Measuring long distances with Swiss precision

There are many applications where large distances need to be measured as quickly as possible and with a high degree of accuracy for positioning, surveying or monitoring tasks. Sensors UK managing director David White looks at how Dimetix laser distance sensors can meet these requirements with precision, robustness, flexibility and speed.

Typical applications that require precise measurement of long distances range from stacker cranes automatic storage and retrieval systems (ASRS) in distribution centres, fill-level controls in large tanks and silos through to systems for processing metal tubes or in machinery used for cutting beams or planks to length. Moreover, steel up to a temperature of 1,000°C can be measured without any problems.

Laser distance sensors traditionally measure either the time of flight or the phase shift. The time of flight measurement is fast, but often due to the demanding time measurement not accurate enough. The phase shift measurement is distance dependent and much more accurate, but due to more complex evaluation, it is not as fast as the pure time of flight measurement.

The Swiss sensor technology specialists at Dimetix therefore combine the advantages of both measurement methods of their laser distance sensor by using both time of flight and phase shift.

In order to achieve high measurement speed, the method uses a high-frequency modulation of the laser amplitude and evaluates the phase and the spacing of these modulated high-frequency signals (bursts). This allows the distance-dependent time shift of the individual pulse packets to be quickly determined, as well as the phase shift of the individual pulse within the modulated packets. Depending on the device type, the Dimetix sensors are therefore suitable for distances from 0.05 to 500 m and measure with an accuracy of ±1 mm with a repeatability of ±0.3 mm.

Monitoring of a railway tunnel

As an example of the Dimetix laser distance sensors in action, during construction work on Bern’s main railway station, an automatic monitoring system was installed to detect potentially dangerous deformations of the tunnel vault at an early stage. Normally, fixed tachymeters installed in the tunnel are used for this purpose, which periodically measure the position of many reflecting prisms mounted on the tunnel vault. In this case, however, the visibility of the tunnel ceiling was restricted by cross braces.

In order to detect deformations precisely, a two-stage measuring principle was used. Tachymeters measure the position of the crossbars, while around 20 Dimetix laser sensors measure the distances between the crossbars and the tunnel ceiling. This saved costs for additional tachymeters.

The measured values are processed and evaluated in the control system on site. If the safety limit values are exceeded, the responsible persons automatically receive a notification by email or SMS. A particular challenge was the required 24-hour availability of the sensors during the construction work, because due to the high traffic density, access to the tunnel was only possible to a limited extent. Thanks to the professional support of the sensor manufacturer, the project was implemented quickly and unbureaucratically.

Bridge monitoring

Another application where the Dimetix laser distance sensors have proven their worth is in bridge monitoring. Bridges are constantly exposed to weather, heavy loads and movement. In order to detect possible deformations without causing traffic disruptions during the tests, methods are available that continuously measure and report changes on the bridge.

Thanks to the high accuracy and measurement rates of up to 250 Hz, the Dimetix laser distance sensor can detect even the smallest movements. Due to the long range, flexible mounting near the bridge is also possible.

The data collected by the sensors is transmitted to an edge gateway from the company Welotec and processed there. The complete cloud integration of the gateway in Azure IoT and Azure Edge allows data to be processed and applications to be deployed in a decentralised manner. The software environment and integrated firewall also ensure maximum security; users benefit from secure remote access. The data stored in the cloud is displayed in dashboards and linked to an alert system. In the event of a conspicuous measurement on the bridge, the operators can therefore act immediately and take the necessary measures.

Dimetix has been developing and producing laser distance sensors for over 20 years to meet the highest quality requirements for the international market.