Disclosed a sensing apparatus having a frame element and a displaceable element mounted relative to the frame element. The sensing apparatus comprises a plurality of displacement sensor elements each configured to provide a displacement sensor output signal indicative of a displacement between the frame element and the displaceable element, wherein the plurality of displacement sensor elements are arranged at different spatial locations relative to the displaceable element and configured to provide a displacement sensor output signal indicative of a displacement between the frame element and the displaceable element at the respective spatial location. The sensing apparatus further comprises processing circuitry configured to obtain the displacement sensor output signals from the plurality of displacement sensor elements and determine whether displacement of the displaceable element is a valid displacement by comparing at least the ratio between the displacement sensor output signals to one or more expected ratios.