Various factors that affect the temperature measurement of the slab
(1) Surface condition
The measuring object is a stainless steel plate, and the emissivity is related to the surface roughness and oxidation degree of the object. For smooth and clean surfaces, the emissivity of the object is 0.05-0.5. If the degree of oxidation of the surface increases, the emissivity becomes larger. When the oxide film on the surface of the object is above 10um, the emissivity tends to be stable.
The use of a monochromatic thermometer will be affected by the change of emissivity, especially when measuring stainless steel, the change of emissivity has a great influence on the temperature measurement result. When using a two-color thermometer, the influence of emissivity can be avoided. When measuring similar metal materials, you only need to calibrate it once.
(2) The influence of thermal radiation
The temperature of the cast slab is very high and the volume is large. The temperature of ordinary instruments can only reach 85°C, and it is generally recommended to use a temperature of less than 50°C. Even if the military-grade products are used, the requirements cannot be met. The fiber-optic thermometer must be used. The sensor head and the detector are separated. The sensor head can withstand a high temperature of 250°C without cooling. The detector is installed in a place where the ambient temperature is low. When the ambient temperature is high, the detector can also be cooled by water, which can greatly increase the service life of the instrument.
(3) Iron oxide scale
Using a special software algorithm, it can avoid the influence of the oxide scale on the temperature measurement results. To judge the emissivity characteristics of the oxide scale, the sampling time of the system must be fast enough (above 10ms), the signal needs to be collected synchronously without delay, and the collected signal must be selected. The comprehensive application of various software algorithms can avoid the influence of oxide scale on the temperature measurement accuracy.
(4) Water vapor and dust in the optical channel
Using a two-color thermometer can basically avoid the influence of water vapor and dust. Even if the signal of the measured object drops by 95%, it will not affect the temperature measurement. Using a dual-wavelength infrared thermometer in the 0.8-1um band can avoid the influence of water vapor. The water vapor is basically transparent in the 0.8-1um band.
refers to relevant information to explain the influence of water vapor on temperature measurement under different measuring distances and measuring temperatures.
The influence of the two-color thermometer on water vapor and certain dust is basically negligible, but the influence of these factors is completely avoided. An extension rod is designed, and compressed air is added to blow it to keep the optical channel clean. The position of the thermometer and the thickest measuring slab can be kept 20cm. In this way, the equipment can be basically maintenance-free.
(5) The influence of water film on the slab surface
The temperature measurement accuracy of the infrared thermometer is related to the water mist of the water film on the surface of the slab. The thicker the water film medium, the more the surface radiation energy attenuates. Refer to the following documents:
Due to the impact of cooling water, there are certain water accumulation areas and certain water film in the casting billet in the second cold zone of continuous casting. Even if a two-color thermometer is used, these areas should be avoided as much as possible. In the actual measurement, a two-color thermometer below 1.1um is selected for measurement and the temperature is corrected.