K-OP optical strain gauges from HBM offer advantages compared to electrical strain gauges. They are suited to material tests of fiber composites; tests with up to 10 million load cycles with alternating strain of ±5.00 µm/m are possible. The units are based on fiber Bragg gratings. As the strain is measured purely optically, an electric signal is not necessary. This makes use in explosive atmospheres with electromagnetic interference or even high-voltage applications possible without difficulty. Additionally, several optical strain gauges can be attached to a fiber, enabling implementation of parallel measurements. Glass fiber lengths of several hundred meters are possible.