For use in gas turbines, sensors must be designed to be extremely temperature resistant and no "normal" metal alloys or plastics may be used. Consequently, Piezocryst exclusively uses refractory metal alloys, precious metals, sapphire elements and sensing elements made from single crystalline gallium phosphate (GaPO4). Even the cables are exposed to extreme thermal stress, and cooling air temperatures can exceed 500°C, excluding the use of conventional plastic insulated cables. Piezocryst uses what is known as a hardline cable; a metal cable made of extreme temperature resistant nickel-based alloy in which the conductors are embedded in compacted ceramic powder. By implementing these measures, the sensors (including the cable) can be used at a maximum operating temperatures of up to 700°C.