources, strong magnetic fields, etc. to prevent external interference. 6) The thermocouple mounting position should be kept as vertical as possible to prevent deformation of the protective tube at high temperatures. However, in the presence of flow, the thermocouple must be installed at an incline. If possible, install the thermocouple at the bend of the pipe. If horizontal installation is required, it should be supported by fire bricks or metal brackets.

Industrial thermal resistance installation Note: 1) The thermal resistance should not be installed near the door or near the heated object. The junction box cannot touch the container wall of the measured medium. The ambient temperature should not exceed 100°C, and strong vibrations should be avoided; 2) The insertion depth of the protection tube should not be less than 8 to 10 times of the outer diameter of the protection tube; 3) When measuring the surface temperature, the temperature sensing element and the measured object must be made In close contact, and the surface to be measured should be kept clean and clean; 4) For the thermal resistance to withstand pressure, the seal at the sealing surface must be strictly guaranteed;

Due to the thermal inertia of the industrial thermocouple, the indicator value of the instrument lags behind the change in the measured temperature, and this effect is particularly pronounced when performing rapid measurements. For this reason, industrial thermocouples with a smaller diameter of the protective tube and a smaller diameter of the thermal electrode are used as much as possible. When the temperature measurement environment permits, the protection tube can even be removed. The hysteresis of an industrial thermocouple is characterized by its time constant. Due to the measurement lag, the amplitude of the temperature fluctuation detected by the industrial thermocouple is smaller than the amplitude of the fluctuation of the furnace temperature. The greater the measurement lag, the smaller the amplitude of the fluctuation of the industrial thermocouple and the greater the difference from the actual furnace temperature. When using an industrial thermocouple with a large time constant to measure or control the temperature, the temperature displayed by the instrument will fluctuate little, but the actual furnace temperature may fluctuate greatly. In order to accurately measure the temperature, an industrial 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 industrial 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 method is to minimize the number of hot ends. size. In order to protect the industrial thermocouple in use, it usually has a protective sleeve, which greatly increases the time constant of the industrial thermocouple, and makes the dynamic measurement accuracy worse, that is, the difference between the temperature of the industrial thermocouple and the temperature of the furnace Big. However, the opposite is reflected, which makes it easy for operators to mistake that the furnace temperature fluctuates little. Therefore, in the temperature measurement of the heat treatment furnace, the time constant of the protection sleeve should be reduced as much as possible. Usually, the material with good thermal conductivity, a thin tube wall, and a small-diameter protection sleeve are used. In a more precise temperature measurement, no protection sleeve is used. The bare wire thermocouple of the tube, but the thermocouple is easily damaged, should be corrected and replaced in time.