The fever screening system is composed of an IR ( thermal) camera, CPU and AI fever detection software and a black body. IR camera is composed of two cameras, one is the IR camera, which is used for measuring the temperature; the other is a visible light camera, which is used for taking the picture and face recognization.
The IR camera can collect the IR magnetic wave from the human body and display it by way of the thermal colors. For the reason that the carbon dioxide will absorb part of the IR magnetic wave when it is traveling in the air, so finally the IR magnetic wave will become damping, the measured temperature by IR camera will not be accurate enough. That is why the accuracy of IR camera for thermal applications such as fever screening for COVID19 itself is easily to be interfered by the environment. The black body can work as the infrared temperature calibrator and it can absorb all the electromagnetic radiation and no reflection of them (emissivity=1), thus it can be used for the calibration on the IR camera. This is done by comparing the preset temperature on the black body with the temperature measured by the IR camera, the environment inference on the IR camera can be lowered and the accuracy of the IR camera will be improved. This is crucial because with the use of the black body in human fever detection, the temperature reading will not be accurate thus defeat the whole purpose of deploying such an expensive system.
The larger the thermal capacity of the black body is, the effective radiation is bigger, then the temperature will be more easily to be stable in a different environment and thus the thermal balance can be kept. The other fact is that the temperature from the IR camera will be the skin temperature which is close to the body temperature, but not the body temperature as shown difference in the table below:
This is the second tolerance in the actual measurement of temperature, which needs to be calibrated, too. This calibration can be realized by the software automatically; The details will be instructed below. The visible light camera is built-in for the purpose to distinguish the target in the field of view to be human or not, for the reason that the animals or other objects will have the temperature.