RAILPROF - BACKGROUND & WELD GEOMETRY STANDARDS
Gradient rather than versine.
From the right-hand graphs it is
obvious that the contact force
does not correlate (9 %) with
the versine (geometry),
whereas the inclination (QI)
very well correlates (91 %) with
the force. This means, amongst
others, that a steel
straightedge, as still in use on a
wide scale, is absolutely
Quality Index (QI) on Smartphone screen.
Blue line represents the vertical geometry, orange line is QI. The person doing the finish grinding can immediately see where the QI is exceeding the norm (by definition QI = 1) - in this case 6 % - and which spots should be ground. In the figure it is clearly seen that the slope right of the middle is too large and so the center part should be ground to decrease the inclination and thus the maximum QI.
The vertical wheel rail contact force is approximately proportional to the square of the speed. In this way the standards are speed dependent.
Furthermore the contact force is linearly related to the inclination (first derivative dy/dx of the geometry). The inclination is determined from the versines measured with the RAILPROF on a base of 1 m, sampled at an interval of 5 mm. During data processing the samples are averaged (low-pass filtered) via a moving window of 5 samples. This means that the shortest wavelength in the resulting signal is 25 mm. The calculated QI values are based on this signal. See PDA screen below.
According to recent ProRail figures the claimed track maintenance cost reductions of 10 - 20 % are too conservative. Present practice reveals that these figures are more in the order of 20 - 40 %!
With the RAILPROF device the vertical and lateral rail geometry is measured. The measurement is controlled by a smartphone (Windows Phone), which communicates with the RAILPROF via Bluetooth. The measurement data are transferred automatically to the smartphone, which calculates the QI (Quality Index), a measure for the vertical force, directly related to the first derivative of the recorded vertical rail geometry. The admissible QI in relation to the line speed is presented in the table above, which values are presently the official standards used by ProRail in The Netherlands and the tram and metro companies in Holland.