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Nexans has developed a specialised cable to deliver a method of connection for a new generation of sensors that will provide an early warning system for areas of the world at risk from landslides.

The development programme has been carried out by Cabloswiss in collaboration with the Polytechnic of Milan as part of the Prometeo (Public Protection: Methodologies and Operational Technologies) project.

The Nexans sensor cables are being field tested in a continuous monitoring system on Monte San Martino, overlooking the city of Lecco, the site of a previous landslide that caused deaths and serious damage.

The monitoring system is connected by radio to an operations centre at the Polo Regionale di Lecco of Milan Polytechnic, where the data is processed to provide information regarding the condition of the cliff and how it is changing over time.

This will then be used to predict the possible risk of landslide to provide an early warning.

To network the sensors, Cabloswiss developed a specialised cable to meet all the requirements of a system installed in an inaccessible area and subjected to extreme environmental conditions.

The cable, which has to be small in size for easy installation and reduced environmental impact, has two elements, each of which comprises two conductors.

The first element ensures low capacitance and optimal impedance for high-frequency data transmission (at speeds of up to 500kbit/s over 100m), while the second element consists of a pair of power conductors, with a low voltage drop to minimise energy losses.

The cable also offers a high degree of protection against electric shocks, thanks to double shielding, and good resistance to extreme weather conditions (temperatures of -40C) and UV light, which is guaranteed by a special formulation of the PVC insulating compound.

The systems that the Prometeo project aims to develop predict events by monitoring the micro-acoustic emissions in the rocks.

The monitoring systems include both conventional sensors (strain gauges, inclinometers, temperature sensors, geophones) and sensors based on MEMS technology, designed by the Polytechnic of Milan to monitor the occurrence of cracks as they form and grow in the structure of the rock.

Using appropriate processing techniques, this information can provide a threshold indication of activity that acts as an early alarm for a potential landslide.

It would also be possible to perform simulations for emergency management, providing fully up-to-date information that will aid experts and decision makers in handling the emergency.

MEMS are easy to install, thanks to their small size, and they also offer the added advantage of low power consumption that facilitates use in inaccessible areas, where a power network is not always available.

In this case, low power photovoltaic systems are used.

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