Abstract: In a method for limiting the bandwidth of a selected binary signal (B), there is produced a modulated digital signal (D) which presents a continuous series of changes in signal level. The two occurrent logic states (1,0) are each represented by a respective symmetrical pulse train, wherein the frequencies f1, f2 of the pulse trains are mutually different. The higher frequency f2 is equal to the number of bits transmitted each second divided by two herz. The transition between the two pulse trains is arranged so that the integral of the resultant signal will be zero within the duration of three of four data bits. In a preferred embodiment of a coder and decoder each include a code word counter which, together with a combinatory logic circuit (code word table) activates or is activated by a shift register for transmitting or receiving respectively the modulated digital signal.

Abstract: In connection with recirculation of separated sludge to the separation chamber of a centrifuge separator there are normally flow restricting nozzles in the sludge outlets of the separation chamber. Only after all separated sludge has passed through these nozzles it is divided into one discharge flow and one recirculation flow.The invention concerns a centrifugal separator with a recirculation circuit (27, 28, 33, 39, 41, 43, 32, 30, 29) for separated sludge, which is completely free of flow restricting nozzles. The amount of separated sludge, that is allowed to leave the centrifugal separator through the outlet conduit (39) without being recirculated, is determined by setting of valves (22, 40) in the stationary outlet conduits (21, 39) for sludge and clarified liquid, respectively.

Abstract: The invention resides in the provision of a sludge recirculation controlled in this manner within the centrifuge rotor itself. For this reason there has been arranged centrally in the rotor, apart from a previously known reception chamber (10) for separated sludge, a recirculation chamber (14) to which sludge is transferred from the reception chamber (10). An overflow outlet (15) maintains a free liquid surface in the recirculation chamber (14) at a predetermined radial level. Recirculation channels (16), which are formed so that the flow therethrough will automatically be controlled depending upon the viscosity of the separated sludge, will conduct such sludge from the recirculation chamber (14) back to the radially outermost parts of the separation chamber (5).