Particles of radii 0.2 to 3 μm and of different materials were suspended in an electrodynamic quadrupole inside a vacuum chamber and exposed to beams of electrons and ions of energies up to 20 keV and 5 keV, respectively, with the aim to simulate electric charging of cosmic dust particles. It was found that the equilibrium surface electrostatic potential of glass particles of radii 0.2 to 2 μ charged by electrons of energies 1 to 20 keV is always positive. This can be explained by secondary electron emission at lower energies of electrons and by penetration of electrons through particles with subsequent secondary electron emission mainly from the exit side at higher energies. In case of charging by ions electrostatic potential of particles is generally much lower than expected values and interpretation of results of measurement is more complicated. The most promising way to eliminate instrumental influences disturbing processes of charging seems to be a construction of a smaller suspension system in which these influences would be negligible. Parameters of such a suspension system were derived from results of measurements.