MSRCA
MSRCA on a Hi-Rail Vehicle
Hi-rail vehicles are used for track inspection on many railway systems, particularly on freight lines in North America, Australia and elsewhere, where a vehicle that runs on both road and track is vital for access in remote locations. RailMeasurement Ltd have produced a corrugation measuring system for one such hi-rail vehicle that is also fitted with a transverse profile measuring system and video cameras to detect railhead defects. The requirement was to measure corrugation over the wavelength range 30-1500mm at speeds of up to 50km/h and with sufficient accuracy to demonstrate reliably that residual corrugation at short wavelengths was within the extremely demanding requirements of the European Standard for reprofiling, EN13231-3:2006. Measurements from this vehicle are used to produce the grinding programme for a large railway system and to assess whether grinding has been undertaken to specification. The MSRCA comprises a measuring head for each rail, signal conditioning electronics, and an industry-standard laptop loaded with application software to perform the measurements and provide the data analysis.
Validation
The MSRCA has been validated by assessing the effects of speed and direction of travel on measurements, and also by comparing CAT measurements (made at walking speed) with MSRCA measurements made at its operating speed of up to 50km/h. Examples of reproducibility at 20km/h and 50m/h of the unfiltered irregularities measured with the MSRCA over 50m of track and of irregularities in the 30-100mm wavelength range measured over 500m of the same site are shown below. A comparison of CAT and MSRCA measurements over a different 500m test section with severe discrete irregularities is also shown. Correlation of MSRCA and CAT measurements is extremely good considering not only the condition of the test site but also that the MSRCA is measuring at 50km/h.
Correlation of MSRCA measurements of unfiltered displacement over 50m of track at 20km/h and 50km/h
Correlation of MSRCA measurements of moving average of RMS amplitude of irregularities, 30-100mm wavelength range, over 500m of track at 20km/h and 50km/h
Correlation of CAT measurements of left and right rails (red) and MSRCA measurements at 50km/h (green) over a 500m site with severe discrete irregularities
Use of MSRCA for approval of reprofiling work
The MSRCA is used not only to help plan grinding but also to assess whether grinding has been undertaken satisfactorily. An example of measurements from 400m of track after grinding is shown below. The finish on the left rail is clearly better than that on the right rail. Both rails are finished to well within the requirements of EN13231-3:2011 and this can be demonstrated by measurements taken at tens of km/h with the MSRCA.
MSRCA measurements of ground rail, filtered displacement in 30-100mm wavelength range over 400m. Both rails are finished to the requirements of EN13231-3:2011 (<10% exceedence of +/-0.010mm) but residual corrugation on the right rail is greater and there are irregularities at many of the welds.
Use of MSRCA for approval of reprofiling work
Measurement of long wavelength irregularities relevant to ground-borne noise and vibration
Long wave irregularities excite low frequency vibration that is experienced by those adjacent to the railway as ground-borne noise and vibration. Measurements made with the CAT have been used to obtain good correlation not only between predicted and measured levels of ground-borne vibration[1] but also between the measured reduction in ground-borne noise at several locations on an underground railway and the corresponding reduction in long wave irregularities following grinding. Although the MSRCA has not yet been used for this application, we believe that its excellent performance at long wavelengths would make it a better instrument for routine use and possibly also a more accurate instrument than the CAT for measuring the long wavelength irregularities that excite ground-borne noise and vibration.
Further information on the accuracy and repeatability of our corrugation measurement products is given here, whilst a comparison of our product specifications and use is available here.
[1] Triepaischajonsak N, Thompson DJ, Jones CJC, Ryue J and Priest JA, “Ground vibration from trains: experimental parameter characterization and validation of a numerical model”, Jnl of Rail and Rapid Transit, Procs of ImechE, 225F, 140-153.