With expenditure on the railway network being closely controlled, and budgets being squeezed, there is a drive to make equipment of all types do more for less money. In response to this, Topcon has developed a new Track Measurement Device (TMD).

The aim was to produce a competitive, highly accurate, easy to use, lightweight and cost- accessible device for all common tasks on track associated with the determination of geometric parameters.

This new device is the GG-05. It is a lightweight (17kg), rugged, alloy-constructed, active TMD that is highly portable with quick and easy assembly at the track side. The unit is also easily transported in a supplied roof rack and soft padded bags with only one person needed to manually assemble it without tools.

The Topcon GG-05 uses remote data logging, transferring the track data – including cant, gauge and chainage – to all the available data ports (Bluetooth, radio and serial) simultaneously and continuously, meaning that it can be used in three modes depending on the application that the user requires.

Track Geometry

The first mode is ‘Relative Measurement for Checking Track Geometry’. This requires that the GG-05 issued with either a Topcon FC-25A or FC-236 logger running TMD CE software. In this mode of measurement, the TMD records cant, gauge and chainage and transfers these values, via a Bluetooth connection, to a data logger. Results are displayed in the TMD CE software and can be recorded to a text file format.

This data collection method can be automated with the user determining the data collection interval in meters within the TMD CE software or it can be manually carried out by selecting the ‘record’ button on the screen of the Topcon logger. Calibration can also be carried out directly on the TMD.

Absolute kinematic

The second method of measurement for the TMD is Absolute Kinematic. This can be used to assist with the re-alignment and maintenance of existing rail track, positioning and checking new track and making distance measurements. The items required for this measurement mode are a GG-05 Rail TMD, Topcon robotic total station, 360o prism, RailSURV software on the total station and Rail+ PC software.

This method uses a robotic total station to track the 360° prism mounted on the TMD. Cant and gauge are continuously transferred back to the robotic total station. The data is synchronised, recorded and stored remotely in the robotic total station using the on board RailSURV software. Measurement intervals are determined by time in seconds by the user. This means that the data is automatically recorded without the need to halt the TMD.

In the offline mode, the collected synchronised data would be processed in the Rail+ PC software to create absolute positions along the track axis/centreline to be processed against an existing design.

The results can be used to calculate lifting and sluing values that can be exported out to tamping machines in industry standard formats as well as producing graphical drawings of the vertical and horizontal differences of the track to the design.

Stop and go

The third and final method of data collection for the TMD is the ‘Absolute Stop and Go’ method. This requires the same kit as the Kinematic method and has the robotic total station tracking the TMD as above. However, this method requires the operator to stop the movement of the TMD along the track at pre-determined intervals (in meters) for the robotic total station to take more accurate positions to the 360° prism. These metered intervals are determined by the odometer wheel of the TMD which emits a loud beep to indicate when the desired meterage has been reached.

Once the TMD has come to a stop, the total station records the prism position. The data that is collected in this way can be processed in Rail+ software in the same off-line method mentioned above and is the most accurate method of recording the track axis/centreline positions.

This method also gives the user the opportunity to work in the online mode of the Rail+ software when used with a ruggedised PC mounted onto the TMD. In this online method the data from the total station is combined with the track data at the TMD and transferred to the computer via Bluetooth. The appropriate design is imported into the Rail+ software and differences from the track are calculated and displayed in situ while the TMD is on the track. Once again this information can also be exported in industry standard formats for tamping machines.

Additional benefits

One of the many benefits of the GG-05 TMD is the unique integration of the odometer and spring-loaded gauge sensor into a fully isolated unit to stop signal transfers between the left and right rail. The spring-loaded nature of the gauge sensor means that the flange of the rail wheel fits into the correct position against the running edge of the track automatically. The TMD operator is not required to lock the unit into place manually so that the TMD can be taken on and off track easily and quickly by only one person.

In addition, the GG-05 has a fully integrated control unit that contains the central processor of the TMD, a dual-axis inclinometer (for cant measurement), spread spectrum radio, Bluetooth, battery and antenna, all in one housing. Externally, the GG-05 has only a power button and serial port for simplicity of use.

The GG-05 is a worthy addition to Topcon’s range of precise satellite positioning products and software solutions for surveying and civil engineering, earthworks and rail construction.