# Indirect Assessment of Railway Infrastructure Anomalies Based on Passenger Comfort Criteria
## 4 Indirect Method for Infrastructure Condition Assessment Based on Comfort Criteria
### Condition-Based Maintenance Identification Methodology
#### 4.2.1 Data Acquisition System  
The data acquisition system comprises one 3-axial accelerometer and a GPS measurement; both components log data to a uSD card. Sensors were mounted on board multiple trains. Their location inside the rail train was defined based on points corresponding to the train's beginning, middle, and end. Moreover, each of these locations was defined as to the rear of the respective bogie.  
\begin{table}
\begin{tabular}{c c c c} \hline  & **X-Axis** & **Y-Axis** & **Z-Axis** \\ \hline Floor & W\({}_{\text{k}}\) and k\({}_{\text{x}}\) = 0.25 & W\({}_{\text{k}}\) and k\({}_{\text{y}}\) = 0.25 & W\({}_{\text{k}}\) and k\({}_{\text{z}}\) = 0.40 \\ Seat surface & W\({}_{\text{d}}\) and k\({}_{\text{x}}\) = 1.0 & W\({}_{\text{d}}\) and k\({}_{\text{y}}\) = 1.0 & W\({}_{\text{k}}\) and k\({}_{\text{z}}\) = 1.0 \\ Seatback & W\({}_{\text{c}}\) and k\({}_{\text{x}}\) = 0.80 & W\({}_{\text{d}}\) and k\({}_{\text{y}}\) = 0.50 & W\({}_{\text{d}}\) and k\({}_{\text{z}}\) = 0.40 \\ \hline \end{tabular}
\end{table}
Table 2: Frequency weighting curves and multiplying factors defined by ISO 2631 for comfort analysis of a seated passenger.  
\begin{table}
\begin{tabular}{c c} \hline \(a_{v}\)(m/s\({}^{2}\)) & **Ride Comfort** \\ \hline \(\leq\)0.315 & Not uncomfortable \\
0.5–0.63 & A little uncomfortable \\
0.63–0.8 & A little uncomfortable to fairly uncomfortable \\
0.8–1.0 & Fairly uncomfortable to uncomfortable \\
1.0–1.25 & Uncomfortable \\
1.25–1.6 & Uncomfortable to very uncomfortable \\
1.6–2.0 & Very uncomfortable \\
2.0–2.5 & Very uncomfortable to extremely uncomfortable \\ \(\geq\)2.5 & Extremely uncomfortable \\ \hline \end{tabular}
\end{table}
Table 3: ISO 2631 comfort evaluation scale. Adapted from [47].  
Floor vibration measurements were conducted by the 3-axial accelerometer (PCE-VDL-24I, PCE Instruments, Southampton, UK), with a measurement range of \(\pm\)16 g, resolution of 0.004 g, and sampling rate between 0 and 2400 Hz, which permits data recording and follows ISO 2631 requirements [54]. As discussed, the standard defines the frequency range between 0.5 and 80 Hz as the most relevant for comfort evaluation. Thus, a sample rate of 200 Hz was set, respecting the Nyquist theorem and preventing aliasing.  
The GPS geographic location was obtained from a system composed of a GPS logger [55] connected with a RedBoard Quiic [56]; it was programmed to retrieve data concerning location and rail vehicle speed and record them on a \(\mu\)SD card at 1 Hz. For future data processing analysis, it is fundamental to synchronise data; thus, vibration and geographic measurements were obtained synchronously. Figure 6 shows the data acquisition system, including the vibration measurement and GPS units.  
As discussed, experiments were run on multiple AP and IC trains, which have different structural designs. Figure 7 illustrates both types of trains.  
Figure 6: Data acquisition system: (**a**) 3-axial accelerometer pad; (**b**) GPS system.  
Figure 7: _Cont._