A signal filtering device acquires a pressure signal from a pressure sensor in a blood processing apparatus having a known disturbance generator that generates a disturbance in the pressure signal. The signal filtering device obtains (401) a current set of principal components representing the disturbance. The respective principal component in the current set is generated by Principal Component Analysis, PCA, of a plurality of characteristic waveforms representing the disturbance. The signal filtering device further operates to detect (403) presence in the pressure signal of a current disturbance that originates from the disturbance generator, computes (404) a scaling factor for the respective principal component with respect to the current disturbance, and subtracts (405) the respective principal component, scaled in magnitude by the respective scaling factor, from the pressure signal. The signal filtering device may be associated with or included in the blood processing apparatus.
