The hardware required for the HSRCA is simple: accelerometers mounted on the axleboxes and a computer. We have installed systems for test purposes in less than a day.
RailMeasurement’s HSRCA is designed for routine surveys of longitudinal irregularities on rails at typical line speeds. Irregularities include corrugation, welds, joints and acoustic roughness. The measurements produced are in a form that can be used directly for prioritisation and planning of maintenance such as grinding and weld straightening.
The HSRCA hardware is relatively simple: accelerometers on both axleboxes of a wheelset and a tachometer. The existing tachometer signal from a service vehicle is normally used. A self-contained system can run on an industry-standard laptop, and the equipment is sufficiently compact that it can be carried by two people. Temporary installation on a vehicle, such as might be undertaken for a short-term survey of a small network, can be completed in less than a day.
Our earliest installation of an axlebox-accelerometer system was for Australian National railways (AN) in the late 1980s. This system operated reliably for at least a decade to help programme rail grinding and weld straightening over the entire AN system. AN’s concerns were primarily long-wave corrugation and bad welds.
This shows a later installation of an HSRCA on a test train, in a project to find whether our system could be used for “noise monitoring” i.e. to show the sections of track where irregularities would give rise to high noise levels. The measurements of greatest interest here were accordingly of relatively short wavelength irregularities, essentially “acoustic roughness”. Repeatability and effects of speed were examined on different test sites, and a comparison was made of measurements from the HSRCA and from manual, datum instruments.
Although it is believed by some that the severity of corrugation can be found simply by double integration of the axlebox acceleration, this is not the case. However, the deficiencies of systems based on this incorrect assumption are not apparent unless they are “validated” by comparing measurements to those made using a more accurate instrument. The HSRCA supplied by RailMeasurement Ltd is not only based on a sound understanding of the underlying theory (which was indeed included in Dr Grassie’s PhD thesis), but is also a development of the original axlebox accelerometer system devised by Lewis and Richards of British Rail Research, with whom Dr Grassie had the pleasure of working. The HSRCA has a pedigree that is second to none. Validation is undertaken by measuring not only repeatability and reproducibility over a section of track, but also by assessing “accuracy” relative to a more accurate instrument. This is usually RailMeasurement’s CAT.
Measurements from different test sites (left at 747.13km, right at 799.3km), showing very good reproducibility of HSRCA measurements on both rails at both test sites at speeds of about 120-140km/h. Nascent corrugation is apparent at one site, residual grinding marks at the other, and periodicity from sleeper spacing at both sites.
HSRCA measurements from a system that was designed for a client whose main concern was relatively long wavelength corrugation, and where measurements had to be made at relatively low speed (<80km/h). There is very good reproducibility of measurements in forward and reverse directions and at speeds in the range 30-80km/h for both 300-1000mm and 1000-3000mm wavelength ranges.