Abstract: A sensing system for sensing rotational speed of a shaft in a gas turbine engine, comprising: a target, the target fixed to the shaft in use, the target comprising at least one ferrous target element radially spaced from the shaft, and a first magnetic probe assembly comprising a first pole piece element and a second pole piece element, wherein the first pole piece element and the second pole piece element are radially spaced from one another so that the at least one ferrous target element passes proximate to and between the first and second pole piece elements as the target rotates, so that radial movement of the at least one ferrous target element away from one of the first and second pole piece elements results in simultaneous and corresponding radial movement of the at least one ferrous target element towards the other of the first and second pole piece elements.

Abstract: The invention provides a transformer probe for sensing movement of a body of magnetic material, having multiple output channels wherein the output in each output channel is substantially unaffected by faults in other output channels.

Abstract: The invention provides a transformer probe for sensing movement of a body of magnetic material, having multiple output channels wherein the output in each output channel is substantially unaffected by faults in other output channels.

Abstract: A gas turbine shaft speed sensor including a sensing coil comprised of a central conducting wire, the sensor and conducting wire is surrounded by a layer of mineral insulator and the mineral insulator is surrounded by a metallic, non magnetic, sheath. A sensing coil formed with this construction allows the high operating temperatures and is robust.