A method for building a rulebase includes receiving a plurality of rulebase components. The single-stage converter includes a power factor improving unit, a bridge diode unit, a voltage smoothing condenser, a transformer circuit unit, and a main switch. The ground end is connected to the power supply. The means for maintaining a false-alarm rate at a substantially constant value comprise computing means configured to compute a detection threshold on the basis of a signal supplied by the filtering means, and decision means configured to detect the SSR signal on the basis of the detection threshold and of the signal supplied by the filtering means. The controller on the substrate controls the system operation.