It has long been standard in combustion engines: detectors recognise when an oil change is necessary, for example, and thus save unnecessary inspections. Electric motors also show signs of wear. Inside, they usually consist of tightly wound copper wires coated with an insulating resin. This insulation changes over time. It becomes brittle because it is degraded by heat and chemical processes. From the outside, however, it is not possible to tell whether the insulation of the wires inside is still intact or whether the entire motor needs to be replaced.
On behalf of the special chemicals company Altana, which produces special resin systems for such insulation, scientists from the University of Halle-Wittenberg (MLU) were looking for a solution to this problem. To date, the developers have focused on how much material is degraded under certain conditions. Based on these findings, they worked out projections of how long it would take before replacement was necessary. However, the actual wear depends on the conditions of use, especially the temperature. The chemist Alexander Funtan from MLU therefore developed a test apparatus with which he could analyse over several months for four different resin systems which degradation products are produced at different temperatures.
He found that the four resin systems consistently released a certain alcohol under the different temperature conditions. The researchers therefore looked for a sensor molecule for this alcohol. That is, a substance that is easily detectable and changes its properties when the alcohol binds to it. The sensor molecule must be able to withstand high temperatures and must not change the electrochemical properties of the insulation. A particular dye was chosen. Normally, it glows reddish orange under UV light; when it binds alcohol, the colour spectrum shifts to a bright green.
The different colour spectra can then be analysed with special equipment that could be built directly into the engine. This makes it possible to see whether a replacement is necessary