Patent ID: 6862536

Claim:
A measuring system for measuring properties of particles in a medium flow, said measuring system comprising: a sensor comprising at least one sensing element placed in the flow of medium, so that an electric charge of a moving particle induces an electric signal in the sensing element, and a processing unit with a signal-processing unit connected to the sensor to collect the signals from the sensing element, wherein the measuring system comprises filtering means for filtering collected signals, said filtering means arranged to pass signals at a relevant frequency band or at relevant frequency bands, said filtering means being connected to said signal-processing unit for feeding said passed signals to the signal-processing unit, wherein the relevant frequency band or frequency bands are arranged to correspond to a frequency band or frequency bands defined by frequencies which exist in consequence of one or more process equipment or a process occurrence affecting to the medium flow, and wherein said filtering means is arranged to pass signals at the relevant frequency band or bands corresponding to a frequency band or frequency bands defined by fans causing the movement of the medium flow, so that at least one frequency band defined by one fan is defined so that a lower limiting frequency of the frequency band is related to a minimum revolution speed of the fan, and so that an upper frequency limit of the frequency band is related to a maximum revolution speed of the fans multiplied with number of wings of the fans.