# Performance Evaluation of Track Curvature Sensor for
## 3 On-Track Performance Evaluation of the Curvature Sensor  
A test run to evaluate the performance of the curvature sensor prototype while installed on the railway vehicle was conducted on a test track. As for the test vehicle, an urban electric railway train used to analyze the validity of the curvature measurement method in the previous section was used. Figure 14 shows the shape of the curvature sensor installed on the test vehicle. The test track is the same as the test track section used as the track model for simulation in the previous section. The running speed of the test vehicle was performed three times at the commercial operating speed, as in Case-1 (Test-1, Test-2, Test-3), and once at a speed that decreased by 50%, as in Case-2 (Test-4). Figure 15 is the curvature measurement result (Test-1-Test-3) measured three times under the Case-1 speed condition and compared with the track inspection data. Figure 16 is a graph comparing track inspection data as a result of curvature measurement (Test-4) tested under a speed condition (Case-2) that was reduced by 50% of the operating speed to analyze the performance of the curvature sensor according to running speed variation. Throughout the entire test section, all curvature measurement test results are shown to be consistent with track inspection data. The detailed analysis results of the six curves with a curve radius of 1000 m or less, i.e., a curvature of 1 or more, for the Case-1 running  
Figure 13: Functional test for curvature sensor. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Radius (m)**} & \multicolumn{2}{c}{**Curvature**} & \multirow{2}{*}{**Stroke (mm)**} & \multirow{2}{*}{**Test Result (m)**} & \multirow{2}{*}{**Error (\%)**} \\  & **(1/km)** & & & \\ \hline
75 & 13.33 & 96.6 & 74.92 & 0.10 \\
100 & 10.00 & 72.5 & 99.86 & 0.14 \\  
Among the curvature measurement results (Test-1-Test-3) and the trajectory measurement data under Case-1 speed conditions, the minimum was 0.8%, the maximum was 4.0% and the average was 2.8%. The deviation of the curvature measurement result (Test-4) measured under the Case-2 speed condition was 0.9 to 4.1%. This can be seen as a level almost similar to the deviation of the curvature measurement result under the Case-1 speed condition. This can be seen as a result consistent with the trend of the Case-2 analysis result of the curvature measurement simulation in the previous section. From this, it can be confirmed that the curvature measurement method has little effect on the running speed. Therefore, the track inspection data also include a measurement error of the track measurement system, so it is not an accurate curvature for the test section curve, but even considering this, the curvature measurement result of Table 4 is considered to be a relatively good result. In addition, examining the deviation according to the measurement curvature, as shown in Figure 18, the larger the curvature, the smaller the deviation tends to be. If a certain measurement error exists, it has a relatively large effect on a large radius curve with a small curvature compared to a small radius curve with a large curvature. This means that in the case of a curve with a large curvature, the larger the curvature, the larger the displacement of the curvature sensor, and the larger the ratio of the measured values to the measurement system error, so the effect of the error becomes relatively small. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Curvature (1/km)**} & \multicolumn{4}{c}{**Deviation (\%)**} \\
**Curve** & **Track** & **Test-1** & **Test-2** & **Test-3** & **Test-4** & **Test-1** & **Test-2** & **Test-3** & **Test-4** \\ \hline C1 & 1.33 & 1.29 & 1.37 & 1.39 & 1.39 & 3.2 & 3.0 & 4.0  
Figure 17: Curvature test result for each curve.