Measuring infrared temperature with infrared thermometer

1, types of infrared temperature measuring instruments

There are three main types of infrared thermometers: infrared thermal imager, infrared thermal imager and infrared thermometer (point thermometer). In the 1960s, China successfully developed the first infrared thermometer, and since the early 1980s, it has successively produced small target and long-distance thermometers suitable for the production characteristics of the power industry, such as Xiguang IRT- 1200d, HCW-Ⅲ, HCW-ⅴ, etc. YHCW-9400 model; WHD40 15 (double aiming, target D 40mm, farthest 15 m) and WFHX330 (optical aiming, target D 50 mm, farthest 30 m). PM-20, 30, 40, 50, HAS-20 1 American thermometer; TPT20, 30, 40 and 50 of AGA company in Sweden are also widely used. DL-500e can be applied to 1 10 ~ 500 kV substation equipment with clear image and accurate temperature. The infrared thermal imager mainly includes TVS-2000, TVs- 100 in Japan, PM-250 in the United States and AGA-TVs-100,550,570 in Sweden. The domestic infrared thermal imager was successfully developed in Kunming, realizing localization.

2. The working principle of infrared thermometer

Understanding the working principle, technical indicators, environmental working conditions and operation and maintenance of infrared thermometer is the basis for users to correctly select and use infrared thermometer. The optical system collects the infrared radiation energy of the target in its field of view, and the size of the field of view is determined by the positions of the optical components and the thermometer. Infrared energy is focused on the photodetector and converted into corresponding electrical signals. The signal is corrected by the amplifier and signal processing circuit according to the algorithm inside the instrument and the target emissivity, and then converted into the temperature value of the measured target. In addition, the environmental conditions of the target and thermometer, such as temperature, atmosphere, pollution and interference, should be considered and the correction methods should be considered.

All objects whose temperature is higher than absolute zero are constantly emitting infrared radiation energy into the surrounding space. The magnitude and wavelength distribution of infrared radiation energy of an object are closely related to its surface temperature. Therefore, by measuring the infrared energy radiated by the object itself, its surface temperature can be accurately measured, which is the objective basis of infrared radiation temperature measurement.

Law of blackbody radiation: blackbody is an idealized radiator, which absorbs all wavelengths of radiation energy without energy reflection and transmission, and its surface emissivity is 1. It should be pointed out that there is no real blackbody in nature, but in order to understand and obtain the distribution law of infrared radiation, we must choose a suitable model in theoretical research, which is Planck's quantized oscillator model of body cavity radiation, and thus derive Planck's law of blackbody radiation, that is, blackbody spectral radiance expressed by wavelength, which is the starting point of all infrared radiation theories, so it is called blackbody radiation law.

Influence of object emissivity on radiation temperature measurement: Almost all the actual objects in nature are not blackbody. The radiation amount of all practical objects depends not only on the radiation wavelength and the temperature of the object, but also on the material type, preparation method, thermal process, surface condition and environmental conditions. Therefore, in order to apply the law of blackbody radiation to all practical objects, it is necessary to introduce a proportional coefficient related to material properties and surface state, that is, emissivity. This coefficient indicates the closeness between the thermal radiation of the actual object and the blackbody radiation, and its value is between zero and less than 1. According to the radiation law, as long as the emissivity of the material is known, the infrared radiation characteristics of any object are known.

The main factors affecting emissivity are: material type, surface roughness, physical and chemical structure and material thickness.

When measuring the temperature of a target with an infrared radiation thermometer, it is necessary to measure the infrared radiation of the target within its wavelength range first, and then calculate the temperature of the target with the thermometer. Monochrome thermometer is proportional to the radiation in the band; The two-color thermometer is directly proportional to the radiation ratio of the two bands.

Infrared system: The infrared thermometer consists of optical system, photodetector, signal amplifier, signal processing, display and output. The optical system concentrates the infrared radiation energy of the target in its field of view, and the size of the field of view is determined by the optical components of the thermometer and its position. Infrared energy is focused on the photodetector and converted into corresponding electrical signals. The signal is corrected by the amplifier and signal processing circuit according to the internal processing of the instrument and the algorithm of target emissivity, and then converted into the temperature value of the measured target.