Abstract: A method and apparatus useful in measuring the size, charge, velocity and concentration of particles in polydispersed systems, and particle concentrations of monodispersed aerosols. A particle flow to be evaluated is conducted through at least one active electric field sensor, which may be constructed in an annular, point, or segmented annular configuration. The charge induced by each particle on the sensor is fed to an active charge amplifier. The output signal of the amplifier serves as input signal for a measured value indicator. The amplifier is a component for a measured value evaluation circuit, which consists of at least one capacitor, one resistor and the amplifier and, which is preferably integrated into the arrangement of the sensor. A computer or microprocessor is used in analyzing the sensor output to determine desired parameters descriptive of the particles and their movement. The particle flow may be charged prior to measurement and the particles may also be separated according to charge.