Scientists of KIT and Karlsruhe University of Applied Sciences have developed hybrid sensors that can detect smoldering Cable fires at an early stage by analyzing the plastic vapors released by overheated insulating cables.

The novel sensors combine measurement processes with data evaluation and the research is reported in the Sensors & Transducers Journal.

A smoldering Cable can be detected with a little luck before it starts burning: The plastic coating changes color, there is a smell of burning. Hybrid sensors might detect the risk of cable fires earlier, 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 analyze 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,” explained Dr. Hubert Keller, Simulation and Measurement Project Head of KIT’s Institute for Applied Computer Science.

The sensitive and 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 mold gases during food control, explosive gases in fertilizer 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, i.e. 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.

Combination of sensor technology and analysis method was funded with 1.3 million euros for a duration of three years under the hybrid sensor platform project. The project team consisted of computer scientists and mathematicians of KIT, Karlsruhe University of Applied Sciences, and two industry partners.