What are the effects of external interference on infrared thermometers?
The infrared thermometer is an optical measuring device in principle, and it is often interfered by the outside world in the measurement. These disturbances can be divided into disturbances on the measured surface and disturbances in the optical path.
Disturbances on the measured surface mainly include emissivity and extraneous light. According to Stephen Boltzmann's law, the total radiant energy of an object is E=eoT4. For a black body, because the blackness e=1, the temperature can be directly known by measuring the radiation energy with an infrared thermometer. But for general objects, the radiant energy is not only related to temperature, but also related to surface blackness. Blackness is related to many factors, such as the type of substance, temperature, wavelength and surface state. Only by knowing the blackness of the surface of the object or taking the method of measuring the blackness temperature at the same time before the measurement can the real temperature of the object surface be measured correctly.
Extraneous light refers to components that are incident on the surface to be measured from other light sources and reflected, and are mixed into the measurement light. Sunlight during outdoor temperature measurement, and sunlight from the skylight, lighting, and nearby heating furnaces when measuring indoors are all sources of external light. When measuring the temperature of heated objects in the furnace, the furnace wall is the source of extraneous light. The higher the temperature of the light source of external light, the stronger the gloss or the lower the blackness of the surface of the opaque body, the stronger the influence on the temperature.
If you want to qualitatively judge whether the measurement system is disturbed by external light, you can enclose the surface to be measured to block the external light. At this time, pay special attention to whether the indication of the thermometer changes. If the indicated value does not change, it means that the external light has no effect on the measuring system. If it is affected, the measurement direction should be changed or a shading device should be installed.
Generally, the space distance necessary for measurement between the measured surface and the infrared thermometer is called the optical path. In the rolling production, the online thermometer is used to measure the surface temperature of the rolled piece. It is necessary to pay attention to the various effects of the harsh environment of the rolling production on the radiation infrared temperature measurement. For example, in order to cool the equipment or the rolled piece, there are often water films and oil films on the surface of the rolled piece, and their size, thickness and position are constantly changing, and there is water vapor with a constantly changing concentration in the optical path. In addition, there are a lot of dust and absorbing media such as carbon dioxide suspended in the air on site. Sometimes there are scale-like rust spots and dirt and other attachments on the surface of the rolled piece. In some special occasions (such as in a furnace), there may be a flame in the optical path. The flame not only absorbs radiant energy, but also emits a large amount of energy to the outside, which will bring great errors to the measurement, and even make the measurement difficult. Media such as water film, water vapor, carbon dioxide and sulfur dioxide have selective absorption of radiant energy, while dust has no selective absorption of radiant energy, but is often accompanied by scattering.
The above-mentioned various interferences on the surface to be measured and in the optical path will inevitably affect the radiation infrared temperature measurement and cause measurement errors. Therefore, in the actual temperature measurement, An analyzes the influence of various interferences on the measurement accuracy to obtain difficult-to-accurate temperature measurement data.
When choosing an infrared thermometer, the purpose of use must first be clarified. For example, the external temperature measuring instrument used for experimental research mainly focuses on its performance and measurement accuracy when selecting. When it is used in production, such as temperature monitoring, temperature control, etc., it should pay attention to the long-term stability of the instrument and the convenience of maintenance and operation on the basis of meeting the general requirements in performance.
In the production process of pressure processing, due to the different types of products (plates, profiles, pipes, etc.), the temperature measurement conditions are also different; it is necessary to analyze and eliminate various interferences according to the specific temperature measurement conditions, and select a suitable infrared temperature measurement instrument. Take a temperature measurement.
