Читать книгу Electronics in Advanced Research Industries - Alessandro Massaro - Страница 27

The processes controlling the temperature represent many times a fundamental element to guarantee an optimal quality of the worked piece. The temperature check is performed directly on the processed piece or is related to the working environment as for a temperature‐controlled room. Excessive rise in temperature may generate thermal damage in the processed materials. Specifically, monitoring the tool's temperature range is of fundamental importance. A function of IRT is to check during the time the correct processing as for cutting, welding, or surface treatments. The basic physical principles of an IR thermal camera in monitoring processes are indicated in Figure 1.10 (a), indicating all the signals involved for a radiometric measurement which are:

(1.3)

(1.4)

(1.5)

(1.6)

(1.7)

where C + D + E is the total radiated power, σ is the Stefan–Boltzmann constant, ε_Target is the emissivity of the object to detect (target), τ_a is the environment transmittance, T_Target is the temperature of the object, and T_a is the environment temperature.

Figure 1.10 (a) Infrared thermal camera signals. (b) AOV and FOV simplified definitions.

The timing of the measurement acquisition and the movement control of the thermal camera are two relevant factors for object temperature checking. Concerning camera systems, the angle of view (AOV) and the field of view (FOV) in degrees are, respectively, expressed in Figure 1.10b as:

(1.8)

(1.9)

The AOV is a measurement (in degrees) of how much of an object is viewed through the lens, and is measured horizontally, vertically, or diagonally. The FOV is a measurement of object distance and it requires the knowledge of the distance from the optical center of the lens to the object to detect. In a 3D space the FOV is defined horizontally, vertically, and diagonally.