Measuring flow is essentia ìn the process and oil & gas ìndustry. In the oil and gas industry, orifice plates and vortex meters are popular, since their lack of moving parts makes them robust. However, the need for electronics limits maximum process temperatures to 150 to 200'C. Special electronics can go up to 1100'C, but this makes the meter very costly and in most of the cases less accurate. TNO has developed a novel sensor which can accurately measure flow at elevated temperatures using fìbre optic technology.