The RCA was originally designed and developed for use with reprofiling trains. However, it became clear that this was a sufficiently accurate instrument to give a reliable method of measuring irregularities, even the tiny irregularities that are significant for acoustics purposes. Tests have demonstrated that the RCA measures these irregularities over the vast majority of the narrow wavelength ranges included in acoustics standards EN15610 and EN ISO 3095. Indeed it measures irregularities of several metres wavelength reliably. The equipment therefore offers a means of measuring irregularities that are responsible for ground-borne noise and vibration. It may well be the only equipment that is available for this purpose with which measurements can reliably be undertaken over such a wide wavelength range. The RCA appears to be measure long waves (greater than 1m) more reliably than the CAT.
RCA and CAT measurements of two rails superposed for a 500m test site, showing irregularities in 10-30mm, 30-100mm and 100-300mm wavelength ranges plus one-third octave spectra. The one-third octave spectra are shown here up to 1m wavelength. Repeatability measurements for the RCA indicate that this produces reliable measurements up to at least 3m wavelength.
A presentation from the 11th International Workshop on Railway Noise (IWRN11) can be downloaded that is particularly relevant to measurement of long-wave irregularities. This presents measurements from both RCA and CAT and compares the repeatability of these two instruments.
Consecutive RCA measurements over 500m of track showing RMS moving averages in the 30-100mm and 100-300mm wavelength ranges. The discrete irregularities can be seen clearly. Many of the places where these are opposite one another and also uniformly spaced e.g. at 427.5-427.6km are bad welds or joints on short rail. Most of the defects at 427.8-428.0km are so-called “studs” or “squats”. The RCA software tabulates the discrete irregularities. Repeatability of the two sets of measurements is excellent on both rails and in both wavelength ranges.