## 2 Proposed Methodology
### Database  
In the database stage, the acquisition of several thermographic images is performed with the aim of generating a real experimental database. Thus, for this work, images were obtained from an experimental test bench based on an electromechanical system (Figure 2). The components are as follows: a 1.5 kW WEG induction motor mechanically coupled by means of rigid coupling to a BALDOR 4:1 gearbox; the latter is, in turn, connected by means of another rigid coupling to a BALDOR direct current generator. This generator produces approximately 20% of the rated load of the induction motor under working conditions. The tests were carried out for a period of eighty minutes. This is the estimated time for the motor to reach a steady state. The operating frequency of the motor was 50 Hz. Thermographic images were taken every minute for the duration of the test; at the end, 80 thermographic images were taken for each test. Thermal images were acquired using the grayscale color palette. A FLIR GF320 thermographic camera with a resolution of 320 \(\times\) 240 pixels and a thermal sensitivity of \(<\)15 mK at 30 \({}^{\circ}\)C was used for thermal imaging. The camera operates in the spectral range of 3.2-3.4 \(\mu\)m. In addition, a Fluke 975 air quality meter was used to measure the environmental conditions in the test room. The emissivity used was 0.95 [6].  
The experimental matrix is shown in Table 1. The gears of the gearbox were operated in three conditions with no tooth wear (healthy), with 50% wear, and with 75% wear. In the  
Figure 1: The proposed non-invasive methodology for the detection of multiple failures in electromechanical systems.  
Figure 2: Experimental test bench—electromechanical system.  
case of the induction motor, it was worked under four conditions: in a healthy state, with a broken bar, with misalignment, and with an outer bearing.  
Images of the mechanical elements used in this work are shown in Figure 3. Figure 3a-c show the gears used in the gearbox in a healthy condition with 50% and 75% wear, respectively. The mechanical failures induced in the induction motor are shown in Figure 3d-f, which are a broken bar, outer bearing, and misalignment, respectively. The wear areas of the gear teeth are machined with a tungsten cutter, and then a lapping process is performed. For bearing damage, a 1.5 mm hole was drilled in the outer bearing race. For one broken bar, the rotor was drilled 8 mm deep. Finally, for misalignment, the free end of the induction motor was displaced by 5 mm in the horizontal plane.  
For each tested condition, the thermographic images are continuously acquired every 30 s for 35 min; thus, a total of 80 thermographic images were obtained for each test in the thermal steady regime. It is important to note that only 50 images were used for this work. The first 15 min were discarded because there were no significant temperature changes during this time; similarly, the last 15 min were discarded because the steady state of the operation had already been reached and, therefore, there were no significant temperature differences [14]. As a result, considering all classes, a total of 600 thermographic images were obtained. The resolution of each image was 320 \(\times\) 240 pixels.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Class** & **Wear of the gearbox Gears** & **Induction Motor Condition** \\ \hline
1 & & Healthy (HLT) \\
2 & Healthy & Outer Bearing (OB) \\
3 & & One Broken Bar (BB) \\
4 & & Misalignment (MAL) \\ \hline
5 & & Healthy (HLT-GB50) \\
6 & 50\% of wear & Outer Bearing (OB-GB50) \\
7 & & One Broken Bar (BB-GB50) \\
8 & & Misalignment (MAL-GB50) \\ \hline
9 & & Healthy (HLT-GB75) \\
10 & 75\% of wear & Outer Bearing (OB-GB75) \\
11 & & One Broken Bar (BB-GB75) \\
12 & & Misalignment (MALGB75) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Matrix of experiments.  
Figure 3: Mechanical elements. (**a**) Healthy gear; (**b**) gear with 50% wear; (**c**) gear with 75% wear; (**d**) one broken bar; (**e**) outer bearing; and (**f**) misalignment.