The Knowledge of thermal imaging temperature camera (part 1)
Thermal imaging temperature camera
If the signal obtained from the thermal imaging camera has a linear relationship with the temperature of the object, then our article can be very simple. The temperature camera of products on the market will also be very accurate, but the reality is often much more complicated.
The raw data read from the detector can only qualitatively describe the heat radiation distribution in the scene, but to convert it to temperature, a quantitative process is required.
Calibration (also called calibration, or directly called Calibration will be more accurate) can be understood as reverse engineering. In a laboratory environment, blackbody radiation theory is used, a blackbody is used as a reference source, and thermal imaging systems are used to collect data at different temperatures. Radiation data, and then fit the relationship curve between radiation data and temperature based on the radiation data and the real temperature of the black body.
In the actual temperature camera application, the absolute temperature of the target can be calculated according to the calibration curve and the gray value of the collected target to achieve temperature camera.
During the calibration production process, companies with more money can allocate more black bodies, which can reduce the error of the black body, and the calibration data obtained will be more accurate. Second, the production speed will be faster (anxiously waiting for the black body to heat up and stabilize is also A kind of suffering). The process of fitting the curve does not need to be too complicated, and the temperature sampling is more dense, and each segment can be approximated to linearity.
2. Non-uniformity calibration
The above calibration process can be understood as establishing the relationship between the response of a point of the detector and the temperature. Affected by the process, the response characteristics of each point on the area array detector are not consistent. How do we determine the mapping relationship of each point? Obviously, it is not appropriate to calibrate each point once. At the same time, for different lenses, the transmittance of the central area and the edge area are different (the transmittance of the central area will be much higher than that of the edges).
At this time, the engineer began to exert his strength again. As you can see, thermal imaging equipment is usually equipped with a baffle. The function of this baffle is called "leveling" as the saying goes.
The baffle is made of materials with high emissivity and uniform heat conduction. When the baffle covers the detector, the detector receives the heat radiation of the baffle, and the output at each point should be the same temperature. Through the baffle, we can establish a mapping relationship of the area array. This mapping relationship will be affected by the surface temperature of the detector. Therefore, when the detector is first turned on, the temperature changes greatly and the leveling process will be more frequent. After the stable operation, the leveling will be less.
Through the above two steps, we can basically establish the relationship between the response of each point on the detector and the temperature.
The Knowledge of thermal imaging temperature camera (part 1) - Safeagle