The present invention relates to a control system comprising a control input device (10) having a movable magnet (13), a pole-piece frame arrangement positioned about the magnet (13) and positioned therein at least two magnetic flux sensors (22) for sensing movement of the magnet (13) in a given direction. The control system further comprises a monitoring arrangement for monitoring the output signal of each of the sensors (22) and permits the input device (10) to control the system only when the output of the sensors (22) are within a predefined range. This multiple sensing provides a fail-safe in the event that one of the sensors (22) generates an erroneous signal.