## 4 Results of the Measurements and Analyses
### Interval Plots  
In further analyses, the distribution of the power dissipated in TR_A and TR_B transistors and the temperatures of their cases were investigated, taking into account the arrangement and position of the transistors in the tested PCB modules. It was also checked whether the transistor models significantly differ in the value of the R\({}_{\text{th}}\) parameter under similar control conditions. The Interval Plot presented in Figure 6a was performed in the Minitab program, which shows the changes in the power dissipated in both transistors. It can be concluded from this figure that when we compare the changes in the emitted power for the tested transistors, they are statistically different. The average values of this power for the TR_A transistor are P\({}_{\text{gr}}\) = 21.7 W, and for TR_B, P\({}_{\text{gr}}\) = 22.7 W. In practice, the changes in this power are very small, of the order of 2 W, which is about 10% in relation to the average value. Comparing the value of the power dissipated for the same type of transistors, it can be seen that the difference in the range of power changes is even smaller. For example, for the TR_B transistors, the average value of this power differed by only 0.3 W. However, the full range of changes is within the range \(\Delta\)P = 1 W, which is only a 2.5% change in the value of this power in relation to its average value. Therefore, it can be assumed that the power dissipated on both transistors was similar, and that its possible fluctuations should not significantly affect the differences in the values of their thermal parameters and the temperature on the transistors' cases. In order to verify this assumption, the temperature distribution measured on individual transistors was also examined using the Interval Plot (Figure 6b). Although the value of the power dissipated on both types of transistors was similar, the temperature values on their cases for positions TR_A1, TR_A3 and TR_B2 also converged, and the average temperature value was at the level of T\({}_{\rm av}\) = 80 \({}^{\circ}\)C, in one case, it was noticed that one of the transistors, described as TR_B4, heats up more than the others. The extreme transistor type BLC9G22 LS-160 VT reached temperature values from 8 \({}^{\circ}\)C to even 16 \({}^{\circ}\)C higher than the others. The average temperature on the case of this transistor was T\({}_{\rm av}\) = 87 \({}^{\circ}\)C. This situation occurred for each of the tested electronic modules. It is probable that the smaller mass area on the heat dissipation PCB causes a higher temperature for this extreme device. From the results of the analyses presented in (Figure 6b), it was also noticed that the fluctuations of the measured temperatures for the extreme position of the TR_B transistor were significantly smaller compared with the other tested transistors in positions 1, 2 and 3. For the TR_B4 transistor, small power changes on the order of \(\Delta\)P = 1 W (Figure 6a) resulted in slight changes in temperature \(\Delta\)T = 30 \({}^{\circ}\)C. This is only a 2% change in relation to the average value of the temperature released by the case of this transistor. However, the largest range of changes in this temperature could be observed for both the TR_A type transistors, where, with power changes of only \(\Delta\)P = 1.5 W, temperature changes in the range of \(\Delta\)T = 15 \({}^{\circ}\)C were obtained. This is about a 15% change in the temperature value from its average value. Continuing the considerations, on the basis of the performed temperature measurements and with specific actuation of the transistors, their thermal resistance R\({}_{\rm th}\) was determined [27]. The distribution of the obtained results was illustrated using the Box Plot functions in the Minitab program. The distributions of the thermal resistance R\({}_{\rm th}\) for the individual transistors placed in all four positions, with P = 21.5 W \(\pm\) 10%, are shown in Figure 7a.