[en] Non-statistical event-by-event fluctuations are considered as an important signal for the critical endpoint of the QCD phase diagram. Event-by-event fluctuations of different observables are thus investigated in detail in current experiments but are also an important observable to be studied at the future CBM experiment at FAIR. In this work we present the energy and centrality dependence of event-by-event fluctuations of particle yield ratios measured by the NA49 experiment in Pb+Pb collisions at 20-158 AGeV. Systematic studies of the influence of the dE/dx resolution on the particle identification and the centrality bin size were performed. Results can be compared to event-by-event fluctuations measured by NA49 for different observables such as < p_t> or the mean charged particle multiplicity. Main results of these studies are an increase of absolute value of the dynamical particle ratio fluctuations with decreasing centrality for all considered ratios, saturation of the K/π and K/p ratio fluctuations for peripheral Pb + Pb collisions at 158A GeV and scaling of the energy and centrality dependences of the p/π ratio fluctuations with N_pN_π. The measured energy and centrality dependences of the K/π and K/p ratio fluctuations scale with N_K in a different way. The saturation of the mentioned ratios fluctuations was attributed to the development of pronounced spike at zero in the eventwise ratio distributions, which, as was shown by Monte Carlo simulations, influence the measured fluctuations in the very peripheral Pb + Pb collisions at 158A GeV. In future, the CBM experiment at FAIR will investigate the intermediate region of the QCD phase diagram in great detail searching for the first order phase transition line and the expected critical endpoint. It is therefore important to closely investigate its sensitivity towards particle ratio fluctuations in Au+Au collisions at 10-45 AGeV beam energy. Detailed simulation studies are presented. As an outcome of these feasibility studies we conclude that the CBM experiment will be able to provide high quality data on the subject of the event-by-event fluctuations of particle yield ratios with sensitivity in the order of 1%. (orig.)