Definition
NIR thermal imager is a detection instrument based on the near-infrared band, which usually refers to the wavelength range of about 0.78 to 2.5 microns, for non-contact temperature distribution imaging. It enables indirect analysis of the target temperature field or the composition of a specific substance by capturing the near-infrared energy radiated or reflected from the object's surface and converting it into a visualized image of the heat distribution. This technology is widely used in industrial process monitoring, agricultural evaluation, material research, and security, making it an efficient non-destructive testing tool.
Principle
The working principle of NIR is mainly based on Planck's law of blackbody radiation and Stephen Boltzmann's law. All objects above absolute zero emit electromagnetic waves, and their radiation intensity and wavelength distribution depend on the temperature and emissivity of the object's surface. In the near-infrared band, there is a specific function relationship between the energy radiated by an object and the temperature, and the instrument collects the near-infrared energy radiated by the target through the optical system and converts it into an electrical signal using an infrared detector. After signal processing and algorithm correction, a pseudo-color image is finally generated that reflects temperature differences or material properties. For reflection measurements, the instrument also needs to combine a specific wavelength of light source to analyze the absorption and reflection characteristics of the substance to near-infrared light, which is often used for component identification.
The relationship between radiant energy and temperature can be expressed as:M = εσT4, among themMis the degree of radiation,εis the emissivity,σis the Stephen-Boltzmann constant,TAbsolute temperature.
Measurement method
The measurement methods of near-infrared thermal imagers can be divided into two categories: passive and active. Passive measurement directly detects the near-infrared energy radiated by an object itself, and is suitable for temperature distribution monitoring, such as equipment overheating detection. Active measurement requires an external near-infrared light source to illuminate the target and identify the composition of substances by analyzing reflection or transmission spectra, such as the analysis of moisture content of agricultural products. The measurement process typically includes instrument calibration, environmental parameter setting, image acquisition, and data processing steps. Calibration requires the use of standard blackbody sources to reduce system errors; environmental parameters such as ambient temperature, humidity and measurement distance need to be recorded and calculated; Data processing needs to be compensated according to factors such as emissivity and atmospheric transmittance to improve measurement accuracy.
Influencing factors
The measurement results of NIR thermal cameras are influenced by a variety of factors. The target surface emissivity is a key parameter, and the emissivity of different materials and surface states varies greatly, so it needs to be accurately set or measured. Environmental conditions such as ambient temperature, air humidity, and atmospheric water vapor and carbon dioxide absorb some of the near-infrared radiation, affecting energy transmission. The measurement distance and viewing angle change the radiation flux received by the instrument and must be operated within the effective field of view. Interference from external light sources, such as solar radiation or near-infrared components in artificial lighting, can affect passive measurements. In addition, the noise equivalent temperature difference, spatial resolution, and spectral response range of the instrument will also determine its applicable scenarios and data quality.
Application:
In the industrial field, near-infrared thermal imaging cameras are commonly used for thermal fault diagnosis of electrical equipment, temperature monitoring during welding processes, and internal defect detection of composite materials. In agriculture, it can be used for crop water stress assessment, fruit ripeness discrimination and soil composition analysis. In the field of scientific research, it plays a role in the study of thermal properties of materials and the monitoring of chemical reaction processes. In security and search and rescue, it can be used for night surveillance or life detection. In the energy industry, it is used for solar panel hot spot detection or building thermal performance evaluation. These applications are based on their non-contact, rapid imaging, and quantitative analysis.
Selection
When choosing a near-infrared thermal imager, it is necessary to comprehensively consider the technical parameters and application requirements. The type of detector and the material affect the spectral response range, such as indium, gallium, and arsenic detectors, which are suitable for shortwave near-infrared. Spatial resolution determines image detail and needs to match the target size to the measurement distance. The temperature measurement range and accuracy should cover the intended application scenarios. Frame rate is important for dynamic process monitoring. The focal length of the optical lens determines the size of the field of view, and interchangeable lenses increase flexibility. Data interfaces and software functions need to be compatible with existing analytical processes. In addition, environmental adaptability such as protection level and operating temperature range are of concern in the field or in harsh industrial environments. It is recommended to conduct a comprehensive evaluation according to the specific measurement object, accuracy requirements and operating conditions.