What is measured
Track geometry describes the position of the two rails: gauge, cant, twist, alignment and top (longitudinal level), recorded continuously along the track together with distance and, on most systems, GPS position. These five parameters are the basis of every acceptance and maintenance decision on a line and the subject of EN 13848. KZV measures them in two ways. By contact: measuring wheels for gauge and twist, a measuring chord for alignment and top. Or with an inertial measurement unit (IMU) for alignment and top. The advantage of the IMU is that it has no alignment offset, which a contact chord always keeps to a small degree. Its limit is speed: on a hand-pushed trolley the drift of the gyro over a long, slow run spoils the long wavelengths (D2), so D2 from an IMU works mainly on towed and vehicle-mounted systems at 20 km/h and more. The two can be combined: in the hybrid MMD, gauge and twist come from contact, alignment and top from the IMU, and the chord stays as a check on the IMU. TURTLE can carry an IMU as well, and one can be fitted to a KRAB trolley. The evaluation against the limits of your network (local defects, section quality, quality indices) and the reports are made in KRAB 11.
Which system?
- Hand-pushed trolleys for inspection walks. KRAB U-LIGHT (22 kg, one person carries it off the track, geometry only), KRAB S-LIGHT (32 kg, gauges from 760 to 1676 mm, every add-on: rail profiles, LPS clearance scanning, switch inspection), T-TROLLEY (23 kg; gauge, cant, twist and distance; gauges from 600 to 1676 mm) and T-METIX, the same trolley with a laser for the position of objects around the track.
- Towed or vehicle-mounted for long campaigns. KRAB Heavy is towed behind a rail vehicle at up to 25 km/h, TURTLE at up to 30 km/h on railway and tram networks, and MMD is a measuring undercarriage built for your vehicle, measuring under load at about 40 km/h.
- Special track. VIPER for grooved tram rails, RWT for rubber-tyred metro and guided transit systems.
During the run the data is recorded with KrabDroid 3.0 on Android or Krab OnBoard on Windows, with the signals on screen in real time.
