An assembly comprising a flow channel , a control flap which is movably mounted within the flow channel , and a volumetric-flow controller , in particular for air-conditioning and ventilation systems, for adjusting the control flap , the volumetric-flow controller comprising: - a measurement channel having a channel inlet and a channel outlet for connection to the flow channel in order to form a separate bypass channel branched from the flow channel , - a differential pressure sensor arranged in the measurement channel for measuring a differential pressure prevailing in the flow channel and for outputting a corresponding electrical measurement signal, and - a control unit for electrically activating a flap drive in dependence on the electrical measurement signal outputted by the differential pressure sensor in order to set a desired volumetric flow rate in the flow channel , wherein at least one air quality sensor for measuring an air quality prevailing in the flow channel and for outputting a corresponding electrical measurement signal is arranged in the measurement channel , wherein the at least one air quality sensor has a sensor surface which is arranged in the measurement channel parallel or approximately parallel to the direction of flow of the air flowing past the sensor surface , and wherein the control unit is configured to electrically activate the flap drive also in dependence on the electrical measurement signal outputted by the at least one air quality sensor , wherein the volumetric-flow controller is connected to the flow channel by its channel inlet and its channel outlet in order to form a separate bypass channel branched from the flow channel , and comprising a flap drive which is electrically activated by the control unit for moving the control flap in dependence on the electrical measurement signals outputted by the differential pressure sensor and by the at least one air quality sensor . - a measurement channel having a channel inlet and a channel outlet for connection to the flow channel in order to form a separate bypass channel branched from the flow channel , - a differential pressure sensor arranged in the measurement channel for measuring a differential pressure prevailing in the flow channel and for outputting a corresponding electrical measurement signal, and - a control unit for electrically activating a flap drive in dependence on the electrical measurement signal outputted by the differential pressure sensor in order to set a desired volumetric flow rate in the flow channel , wherein at least one air quality sensor for measuring an air quality prevailing in the flow channel and for outputting a corresponding electrical measurement signal is arranged in the measurement channel , wherein the at least one air quality sensor has a sensor surface which is arranged in the measurement channel parallel or approximately parallel to the direction of flow of the air flowing past the sensor surface , and wherein the control unit is configured to electrically activate the flap drive also in dependence on the electrical measurement signal outputted by the at least one air quality sensor , wherein the volumetric-flow controller is connected to the flow channel by its channel inlet and its channel outlet in order to form a separate bypass channel branched from the flow channel , and comprising a flap drive which is electrically activated by the control unit for moving the control flap in dependence on the electrical measurement signals outputted by the differential pressure sensor and by the at least one air quality sensor . <EOS>