[en] The potential relaxation instability (PRI) was until recently experimentally observed mostly in Q-machines. The description of plasma dynamics during the oscillation was put together with the help from results of one-dimensional particle computer simulations. In the Plasma Physics Laboratory at the Reactor Centre Podgorica we have shown, that PRI can be excited also in the discharge plasma device with the proper electrode arrangement. At the same time we have simulated the instability with the two-dimensional particle computer model. We have set the simulation parameters close to our experimental arrangement. Then we have monitored the collector current and time development of the space potential and the plasma density along the axis together with the development of ionic and electronic phase space. We have divided PRI into ionic and electronic phase considering typical rate of change of plasma parameters and described the dynamics of instability in both phases. During the oscillation in the plasma device we could monitor only the collector current and the plasma potential on one spot, so we have compared the dependence of these quantities on external parameters in the experiment and in the simulation. We have varied the length of the system, the collector voltage and density of the magnetic field and measured the frequency of the oscillation. We have compared also the time development of the plasma potential in front of the collector. The results of the experiment and the simulation have been very consistent. Therefore we can conclude, that the plasma dynamics in our experimental device is qualitatively the same as described on the basis of the computer(author)