Sensor detects cable fire before it starts burning

Novel hybrid sensors can now detect the risk of fires before they can even be noticed by smell or discolouration of cable insulations.

Fires are frequently caused by smouldering cables. A smouldering cable can be detected with a little luck before it starts burning — the plastic coating changes colour, there is a smell of burning.

The sensors, developed by scientists at KIT and Karlsruhe University of Applied Sciences, now help detect such smouldering fires at an early stage by analysing the plastic vapours released by overheated insulating cables. The sensors consist of four areas with different metal oxides. They change their temperature-dependent electric resistance when they come into contact with gases.

These hybrid sensors combine measurement processes with data evaluation and might detect the risk of cable fires even before they are perceived by eyes and nose. They detect the gases released from the plastic coating due to heating and reliably identify and analyse the gas mixture and its concentration. In addition, they can also detect interfering gases, such as propene or carbon monoxide, and, hence, exclude false alarms. To this end, the hybrid sensors do not only possess a gas-detecting sensor chip, but also the computation capacity and algorithms needed for evaluating measured data.

“The combination of a smart evaluation process with physical measurement is the basic idea of this development,” said Dr Hubert Keller, simulation and measurement project head of KIT’s Institute for Applied Computer Science.

The highly sensitive and very reliable hybrid sensors might increase safety in cable ducts. In addition, their capability of finding gas mixtures and determining individual gas concentrations might be useful for detecting toxic mould gases during food control, explosive gases in fertiliser silos or leaks of natural gas pipelines.

“Hybrid sensors can be used anywhere as separate systems or in a network. They may also be combined with classical safety technology, such as infrared cameras,” said Keller.

“For the development of the sensor, we use the effect that various gases react in different ways with gas-sensitive metal oxides as a function of temperature,” said Professor Dr Heinz Kohler of the Institute of Sensor Technology and Information Systems (ISIS) of the Karlsruhe University of Applied Sciences. “This effect is the basis of a self-heated, temperature-controlled sensor chip with four sensors, ie, a sensor array. The sensor array is heated cyclically and cooled down again. Simultaneous measurement of electric resistance or conductance yields four specific conductance signatures, the evaluation of which provides information on the composition and concentration of the gas.”