Super Low Weight MeasuringTrolley for Track Geometry

KRAB Slight

The KRAB Slight system is the latest step of Krab evolution. It was designed with focus on low weight and easy operation.]The measurement speed is limited to approx. 15kph. The trolley weights app. 30kg, only one operator is capable to take it away from the track. On-board computer has enough memory for at least 2000km; its battery works 8 hours without charging. The trolley has versatile adjustable nominal gauge in wide range as an option (for example 760–1676mm).


The trolley has to be provided by two special shoulders bearing isolated rollers. These shoulders are applicable to existing trolley as an additional part. The rollers can be lift up to transporting position and activate to measuring position very easily.

Basic Technical Data:

  • Mass of shoulders: +4 kg
  • Accuracy: better then 1 mm for all switch values
  • The rollers measure:
  • width of open tongues
  • groove of the guard rail
  • groove of the wing rail and frog
  • backgauge
Measuring Software

Extra part of measuring program Krab8vNET supports the data collecting at discrete switch location in the form of special events. Each such event contains the name of the station, switch nr. measured values and values coming from visual inspection.

Analysis software SWITCH™

This advanced software tool automatically couples the main and turnout branches of the switches, parses the events and builds Switch Inspection Report.


The trolley’s central body is made of a square profile, which increases stiffness and robustness of the system.
The electrically insulated wheels are provided by flanges.
Permanent contact of the wheel flanges and running rail edge is provided by springs.
A special apparatus having two degrees of the freedom in translation is at the central part of the longitudinal chord.
It scans vertical and lateral rail versine.
The trolley can be run by its own electric motor.
The wheel surface treatment is executed in hard chromium.
The trolley surface finish is yellow powder paint.
The arresting mechanism is controlled by rope & bowden and two levers on pushing rod when the trolley passes through the frog.


During the measuring run the following so called primary track values are scanned in space interval of 0.25 m:

  • gauge (potentiometer transducer on the left wheel)
  • alignment (lateral versine) of the right rail
  • top (vertical versine) of the right rail
  • cant (new, high reliable and precise inclinometer)
  • quasi-twist on the twist base 0.9 m (option; it increases the precision of the final cant measuring)
  • track gradient (option)
  • track distance (odometer-optical encoder)
  • measuring speed

The real time processing of signals from the sensors is performed by the on-board rugged PDA computer TDS Nomad, whereby the following items are warranted:

reading and scanning of signals given above
on-line processing of the signals:
smoothing of long wave part
optical signaling when the geometry data exceed the selectable thresholds
display of numerical values of the geometry data
entry of the geometry data into non-erasable storage of on-board computer at the distance 0.25 m. The measuring distance is limited by computer memory, typically 2000 km.
entry of the informational description of the track section to be measured
entry so called events (mud spots in ballast, damaged sleepers etc.) with exact position along the distance



After the measuring, the collected raw geometry data are transferred from the on-board computer into any PC computer. Sophisticated assessment software computes so called actual geometry (with unit transfer function) in the waveband λ=1÷25m via FFT (Fast Fourier Transformation) technique. Thus the following items are available:

actual alignment and level in waveband λ=1÷25m
separation of all geometric signal into long wave (λ>25m) and short wave (λ<25m) parts.) so called section assessment – statistic evaluation of the track geometry based on standard deviation and quality index table of local defects, print out of geometrical lay and tables) Example of track geometry graph printed by assessment software Krab8.2 BASIC TECHNICAL DATA:

  • 2 kg auxiliary twist arm
  • Mass: 30 kg basic form
  • 20 hours without battery charge
  • working temperature: -5÷55 °C.

Easily folded for fast transport.

KRAB-Slight can be used for switch point inspection as an option. The extra auxiliary rollers for flange groove width measuring have to be mounted on the basic trolley. Measuring program is provided by special part of switch point measuring. Extra analysis software SWITCH™ is available for off-line data manipulation, analysis and the Inspection Report print out. The switch point is understood as an integral part of the track.

So, the regular scanning of the track geometry values runs at background and important discrete location of the switch points are measured in detail when trolley stops.