For noise correction in connection with a flat-panel x-ray detector, noise signals of a dark reference area are checked for deviations exceeding a specified threshold which, if any are present, will be taken into consideration separately for calculating the correction factor derived from the noise signal. The thread includes data that collectively describes states and relationships of interrelated tasks of the process. The relationship between the modulus of elasticity of the actuator and the modulus of elasticity of the sensor satisfies S<A. In a further refinement, to maintain the shaft and gap within an optimum spacing, a magnet is mounted to provide an axially directed magnetic force on the shaft which works against the axial force created by shaft end thrust bearing. The rails are horizontally offset from two axis defined by the pulley. The magnitude of convection of urea aqueous solution generated in a storage tank 41 is determined based on temperature information detected by the urea sensor 74.