[en] The principle is described of a control circuit for an apparatus for filtering radioactive products, consisting of a scrubber circuit for the control and final treatment of the gas discharged into the environment. Connected to the circuit is a detection unit for generating a discrete signal whose pulse rate is proportional to the radioactivity of the medium flowing through the detection unit. The output of the detection unit is fed to the pulse ratemeter block whose output is connected to one of the two inputs of the comparator block. The other input is connected to the preselector of the measured intensity limit. The comparator block output is fed to the control block. (B.S.)