We aim first time investigation of large scale circulation in turbulent convective flow in gaseous fluid, applied to Rayleigh-Bénard cell with large aspect ratio $\Gamma=20$ and Rayleigh numbers $Ra=10^5 - 5 \times 10^8$. By gradually increasing $Ra$, the change from weak to strong turbulence is to be understood and thus does the convective flow long term stabilize/oscillate. $Ra$ will be controlled by compressing the working gas sulfur hexaflouride $SF_6$ up to $10 bar$ in the SCALEX facility of Ilmenau. The temperature difference between hot and cold wall of the convective cell will be largely varied to switch between Oberbeck-Boussinesq and non-Oberbeck-Boussinesq behavior, checking the stability of oscillations for constant $Ra$ and Prandtl numbers $Pr$. The convective flow of heat will be monitored by particle imaging velocimetry and the experimental results will be cross checked by numerical simulations. Additional new methods for contactless temperature measurements will be introduced.