Installation method of temperature sensor

When installing and using the temperature sensor, pay attention to the following matters to ensure the best measurement effect:

1. Errors caused by improper installation

For example, the installation position and insertion depth of the thermocouple cannot reflect the real temperature of the furnace. In other words, the thermocouple should not be installed too close to the door and heating place, and the insertion depth should be at least 8 ~ 10 times the diameter of the protective tube; The gap between the protective sleeve and the thermocouple wall is not filled with insulating material, resulting in heat overflow or cold air intrusion into the furnace. Therefore, the gap between the thermocouple protection tube and the furnace wall hole should be sealed with insulating materials such as refractory mud or asbestos rope to avoid the influence of cold and hot air convection on the temperature measurement accuracy; The cold end of the thermocouple is too close to the furnace body, so that the temperature exceeds 100; The installation of thermocouples shall avoid strong magnetic field and electric field as far as possible. Therefore, thermocouples and power cables shall not be installed in the same conduit to avoid errors caused by interference; Thermocouples cannot be installed in areas where the measured medium rarely flows. When using thermocouple to measure the temperature of gas in the pipe, the thermocouple must be installed against the flow direction and in full contact with the gas.

2. Error caused by insulation deterioration

If the thermocouple is insulated, there is too much dirt or salt slag in the protective tube and support plate, resulting in poor insulation between the thermoelectric dipole and the furnace wall, which is more serious at high temperature, which will not only cause the loss of thermoelectric potential, but also introduce interference, and the resulting error can sometimes reach Baidu.

3. Error introduced by thermal inertia

Due to the thermal inertia of the thermocouple, the indicated value of the instrument lags behind the change of the measured temperature, which is particularly prominent in rapid measurement. Therefore, thermocouples with extremely thin thermoelectricity and small diameter should be used as far as possible. When the temperature measurement environment permits, the protective tube can even be taken away. Due to the measurement lag, the temperature fluctuation detected by the thermocouple is less than that of the furnace temperature. The larger the measurement lag is, the smaller the fluctuation range of thermocouple is, and the greater the difference between thermocouple fluctuation and actual furnace temperature is. When the thermocouple with large time constant is used to measure or control the temperature, the temperature displayed by the instrument fluctuates little, but the actual furnace temperature may fluctuate greatly. In order to accurately measure the temperature, the thermocouple with small time constant should be selected. The time constant is inversely proportional to the heat transfer coefficient and is directly proportional to the density and specific heat of the material with the diameter of the hot end of the thermocouple. To reduce the time constant, the most effective way is to increase the heat transfer coefficient and reduce the size of the hot end as much as possible. In use, protective sleeves with good thermal conductivity, thin pipe wall and small inner diameter are usually used. In more accurate temperature measurement, the bare wire thermocouple without protective sleeve is used, but the thermocouple is easy to be damaged and should be corrected and replaced in time.

4. Thermal resistance error

At high temperature, if there is a layer of coal ash on the protective tube and dust is attached to it, the thermal resistance will increase and hinder heat conduction. At this time, the temperature indication value is lower than the real value of the measured temperature. Therefore, the outside of the thermocouple protection tube should be kept clean to reduce errors.

Application fields:

Temperature sensor is the earliest developed and most widely used sensor. The market share of temperature sensor is much higher than that of other sensors. From the beginning of the 17th century, people began to measure temperature. With the support of semiconductor technology, semiconductor thermocouple sensor, PN junction temperature sensor and integrated temperature sensor have been developed in this century.

If two conductors of different materials are connected to each other at a certain point, there will be potential difference in the unheated part of the heating connection point. The value of this potential difference is related to the temperature of the measuring point of the unheated part and the material of the two conductors. This phenomenon may occur over a wide temperature range. The temperature difference of the unheated part can be accurately measured if the temperature difference of the heated part is accurately measured. It is called "thermocouple" because it must have two different conductors. Thermocouples of different materials are used in different temperature ranges, and the sensitivity is also different.

Thermocouple sensors have their own advantages and disadvantages. It has low sensitivity and is easily affected by environmental interference signal and preamplifier temperature drift. It is not suitable for measuring small temperature changes. Because the sensitivity of thermocouple temperature sensor is independent of the thickness of material

Development status:

In recent years, the process of China's industrial modernization and the sustained and rapid growth of the electronic information industry have driven the rapid rise of the sensor market. As an important sensor, temperature sensor accounts for more than 40% of the total demand of the whole sensor. Temperature sensor is a kind of semiconductor device, which uses the characteristics of NTC resistance changing with temperature to convert non electrical physical quantities into electrical quantities, so as to accurately measure and automatically control the temperature. Temperature sensors are widely used in temperature measurement and control, temperature compensation, flow, flow and wind speed measurement, liquid level indication, temperature measurement, ultraviolet and infrared light measurement, microwave power measurement, etc. It is widely used in color TV, computer, color display, switching power supply, water heater, refrigerator, kitchen equipment, air conditioner, automobile and other fields. In recent years, the rapid growth of automotive electronics and consumer electronics industry has led to the rapid growth of China's demand for temperature sensors.