A control system (54) for an X-ray scanner, the system comprising an input (Din) arranged to receive an input signal identifying which of a plurality of electron emitters (25) is to be active, and to produce a plurality of outputs (HVout0 ... HVout 31) each arranged to control operation of one of the emitters. The system further comprising output monitoring means (612) arranged to monitor each of the outputs and generate a feedback signal indicating if any of the outputs exceeds a predetermined threshold (VREF).
