Lack of Thermogram Sharpness as Component of Thermographic Temperature Measurement Uncertainty Budget

Abstract

The number of components of a thermographic temperature measurement uncertainty budget and their ultimate contribution depend on the conditions in which the measurement is performed. The acquired data determine the accuracy with which the uncertainty component is estimated. Unfortunately, when some factors have to be taken into account, it is difficult to determine the value of the uncertainty component caused by the occurrence of this factor. In the case of a thermographic temperature measurement, such a factor is the lack of sharpness of the registered thermogram. This problem intensifies when an additional macro lens must be used. Therefore, it is decided to commence research to prepare an uncertainty budget of thermographic measurement with an additional macro lens based on the B method described in EA-4/02 (European Accreditation publications). As a result, the contribution of factors in the uncertainty budget of thermographic measurement with additional macro lens and the value of expanded uncertainty were obtained.

The Solution for the Thermographic Measurement of the Temperature of a Small Object

“…As a result of correctness tests run for the reading of distance d, the dependence of δ = f(d) was plotted (Figure 8). In order to determine the influence of the sharpness of the recorded thermogram on the thermographic error, the measure of sharpness based on the change of derivatives in both directions (vertical and horizontal), EOG (Energy of Gradient), was used [17,19]. The results obtained with the mathematical measure of sharpness were normalized.…”

“…Consequently, due to the lower power of IR radiation absorbed by the array of IR detectors, the amplitude value of the output detector signal is lower [14][15][16][17]. In the case of microscopic thermography, due to the small values of d, the values of τ a and ω have little influence on the indication of the thermographic camera [19]. The value of d is important in microscopic thermography, because due to the shallow depth of field of the lenses used, even a slight change in d (in the order of a tenth of a millimeter) changes the sharpness of the recorded thermogram [18].…”

“…In order to correctly assess temperature distribution on the housing of electronic components, it is necessary to take into account all factors that can influence the measurement [ 6 , 7 , 8 ]. The most important of them include the value of the emissivity coefficient ε [ 9 ], the reflected temperature ϑ r [ 10 ], the distance between the lens and the observed object d [ 11 ], the ambient temperature ϑ a [ 12 ], the temperature of the external optical system [ 13 ], the transmittance of the external optical system [ 14 , 15 ], the relative humidity ω [ 16 ], the viewing angle β [ 7 ], and the sharpness of the recorded thermogram [ 17 , 18 , 19 ]. An assessment of the influence of the abovementioned factors on the accuracy of the thermographic temperature measurement of small-sized electronic components is possible thanks to the use of a microscopic thermography stand.…”

“…An assessment of the influence of the abovementioned factors on the accuracy of the thermographic temperature measurement of small-sized electronic components is possible thanks to the use of a microscopic thermography stand. Depending on the conditions in which the measurement is performed, the influence of individual factors on the result of the thermographic temperature measurement will differ [ 19 ]. Some parameters will have a greater effect when the value of d is large (kilometers) and other will have a greater impact in microscopic thermography ( d measured in millimeters).…”

“…As a result of the conducted research, it has been confirmed that in the case of thermograms classified as sharp, the error value of the temperature measurement is lower than in the case of thermograms classified as out-of-focus. Taking into account the unsharpness of the thermogram increases the reliability of diagnosing potential damage to electronic devices caused by the temperature increase in electronic components [ 17 , 19 ].…”